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ELECTRICIAN, NSQF (LEVEL - 5), , 4th Semester, TRADE THEORY, SECTOR: Electrical, , DIRECTORATE GENERAL OF TRAINING, MINISTRY OF SKILL DEVELOPMENT & ENTREPRENEURSHIP, GOVERNMENT OF INDIA, , NATIONAL INSTRUCTIONAL, MEDIA INSTITUTE, CHENNAI, Post Box No. 3142, CTI Campus, Guindy, Chennai - 600 032, (i), , Copyright @ NIMI Not to be Republished

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Sector, , : Electrical, , Duration : 2 - Years, Trade, , : Electrician 4th Semester - Trade Theory - NSQF (LEVEL - 5), , Copyright@2018 National Instructional Media Institute, Chennai, First Edition :, , December 2018, , Copies : 10,000, , Rs.260/-, , All rights reserved., No part of this publication can be reproduced or transmitted in any form or by any means, electronic or mechanical, including, photocopy, recording or any information storage and retrieval system, without permission in writing from the National, Instructional Media Institute, Chennai., , Published by:, NATIONAL INSTRUCTIONAL MEDIA INSTITUTE, P. B. No.3142, CTI Campus, Guindy Industrial Estate,, Guindy, Chennai - 600 032., Phone : 044 - 2250 0248, 2250 0657, 2250 2421, Fax : 91 - 44 - 2250 0791, email : [email protected], [email protected], Website: www.nimi.gov.in, , (ii), , Copyright @ NIMI Not to be Republished

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FOREWORD, The Government of India has set an ambitious target of imparting skills to 30 crores people, one out of, every four Indians, by 2020 to help them secure jobs as part of the National Skills Development Policy., Industrial Training Institutes (ITIs) play a vital role in this process especially in terms of providing skilled, manpower. Keeping this in mind, and for providing the current industry relevant skill training to Trainees,, ITI syllabus has been recently updated with the help of Mentor Councils comprising of various stakeholder's, viz. Industries, Entrepreneurs, Academicians and representatives from ITIs., National Instructional Media Institute (NIMI), Chennai has come up with instructional material to suit the, revised curriculum for Electrician 4th Semester Trade Theory NSQF (LEVEL - 5) in Electrical sector, under Semester Pattern required for ITIs and related institutions imparting skill development. The, NSQF (LEVEL - 5) will help the trainees to get an international equivalency standard where their skill, proficiency and competency will be duly recognized across the globe and this will also increase the, scope of recognition of prior learning. NSQF (LEVEL - 5) trainees will also get the opportunities to promote, life long learning and skill development. I have no doubt that with NSQF (LEVEL - 5) the trainers and, trainees of ITIs, and all stakeholders will derive maximum benefits from these IMPs and that NIMI's effort, will go a long way in improving the quality of Vocational training in the country., The Executive Director & Staff of NIMI and members of Media Development Committee deserve appreciation, for their contribution in bringing out this publication., Jai Hind, , RAJESH AGGARWAL, , Director General / Addl. Secretary,, Ministry of Skill Development & Entrepreneurship,, Government of India., , New Delhi - 110 001, , (iii), , Copyright @ NIMI Not to be Republished

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PREFACE, The National Instructional Media Institute (NIMI) was established in 1986 at Chennai by then Directorate, General of Training (D.G.T), Ministry of Labour and Employment, (now under Directorate General of Training, (D.G.T), Ministry of Skill Development and Entrepreneurship) (MSDE) Government of India, with technical, assistance from the Govt. of the Federal Republic of Germany. The prime objective of this institute is to, develop and provide instructional materials for various trades as per the prescribed syllabi (NSQF) under, the Craftsman and Apprenticeship Training Schemes., The instructional materials are created keeping in mind, the main objective of Vocational Training under, NCVT/NAC in India, which is to help an individual to master skills to do a job. The instructional materials, are generated in the form of Instructional Media Packages (IMPs). An IMP consists of Theory book,, Practical book, Test and Assignment book, Instructor Guide, Audio Visual Aid (Wall charts and, Transparencies) and other supporting materials., The trade theory book provides related theoretical knowledge required to enable the trainee to do a job., The test and assignments will enable the instructor to give assignments for the evaluation of the performance, of a trainee. The wall charts and transparencies are unique, as they not only help the instructor to effectively, present a topic but also help him to assess the trainee's understanding. The instructor guide enables the, instructor to plan his schedule of instruction, plan the raw material requirements, day to day lessons and, demonstrations., IMPs also deals with the complex skills required to be developed for effective team work. Necessary care, has also been taken to include important skill areas of allied trades as prescribed in the syllabus., The availability of a complete Instructional Media Package in an institute helps both the trainer and, management to impart effective training., The IMPs are the outcome of collective efforts of the staff members of NIMI and the members of the Media, Development Committees specially drawn from Public and Private sector industries, various training institutes, under the Directorate General of Training (DGT), Government and Private ITIs., NIMI would like to take this opportunity to convey sincere thanks to the Directors of Employment &, Training of various State Governments, Training Departments of Industries both in the Public and Private, sectors, Officers of DGT and DGT field institutes, proof readers, individual media developers and coordinators,, but for whose active support NIMI would not have been able to bring out this materials., , R. P. DHINGRA, EXECUTIVE DIRECTOR, , Chennai - 600 032, , (iv), , Copyright @ NIMI Not to be Republished

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INTRODUCTION, This manual for trade Theory is intended for use in the ITI class room. It consists of a series of lessons that are, to be completed by the trainees during the Third semester of course is the Electrician trade under Electrical, Sector. It is National Skills Qualifications Framework NSQF (LEVEL - 5), supplemented and supported by, instructions/information to assist the trainees in performing the exercises. The syllabus for the, 4th Semester Electrician NSQF (LEVEL - 5) Trade under Electrical Sector Trade Practical is divided into, Seven modules.The allocation of time for the various modules is given below:, Module 1 - Electronic Practice, , 15 Exercises, , 175 Hrs, , Module 2 - Control Panel Wiring, , 5 Exercises, , 100 Hrs, , Module 3 - AC/DC Motor Drives, , 3 Exercises, , 50 Hrs, , Module 4 - Inverter and UPS, , 6 Exercises, , 75 Hrs, , Module 5 - Power Generation and Substation, , 7 Exercises, , 50 Hrs, , Module 6 - Transmission and Distribution, , 7 Exercises, , 50 Hrs, , Module 7 - Circuit Breakers and Relays, , 5 Exercises, , 25 Hrs, , 48 Exercises, , 525 Hrs, , Total, , The syllabus and the content in the modules are interlinked. As the number of workstations available in the, electrical section is limited by the machinery and equipment, it is necessary to interpolate the exercises in the, modules to form a proper teaching and learning sequence. The sequence of instruction is given in the schedule, of instruction which is incorporated in the Instructor's Guide. With 25 practical hours a week of 5 working days, 100 hours of practical per month is available., The procedure for working through the 48 exercises for the 4th semester with the specific objectives to be achieved, as the learning out comes at the end of each exercise is given in this book., The symbols used in the diagrams comply with the Bureau of Indian Standards (BIS) specifications., This manual on trade Theory forms part of the Written Instructional Material (WIM), which includes manual on trade, practical and assignment/test., , (vi), , Copyright @ NIMI Not to be Republished

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CONTENTS, Lesson No., , Title of the Lesson, , Page No., , Module 1 : Electronic Practice, 4.1.160, , Circuit board soldering and resistor colour coding, , 1, , Soldering technique, , 2, , 4.1.161, , Semiconductor theory/active and passive components, , 10, , 4.1.162, , PN Junction-semiconductor diodes, , 16, , 4.1.163, , Rectifiers, , 21, , 4.1.164, , Transistors, , 29, , 4.1.165, , Transistor biasing and characteristics, , 34, , 4.1.166, , Transistor as a switch, series voltage regulator and amplifiers, , 40, , 4.1.167, , Function generator and cathode ray oscilloscope (CRO), , 47, , 4.1.168, , Printed circuit boards (PCB), , 52, , 4.1.169, , Power electronic devices - UJT and FET, , 55, , 4.1.170, , Power supplies - troubleshooting, , 63, , 4.1.171, , Power control circuit using SCR,DIAC,TRIAC & IGBT, , 69, , 4.1.172, , Integrated circuit voltage regulators, , 77, , 4.1.173, , Binary numbers, logic gates and combinational circuits, , 82, , 4.1.174, , Wave shapes - oscillators and multivibrators, , 88, , Module 2 : Control Panel Wiring, 4.2.175 to 4.2.177, , 4.2.178 & 4.2.179, , Control elements, accessories - layout of control cabinet, , 98, , Power and control circuits for three phase motors, , 106, , Installation of instruments and sensors in control panel and its, performance testing, , 119, , Module 3 : AC/DC Motor Drives, 4.3.180, , AC/DC drives, , 121, , 4.3.181 & 4.3.182, , Speed control of 3 phase induction motor by VVVF/AC drive, , 127, , Module 4 : Inverter and UPS, 4.4.183, , Voltage stabilizer and UPS, , 136, , 4.4.184, , Emergency light, , 144, , 4.4.185, , Battery charger and inverter, , 146, , 4.4.186 & 4.4.187, , Stabiliser, battery charger, emergency light, inverter and UPS, , 151, , 4.4.188, , Installation of inverter in domestic wiring, , 157, , (vii), , Copyright @ NIMI Not to be Republished

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Lesson No., , Title of the Lesson, , Page No., , Module 5 : Power Generation and Substation, 4.5.189, , Sources of energy - Thermal power generation, , 161, , 4.5.190, , Hydel power plants, , 172, , 4.5.191 & 4.5.192, , Visiting of electrical substation, , 176, , Electrical substations, , 177, , Electrical power generation by non conventional methods, , 184, , Tidal power generation, , 188, , Magneto hydro dynamic (MHD) power generation, , 190, , Power generation by solar and wind energy, , 192, , Wind power generation, , 197, , 4.5.193, , 4.5.194 & 4.5.195, , Module 6 : Transmission & Distribution, 4.6.196 to 4.6.198, , Electrical supply system - transmission - line insulators, , 199, , Line insulators, , 203, , Overhead lines /poles erection-fastening of insulator, , 208, , Joining of aluminium conductors, , 216, , 4.6.201, , Domestic service line - IE rules, , 219, , 4.6.202, , Bus-bar system - power tariff terms and definitions, , 222, , Power tariff - terms and definitions, , 225, , 4.6.199 & 4.6.200, , Module 7 : Circuit Breakers and Relays, 4.7.203 & 4.7.204, , Line protective relays - types - operation, , 228, , 4.7.205 & 4.7.206, , Circuit breakers - parts - functions- tripping mechanism, , 233, , Tripping mechanism of circuit breakers, , 239, , Repair and maintenance of CBs, , 241, , 4.7.207, , (viii), , Copyright @ NIMI Not to be Republished

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ASSESSABLE / LEARNING OUTCOME, On completion of this book you shall be able to, • Detect the faults and troubleshoot inverter, stabilizer, battery charger, emergency light and UPS etc., • Plan, assemble and install solar panel, • Erect overhead domestic service line and outline various power, plant layout., • Examine the faults and carryout repairing of circuit breakers., • Identify the control and functional switches in C.R.O and measure, the DC and AC voltage, frequency time period., • Construct and test a half and fullwave rectifiers with and without, filter circuits., • Draw and wire up the control panel for forward/ reverse operation, of induction motor., • Control speed and reverse the direction of rotation of different type, of three phase induction motor using VVVF control /AC drive, , (ix), , Copyright @ NIMI Not to be Republished

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ELECTRICIAN 4TH SEMESTER SYLLABUS, Fourth Semester Duration: Six Month, Week, No., , Learning outcome, Reference, , Professional Skills, (Trade Practical), With Indicative Hours, , Professional Knowledge, (Trade Theory), , 79, , • Assemble simple, electronic circuits, and test for, functioning., , 160. Determine the value of resistance, by colour code and identify types., (10 Hrs), 161. Test active and passive electronic, components and its applications., (15 Hrs), , Resistors - colour code, types and, characteristics., Active and passive components., Atomic structure and semiconductor, theory., , 80-81, , • Assemble simple, electronic circuits, and test for, functioning., , 162. Determine V-I characteristics of, semiconductor diode. (10 Hrs), 163. Construct half wave, full wave and, bridge, rectifiers, using, semiconductor diode. (10 Hrs), 164.Check transistors for their, functioning by identifying its type, and terminals. (10 Hrs), 165. Bias the transistor and determine, its characteristics. (10 Hrs), 166. Use transistor as an electronic, switch and series voltage regulator., (10 Hrs), , P-N, junction,, classification,, specifications,, biasing, and, characteristics of diodes., Rectifier circuit - half wave, full wave,, bridge rectifiers and filters., Principle of operation, types,, characteristics and various configuration, of transistor., Application of transistor as a switch,, voltage regulator and amplifier., , 82-83, , • Assemble simple, Electronic circuits, and test for, functioning., , 167. Operate and set the required, frequency using function generator., (12 Hrs), 168. Make a printed circuit board for, power supply. (10 Hrs), 169. Construct simple circuits containing, UJT for triggering and FET as an, amplifier. (12 Hrs), 170. Troubleshoot defects in simple, power supplies. (16 Hrs), , Basic concept of power electronics, devices., IC voltage regulators, Digital Electronics - Binary numbers,, logic gates and combinational circuits., , 84-85, , • Assemble simple, electronic circuits, and test for, functioning., , 171. Construct power control circuit by, SCR, Diac, Triac and IGBT. (15 Hrs), 172. Construct variable DC stabilized, power supply using IC. (10 Hrs), 173. Practice on various logics by use, of logic gates and circuits. (15 Hrs), 174. Generate and demonstrate wave, shapes for voltage and current of, rectifier, single stage amplifier and, oscillator using CRO. (10 Hrs), , Working principle and uses of, oscilloscope., Construction and working of SCR, DIAC,, TRIAC and IGBT., Principle, types and applications of, various multivibrators., , 86-87, , • Assemble, accessories and, carry out wiring, of control, cabinets and, equipment., , 175. Design layout of control cabinet,, assemble control elements and, wiring accessories for:, (i) Local and remote control of, induction motor. (15 Hrs), (ii) Forward and reverse operation, of induction motor. (10 Hrs), , Study and understand Layout drawing of, control cabinet, power and control, circuits., Various control elements:, Isolators, pushbuttons, switches,, indicators, MCB, fuses, relays, timers, and limit switches etc., , (x), , Copyright @ NIMI Not to be Republished

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ELECTRICIAN 4TH SEMESTER SYLLABUS, Fourth Semester Duration: Six Month, Week, No., , Learning outcome, Reference, , Professional Skills, (Trade Practical), With Indicative Hours, , Professional Knowledge, (Trade Theory), , (iii) Automatic star-delta starter, with change of direction of, rotation. (15 Hrs), (iv) Sequential control of three, motors. (10 Hrs), 88-89, , • Assemble, accessories and, carry out wiring, of control, cabinets and, equipment., , 176. Carry out wiring of control cabinet, as per wiring diagram, bunching of, XLPE cables, channeling, tying, and checking etc. (15 Hrs), 177. Mount various control elements, e.g. circuit breakers, relays,, contactors and timers etc. (10 Hrs), 178. Identify and install required, measuring instruments and, sensors in control panel. (10 Hrs), 179. Test the control panel for its, performance. (15 Hrs), , Wiring accessories: Race ways/ cable, channel, DIN rail, terminal connectors,, thimbles, lugs, ferrules, cable binding, strap, buttons, cable ties, sleeves,, gromats and clips etc., Testing of various control elements and, circuits., , 90-91, , • Perform speed, control of AC, and DC motors, by using solid, state devices., , 180. Perform speed control of DC motor, using thyristors / DC drive. (18 Hrs), 181. Perform speed control and, reversing the direction of rotation, of AC motors by using thyristors /, AC drive. (18 Hrs), 182. Construct and test a universal, motor speed controller using SCR., (14 Hrs), , Working, parameters and applications of, AC / DC drive., Speed control of 3 phase induction motor, by using VVVF/AC Drive., , 92-94, , • Detect the faults, and troubleshoot, inverter, stabilizer,, battery charger,, emergency light, and UPS etc., , 183. Assemble circuits of voltage, stabilizer and UPS. (15Hrs), 184. Prepare an emergency light., (10 Hrs), 185. Assemble circuits of battery, charger and inverter. (15 Hrs), 186. Test, analyze defects and repair, voltage stabilizer, emergency light, and UPS. (15 Hrs), 187. Maintain, service and troubleshoot, battery charger and inverter., (10 Hrs), 188. Install an Inverter with battery and, connect it in domestic wiring for, operation. (10 Hrs), , Basic concept, block diagram and, working of voltage stabilizer, battery, charger, emergency light, inverter and, UPS., Preventive and breakdown maintenance., , 95, , • Erect overhead, domestic service, line and outline, various power, plant layout., , 189. Draw layout of thermal power plant, and identify function of different, layout elements. (5 Hrs), 190. Draw layout of hydel power plant, and identify functions of different, layout elements. (5 Hrs), , Conventional and nonconventional, sources of energy and their comparison., Power generation by thermal and hydel, power plants., , (xi), , Copyright @ NIMI Not to be Republished

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ELECTRICIAN 4TH SEMESTER SYLLABUS, Fourth Semester Duration: Six Month, Week, No., , Learning outcome, Reference, , Professional Skills, (Trade Practical), With Indicative Hours, , Professional Knowledge, (Trade Theory), , 191. Visit to transmission / distribution, substation. (10 Hrs), 192. Draw actual circuit diagram of, substation visited and indicate, various components. (5 Hrs), 96, , • Plan, assemble, and install solar, panel., • Erect overhead, domestic service, line and outline, various power, plant layout., , 193. Prepare layout plan and Identify, different elements of solar power, system. (05 Hrs), 194. Prepare layout plan and Identify, different elements of wind power, system. (05 Hrs), 195. Assemble and connect solar panel, for illumination. (15 Hrs), , 97, , • Erect overhead, domestic service, line and outline, various power, plant layout., , 196. Practice installation of insulators Transmission and distribution networks., used in HT/LT line for a given Line insulators, overhead poles and, voltage range. (5 hrs), method of joining aluminum conductors., 197. Draw single line diagram of, transmission and distribution, system. (5 Hrs), 198. Measure current carrying capacity, of conductor for given power, supply. (5 hrs), 199. Fasten jumper in pin, shackle and, suspension type insulators., (10 Hrs), , 98, , • Erect overhead, domestic service, line and outline, various power, plant layout., , 200. Erect an overhead service line pole, for single phase 230 V distribution, system in open space. (10 Hrs), 201. Practice on laying of domestic, service line. (10 Hrs), 202. Install bus bar and bus coupler on, LT line. (5 Hrs), , Safety precautions and IE rules, pertaining to domestic service, connections., Various substations., Various terms like - maximum demand,, average demand, load factor, diversity, factor, plant utility factor etc., , 99, , • Examine the faults, and carry out, repairing of, circuit breakers., , 203. Identify various parts of relay and, ascertain the operation. (5 Hrs), 204. Practice setting of pick up current, and time setting multiplier for relay, operation. (5 hrs), 205. Identify the parts of circuit breaker,, check its operation. (5Hrs), 206. Test tripping characteristic of circuit, breaker for over current and short, circuit current. (5 hrs), 207. Practice on repair and, maintenance of circuit breaker., (5 hrs), , Types of relays and its operation., Types of circuit breakers, their, applications and functioning., Production of arc and quenching., , (xii), , Various ways of electrical power, generation by non-conventional methods., Power generation by solar and wind, energy., Principle and operation of solar panel., , Copyright @ NIMI Not to be Republished

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ELECTRICIAN 4TH SEMESTER SYLLABUS, Fourth Semester Duration: Six Month, Week, No., , Learning outcome, Reference, , Professional Skills, (Trade Practical), With Indicative Hours, , Professional Knowledge, (Trade Theory), , 100-101 Project work / Industrial visit, Broad Areas:, a) Battery charger/Emergency light, b) Control of motor pump with tank level, c) DC voltage converter using SCRs, d) Logic control circuits using relays, e) Alarm/indicator circuits using sensors, 102-103, , Revision, , 104, , Examination, , (xiii), , Copyright @ NIMI Not to be Republished

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Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.160, , Circuit board soldering and resistor colour coding, Objectives: At the end of this lesson you shall be able to, • distinguish between eyelet board, lug board and PCB, • explain the preparation of components for mounting and method of soldering on boards, • explain the inspection of solder joints and defects in soldered joints, • explain construction, types, function, colour coding and application of resistors in circuits., In assembling of electronic circuits using components, it, is required to layout (arrange), mount and wire the, components in a systematic manner. In wiring the electronic, circuits depending upon the circuit, different types of, boards are used., , The required circuit pattern on the laminated board is, made by process called “etching”. Etching is the process, of removing the portion of the metal foil, leaving behind only, the required portion refer Fig 3., , Type of boards, 1 Eyelet board, 2 Lug or tag board, 3 Printed Circuit Boards (PCB’s), Eyelet Board (Fig 1) : In this, eyelets are riveted on, perforated bakelite boards. Refer Fig 1. In this type of, board, eyelets can be riveted only to a limited number,, depending on the lay-out of the circuits., , Lug or tag board (Fig 2) : In this type of boards, brass, lugs are riveted in rows on insulated board like bakelite. In, this type, components are to be arranged, and circuits are, to be made without altering the lug position., , For general purpose, printed circuit boards are readily, available to design and develop electronic circuits. They, are also called as matrix boards. A strip type matrix board, is shown in Fig 4., , Securing and fixing of components: Mounting of, components on eyelet board / lug board / tag board or PCB, involves 4 main activities, namely,, 1 Preparation of component leads and surfaces to be, soldered., 2 Shaping the components leads., 3 Bending and trimming the excess length before, soldering., 4 The order of mounting and soldering., , PCB (Printed circuit board) : A printed circuit board in, which inter connecting wires are replaced by a thin, conducting surface called copper on silver foil which is, moulded in one side of the insulated board. The insulating, board is generally made up of phenolic (or) paper or fibre, glass or epoxy., , 1 Preparation of components leads and surfaces, etc.: Dust, oil, oxide layer paint or any protective, coating on the component leads and surfaces must be, removed at places where soldering has to be done., 2 Shaping the components: The shape to which the, components leads are to be bent depends up on the, manner in which the component is to be mounted., Care should be taken to reduce the thrust on the, component., , Copyright @ NIMI Not to be Republished, , 1

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Depending on the type of component lead, and the space, available on the PCB, component can be mounted either, vertically (or) horizontally as in Fig 5., , 3 Bending and trimming : Once the components leads, are inserted into the holes of PCB, lead length in excess, (0.5 mm to 3 mm), from the PCB surface should be, trimmed, using side cutting pliers as in Fig 6., , After cutting the excess lead length, the component lead, must be bend and terminated, on PCB., 4 Order of mounting: Mount the components in the, order as per layout, and should be easy to trace the, circuit, as per connection diagram., The technique used for soldering is explained in subsequent, lesson., , Soldering technique, Objectives : At the end of this lesson you shall be able to, • list the critical factors and stages in soldering, • list the steps involved in selecting and preparing the materials, • list the different shapes of tips and inspection of soldering iron, • state the functions of soldering iron stand and inspection of soldering iron, • state the technique of soldering electronic components and effect of residual flux, • state the defects in soldering joints., Soldering, Soldering is the process of joining two metals for a, permanent joint/connections. The bonding of two metals, done by using alloy of two metals-lead and tin called solder, in different ratios to solder electronic component like, resistors, capacitor, transistor etc., Soldering a joint: Selection and preparation of the, soldering materials and cleaning the surfaces to be, soldered are the most time consuming phase of making a, solder joint. Heating the joint and applying solder is the, least time consuming but, all these steps contribute, heavily for the good soldered joint., Critical factor during soldering, 1 Controlling the temperature of the workpiece., 2 Limiting the time that a workpiece is to be held at, soldering temperature., These factors are specially critical while soldering, electronic components like resistors, capacitors,, transistors, ICs etc., Failure of correct, time and, coordinate the heating of the joint and add solder, will, result in a poor quality joint and may even damage the, components., 2, , Stage in soldering: The soldering process can be divided, into several distinct stage or phases as given below:, 1 Selection and preparation of materials, 2 Cleaning the surfaces to be soldered, 3 Heating the joint and adding solder, 4 Cooling the joint, 5 Cleaning the joint, 6 Inspecting the joint., 1 Selection and preparation of materials, Selection of soldering iron wattage : Soldering irons, are available in different wattage ratings starting from 10, watts to several 100 watts. The wattage of a soldering iron, specifies the amount of heat it can produce. As a thumb, rule, higher the physical dimension of the workpiece,, higher should be the wattage rating of the soldering iron., Some of the suggested wattage of soldering iron are given, below:, i) For soldering, less temperature sensitive component, such as, resistors on lug boards or tag boards, use 25, to 60W iron. For soldering on printed circuit boards,, use 10 to 25 W iron., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished

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ii) For soldering highly temperature sensitive components, such as, diodes, transistors and integrated circuits,, use 10 to 25 watts iron., Selection of soldering iron tip: To ensure that the joint, is heated to the required temperature ideally,, – the area of the tip face should be approximately equal, to the area of the joint to be soldered, – the tip should be long enough to allow easy access to, the joint., -, , the tip should not be too long, as this may result in the, low temperature at the tips working face., , In most soldering irons, the tip can be easily removed and, can be replaced., Selection of tip shape: Suggested soldering tip shapes, and their application are given below;, Type of soldering tip shape, , Application, , Wires, resistor and, the passive components, on lug boards, , CHISEL TIP, , All miniature electronic, components except ICs on, to lug boards and printed, circuit boards (PCB), , BEVEL TIP, , Integrated circuits (ICs), on to printed circuit boards, (PCBs), , CONICAL TIP, , Selection of solder and flux: For electronic soldering, applications, solder of tin and lead of 60/40 proportion is, used. This solder proportion has a melting point of 200°C, which is the required temperature for general purpose, soldering irons., For electrical purpose, resin core solders are used., For ease of application, the flux used in addition to the, cored flux in solder, should be in paste form., Flux is a chemical substance which has acidic properties., Therefore, it is advised not to touch the flux by hand. Use, a stick or a thin stiff brush to apply flux on the work pieces., Hands should be washed after soldering work., , Inspection of soldering iron: Most soldering irons are, powered by AC main voltage. This voltage level is high and, can give shock if one is careless. Soldering irons will, generally have lengthy mains cable. While using the iron,, the mains cable gets twisted and will have to bear physical, stain. Because of this strain, the insulation of cable may, get cut. This may lead to live wires protruding out. The live, wires give severe electrical shocks if it touches the user., Hence, a thorough inspection of the soldering iron cable is, a must before using it., Preparation of soldering iron for soldering: The, soldering bit tip should be cleaned, heated and tinned, before starting the soldering work., Cleaning the surfaces to be soldered: Before joining, two pieces of metal by soldering, the joining surfaces, should be cleaned to remove foreign matters over the, surface. Also the jointing surfaces should be free from, grease grit or oil. this could be achieved by using either, a knife or by a sand paper and cloth., 2 Heating the joint and adding solder: Tips for, heating and applying solder to a joint to be soldered are, given below:, – Do not apply too much flux on a joint in one place., Apply a small amount of flux around the joint. Do not, allow the flux to flow outside the area to be soldered., – Place the iron tip at the joint such that the tip gets, maximum contact with parts to be joined as in Fig 2, , Soldering stand: Soldering stand plays an important role, of retaining the soldering iron tip temperature around the, required soldering temperature. The soldering stand should, not allow the external temperature to cool the bit. At the, same time the stand should not contain all the heat, generated., Soldering stands are specially designed as in, Fig 1 to fulfill the above requirements. Such a design also, prevents accidental burn injuries to the user of the soldering, iron and the stand remains stable mechanically., Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished, , 3

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Slowly feed the solder into the joint starting close to the, soldering tip and moving towards the edge of the joint as, in Fig 3, , Continue applying the solder to the joint until complete, wetting of the joint has been achieved and the joint has a, concave fillet as in Fig 4, , After enough solder has been applied and solder wire, removed, keep the soldering iron tip on the joint for a, moment to ensure that all the flux on the joint has reached, the soldering temperature. This will allow majority of the, acids within the joint to break down, which otherwise will, corrode the joint after a period of time., Generally the time taken to make a good soldered joint is, between 3 to 7 seconds from applying the soldering iron, to and removing the soldering iron., 3 Cooling the joint: Tips for cooling a solder joint are, given below:, – Allow the joint to cool without assistance, do not blow, air from your mouth or from any other source to cool the, joint. Forced cooling, cools the joint much earlier than, it has to, resulting in a dry and brittle solder joint which, will lead to mechanical and electrical defects of the, joint., – Do not move any part of the joint while it is cooling. This, disturbs the chemical bonding taking place. Movement, of the joint while it is cooling results in a dry joint., 4 Cleaning the joint : When a solder joint is made, the, amount of flux applied should be just sufficient to make, a good joint. But, quite often, there will be a brown, waxy substance left on the joint. This is nothing but the, flux residue. In its original state this residue is corrosive., Hence, the flux residue or excess flux must be removed, from the joint before soldering can be considered as, complete., If the flux residue and excess flux are not properly, removed, their corrosive nature of the flux will gradually, destroy the component leads and the circuit board. The, flux residue is also sticky and, if not removed, will collect, dust and debris leading to circuit failure., 4, , Removal of flux residue requires the use of solvents. The, type of solvent depends on the flux used., Iso Propyl Alcohol (IPA) is one of the solvents used for, removing residual flux. It is available either undiluted or, pre-mixed with water and can be obtained in pump sprays,, aerosols, cans and drums depending on the quantity and, style of use., Cleaning using water/IPA solution: Determine the, right method of application. (spray or liquid). Apply the, solvent to the soldered joint. Use a clean brush, or some, other type of stiff brush, to gently scrub the joint as in, Fig 5, to help dissolve the residue, taking care to avoid, splashing the mixture., , When the residue has been dissolved, dry the joint with a, lint-free cloth to remove as much of the dissolved residue, as possible., Inspection of soldered joints: Soon after making a, solder joint, as a quick check, the following features of the, solder joint should be checked:, 1 Soldered joint must be bright and shiny., 2 Soldered joint must be smooth and symmetrical., Surface colour - The surface of a correctly soldered joint, will be glossy, silvery and uniform in colour., Surface texture - The surface texture of a correctly, soldered joint will be smooth, even and non-grainy. There, shall be no signs of pitting on the surface of the solder., Common soldering defects: Defects in solder joints can, be grouped as follows:, 1 Temperature defects, 2 Wetting defects, 3 Solder quantity defects, 4 Mechanical defects., Temperature defects: Temperature defects are caused, by excessive or insufficient heating of the joint during the, soldering process., Defects due to excessive heating: The solder on an, overheated joint will have grainy tenure, dull grey colour, and pitted., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished

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Too much heat can lead to one or more of the following, defects:, – Overheating of the resin flux, causes the flux to char, and lose its ability to remove oxides. Lumps of charred, flux gets trapped in the solder forming pits and voids., – Overheating of the solder, causes excessive alloying, between the copper parts of the connection and the tin, content of the solder. This in turn causes localized, depletion of the tin and results in a brittle joint., – Excessive oxidisation of the solder. The oxidised, solder forms a poor bond with the other parts of the, joint., , Wetting defects are easily recognised by the inability of, the solder to cover all the metal surfaces at the joint and, the formation of a large dihedral angles as in Fig 6., , Defects due to insufficient heating: Too little heat can, lead to one or more of the following defects:, , On severely tarnished surfaces, the solder will not flow, over the tarnished surface(non-wetting) or the solder, initially flows over the tarnished surface, but then retreats, leaving small globules of solder on the surface (de-wetting), as in Fig 6., , A defect known as a cold joint. A cold joint occurs when, the flux is unable to remove the tarnish from the joint. At, low soldering temperature the flux is only partly activated., Therefore, it is less effective in removing tarnish., Insufficiently heated solder joint results in,, – poor wetting of the joint, – a course solder fillet, , Solder quantity defects(Refer Fig 7 and 8): Solder, quantity defects are due to either too little or too much, solder applied to a connection., Too little solder results in a small size of the solder fillet as, in Fig 7. The small solder fillets makes a joint weak., , – solder steps at the edges, The effects of a cold joint are,, – high electrical resistance, – low mechanical strength, – dry solder joint, A defect known as a dry joint occurs when the solder is too, viscous to push the flux away from the component lead., A layer of the flux becomes trapped around the lead. This, layer of flux causes a weak bond and hence a poor, electrical connection., Causes of incorrect soldering temperatures, A common indicator of incorrect soldering temperature is, the formation of small peaks at the tip of the joint as the, iron is pulled away. These peaks will be formed at either, too high or too low soldering temperature., , Too much solder results in convex solder fillets as in, Fig 8. This defect is recognised by the large size and the, convex shape of the fillets., , Incorrect soldering temperature may be due to,, – incorrect wattage of the soldering iron, – incorrect soldering tip selection, – insufficient heating of the soldering iron, – poor soldering technique, leading to poor heat transfer, from the tip of the iron to the joint., Wetting defects (Refer Fig 6), The degree of wetting of a joint depends greatly on the, cleanliness of the parts to be joined., , Mechanical defects: Mechanical defects of a solder joint, are caused by;, – the movement of parts of a joint while the solder is, cooling., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished, , 5

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Movement during cooling causes severe dislocation of the, crystalline structure of the solder. This results in a weak, joint which may fracture later and cause high electrical, resistance or an intermittent fault when the circuit is in, use. A joint moved before cooling will have a frosted, appearance with fractures., , One type of Wire-wound resistor is called as fusible, resistor enclosed in a porcelain case. The resistance is, designed to open the circuit when the current through it, exceeds certain limit., , – stresses imposed on the joint as it cools., , These are made of fine carbon or graphite mixed with, powdered insulating material as a binder in the proportion, needed for the desired resistance value. Carbon-resistance, elements are fixed with metal caps with leads of tinned, copper wire for soldering the connection into a circuit., Fig 10 shows the construction of carbon composition, resistor., , Stresses on the joint are usually as a result of inadequate, stress relief bends in the leads of components. A, stressed joint usually breaks due to the expansion and, contraction of components while in use, due to temperature, variations., , 2 Carbon composition resistors, , Blowing on the soldered joint to attempt to speed up, cooling will introduce several additional cooling stresses., Connections that have been disturbed as they cool usually, have a frosted appearance., Never forget the rule, if the quality or reliability of the joint, is in doubt, de-solder the joint and re-solder it fresh., Resistors: These are the most common passive component, used in electronic circuits. A resistor is manufactured with, a specific value of ohms (resistance). The purpose of, using a resistor in circuit is either to limit the current to a, specific value or to provide a desired voltage drop (IR). The, power rating of resistors may be from 0.1 W. to hundreds, of Watts., , Carbon resistor are available in values of 1 ohm to 22, megohms and of different power ratings, generally 0.1,, 0.125, 0.25, 0.5 and 2 watts., 3 Metal film resistors ( Fig 11), , There are four types of resistors, 1 Wire-wound resistors, 2 Carbon composition resistors, 3 Metal film resistors, 4 Carbon film resistors, 1 Wire-wound resistors, Wire-wound resistors are manufactured by using resistance, wire (nickel-chrome alloy called Nichrome) wrapped around, an insulating core, such as ceramic porcelain, bakelite, pressed paper etc.Fig 9, shows this type of resistor.The, bare wire used in the unit is generally enclosed in insulating, material. Wire wound resistors are used for high current, application. They are available in wattage ratings from one, watt to 100 watts or more. The resistance can be less than, 1 ohm and go up to several thousand ohms. They are also, used where accurate resistance values are required., , Metal film resistors are manufactured by two processes., Thick film resistors are pasted with metal compound and, powdered glass which are spread on the ceramic base and, then backed., Thin film resistors are processed by depositing a metal, vapour on a ceramic base. Metal film resistors are, available from 1 ohm to 10 MΩ, upto 1W. Metal film, resistors can work from 120°C to 175°C., 4 Carbon film resistors (Fig 12), , In this type, a thin layer of carbon film is deposited on the, ceramic base/tube. A spiral groove is cut over the surface, to increase the length of the foil by a specialised process., , 6, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished

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Carbon film resistors are available from 1 ohm to few, Meg ohm and up to 2W and can work from 85°C to 155°C., All the above four types of resistors are coated with, synthetic resin to protect them against mechanical, damages and climatic influences, It is therefore, difficult to, distinguish them from each other externally., , It is provided with 3 terminals as shown in Fig 13 and 14., They are available with carbon tracks (Fig 13) and wire, wound (Fig 14) types. Trimmer potentiometers (or), resistor which can be adjusted with the help of a small, screw driver. (Fig 15)., , Specification of resistors: Resistors are specified, normally with the four important parameters, 1 Type of resistor, 2 Nominal value of the resistors in ohm (or) kilo ohm (or), mega ohm., 3 Tolerance limit for the resistance value in percentage., 4 Loading capacity of the components in wattage, Example, 100 ± 10% , 1W, where as nominal value of resistance is, 100Ω., The actual value of resistance may be between 90 Ω to, 110 Ω, and the loading capacity is maximum 1 watt., The resistors can also be classified with respect to their, function as, 1 Fixed resistors, 2 Variable resistors, Fixed resistors : The fixed resistors is one in which the, nominal value of resistance is fixed. These resistors are, provided with pair of leads. (Fig 10 to 12), Variable resistors (Fig 13) : Variable resistors are those, whose values can be changed. Variable resistors includes, those components in which the resistance value can be, set at the different levels with the help of sliding contacts., These are known as potentiometer resistors or simply as, a potentiometers., , Resistance depends upon temperature, voltage,, light: Special resistors are also produced whose resistance, varies with temperature, voltage, and light., PTC resistors (Sensistors) : Since, different materials, have different crystal structure, the rate at which resistance, increases with raising temperature varies from material to, material. In PTC resistor (positive temperature coefficient, resistor), as the temperature increases, the resistance, increases non linearly. For example, the resistance of, PTC at room temperature may be of nominal value 100 Ω, when the temperature rises say 10°C, it may increase to, 150 Ω and with further increase of another 10°C, it may, increases to 500 Ω., NTC Resistors (Thermistors) : In case of NTC resistors, (Negative temperature co-efficient resistors) as the, temperature increases, the value of resistance decreases, non-linearly, For example, NTC resistor, which has nominal, value of resistance is 500 Ω at room temperature may, decrease to 400 Ω with the rise of 10°C temperature and, further decrease to 150 Ω when the temperature rises to, another 10°C., The PTC and NTC resistors can perform switching operation, at specific temperature. They are also used for, measurements and temperature compensators., VDR (Varistors) : The VDR (Voltage dependent resistor), resistance falls non-linearly with increasing voltage. For, example, a VDR, may have 100 Ω resistance at 10 V, and, it may decrease to 90 Ω at rise in 5V. By further increasing, the voltage to another 5V, the resistance may fall to 50 Ω., The VDRS are used in voltage stabilisation, arc quenching, and over voltage protection., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished, , 7

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Light dependent resistor (LDR): The LDRs are also, known as photo- conductors. In LDRs the resistance falls, with increase in intensity of illumination. The phenomena, is explained as the light energy frees some electron in the, materials of the resistors, which are then available as extra, conducting electrons. The LDR shall have exposed surface, to sense the light. These are used for light barriers in, operating relays. These are also used for measuring the, intensity of light., Marking codes for resistors, Commercially, the value of resistance and tolerance value, are marked over the resistors by colour codes (or) letter, and digital codes., Resistance and tolerance value of colour coded, resistors., The colour codes for indicating the values to two significant, figure and tolerances are given in Table 1 as per IS:8186., Table 1, Values to two significant, figures and tolerances, corresponding to colours, Colour, , First, Band/, Dot, , Second, Band/, Dot, , Third, Band/, Dot, , Fourth, Band/, Dot, , First, Figure, , Second Multiplier Tolerance, Figure, , Example, Resistance value : If the colour band on a resistor are in, the order- Red, Violet, Orange and Gold, then the value of, the resistor is 27,000 ohms with +5% tolerance., First, colour, , Second, colour, , Third, colour, , Fourth, colour, , Red, , Violet, , Orange, , 2, , 7, , 1000(10 ), , Gold, 3, , ±5%, , Tolerance value: The fourth band (tolerance) indicates, the resistance range within which is the actual value falls., In the above example, the tolerance is ±5%. ±5% of 27000, is 1350 ohms. Therefore, the value of the resistor is any, value between 25650 ohms and 28350 ohms. The, resistors with lower value of tolerance (precision) are, costlier than normal value of resistors., , Silver, , —, , —, , 10, , ± 10 %, , For less than ten ohms, the third band will be either golden, or silver., , Gold, , —, , —, , 10, , ±5%, , The colours are,, , Black, , —, , 0, , 1, , —-, , Gold -, , 10-1, , =, , 1/10 = 0.1, , Brown, , 1, , 1, , 10, , ±1%, , Silver -, , 10-2, , =, , 1/100 = 0.01, , Red, , 2, , 2, , 102, , ±2%, , Orange, , 3, , 3, , 103, , —-, , Yellow, , 4, , 4, , 104, , Green, , 5, , 5, , Blue, , 6, , Violet, , -2, -1, , Example (Refer Fig 17), , —-, , Colour of, Ist Band, Orange, , Colour of, 2nd Band, White, , Colour of, 3rd Band, Gold, , 105, , —-, , 3, , 9, , 1/10, , 6, , 10, , —-, , 7, , 7, , 7, , 10, , —-, , Grey, , 8, , 8, , 108, , —-, , White, , 9, , 9, , 10, , —-, , None, , —, , —, , —, , ± 20 %, , 6, , 9, , The two significant figures and tolerances colour coded, resistors have 4 bands of colours coated on the body as, in Fig 16., The first band shall be the one nearest to one end of the, component resistor.The second, third and four colourbands, are shown in Fig 16., 8, , The first two colour bands indicate the first two digits in the, numeric value of resistance. The third colour band, indicates the multiplier.The first two digits are multiplied, by the multiplier to obtain the actual resistance value. The, forth colour band indicates the tolerance in percentage., , thus, the value of resistor is 39/10 or 3.9 ohms., , Large value resistances are expressed in kilo ohms and, megohms. Letter 'k' stands for kilo and M stands for, mega. One kilo equals 1000 (103) and one mega equals, 1000000 (106). The resistance values are expressed as, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished

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1000 ohms, , =, , 1k, , 1800 ohms, , =, , 1k 8, , 100 ohms, , =, , 0.1 k, , 10000 ohms, , =, , 0.1 M, , 1500000 ohms, , =, , 1 M 5., , Preferred values for resistors: It is not possible to, manufacture all values of resistors right from one ohm to, a million ohms. So only a set of preferred values of, resistors are generally made. Also in the manufacturing, process, in which thousands of resistors are made in a, day, it is not possible to adjust every ordinary resistor to, an exact value. The term ‘tolerance’ denotes the acceptable, deviation in the resistance value of a resistor.The usual, specified tolerances are ±5%, ±10% and ±20% for the, ordinary resistors. The precision resistors may have, selected tolerances as close as ±0.1%. In each tolerance, range, a set of preferred values are available refer Table 2., Table 2, , E12 Series, Tolerance, ± 10 percent, , E 24 Series, Tolerance, ±5 percent, , E12 Series, Tolerance, ± 10 percent, , E 6 Series, Tolerance, ±20 percent, , 5.6, , 5.6, , —, , 6.2, , —, , —, , 6.8, , 6.8, , 6.8, , 7.5, , —, , —, , 8.2, , 8.2, , —, , 9.1, , —, , —, , Letter and digit code for resistance values: In this, system of coding, numbers and letter are used. Generally, three or four, or five characters consisting of, 1 Two figures and letters, 2 Three figures and letter,, 3 Four figures and letters are used as the case may be., , Preferred series of values for resistors, with ordinary tolerances, E 24 Series, Tolerance, ±5 percent, , Table 2 contd., , E 6 Series, Tolerance, ±20 percent, , 1.0, , 1.0, , 1.0, , 1.1, , —, , —, , 1.2, , 1.2, , —, , 1.3, , —, , —, , 1.5, , 1.5, , 1.5, , 1.6, , —, , —, , 1.8, , 1.8, , —, , 2.0, , —, , —, , 2.2, , 2.2, , 2.2, , 2.4, , —, , —, , 2.7, , 2.7, , —, , 3.0, , —, , —, , 3.3, , 3.3, , 3.3, , 3.6, , —, , —, , 3.9, , 3.9, , —, , 4.3, , —, , —, , 4.7, , 4.7, , 4.7, , 5.1, , —, , —, , The letter R.K. and M. shall be used for multipliers of the, resistance values expressed in ohms R = (10°) = 1, k =103, = 1000, M = 10 6 = 1 000000, For example (Fig 18), 0.1Ω is coded as R10 and 1200 Ω or 1.2k Ω is coded as, 1.2 kΩ similarly 1500000 Ω or 1.5 M Ω is coded as, 1 M 5., For symmetrical tolerance in percentage the following, letter shall be used for indicating tolerance of the resistance, ±5% = J, ±10% = K, ±20% = M, For example (Refer Fig 18), 1 1.5 Ω ±10% 1 W is letter coded as K 1R51W, 2 330 Ω ±20% 0.5 W is letter coded as M 330R 0.5W, 3 2.7 K Ω ±5% 2W is letter coded as J 2K72W, 4 1M Ω ±20% 1 W is letter coded as M 1M1W, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.160, , Copyright @ NIMI Not to be Republished, , 9

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.161, , Semiconductor theory-Active and passive components, Objectives: At the end of this lesson you shall be able to, • explain atom conductor, semiconductor, insulator and atomic structure, • state the function of N and P type semiconductor, PN junction, depletion region, • state the coding of semiconductor devices and its meaning, • explain active and passive components, symbols - uses., Atom, The very tiny fundamental unit of an element which is, capable of independent existence is the atom. An atom, of any element consists of a central core called Nucleus., A number of small particles called electrons move around, the central core., The nucleus contains protons and neutrons. A proton in, the nucleus possess a positive electrical charge. An, electron in an atom possess negative electrical charge. In, normal state, the atom is electrically neutral, that is the, number of electrons is equal to the number of protons in, the nucleus., , themselves in different orbits. There are 2 electrons in the, first orbit, 8 electrons in the second orbit, and 18 electrons, in the third orbit. The fourth orbit is the outer or valence orbit, which contains 4 electrons., Fig 1b shows a silicon atom. It has 14 protons in the, nucleus and 14 electrons in 3 orbits. There are 2 electrons, in the first orbit and 8 in the second orbit. The remaining, 4 electrons are in the outer or valence orbit., , For stability of materials (solids), the valence (outer most), shell of an atom should contain either 8 or more number, of electrons, if it is to be complete.The above stability, keeps the atoms and the molecules together in a solid, state., There are three important kinds of bonding amongst the, atoms and the molecules of a solid. They are i) ionic ii), covalent and iii) metallic bonds., Examples of solids under different bondings are,, lonic bond, , :, , sodium chloride, , Covalent bond, , :, , silicon and germanium, , Metallic bond, , :, , metals like copper, , Difference between conductors insulators and semi, conductors: We are familiar with conducting and insulating, materials. Conducting materials are good conductors of, electricity. Insulating materials are bad conductors of, electricity. There is another group of materials called as, semiconductors, such as germanium and silicon. These, are neither good conductors nor good insulators., , In semiconductor materials, the atoms are arranged in an, orderly pattern called a crystal lattice structure. If a pure, silicon crystal is examined we find that the four electrons, in the outer (valence) shell of an atom is shared by the, neighbouring atoms as in Fig 2., , The conductors on valence electrons are always free. In, an insulator the valence electrons are always bound., Whereas in semi conductors the valence electrons are, normally bound but can be set free by supplying a small, amount of energy. Several electronic devices are made, using semi conductor materials., Semi conductors - Atomic structure: Germanium (Ge), and silicon (Si) are examples of semi conductors. Fig 1a, shows a germanium atom. In the centre is a nucleus with, 32 protons. 32 revolving electrons are distributed, 10, , Copyright @ NIMI Not to be Republished

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The union of atoms sharing the valence electrons is called, a covalent band.That means a valence electron being, shared by two adjacent atoms. Each atom appears to, have a full outer shell of eight electrons., Types of semiconductors : A pure semiconductor is, called an intrinsic semiconductor. For example, a silicon, crystal is an intrinsic semiconductor because every atom, in the crystal is a silicon atom. One way to increase, conductivity in a semiconductor is by ‘doping’. This, means adding impurity atoms to an intrinsic semiconductor., The doped semi-conductor is known as an extrinsic, semiconductor., , electron. The number of such free electrons is controlled, by the amount of arsenic added to the crystals., In N-type, the free electrons are called the majority, carriers, and the holes minority carriers., P-type semiconductor : To obtain more holes, a pure, silicon crystal is doped with elements such as aluminum, or boron or gallium. The atoms of each of these elements, have three electrons only in their outer orbit. Adding, gallium to pure silicon crystals allows the atoms of the two, elements to share seven electrons. (Fig 5), , The residual heat at room temperature (300K) is sufficient, to make a valence electron of an intrinsic semiconductor, to move away from the covalent bond and then the covalent, bond is broken, and the electron becomes a free electron, to move in the crystal. This is shown in Fig 3., , A hole is created in the place of the eighth electron. Now, that the number of holes exceeds the number of free, electrons the substance becomes ‘P’ type material. The, holes in P-type are the majority carriers, and the free, electrons are the minority carriers., PN Junction : A PN junction is formed by combining P, and N type materials. The surface where they meet is, called the PN junction. A PN junction is illustrated in, Fig 6., , When an electron breaks a covalent bond and moves, away, a vacancy is created in the broken covalent bond., This vacancy is called a ‘hole’. A hole has a positive, charge. When a free electron is liberated, a hole is, created., N - type semiconductor : A semiconductor with excess, of electrons is called N-type. To obtain excess free, electrons the element doped with the semiconductor, material is arsenic, or antimony or phosphorus. Each of, these atoms has five electrons in its outer orbit. (Fig 4), The free electrons in the N-regions diffuse across the, junctions into the P-region. The free electrons lose energy, and recombine with the holes in the P-regions.This, recombination eliminates a free electron and a hole., When the electron moved from the N-region and diffused, across the junction, it leaves the atom to be a positive ion., , Because the outer orbits of the atoms can hold eight, electrons, no hole is available for the fifth electron in the, arsenic atoms to move into. It, therefore, becomes a free, , The positive ion is not balanced by a negative charge in the, N-region. The hole is eliminated in the P-region by, recombination. The elimination of the hole and its positive, charge leaves the atom to be a negative ion in the P-region., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.161, , Copyright @ NIMI Not to be Republished, , 11

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The ions in the crystal structure are fixed and cannot, move. Thus, a layer of fixed charges is formed on the two, sides of the junctions. This is shown in Fig 7., , A, , – diode or rectifier, , AP – photo-diode, AZ, , – voltage regulator diode, , C, , – transistor, , CP – phototransistor, The group of figures in a serial number indicating a, particular design or development., Present system : This system consists of two letters, followed by a serial number. The serial number may, consists of three figures of one letter and two figures, depending on the main application of the device., The first letter indicates the semiconductor material used., A Germanium, There is a layer of positively charged ions on the N-side, and on the P-side of the junction there is a layer of, negatively charged ions. An electric field is created across, the junction between the oppositely charged ions. This is, called a junction field. The junction field is also known as, ‘barrier’. The distance between the sides of the barrier is, the ‘width’ of the barrier., Depletion region : The carrier in the vicinity of the, junction are involved in forming the junction. Once the, junction field is established, no carriers can move through, the junction. Hence the junction field is called ‘depletion, region’ or ‘space charge region’. This layer is called the, depletion layer, because there are neither free electrons, nor holes present. This depletion region prevents further, movement of electrons from the N-material to the, P-material and thus an equilibrium is reached., The intensity of the field is known as ‘barrier height’ or, ‘potential’ hill’. The internal voltage set up due to positive, and negative ions at the junction is called barrier potential., If any more electrons have to go over from the N-side to, P-side, they have to over come this barrier potential. This, means, only when the electrons on the N-side are supplied, with energy to overcome the barrier potential they can go, over to the P-side., In order to cancel the barrier potential and the electrons, to cross over a potential difference of 0.7 V is required for, a silicon diode and 0.3 V for a germanium diode. The, barrier voltage is more for silicon because its lower atomic, number allows more stability in the covalent bonds. The, barrier potential decreases at higher temperatures., Old system : Some earlier semiconductor diodes and, transistors have type numbers, consisting of two or three, letters followed by group of one, two or three figures. The, first letter is always ‘O’, indicating a semi-conductor, device., , B Silicon, C Compound materials such as gallium arsenide, R Compound materials such as cadmium sulphide, The second letter indicates the general function of the, device., A detection diode, high speed diode, mixer diode, B variable capacitance diode, C transistor for I.F. applications (not power types), D power transistor for A.F. applications (not power types), E tunnel diode, F transistor for A.F. applications (not power types), G multiple of dissimilar devices, miscellaneous devices, L power transistor for a.f. applications, N photo-coupler, P radiation sensitive device such as photo-diode, phototransistor, photo-conducive cell, or radiation detector, diode, Q radiation generating device such as light-emitting diode, R controlling and switching devices (e.g. thyristor) having, a specified breakdown characteristic (not power types), S transistor for switching applications (not power types), T controlling and switching power device (e.g. thyristor), having a specified breakdown characteristic., U power transistor for switching applications, X multiplier diode such as varactor or step recovery diode, Y rectifier diode, booster diode, efficiency diode, Z voltage reference or voltage regulator diode, transient, suppressor diode., , The second (and third) letter(s) indicate the general class, of the device., 12, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.161, , Copyright @ NIMI Not to be Republished

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The remainder of the type number is a serial number, indicating a particular design or development, and is in one, of the following two groups., , The colour coding of capacitors and resistors are same., Where as, in the case of fixed capacitors, the colour coded, unit shall be in Picofarads., , a Devices intended primarily for use in consumer, applications (radio and television receivers, audioamplifiers, tape recorders, domestic appliances, etc.), The serial number consists of three figures., , For letter coding, incase of capacitor, the letter ‘p’, ‘n’, ‘μ’, shall be used as multipliers. Where p = 10-12, n= 10-9 and, μ = 10-6 farads, and letter code for tolerance on capacitor, is the same as in resistor., , b Devices intended mainly for applications other than (a), e.g. industrial, professional and transmitting, equipments., The serial number consists of one letter (Z,Y,X,W etc), followed by two numbers (digits), The International System follows letters 1N, 2N, 3N etc, followed by four numbers., 1N, , indicates single junction, , 2N, , indicates two junction, , 3N, , indicates three junctions., , Inductor: The ability of the conductor to induce voltage in, itself, when the current changes in it is called as self, inductance (or) simply inductance. A coil introduced in a, circuit to have inductance is called as inductor. Different, type of inductors are shown in Fig 8. The unit of inductance, is “Henry”. Commercially a coil may have inductance in, Millihenry (10-3H), or in Microhenry (10-6H)., , The number indicates internationally agreed manufacturer’s, code e.g. 1N 4007, 2N 3055, 3N 2000., Again, manufacturers use their own codes for, semiconductor devices. Manufacturers in Japan use 2SA,, 2SB, 2SC, 2SD etc. followed by a group of numbers e.g., 2SC 1061, 2SA 934, 2SB 77. Indian manufacturers have, their own codes too., Passive and active electronic components, Introduction: The Components used in electronic circuits, can broadly grouped under two headings., , While specifying the inductance the following factors to be, considered, , – passive components, , •, , nominal value of inductance in Henry / Millihenry /, Microhenry., , •, , tolerance in percentage (±5/10/20%), , •, , type of winding like single layer, double layer, multilayer, and pie (p) etc., , •, , type of core like air core, iron core, ferrite core, , •, , type of application like audio frequency (AF), Radio, frequency (RF) coupling coil, filter coil etc.,, , – active components, Passive components: Components like resistors,, capacitors, and inductors used in electronic circuit are, called as passive components. These components by, themselves are not capable of amplifying or processing an, electrical signal. However these components are equally, important in electronic circuit as that of active components,, without the aid of passive components, a transistor (active, components) cannot be made to amplify electrical signal., Circuits formed with passive components obey the electrical, circuits laws such as ohm’s law, Kirchoff’s Laws etc.,, Resistors: The components whose purpose to introduce, resistance in the circuit is called as resistors. Other, details of resistors are dealt in earlier lessons., Capacitor: The components whose purpose to introduce, capacitance in the circuit is called as capacitor. The unit, of capacitance is ‘FARAD’. Commercially capacitors are, available in Microfarad (μF), Nanofarad (nF) and, Picofarads (pF)., , In an electronic circuit some time, it is also required to vary, the inductance., The inductance of a coil can be varied by:•, , providing tapped inductive coil, as in Fig 9 or, , •, , adjusting the core of a coil as in Fig 10., , However, all inductor coils have inherent resistance due to, the resistance of the winding wire in the coil. Further the, maximum current that can be safely carried by an inductor, depends upon the size of the winding wire used., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.161, , Copyright @ NIMI Not to be Republished, , 13

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SCR (Silicon controlled rectifier) : Figure 14a shows, the physical appearance of one type of SCR and the, symbol is shown in Fig 14b. SCRs are also called, thyristors and used as switching devices., , Active components, In electronic circuit, the components, other than passive, are known as active components. Namely, transistors,, diodes, SCRs Vacuum tubes etc.,, Active components : In electronic circuits, components, other than resistors, capacitors and inductors are also, used. Namely, transistors, diodes, vacuum tubes, SCRs,, diacs, zener-diode (Fig 11) etc. The application of electrical, circuit laws (Ohm’s law etc.) in the circuit containing the, above components will not give correct results. i.e. these, components do not obey. Ohm’s law, Kirchoff’s law etc., These components are called active components., , Diac : A diac (Fig 15a) is a two-lead device like a diode., It is a bidirectional switching device. Its symbol is shown, in Fig 15b., , The different active components and the method of, representing them by symbols in the circuit diagram are, given below (Fig 11), , Triac : A triac is also a semiconductor device with three, leads like two SCRs in parallel. The triac can control the, circuit in either direction. (Fig 16), , The different types of diodes (Fig 12) used for specific, purposes are represented by the symbols given., Transistor : Figure 13a shows the physical appearance of, transistors. There are two symbols to represent a transistor., (Fig 13b). The selection of a symbol is based on either the, NPN or the PNP type of transistor., 14, , Bridge rectifier or diode bridge : It is a single package, of four semiconductor diodes connected in bridge circuit., The input AC and the output DC leads are marked and, terminated as shown in the Figure 17., UJT (Uni-junction transistor) : It has two doped regions, with three leads and has one emitter and two bases, (Fig 18)., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.161, , Copyright @ NIMI Not to be Republished

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FET (Field effect transistor) : Fig 19a give a pictorial view, of the component, and the related symbol to represent the, field effect transistor is shown in Fig 19b. The selection of, the symbol is based on whether the FET is a ‘N’ channel, or a ‘P’ channel one., , In the active components few basic components discussed, have and many more advanced components associated, with modern circuits are in use., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.161, , Copyright @ NIMI Not to be Republished, , 15

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.162, , PN Junction - semi conductor diodes, Objectives: At the end of this lesson you shall be able to, • explain diffusion in PN junction and barrier potential, • explain forward and reverse biasing of PN junction and semi conductor diodes and its VI characteristics, • state the applications specifications and classification of diodes, • state the different industry standards for diode numbering and finding equivalents of diode, • state the method of testing diode and identifying the polarity, • state special diodes and their functions and PIV., PN junction: A diode is made by combining P and N, materials. The surface at which these materials meet is, the PN junction., Diffusion occurs when P and N materials are joined, together.(Fig 1) some electrons in the N material, near the, junction, are attracted to the holes in the P material, thus, leaving holes in the N material. The diffusion of electrical, charges produces a potential difference in a small area, near the junction (Fig 2).As a result, the material will, conduct in one direction but not in the opposite direction., For this reason, the area in which this emf exists is called, a barrier., , The internal barrier potential (Vb) : Although it is an, internal contact potential that cannot be measured directly,, the effect can be overcome by 0.3V for a Ge junction or 0.7, V for Si. The barrier voltage is more for Si because its lower, atomic number allows more stability in the covalent bonds, as already stated., The PN junction, with the depletion zone magnified, shows, the iron that has +ve and -ve charges produce the internal, contact potential Vb at the barrier. (Fig 2), A PN device is knows as a diode. The diode and its symbol, are in Fig 3. This type of construction permits the current, to flow in one direction but not in the opposite direction., Biasing the PN junction, Forward Bias : A forward-biased PN junction is in Fig 4, The positive terminal is connected to the P-side and the, negative terminal of the DC supply is connected to the, N-side of the junction., , 16, , A current will flow through the diode as in the, Fig 4. The positive terminal for the battery attracts, electrons from P material, leaving an excess of holes., Because electrons are drifting away from the junction, the, excess holes tend to accumulate near the junction. At the, same instant, electrons from the negative terminal of the, battery are attracted to the less negative N material of the, diode. This action overcomes the barrier at the junction, and allows the electrons to move into the excess holes of, the P material, the result is a continuous flow of electrons, in one direction. The voltage required to move the charge, carries in forward bias conduction called the barrier, voltage., Reverse Bias: If the polarities of the DC supply are as, shown in Fig 5, the PN junction is said to be reversebiased. That is, the P side is connected to the negative, and the N-side is connected to the positive terminals of the, supply. Fig 5 shows the battery connection reversed, (reverse bias). At the same instant, a shift in electrons in, the P material causes the positive holes to appear further, , Copyright @ NIMI Not to be Republished

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away from the junction near the end for the diode, which, is connected to the negative terminal of the battery. This, action produces a wider barrier at the PN junction through, which the electrons cannot flow. (A very small current, leakage may however occur)., , The current in the forward direction increases rapidly upon, reaching the forward voltage Vb which is known as the, barrier potential or the junction potential and the barrier, potential for germanium is 0.3 V and for silicon it is 0.7 V., The behaviour of the PN junction is limited by the maximum, forward current, as too much of current may destroy a, diode due to the excess heat generation., The current in the reverse direction of the junction is very, small. Upon reaching —Vb in the reverse direction, the, reverse current suddenly increases. —Vb in the reverse, direction where the current starts increasing is called the, knee potential or breakdown voltage. Normally the diode, should not be operated in this region. The knee voltage, depends on the type of diode which varies from 3V to 20, kV or more., Application of diodes : Semi conductor diodes are used, for various applications. Some of the major areas of, application are listed below., •, , Modulation and demodulation in communication, receivers., , •, , Switching high speed digital circuits, , •, , Low power and high power rectification, , •, , As surge protectors in EM relay and other circuits., , •, , For clipping, clamping wave-forms., , For different applications, diodes of different current carrying, capacity, different PIV capacity and so on are required., Therefore, manufacturers make diodes to cater to varied, applications with different specifications. Before using a, diode for a particular application, it is a must to find out, whether the voltage, current, and temperature, characteristics of the given diode match the requirement, or not., Important specifications of a diodes, V-I characteristic of PN junction : The static current, voltage characteristic is in Fig 6., , The material : The diode is made-of dopped semiconductor material. This could be Silicon or Germanium, or Selenium.This is important because the cut-in voltage, depends upon the material the diode is made-of. For, example, in Ge diodes the cut-in voltage is around 0.3V,, whereas in Si diodes the cut-in voltage is around 0.7V., Maximum safe reverse voltage : Denoted as VR or Vr, that can be applied across the diode. This is known as, peak-inverse-voltage or PIV. If a higher reverse voltage, than the rated PIV is applied across the diode, it will, become defective permanently., Maximum average forward current : If or IF that a diode, can allow to flow through it without getting damaged., Forward voltage drop : VF or Vf that appears across the, diode when the maximum average current, If flows through, it continuously, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.162, , Copyright @ NIMI Not to be Republished, , 17

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Maximum reverse current : Ivr that flows through the, diode when the maximum reverse voltage, PIV is applied., Maximum forward surge current : Is that can flow, through the diode for a defined short period of time., The maximum junction temperature: The temperature, upto which the diode junction can withstand without mal, functioning or getting damaged., Manufacturer’s code of Diodes : The diodes are printed, with a type number. When this type number is referred to, in the manufacturer’s manual, the detailed specifications, for a particular type, number of the diode, can be obtained., To bring standardization for the diodes and other, components manufactured by different manufacturers., The Manufacturer and Standards Associations have set, certain International Standards for the benefit of users of, the components. The principal industry standard numbering, systems are dealt with here., 1 The JEDEC type code: The EIA in USA maintains a, register of 1N, 2N, types familiarly known as JEDEC, types, which have world wide acceptance., 1N is used as a prefix for semiconductors with one, junction. For example all 1N components refer to diodes, because diodes have one junction. Similarly, prefix 2N is, used with components with two junctions and so on., 2 The PRO-ELECTION type code : The Association, International pro-electron in Europe maintains a register, of Pro-electron type which have wide acceptance in, Europe., Components in the Pro-electron system have,, , The letters after the S has the following significance:, A, , =, , pnp hf, , B, , =, , pnp if, , C =, , npn hf, , D =, , npn if, , Some components will have a type number which does not, match with any of the above said International Standards., Then, these type numbers are particularly known to the, individual manufacturer. These codes are generally referred, to as manufacturer’s house code. However, these type, numbers may conform to one or more of the International, Standards. Almost all standard diode data books lists, popular manufacturers house codes., Diode equivalent: There are several occasions, especially, while servicing electronic circuits, it may not be possible, to get a replacement for a diode of a particular type, number. In such cases one can obtain a diode having, specification closest to the one to be replaced. Such, diodes are referred to as equivalents., Example: In a circuit, diode 1N 4007 is found to be, defective, and if 1N4007 is not available in stock, then, instead of 1N4007, BY 127 can be used as it is the, equivalent for 1N4007., Some data books give these lists of equivalents., Classification of Diode, 1 Based on their current carrying capacity/power handling, capacity, diodes can be classified as, •, , It can handle power of the order of several milliwatts, only, , •, , two letter and numeral code for consumer devices, (Example, BY127 and so on), , •, , three letter and numeral code for industrial devices., (Example, ACY17 and so on)., , •, , The first letter in the pro-electron type code indicates the, type of semiconductor material used in making the device., Example, device numbers starting with A are made of, germanium. Refer to diode data book for further details, and examples., , •, , The second and third letter indicate the applications of the, component. Example, in the type code BY127, the, second letter Y indicates that it is a rectifier diode., , •, , The numeral after the second or third letter is the code, number of its detailed voltage, current and temperature, specification., 3 The JIS type code: In Japan, the JIS, (Japanese, Industrial Standards) code is used. This system of, component numbering is almost universal. In this, system, all component numbers start with 2S, followed by, a letter and several numbers. Example. 2SB364., 18, , low power diode, , medium power diode, It can handle power of the order of several watts only, high power diode, It can handle power of the order of several 100’s of, watts., , 2 Based on their principal application, diodes can be, classified as,, Signal diode, Low power diodes are used in communication circuits, such as radio receivers etc. for signal detection and, mixing, •, , Switching diode, Low power diodes are used in switching circuits such, as digital electronics etc. for fast switching ON/OFF of, circuits, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.162, , Copyright @ NIMI Not to be Republished

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•, , Rectifier diode, Medium to high power is used in power supplies for, electronic circuits for converting AC to DC voltage., , While doing the above test, if a diode shows a very low, resistance in both the forward and reverse biased conditions,, , 3. Based on the manufacturing techniques used, diodes, can be classified as,, •, , point contact diode, A metal needle is connected with pressure on to a, small germanium (Ge) or silicon (Si), , •, , Junction diode, They are made by alloying or growling or diffusing P and, N materials on a semiconductor substrate., , Types of diode packaging : The type of packaging given, to diodes is mainly based on the current carrying capacity, of the diode. Low power diodes have either glass or plastic, packaging. Medium power diodes have either plastic or, metal can packaging. High power diodes will invariably, have either metal can or ceramic packaging. High power, diodes are generally of stud-mounting type., Testing diodes using ohmmeter: A simple ohmmeter, can be used to quickly test the condition of diodes. In this, testing method, the resistance of the diode in forward and, reverse bias condition is checked to confirm its condition., Recall that there will be a battery inside an ohmmeter or, a multimeter in the resistance range. This battery voltage, comes in series with the leads of the meter terminals as, in Fig 7.In Fig 7 the lead A is positive, lead B negative., If the polarity of the meter leads are not known, at first, the polarity of the meter leads can be, determined by using a voltmeter across the, ohm meter terminals., If the positive lead of the ohmmeter, lead A in the Fig 7 is, connected to the anode of a diode, and the negative, (lead B) to the cathode, the diode will be forward-biased., Current will flow, and the meter will indicate low resistance., On the other hand, if the meter leads are reversed, the, diode will be reverse-biased. Very little current will flow, because a good diode will have very high resistance when, reverse biased, and the meter will indicate a very high, resistance., , then, the diode under test must have got damaged or more, specifically shorted. On the other hand, a diode is said to, be open if the meter shows very high resistance both in the, forward and reverse biased conditions., Polarity marking on the diodes: The cathode end of a, diode is usually marked by a circular band or by a dot or, by plus (+) sign. In some diodes the symbol of the diode,, which itself indicates the polarities, is printed on the body, of the diode., Special diodes: All diodes are basically PN junction, diodes and are made according to the application. There, are many special purpose diodes are in use in which zener, diodes widely used for voltage regulation., Zener diode: This diode specially designed for voltage, regulation. A wide range of voltage regulated zener diodes, are available., It is a PN junction diode doped heavily for regulation, purpose. It has a normal VI characteristic when it is, forward biased. But the characteristic are changed abruptly, when it is connected in reverse bias., In the reverse bias condition a leakage current in the order, of Microamps will flow. When the reverse voltage reaches, to a particular designed voltage a sudden breakdown, known as avalanche breakdown happens., When a heavy current flows at constant voltage, the, voltage continue to remain constant. Further increase in, voltage, the current suddenly increases. Fig 8 shows the, reverse characterises of zener diode., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.162, , Copyright @ NIMI Not to be Republished, , 19

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Few more special diodes listed below in Table 1, Sl.No, , Name, , Purpose, , 1, , LED, , Light emitting diode - exhibits light in conduction, , 2, , TUNEL or ESAKI, , Un effected by change in temperature, , 3, , SCHOTTKY, , Fast switching, , 4, , VARICAP, , Varactor -Variable capacitance diode or tuning diode, , 5, , SCHOKLEY, , Constant current diode, , 6, , PHOTO DIODE, , Light dependent diode, , 7, , IMPATT DIODE, , Heavily doped PN layers, , 8, , PIN DIODE, , Low capacitance switching, , 20, , Symbol, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.162, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.163, , Rectifiers, Objectives: At the end of this lesson you shall be able to, • state the purpose of rectifier in power supply circuit, • explain the working of half-wave, full-wave and bridge rectifier circuit, • state the need of filter circuit to rectifier circuits, • state the different types filter circuit for rectifiers and their working., Most of the electronic equipment, both entertainment and, professional, need DC voltage for operation. The power, supply converts AC supply voltage into DC. Diodes are, used as rectifier in a power supply circuit., Half wave rectifier: This simplest form of AC to DC, converter is by using one diode such an AC to DC, converter is known as half-wave rectifier as in Fig 1., , 0.7V. Ignoring the small voltage drop across the diode., We can find the relationship between AC input and DC, output voltage., The AC input wave-form is shown in Fig 1b., Vrms = 0.707 Vp, Vp =, , Vrms, 0.707, , In Fig 1C, the DC output is shown. The diode produces, only half cycle of the Ac input. The average value of this, half wave is the DC output voltage., Vdc =, , 0.318 Vp, , = 0.318 x, , =, , A diode D1 and a load resistance RL in series are, connected across the secondary of a step down transformer, (Fig 1(a). The transformer steps up or steps down the, supply voltage as needed. Further the transformer isolates, the power line and reduces the risk of electrical shock., During the positive half-cycle of the input line frequency,, (Fig 1b) the diode anode is made positive with respect to, the cathode. The diode D1 conducts because it is forwardbiased. Current flows from the positive end of the supply, through diode D1 and RL to the negative terminal of the, input. During this period of time, a voltage is developed, across RL. The polarity of the voltage is as indicated in, Fig 1C., During the negative half cycle of AC input line frequency,, the diode is reverse-biased. Practically no current flows, through the diode and the load RL and there is no voltage, output., DC output: The voltage drop across the forward biased, diode is low, because the resistance of the forward-biased, diode is very low. Ge diode drops 0.3V and Si diode drops, , Vrms, 0.707, , 0.45 Vrms, , For example if the input AC voltage is 24 volts the output, DC of the half wave rectifier will be Vdc = 0.45 x 24= 10.8, V, Vdc, The DC load current is Idc = R, L, , Ripple frequency: From Fig 1 it is evident that the, frequency of the rectified pulsating DC is same as the, frequency of the input AC signal. This is true for all halfwave rectifiers., Peak inverse voltage: Fig 1(a) shows the half-wave, rectifier at the instant the secondary voltage is at its, maximum negative peak., In this condition, since the diode is reverse biased, it, behaves as an open switch as in Fig 2b. Since the diode, is reverse biased, there is no voltage across the load RL., Therefore, from Kirchhoff’s Voltage law, all the secondary, voltage appears across the diode as shown in Fig 2a. This, is the maximum reverse voltage that appears across the, diode in the reverse biased condition. This voltage is called, the peak reverse voltage or more commonly as the peak, inverse voltage (PIV). Therefore, in a half-wave rectifier the, , Copyright @ NIMI Not to be Republished, , 21

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peak inverse voltage across the diode is equal to the -ve, peak value of the secondary voltage Vs(peak). Since the -ve, peak voltage and +ve peak voltage in a sinusoidal wave, is same in magnitude, the peak inverse voltage (PIV), across the diode in a halfwave rectifier can be taken as a, Vs(peak)., , a half wave rectifier driven by the same secondary voltage., , In the example considered earlier, the PIV across the, diode will be,, , Vs(rms ), 24, =, =, 33.9 =, 34 volts, Vs (peak ) =, 0.707 0.707, To avoid break down of the diode used, the PIV appearing, across the diode of the designed HW rectifier must be less, than the PIV rating of the diode. For instance, in the above, example to avoid break down of the diode, the PIV rating, of the diode should be greater than 34 volts., However this condition changes when a filter capacitor is, used in the output DC circuit., , From Fig 3 it i s evident that the average of DC value of, a full wave rectified output is, Vdc = 0.318 Vs(peak) + 0.318 Vs(peak), , Full wave rectifier (FW): A full wave rectifier circuit is in, Fig 3. The secondary winding of the transformer is centretapped. The secondary voltage is divided equally into two, halves, one end of the load RL is connected to the centre, tap and the other end of RL to the diodes., , Vdc = 0.636 Vs(peak), , It is seen that two half-wave rectifiers are conducting on, alternate half cycles of the input Ac., , In terms of Vs(rms) Vdc of full wave rectifier is given by,, , During the positive half cycle of the secondary voltage,, diode D1 is forward-biased and diode D2 is reverse-biased., (Fig 3b) The current flows through the load resistor RL,, diode D1 and the upper half of the secondary winding., During the negative half cycle of secondary voltage, diode, D2 is forward-biased and diode D1 is reverse-biased., Therefore, current flows through the load resistor RL diode, D2 and the lower half of the secondary winding. (Fig 3c), The load current is in the same direction during both the, half-cycles of the AC input. The output of the full-wave, rectifier is shown in Fig 3d., , where, Vs(peak) is the equal peak voltage between the, centre-tap and any one end A or B of the transformer, secondary., , Vs(rms) = 0.707 Vs(peak), , Vs (rms ), 0.9 Vs (rms), Therefore, Vdc =, 0.636 =, =, 0.707, Example, Suppose the secondary voltage of the transformer is 240-24V(rms), the Dc output voltage of a full wave rectifier, using this transformer will be,, For a two diode full wave rectifier, Vdc = 0.9 Vs(rms), , DC output : Since a full wave rectifier is nothing but a, combination of two half-wave rectifiers, the average or DC, value of a full wave rectifier is naturally twice the output of, 22, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished

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Therefore, in the given example, Vdc = 0.9 x Vs(rms) = 0.9 x 24 = 21.6 volts, Ripple frequency in a full wave rectifier: From, Fig 3c it can be seen that two cycles of output occur for, each input cycle of AC voltage. This is because, the full, wave rectifier has inverted the negative half cycle of the, input voltage. As a result, the output of a full wave rectifier, has frequency double the input AC frequency. If mains AC, supply is used as input to a full wave rectifier, the mains, frequency is 50 Hz, the output frequency of the pulsating, DC will be 100 Hz., Note: This increased ripple frequency has certain, advantages when the pulsating DC is smoothed., This will be dealt with in further lesson., Peak inverse voltage: Fig 4 shows the full wave rectifier, at the instant the secondary voltage reaches its maximum, positive value., , Current rating of diodes in a full wave rectifier : If the, load, RL connected in the fullwave rectifier is, say 10Ω the, DC current through it will be,, V, , Idc = dc, 10 Ω, In the example considered above, Vdc = 21.6 volts, 21.6, =, 2.16 amps., Therefore, Idc =, 10, , It is interesting to note this current Idc is shared by the two, diodes D1 and D2. This is because each diode conducts, only for one half cycle. Therefore, the DC current through, each diode is half the total DC load current Idc. Hence, the, maximum current through each diode with 10Ω load will be, 2.16/2 = 1.08 amps. From this it follows that the current, rating (If(max)) of each diode need only be half the, maximum/rated load current., NOTE: In a halfwave rectifier, since there is only one diode,, the current rating of the diode used should be the maximum, current through the load unlike in the case of a full wave, rectifier in which the current rating of the diodes used is, only half the maximum current through the load., Example: In a two diode full wave rectifier, with a load, current requirement of 1.8 amps, what should be the, current ratings of the diodes used?, Since it is a two diode full wave rectifier, the current rating, of each diode should be = 1/2 the total load current., , Applying Kirchhoff’s law around the outside loop, we get,, 2Vs(peak) - Reverse voltage(PIV), across D2 + Forward voltage across D1 = 0, , Therefore If(max) of diodes should be = 1.8 amps/2 = 0.9, amps., It is fine if a diode of 1 amp current rating is used for this, rectifier circuit., , Neglecting the small forward voltage across D1 we have,, 2Vs(peak) = PIV across D2 + 0 = 0, , Disadvantages of TWO DIODE full wave rectifier : The, full wave rectifier using two diodes and centre tap transformer, has the following disadvantages, , or PIV across D2 = 2Vs(peak), , •, , From the above it can be seen that each diode in a fullwave, rectifier must have PIV rating greater than the peak value, of the full secondary voltage. 2Vs(peak), , A centre-tapped transformer that produces equal, voltages on each half of the secondary winding is, difficult to manufacturer and, hence, expensive., , •, , Centre-tapped transformers are generally bulkier than, ordinary transformers, and, hence, occupy larger space., , •, , In a two diode full wave rectifier, only half of the, secondary voltage is made use at a time although it, works in both +ve and -ve half cycles., , In the example considered earlier, the PIV of diodes, should be 2 Vs(peak)., , Vs(peak) =, , Vs(rms), 0.707, , =, , 2 Vs(peak) =, , 2 x Vs(rms), 0.707, , Bridge rectifier :It is a full-wave rectifier. The circuit is in, Fig 5a. In the bridge rectifier four diodes are used. There, is no centre tap on the secondary of the transformer., , 2 x 24, =, =, 68 volts (approx.), 0.707, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished, , 23

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Example: In Fig 5, if the transformer secondary voltage, Vs(rms) is 24 volts, the rectified DC voltage Vdc across the, load RL will be,, From equation ....2, Vdc for a bridge rectifier is given by,, Vdc = 0.9 Vs(rms), In the given example, Vs(rms) = 24 volts, Therefore, Vdc = 0.9 x 24 = 21.6 volts, , During the positive half of the secondary voltage, diodes D2, and D3 are forward-biased. Hence current flows through, diode D2 load resistance RL and D3 to the other end of the, secondary. This is illustrated in Fig 5b. During the, negative half of the secondary voltage, diodes D1 and D4 are, conducting . The current flows through diode D4, resistor, RL and diode D1 to the other end of the secondary. This is, illustrated in Fig 5c., In both cases the current flows through the load resistor in, the same direction. Hence, a fluctuating DC is developed, across the load resistor RL. This is shown in Fig 5d., , NOTE: Using the same transformer, a two-diode, full wave rectifier would have given only 10.8, volts which is half of that of bridge rectifier, output., Ripple frequency - Bridge rectifier: The pulsating DC, output of a bridge is similar to the two diode full wave., Hence as in a two diode fullwave rectifier, the output ripple, frequency of the bridge rectifier is also twice the input AC, frequency., Peak inverse voltage - Bridge rectifier: Fig 7 shows, a bridge rectifier at the instant the secondary voltage has, reached its maximum value., , DC output: Fig 6 shows the input AC and the output, pulsating DC wave-form of a bridge rectifier., This wave-form is similar to that of the full wave rectifier, using a centre-tap transformer. Hence, the average DC, value of the output is,, Vdc = 0,636 Vs(peak), or Vdc = 0.9 Vs(rms), where, Vs(rms) is the full secondary AC rms voltage., NOTE: In a two -diode full wave rectifier Vs(rms), refers to only half for the total secondary, voltage whereas in a bridge rectifier Vs(rms), refers to full secondary voltage., 24, , Diode D4 is ideally short (as it is conducting) and D1 is, ideally open. summing the voltages around the outside, loop and applying Kirchhoff’s law,, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished

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Vs(peak) - PIV across D1 + 0 = 0, or, , PIV across D1 = Vs(peak), , Therefore, the peak inverse voltage across D1 is equal to, the peak secondary voltage Vs(peak), In a similar way, the peak inverse voltage across each, diode will be equal to the peak secondary voltage Vs(peak) of, the transformer secondary. Hence the PIV ratings of the, diodes used should be greater than Vs(peak), Example, , Current rating of diodes in bridge rectifiers : As in the, case of a two diode fullwave rectifier even in a bridge, rectifier is in Fig 5, diode pairs D1, D3 and D2 D4 carry half, the total load current1. This is because each diode pair is, conducting only during one half of the AC input cycle., The only disadvantage of bridge rectifiers, D1, D3 and D2, D4, is that, this circuit uses four diodes for full wave rectification, instead of two as in two-diode fullwave rectifier. But this, disadvantage is compensated by the simple transformer, requirement of the bridge rectifier and higher DC output, level. Hence, bridge rectifiers are the most popular AC to, DC rectifiers for most applications., , In Fig 7 if the transformer secondary voltage Vs(rms) is 24, volts, find the minimum PIV of diodes used. In a bridge, rectifier PIV across the diodes is same and is equal to, Vs(peak), , Encapsulated bridge rectifiers are available as a single, pack with two terminals for AC input and two terminals for, DC output., , Therefore, in the given example,, , The following table provides data for a normally used diode, having the current rating of one ampere., , Vs(rms), 24, PIV = Vsd(peak) =, =, =, 34 volts, 0.707 0.707, , Maximum ratings, Rating, , Symbol, , Type Number, IN 4001 IN 4002 IN 4003, , Peak repetitive, reverse voltage, Working peak, reverse voltage, DC blocking voltage, , VRM(rep), , Unit, , IN 4004 IN 4005 IN 4006 IN 4007, , 50, , 100, , 200, , 400, , 600, , 800, , 1000, , Volts, , VRM(wkg), VR, , Non-repetitive, peak reverse, voltage (half wave,, single phase,, 50 Hz peak), , VRM (nonrep), , 75, , 150, , 300, , 600, , 900, , 1200, , 1500, , Volts, , RMS reverse, voltage, , Vr, , 35, , 70, , 140, , 280, , 420, , 560, , 700, , Volts, , Average rectified, forward current, (Single phase,, resistive load, 50Hz,, TA = 75°C), , Io, , 1.0, , Non-repetitive, (Half sine, wave t=10m sec), , IFM, , 30, , Maximum thermal, resistance junction, temperature to, ambient (lead length, = 25 mm), , TJA, , 85, , Maximum, Operating and, storage junction, temperature range, , TjTstg, , -65 to 175, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished, , Amp, , 25

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Other diode specifications can be obtained from the, data book)., Half wave, Number of diodes, required, , A comparison of half-wave, fullwave and bridge rectifier, is given below in a tabular form, Full wave, , 1, , Bridge, , 2, , 4, , Transformers peak, output voltage, , DC output voltage, in terms of, Vs(peak), , 0.318 Ys(peak), , 0.636V Vs(peak), , 0.636V Vs(peak), , DC output voltage, in terms of Vs(rms), , 0.45 Vs(rms), , 0.9 Vs(rms), , 0.9Vs(rms), , Diode current, rating, , IL(max), , 0.5 IL(max), , 0.5IL(max), , Peak inverse, voltage, , Vs(peak), , 2Vs(peak), , Vs(peak), , Ripple frequency, , finput, , 2finput, , 2finput, , Filter circuits : Alternating current is rectified to provide, a steady DC voltage similar to the output of a battery as, shown in Fig 9a. But the output of rectifiers in a pulsating, DC as in Fig 9b., , 2 RC filter, 3 Series inductor filter, 4 Choke input LC filter, 5 π filter., 1 Capacitor filter : A capacitor filter is the most simplest, and cheapest filter. Here a large value capacitor C is, connected across the load resistor RL as in, Fig 10a. The capacitance offers a low reactance path, to the AC components of current and offers very high, resistance to DC. So all the DC current passes, through the load., , Pulsating DC voltages cannot be used in most of the, electronic circuits. For example a buzzing sound will be, obtained from a radio if these pulsations are not removed, in the output of the rectifiers. The circuits used to filter off, or reduce the pulsation in the DC output of rectifiers are, known as smoothing circuits or popularly as Ripple filters., Ripple : The small voltage fluctuations in the output of a, filter like those shown in figure 9c are called Ripple., Filter circuit components : Filter circuits are normally, combinations of capacitors, inductors and resistors., Types of filter circuits : The different filter circuits in use, are, 1 Capacitor input filter., 26, , Working : When the rectifier output voltage is increasing, the capacitor charges to the peak voltage Vm. After, reaching the positive peak the rectifier output voltage tries, to fall. Observe the wave form in Fig 10b. At point ‘B’ the, capacitor has +Vm volts across it. Since the source, voltage becomes slightly less than Vm, the capacitor will, try to send current back through the diode, which reverse, biases the diode., The diode disconnects the source from load. The capacitor, starts to discharge through the load. Thus the voltage, across load will not fall to zero. The capacitor continues, to discharge until the source voltage becomes more than, the capacitor voltage at point C. The diode again starts, conducting and the capacitor is again charged to peak, value Vm. During the charging period for the capacitor the, rectifier supplies the charging current Ic through capacitor, as well as the load current IL. Thus the current is, maintained through the load always., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished

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Vrip(p-p) =, , IL, ........... (2), Fr C, , Where, Vr(p-p), , = peak-to-peak ripple voltage in volts, , IL = required Dc load current, in Amps, Fr = ripple frequency, in Hz, C = capacitance in Farads, Fixing the permissible Vr(p-p) and knowing f and IL the, required value for C can also be found using this formula, Method 2, Another method of expressing the ripple in the output DC, is by ripple factor r defined as,, Ripple factor, r =, , Vr(rms), Vdc, , where,, r = ripple factor (dimension less), Vr (rms) = rms value for ripple voltages., Vdc is the measured dc voltage at the output., 2 RC filter, A simple RC filter circuit is in Fig 10c. It consists of a, resistor R1 and capacitor C1 connected as shown . The, resistor R1 help the filtering provided by the capacitor by, lengthening the discharge time of the capacitor., 3 Series inductor filter, The figure 10d shows a series inductor filter circuit. An, inductor is a device which has the fundamental property of, opposing any change in current flowing through it. This, property is used in the series inductor filter., , The rate at which the capacitor discharges between points, B and C in Fig 10b depends upon the time constant RLC., longer this time constant is, the steadier is the output, voltage., Calculation of Ripple : While designing a filter circuit the, following methods can be used to calculate theoretically, the ripple voltage in the output of the filter circuit., Method 1, Knowing the required load current, IL, for a given value of, frequency f and capacitance C, the peak-to-peak ripple, voltage can be found using the formula,, , Working : Whenever the current through an inductor, tends to change, a back emf is induced in the inductor, which prevents the current from changing its value. The, operation of a series inductor filter depends upon the, current through it. Therefore this filter can be used, together with a full wave rectifier only. further an increase, in load current result in reduced ripple., 4 Choke-input LC filter, A choke input filter consists of an inductor L in series and, a capacitor C in shunt with load as shown in Figure 10e., Working : An LC filter combines the features of both the, series inductor filter and shunt capacitor filter. The choke, (iron-core inductor) allows the DC component to pass, through easily because it offers no resistance to DC., While the capacitor allows AC ripples to pass through but, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished, , 27

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blocks DC. As a result all the DC current passes through, the load resistor RL. The output wave form of a LC filter is, an shown in Figure 10f., Bleeder resistor : An inductor functions better when large, steady current flows. For optimum functioning of choke, filter a bleeder resistance RB , which by passes the, fluctuating current is included in the circuit as shown in, Fig 10e., , 28, , π filter), 5 PI-Filter (π, This circuit is shown in Fig 10g. It is also called as a, capacitor input filter. This circuit uses one inductor and, two electrolytic capacitors. It is called capacitor-input, filter because C1 is the first filtering component. It is also, called PI filter because the circuit looks like π (Greek letter), Working : The rectifier output first goes to C, which, alternately charge and discharges as in the case of a, capacitor filter. The capacitor C2 also provides a similar, filtering action. The inductor opposes the changes in both, the output of C2 and in the current drawn by the load. Also, the LC filters are capable of removing the voltage spikes at, the input., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.163, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.164, , Transistors, Objectives: At the end of this lesson you shall be able to, • explain the construction of bipolar transistors, • explain the classification and working of PNP and NPN transistors, • state the important packages and type number systems of transistor, • explain the methods of testing transistor., Introduction: Transistor is an active device which can be, compared to the heart of modern electronics. It accepts, small electrical signal either in the form of current or, voltage at the input and then amplifies (increase the, amplitude) and provides a large signal at the output as in, Fig 1. Transistors are used in almost all electronic gadgets, such as radio, TV, tape recorder, computer etc.,, , Transistor are available as bi polar, field effect and, unijunction etc.,, A bipolar junction transistor uses two opposite polarity of, doped semiconductor i.e. ‘N’ type and ‘P’ type., A field-effect transistor uses electrostatic field of charged, carriers for its working., An unijunction transistor uses a single junction of ‘P’ and, ‘N’ type semiconductor., , Before the transistors were invented (1947), certain devices, are used known as vaccum tubes or valves which were, used in amplifiers., , Construction of bipolar junction transistors : The, bipolar junction transistor is a three-element device (emitter,, base, collector) made up of silicon or germanium materials, by various methods like point contact, grown junction,, alloy junction, diffusion junction and epitaxial. The, construction of the transistor and the symbols, NPN and, PNP, are shown in Fig 2., , Compared with the present day transistors the vacuum, tubes were big in size, consumed more power, generated, lot of unwanted heat and were fragile. Hence vaccum, tubes became obsolete as soon as transistors came to, market., Transistors were invented by walter H. Brazil and John, Barlow of Bell Telephone Laboratories on 23rd Dec. 1947., Compared to vaccum tubes transistors have several, advantages. Some important advantages are listed below., •, , Very small in size, , •, , Light in weight, , •, , Minimum power loss in the form of heat, , •, , Low operating voltage, , •, , Rugged in construction, , •, , Long life and cheap., , To satisfy the requirements of different applications, several, types of transistors in different types of packaging are, available. As in diodes, depending upon the characteristics,, transistors are given a type number such as BC 107, 2N, 6004 etc., The characteristics data corresponding to, these type numbers are given in Transistor data books., , A transistor is represented with the symbol shown. The, arrow at the emitter shows the current flow through the, transistor., , Copyright @ NIMI Not to be Republished, , 29

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In most of the transistors, the collector region is made, physically larger than the emitter region since it is required, to dissipate more heat. The base is very lightly doped and, is very thin. The emitter is heavily doped. The doping of, the collector is more than that of the base but less than of, the emitter., Classification of transistors, 1 Based on the semiconductor used, •, , Germanium transistors, , •, , Silicon transistors, , Like in diodes, transistors can be made, using any one of, the above two important semiconductors. However, most, of the transistors are made using silicon. this is because,, silicon transistors work better over a wide temperature, range (higher thermal stability) compared to germanium, transistor., Method of finding the semi conductor used in, Transistor, Transistor data books give information about the semi, conductor used in any particular transistor., In the absence of data, still a quick check can be made, with an ohmmeter to determine whether a transistor is, made from silicon or germanium. In the test of a PNP, transistor in Fig 3 first connect the ohmmeter negative lead, to the collector and the positive lead to the emitter. With, this hook-up a high resistance reading from the emitter to, the collector will be shown., , Then reverse the ohmmeter lead connections, and the, resistance reading will go even higher. If it is possible to, read the ohms on the meter scale, it is germanium, transistor. If the reading is in the megohms-to-infinity, range, it is a silicon transistor., 2 Based on the way the P and N junctions are organised, as in Fig 4, •, , NPN transistor, , •, , PNP transistor, , Both NPN and PNP transistors are equally useful in, electronic circuits. However, NPN transistors are preferred, for the reason that NPN has higher switching speed, compared to PNP., 30, , Operation of NPN transistor : During the normal operation, of the transistor for amplifications the emitter base, junction must be forward-biased, and the base collector, junction must be reverse-biased, as in Fig 5., , If VEB is greater than the barrier potential (0.3 V for, germanium and 0.7 V for silicon), the electrons in the, emitter are repelled by the negative polarity of VEB and sent, to the base. After filling a few holes in the base, these, electrons can flow in either of the two directions. A few of, the electrons are attracted to the positive terminal of VEB,, producing base current IB. Many electrons in the base and, collector are attracted by the high position potential of VCB,, producing collector current Ic. Emitter current IE is equal, to base and collector currents., I E = IB + I c, Working of PNP transistor: For proper operation of a, PNP transistors as amplifier the base emitter junction, must be forward-biased and the collector-base junction, must be reverse-biased as in Fig 6., Holes which are the majority carries are injected from the, emitter into the base region. By the reverse biasing of the, base-collection junction, the collector region is made, negative with respect to the base, and hence holes, which, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.164, , Copyright @ NIMI Not to be Republished

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carry a positive charge, penetrate into to base and flow, across the collector junction and flow into the external, applied voltage., , Method of identifying PNP and NPN transistors :, Whether a transistor is PNP or NPN can be found with the, help of transistor data book., In the absence of data the following procedure may be, adopted to identify the type of transistor whether it is PNP, or NPN., PNP identification : To identify the type of transistor first,, make sure which is the positive lead and which is the, negative lead from the ohmmeter. If necessary, take of the, back for the instrument and check the polarity of the, battery against the lead connections (positive to positive,, negative to negative)., To test the transistor for its type:, 1 Hook the positive lead from the ohmmeter to the base, of the transistor. Fig 7, 2 Connect the negative lead from the ohmmeter first to, one transistor lead, then to the other., 3 If both readings shows high resistance, hook the, negative ohmmeter lead to the base of the transistor., (Fig 7), 4 Connect the positive lead from the ohmmeter first to, one transistor lead, then to he other., 5 If both readings show low resistance, then it is a PNP, transistor., , Continue testing as follows:, 1 Reverse the ohmmeter leads, connecting the positive, lead to the base of the transistor., 2 Connect the negative lead from the ohmmeter first to, one transistor lead, then to the other., 3 If the readings show low resistance, then it is a NPN, transistor., 3 Based on the power handling capacity of, transistors, they are classified as, 1 Low power transistors less than 2 watts, 2 Medium power transistors is 2 to 10 watts, 3 High power transistors more than 10 watts, Low power transistors, also known as small signal, amplifiers, are generally used at the first stage of, amplification in which the strength of the signal to be, amplified is low. For example to amplify signals from a, microphone, tape head, transducers etc.,, Medium power and high power transistors, also known as, large signal amplifiers are used for achieving medium to, high power amplification. For example, signals to be given, to loudspeakers etc. High power transistors are usually, mounted on metal chassis or on a physically large piece, of metal known as heat sink. The function of heat sink is, to, take away the heat from the transistor and pass it to the, surrounding air., Transistor data books give information about the power, handling capacity of different transistor., 4 Based on the frequency of application, , NPN identification : Suppose the ohmmeter tests show, high resistance with the negative ohmmeter lead connected, to the base of the transistor and the other lead is switched, from transistor lead to transistor lead. See Fig 8 for, reference., , •, , Low frequency transistor (Audio Frequency of A/F, transistors), , •, , High frequency transistor (Radio frequency of R/F, transistors), , Amplification required for signals of low or audio range of, frequencies in Tape recorders, PA systems etc., make, use of A/F transistors. Amplifications required for signals, of high and very high frequencies as, in radio receivers,, television receivers etc., use R/F transistors., Transistors data books give information for any particular, transistor as to whether it is a AF of RF transistor., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.164, , Copyright @ NIMI Not to be Republished, , 31

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5 Based on the manufacturing method, •, , Grown junction, , •, , Alloy junction, , •, , Planar contact, , •, , Epitaxial, , •, , Mesa, , The aim of each manufacturing process is to yield, transistors most suitable for a particular type of application., Transistor data books generally do not give information, about the adopted manufacturing process of transistor., However, the relevant details can be obtained from the, transistor manufacturer., 6 Based on the type of final packaging, •, , Metal, , •, , Plastic, , •, , Ceramic, , in the direction of infinite ohms, means an open circuit., Power must be off in the circuit for ohmmeter readings., Preferably, the device is out of the circuit to eliminate any, parallel paths that can affect the resistance readings for a, transistor, low resistance from base to emitter or base to, collector indicate forward bias and when the ohm-meter/, multimeter leads are transferred the resistance should be, very high indicate reverse bias., Probable possibilities are, 1 When the ratio of reverse to forward R is very high, the, junction is good., 2 When both the forward and reverse R are very low,, close to zero, the junction is short-circuited., 3 When both the forward and reverse R are very high,, close to infinity, the junction is open., 4 When both junctions are good transistor is good., 5 For a transistor without terminal details, base can be, identified easily by identifying between collector and, emitter terminal., , Metal packaged transistors are generally used in medium, and high power amplifications. Plastic packaging is, generally used for low power amplification. Some plastic, packages come with a metal heat sink. Such transistors, are used for medium power amplification. Ceramic, packaging is used for special purpose very high frequency, applications, for higher temperature stability etc.,, Some examples of packaging type codes used with, transistors are, TO-3, TO-92- SOT-25 and so on., Transistor data books give information about the type of, packaging and its case outline., , Normally for any power transistor, collector is, connected to the metallic part/case to dissipate, excess heat generated., 6 With a high voltage multimeter (MOTWANE multimeter, with 9 V cell in Ω x 100 range), emitter base junction, shows some reverse resistance due to zener action, which should be treated as high resistance for all, purpose., A germanium transistor has very low forward resistance for, each of junction and a high resistance in the reverse, direction, while a silicon transistor has moderate forward, resistance and infinity reverse resistance., , Three lead devices such as transistors, SCRs, triacs etc.,, are cased in packages numbered as TO (transistor outline), or SOT (semi-conductor outline for transistors) followed, by a number. A number of packages after designs are, rarely used by circuit designers and have become obsolete., Testing of transistor : A transistor can be tested for all, specifications shown in the data book. But verification of, almost all specifications, except a few requires an elaborate, step up and can damage the transistor permanently., The condition of a transistor with two diodes connected, back to back will be as shown in Fig 9(a) & (b), , An ohmmeter can be used to check the junction either for, an open circuit or a short circuit. The short is indicated by, R practically zero ohms. A very high R of many megohms,, 32, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.164, , Copyright @ NIMI Not to be Republished

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Fig 10a shows a NPN transistor and Fig 10b shows a PNP, transistor. The imaginary diodes1 and 2 can be tested as, similar to testing any diode. When a diode is tested, if the, ohmmeter shows high resistance in one direction and low, resistance in another direction, then the diode, corresponding to that diode junction can be regarded as, GOOD. One important point to note in a transistor is that,, both the diodes of the transistor should be GOOD to, declare the transistor as GOOD., , When testing, a transistor using ohmmeter, it is suggested, to use the middle ohmmeter range (Rx 100) because,, ohmmeters in low range can produce excessive current, and ohmmeters in high range can produce excessive, voltage which may be sufficient to damage small signal, transistors., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.164, , Copyright @ NIMI Not to be Republished, , 33

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.165, , Transistor biasing and characteristics, Objectives: At the end of this lesson you shall be able to, • state the need and type of transistors biasing, • state the reason for shifting Q point due to temperature and βdc changes, • state the necessity and importance of transistor characteristics, • state the importance of DC load line and meaning of Q point in transistors characteristics., Need of biasing of transistor, Before any one rides a motor cycle or drives a car, he has, to start the engine and keep the engine running. In simple, terms biasing transistors is similar to keeping the transistor, started before making the real use of it. Once the, transistor is started, like the engine of a car, it can be made, to amplify, like covering the distance by driving the car., Before an AC signal is fed to a transistor, it is necessary, to set up an operating point or the quiescent(Q) point of, operation. Generally this Q point is set at the middle of the, DC load line. Once the Q point is set, then the incoming, AC signals can produce fluctuations above and below this, Q point as in Fig 1., , Further the amplitude variations in current and voltage of, the input signal must not drive the transistor either into, saturation of cut off., Stable Q point: A set Q point of a transistor amplifier may, shift due to increased temperature and transistor β value, changes. Therefore, the objective of good biasing is to, limit this shifting of the Q point or to achieve a stable Q, point., The Q point is nothing but a point in the output characteristic, of the transistor. This point corresponds to a particular, value of IB, IC and VCE. Further , the collector current IC, depends both on IB and β of the transistor. If IB changes,, Ic also changes, and hence, the Q point changes. If β, changes, again IC changes, and hence, the Q point gets, shifted., Shifting of Q point due to temperature: Remember, that a transistor is a temperature sensitive device. Any, increase in the junction temperature results in leakage, current. this increased leakage current in turn increases, the temperature and the effect is cumulative. This chain, reaction is called thermal run away. If this thermal run, away is not stopped, it may result in the complete, destruction of the transistor due to excessive heat. In, transistors, due to this increased leakage current, the, base current increases, and hence, the Q point gets, shifted. This change in the set Q point affects the, performance of the amplifier resulting in distortion., , For the normal operation of a transistor amplifier circuit, it, is essential that there should be, a) a forward bias on the emitter-base junction and, b) reverse-bias on the collector-base junction, In addition, the amount of bias required is important for, establishing the Q point which is dictated by the mode of, operation desired., If the transistor is not biased correctly, it would, 1) work inefficiently and, 2) produce distortion in the output signal., It is desirable, that once selected, the Q point should, remain stable i.e. should not shift its position due to, temperature rise which cause variation in β (VBE) or, leakage currents., 34, , Shifting of Q point due to βdc changes: Practically two, transistors of the same type number may have different, value of β. this is due to the manufacturing process of, transistors. Hence, when a transistor is replaced or, changed, due to different β of the replaced transistor, the, Q point again gets shifted., Therefore, a stable biasing is one which does not shift the, Q-point even if temperature varies and/or the β of the, transistor changes., Different methods for transistor biasing: There are, several ways to bias a transistor for linear operation. This, means, there are several ways of setting up a Q point near, the middle of the dc load line., , Copyright @ NIMI Not to be Republished

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The methods used for providing a bias for transistors, are 1 fixed bias or base bias, , presence of the self-biasing resistor RE reduces the, increase in Ic and improves the operating point stability., , 2 self-bias or emitter bias or emitter feed back bias, , However if βdc increases, the collector current increase., This inturn increases the voltage at the emitter. This, increased emitter voltage decreases the voltage across, the base-emitter junction and therefore, the base current, reduces. This reduced base current results in less, collector current, which partially offsets the increase in Ic, due to increase βdc., , 3 voltage divider bias, Fixed bias or base bias: The circuit in Fig 2 provides a, fixed bias by means of the power source Vcc and the base, resistor RB, , Emitter bias is also referred to as emitter feedback bias., This is because an output quantity, i.e., the collector, current, produces a change in an input quantity i.e., the, base current. The term feedback means a portion of the, output is given back to the input. In emitter bias, the, emitter resistor is the feedback element because it is, common to both the output and input circuits., Referring Fig 3, if we go for further analysis of the circuit we, find if we add the voltages around the collector loop, we, get,, Self-bias arrangements are not practicable for small values, of current because the DC Q point changes due to, , ICRC + VCE +IERE-VCC = 0 ...... (1), , – poor Beta sensitivity, , Since IE approximately equals Ic (as IB is comparatively very, small), equation ..(1) can be arranged as,, , – bias voltages and current do not remain constant, during transistor operation due to temperature variation., Hence, in a base-biased transistor, it is impossible to set, up a stable Q point. Therefore, base biasing of transistors, is not generally done in linear amplifier circuits. However,, base biasing is commonly used in digital circuits, (discussed in further lessons) where transistor are used, as a switch and not as a linear amplifier., 2 SELF BIAS or EMITTER BIAS or emitter feedback, bias: Fig 3 shows a emitter-biased transistor. This, type of biasing compensates for the variations in, temperature and keeps the Q point fairly stable., , IC =, , VCC - VCE, .......... . (2), R C + RE, , If we add voltages around the base loop, we get,, IBRB + VBE + IERE - VCC = 0 ...(3), Since IE=Ic and IB = Ic/ βdc, we can rewrite the equation as,, IC =, , VCC - VBE, .......... . (4), R B + R D /β dc, , From equation...(4), the presence of term β indicates that, Ic is dependent on β. The intention f emitter-feedback bias, to swamp out the effect βdc. This is possible when RE is, made much larger than RB/ βdc. However, in practical, circuits RE cannot be made very large because, large value, of RE takes the transistor out of the linear operating region., Due to this problem, the emitter-feedback bias is almost, as sensitive to changes in βdc as in the base-bias., Therefore, emitter-feedback bias is also not a preferred, form of transistor bias and should be avoided., In emitter-bias, the saturation current will be,, IC(sat) =, , Let the temperature rise-causing rise in Ic and consequently, rise in Ic. Then the current in RE increases. The increased, current in RE increases the DC voltage drop across RE,, reduces the net emitter to the base bias, and the base, current, and hence reduces the collector current. Thus the, , VCC - VCE (sat), RE + R C, , .......... . (1), , When the transistor is saturated, the value of VCE will be, between 0.2 to 0.3V. Hence can be neglected for all, practical purposes., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.165, , Copyright @ NIMI Not to be Republished, , 35

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In Fig 3, the saturation current is,, IC(sat) =, , 12V, = 10.71 mA, 1000 Ω + 120 Ω, , Note:, VCE(sat) of 0.2 volts is neglected., , This type of biasing is known as voltage divider bias, because of the voltage divider formed by resistors R1 and, R2. The voltage drop across R2 should be such that it, forward biases the emitter diode., Emitter current in voltage divider bias : Assume that, the base lead is open as shown in Fig 6b. Looking back, at the unloaded voltage divider,, , When βdc = 100, equation...(4) gives,, 12V - 0.7V, IC =, = 3.3mA, 120Ω + 330 KΩ/100, , When βdc = 300, the same equation...(4) gives,, IC =, , 12V - 0.7V, = 9.262mA, 120 Ω + 330 KΩ/300, , Fig 4 summarizes the calculations by showing the DC load, line and the two Q points. As can be seen, a 3:1 change, in βdc produces almost a 3:1 change in the collector, current. This change is unacceptable as a stable-biased, state., , VTH =, , R2, = VCC ., R1 + R 2, , NOTE: VTH is known as the Thevenin’s voltage., Refer reference books for Thevinin’s theorem., Now assume that, the base lead is connected back to the, voltage divider as in Fig 6a. then, voltage VTH drives the, base of the transistor. In other words, the circuit simplifies, to Fig 6a and the transistor acts like the controlled current, source., , Because the emitter is boot-strapped to the base,, TIP: For linear operation of the transistor, the base resistor, RB should be greater than βRc. A base resistance of less, than βdcRc produces saturation in an emitter feedbackbiased circuit., 3 VOLTAGE-DIVIDER bias: Collector to base bias:, Fig 5 shows a typical voltage-divider bias. This type of, biasing is also called the universal bias because, this, is the most widely used type of biasing in linear, circuits., , IE =, , VTH - VBE, RE, , The collector current Ic will be approximately equal to IE., Notice that βdc does not appear in the formula for emitter, current. This means that the circuit is not dependent on, variations in βdc. This means that the divider-biased, transistor has a stable Q point., Because of the stable Q point, voltage-divider bias is the, most preferred form of bias in linear transistor circuits., Hence, divider bias is used almost universally., Transistor characteristics, In a transistor there are two PN junctions followed by three, voltage parameters VBE, VBC, VCE and three current, parameters IB, IC, IE is in Fig 7., Any change in any one parameter causes changes in all, the other parameters. Hence it is not very easy to, correlate the effect of one parameter with the others. To, have a clear understanding of their relationship a minimum, of two characteristics graphs should be plotted for any, transistor. They are,, , 36, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.165, , Copyright @ NIMI Not to be Republished

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Input characteristic curves can be obtained by plotting IB, on the Y axis against VBE on the X axis. A typical input, characteristic is in Fig 9., The reason for deviation of the characteristic curve for VCE,, 5V and 10V from VCE 0 volt is, at higher values of VCE the, collector gathers a few more electrons flowing through the, emitter. This reduces the base current. Hence the curve, with higher VCE has slightly less base current for a given, VBE. This phenomenon is known as early effect., However for the practical purposes the difference in gap is, so small it can be regarded as negligible., – Input characteristics, – Output characteristics, For simplicity in understanding, consider a commonemitter amplifiers circuit (Fig 8). The two characteristics, graphs are in Fig 9 and Fig 10., , The CE input characteristic curves resemble the forward, characteristic of a PN diode. The input resistance can be, calculated by using the formula., , VBE, 0.02, 0.72 - 0.7, =, = =, 2kΩ, R in =, 20 μ A - 10 μ A 10 μ A, IB, ( μ = micro), The voltage gain can be calculated by using the formula:, V, , gain, , VCE, 10 V - 5 V, 5V, =, =, =, =, 50, IBE, 0.15 μ A - 0.65 μ A, 0.1μ A, , Output CE characteristics: To find the output, characteristics, keep IB=0 micro-amp constant, increase, VCE in regular steps of 1V and note the value of IB at each, step. Repeat the above procedure for IB = 20 micro-amp,, 40 micro-amp and 60 micro–amp., Output characteristics curves can be obtained by plotting, Ic on the Y axis against VCE on the X axis. A typical output, characteristics curve is shown in Fig 10., , The graph at Fig 9 shows the relationship between the, input voltage VBE and input current IB for different values of, VCE, To find the input characteristics from the circuit as in, Fig 8 keep VCE = 0 constant; increase VBE at regular steps, of 0.1V and note the value of IB at each step. Repeat the, above procedure for different value of VCE say VCE = 5V and, 10V., , It is seen that as VCE increases from zero, Ic rapidly, increases to a near saturation level for a fixed value of IB., As shown, a small amount of collector current flows even, when IB= 0. It is called leakage current ICEO. Since the main, collector current is zero, the transistor is said to be cut-off., For simplicity in understanding consider on the output, characteristic curve where IB = 40 μA., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.165, , Copyright @ NIMI Not to be Republished, , 37

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The output resistance can be calculated by the formula, R, , 0, , VCE, 8-2, 6, =, =, =, = 40 k ohms., IC, 2.15 m A - 2m A, 0.15m A, , Current gain can be calculated by the formula, IC, 4mA - 3 mA, 1 mA, Beta β =, =, =, =, 50, IB 80 μ A - 60 μ A, 20 μ A, , In the common base configuration, the current gain can be, calculated by the formula:, IC, 50, β, Alpha α =, = =, = 0.98, IE 1 + β, 1 + 50, , Analysis of common emitter output characteristics, Active region : In the active region the collector junction, is reverse-biased and the emitter junction is forwardbiased. In the active region, the collector current is Beta, times greater than the base current. Thus, a small input, current IB produces a large output current Ic., , Cut off region : In the cut off region, the emitter and, collector junctions are reverse-biased. When the transistor, is operated in the cut off region, it acts as an open switch,, having VCE = Vcc and Ic = 0, Break down region : When the collector voltage is too, large, the collector diode breaks down by a rapid increase, of collector current. Usually, a designer should avoid, operation in the breakdown region because the excessive, power dissipation may destroy the transistor., For instance, a 2N3904 has a collector break down voltage, of 40V. For normal operation, therefore, VCE should be, less than 40V., Maximum power dissipation region : The maximum, power dissipation (Po max), defined as the product of, maximum collector current Ic max and maximum collector, emitter voltage VCE max, restricts the operation to an area on, the output characteristic bounded by a hyperbola., To understand the function of the transistor at active, cut, off, saturation regions and breakdown regions, refer to, Fig 11., , Saturation regions : In the saturated region, the emitter, and collector junctions are forward-biased. When the, transistor is operated in the saturated region, it acts as a, closed switch having VCE = 0 and Ic maximum., Behaviour of Ic for different values of VCE is explained, below:, •, , When VCE is 0, the collector-base diode is not reversebiased. Therefore, the collector current is negligibly, small and this continues upto knee point., , •, , For VCE between 0.7V and 1V, say up to knee point, voltage the collector diode gets reverse-biased. Once, reverse biased, the collector gather all the electrons, that reach its depletion layer. Hence the collector, current rises sharply and then becomes almost, constant., , •, , Above the knee voltage and below the break down, voltage, the collector current does not rise steeply or, the current is almost constant even if the value of VCE, is increased. Thus the transistor works like a controlled, constant current source in this region., , •, , •, , 38, , Assuming that the transistor has a ßdc of approximately, 50, the collector current is approximately 100 times, the base current as in Fig 4 (1mA is 50 times, 20 μA)., If VCE is further increased, beyond the break down level,, VCE(max), the collector-base diode breaks down and, normal transistor action is lost. The transistor no, longer acts like a current. As the collector-base gets, ruptured, the junction is shorted and hence current, increases rapidly above the breakdown point as in, Fig 10., , The collector curves are very important because, from, these curves the following important information required, while designing an amplifier circuit using a particular type, of transistor can be obtained;, •, , DC current gain ß of the transistor at different set DC, values of IB and VCE, , •, , Maximum value of VCE that can be applied for a set, value of IB and Ic., , •, , Maximum value of Ic that can be made to flow for a set, value of IB, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.165, , Copyright @ NIMI Not to be Republished

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Operation point : The position of the operating point on, the DC load line determines the maximum signal that we, can get from the circuit before clipping occurs. The, operating point or quiescent point is a point on the DC load, line which represents the values of Ic and VCE that exist in, a transistor circuit when no input signal is applied. The, best position for this point is midway between cut-off and, saturation point where VCE = 1/2 Vcc., , Under such a condition for the circuit at Fig 12a Ic will be, equal to 10V/kΩ = 10mA, Mark this Ic=10mA point along VCE=0 on the collector, characteristics of the transistor as shown in Fig 13 at, point A., , DC load lines of transistors : To have a further insight, into how a transistor works and in what region of the, collector characteristics does it work better can be seen, using DC load lines., Consider a forward biased transistor as in Fig 12a. Fig 12b, shows the collector characteristics of the transistor used., , For situation (2), assume that VCE is maximum or collector, emitter is open. In that case, the collector current is zero., Therefore,, VCE = Vcc In the circuit at 6a, VCE = VCC = 10V, Mark this point of lC = 0 and VCE = 10 V on the collector, characteristics of the transistor as in Fig 13 at, point B., Connect the two marked points A and B through a straight, line as shown in Fig 13. This line is called the load line., In the circuit at Fig 12a, consider the following two, situations,, – Maximum collector current, Ic(max), – Minimum collector current, Ic, For situation (1) assume that VCE is zero or collector is at, short. In that case, the collector current is limited only by, the collector resistor Rc., Therefore, IC =, , VCC, at ICE = 0, RC, , The point at which the load line intersects the IB = 0 is, known as the cut off point. At cut off, IB = 0; hence emitter, diode is out of forward bias and the transistor action is lost., The point at which the load line intersects IB = IB(sat) is, called the saturation point. At this point the base current, is maximum and the collector current is also maximum., At saturation, the collector diode comes out of the reverse, bias, and hence, the normal transistor action is lost., For a transistor to work in a normal way, i.e. as a controlled, current source, it must not be made to work either in the, cut off or in saturation. Therefore the ideal point would be, somewhere in the middle of these extreme points on the, load line. This middle point is known as Quiescent point, or Q-point as in Fig 13. knowing the Q point we can fix up, the value of resistors RC and RB of the circuit., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.165, , Copyright @ NIMI Not to be Republished, , 39

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.166, , Transistor as a switch, series voltage regulator and amplifiers, Objectives: At the end of this lesson you shall be able to, • explain the function of the transistor at cut-off and saturation condition, • explain the operation of a transistor as a switch and its application, • state the working of series voltage regulator using transistor, • state the classification of amplifiers., The function of a transistor at cut-off condition: The, transistor is operated at cut–off condition when the emitter, and collector junctions are both reverse-biased., , •, , the collector current has maximum possible value, called IC(SAT), , VCE = VCC - (IC x RL) ..... (1), , The operation of transistor as switch: The switching, action for Q1 in Fig 2 illustrates how the output current can, be controlled at the input. Note the following important, operating characteristics., , Since, IB = 0 and Ic = 0 VCE = VCC, , •, , The transistor is said to be cutoff for the simple reason that, it does not conduct any current as in Fig 1a.This, corresponds to a switch in an open state. Therefore, a, transistor at cut off is said to be at open state., , The transistor is normally off, without any output, current unless forward voltage is applied in the baseemitter circuit., , •, , The forward voltage controlling the base current, determines the amount of output current., , Consider the circuit in Fig 1., , The function of a transistor at saturated condition :, The transistor is operated at saturated condition when, both the emitter and the collector junctions are forward, biased., In Fig 1b, if the value of RB and RL are such that VCE tends, to zero, then the transistor is said to be saturated. Putting, VCE = 0 in the equation (1) we get, VCE = 0 = Vcc - IcRL or Ic = Vcc - RL, It should be noted that a transistor, when saturated, acts, as closed switch of negligible resistance., It is obvious that under saturation conditions,, •, 40, , the whole of Vcc drops across RL, , In Fig 2 the control circuit of the input determines the base, current. For the power circuit, the output is the collector, current. An NPN transistor is used for Q1. This type, requires positive VBE forward voltage. The emitter is common, to both (a) the control circuit at the input and (b) the power, output circuit., , The base emitter junction of Q1, in Fig 2 can be forward, biased by the battery B1. Switch S1 must be closed to, apply the forward voltage. Reverse voltage for the collector, of Q1 is supplied by B2.The reverse polarity means that the, N collector is more positive than the base. With switch S1, open, no current flows in the base-emitter (or control), circuit., The reason is that the forward voltage is not applied., Therefore, the resistance from the emitter to the collector, of the transistor is very high. No current flows in the power, circuit, and the lamp does not light., Next, assume that switch S1 is closed. This causes a, small current to flow in the control circuit. R1 is a current, limiting resistor for the base circuit. Therefore, the resistance, from the emitter to the collector of the transistor drops., , Copyright @ NIMI Not to be Republished

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Consequently, a large current flows in the power circuit,, causing the lamp to light., Finally, the opening of the switch S1 in the control circuit, cause the lamp in the power circuit to go out. This is, because the resistance from the emitter(E) to the collector, (C) of Q1 has again increased to near infinity., In summary, a small current in the control circuit causes, a large current to flow in the power circuit. With no current, in the control circuit, the transistor acts like an open, switch. With some current in the control circuit, the, transistor acts like a closed switch., Operation of transistor switching circuit : The schematic, circuit in Fig 3 shows the measured voltages and collector, current Ic in the ‘transistor off’ circuit. Note that only a tiny, leakage current of 1micro amp flows from the emitter to, the collector. The resistance from E to C is calculated as, V, 9V, R=, =, = 9 megohm, I 0.000001 A, , The resistance of the transistor from E to C has dropped, from its previous high value of 9 megohm to a low value of, 4.7 ohm. As a result, the transistor is acting like a closed, switch., The transistor in Fig 3 is said to be at cut off position. It, has reached its maximum resistance from E to C and has, cut off the current. The very tiny current still flowing is due, to minority current carriers in the transistor, which is the, leakage current., The transistor in Fig 4 is said to be at saturation. It has, reached its minimum resistance from E to C, which, produces the maximum collector current. When used as, a switch, the transistor is driven to cut off or to saturation, by the base current caused by the emitter-base voltage., Transistor switching times : Now let us pay attention to, the behaviour of the transistor as it makes a transition from, one state to the other. Consider the transistor circuit in, Fig 5a, driven by the pulse wave-form in Fig 5b. This waveform makes transitions between the voltage levels V2 and, V1. At V2 the transistor is at cut off, and at V1 is applied, between the base and the emitter through a resistor R1, which may be included explicitly in the circuit or may, represent the output impedance of the source in the waveform Fig 5b., , The transistor has a resistance of 9 Megohm, which is like, the open or off condition of a switch., The schematic in Fig 4, shows the measured voltages and, currents in the ‘transistor on’ circuit. First, the voltage from, the emitter to the base has been increased by adjusting, B1. The forward-biased voltage of 0,86V at the emitterbase junction of the transistor causes 1.8 mA to flow in the, control circuit. This current in turn causes the resistance, of the transistor from E to C to drop. The effect is that a, large current of 85mA flows from the collector of the, transistor. The resistance from E to C in Fig 4 is calculated, as, V, 0.4 V, R=, =, I 0.085A, , = 4.7 ohm, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished, , 41

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The response of the collector current Ic to the input waveform, together with its time relationship to that waveform,, is in Fig 5c. The current does not immediately respond to, the input signal. Instead, there is a delay, and the time that, elapses during this delay, together with the time required, for the current to rise to 10 percent of its maximum, (saturation) value ICS = Vcc/RL, is called the delay time td., The current waveform has a nonzero rise time tr which is, the time required for the current to rise from 10 to 90, percent of ICS. The total turn-on time tON is the sum of the, delay and rise time,, tON = td + tr, When the input signal returns to its initial state at t = T, (Fig 5b), the current again fails to respond immediately., The interval which elapses between the transition of the, input waveform and the time when ic has dropped to 90, percent of ICS is called the storage time ts. The storage, interval is followed by the fall time tt, which is the time, required for ic to fall from 90 to 10 percent of ICS. The turn, off time to tOFF is defined as the sum of the storage and fall, times,, , 2 In a zener regulator, the load resistor sees an output, impedance of approximately the zener impedance, RZ, which ranges from a few ohms to a few tens of ohms, (typically 5Ω to 25Ω). This is a considerably high, output impedance because the output impedance of a, ideal power supply should be zero ohms., These two disadvantages of zener regulators are overcome, in a simple series regulator shown in Fig 6., The simple series regulator is in Fig 6a, redrawn in, Fig 6b is nothing but a zener regulator followed by an, emitter follower. A circuit like this can hold the load voltage, almost constant, thus working as a voltage regulator., , tOFF = ts + tF, The application of transistor switch: The transistor, switch is used, •, , as an electronic ON and OFF switch, , •, , in the stable, mono-stable and bi-stable or filp-flop, multi-vibrator circuits, , •, , in the counter and pulse generator circuit, , •, , in the clipping circuits, , •, , as a sweep starting switch in the cathode ray, oscilloscope equipment, , •, , as a relay, but unlike the mechanical relay, the transistor, has no moving mechanical parts., , Classification of the Switching Transistor: Transistor, switches are used very often as they are small and are of, light weight, and they consume low power. The important, specifications of a switching transistor are the numerical, values of delay time, rise time, storage time and fall time., For the TEXAS INSTRUMENTS n-p-n silicon transistor, 2N3830, under specified conditions can be as low as td =, 10 nsec, tr = 50 nsec, ts = 40 nsec and tf = 30 nsec., , The advantages of this circuit are listed below;, 1 Less load on the zener diode, Current through RZ is the sum of current just required to, keep the zener fired and the small base current IB., , Series voltage regulator, , IE, IL, emitter curent, =, =, IB =, Voltage regulated power supply using zener diode is the, β dc of transistor β dc β dc, simplest form of voltage regulator. But, zener voltage, regulators have two main disadvantages:, Since the base current is very much smaller than the, emitter current or the load current, a very small wattage, 1 When the load current requirement is higher, say of the, zener diode itself is sufficient., order of a few amperes, the zener regulator requires a, very high wattage zener diode capable of handling high, For instance for a load of say 1 amp, if the βdc of the, current., transistor is 100, then the zener diode need to handle only,, 42, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished

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I Z = I Z(min) +, , IL, , β dc, , = I Z(min) +, , The collector - emitter voltage across the transistor will be, the difference in the voltage between the input and output., , 1Amp, 100, , Since IZ(min) will generally be in the range of 5 to 10mA,, IZ = 10mA + 10mA = 20mA., 2 Lower output impedance, If the zener resistance, RZ is say 7Ω, then, in a zener, regulator discussed in unit 9, the output impedance of the, power supply will be approximately equal to R Z = 7Ω., Fig 7 shows the output equivalent circuit of the series, regulator at Fig 6. As in Fig 7, the output impedance of the, power supply will be,, , VCE = Vin - Vout, If the input voltage Vin increases, the output voltage Vout, remains constant due to the bootstrapped zener voltage., Therefore, the drop across the collector-emitter, VCE of the, transistor increases compensating the rise in the input, voltage Vi., For example, in the series regulator shown in Fig 6, if Vin, is 15 V and Vout is 12 volts, then, VCE will be,, VCE = Vin - Vout = 15-12 = 3 V., If Vin increases to say 20 V, then VCE increases to 20-12=8, V, thus keeping the output voltage unaltered at 12 volts., Since the collector and emitter of the transistor in Fig 6 is, in series with the input and output terminals, this type of, regulators are known as series voltage regulators., Because the transistor is in series, all the load current, must pass through the transistor. Hence the transistor is, referred to as the pass transistor., Because of the fact, that all the load current must flow, through the pass transistor and that the value of VCE, increases when Vin increases, the wattage rating of the, pass transistor should be high enough to handle the, dissipation., , Z out = r ′e +, , For instance, while supplying a load current of 300 mA,, with Vin at 20 V and Vout at 12V, VCE will be 8 V. Therefore,, the dissipation at the transistor will be,, , RZ, , β, , Since IE is very large (load current), rIe will be comparatively, small, hence the term rIe can be neglected. Therefore, in, Fig 6 the output impedance will be,, , Z out ≅, , RZ, , β, , =, , 7, 100, , To accommodate this, the wattage rating of the chosen, pass transistor should be greater than 2.4 watts., TIP: Allow at least 20% higher rating. For the example, above, choose a transistor of rating 2.4 + 0.48 watts=, 3 watts., , = 0.07Ω, , This low output impedance of 0.07Ω is close to the ideal, output impedance of zero required for a power supply., Working of a simple series regulator, In Fig 6b, the current through RSZ should be atleast equal, to zener breakdown current, plus, base current for the, transistor Q., The voltage across the zener, VZ drives the base of the, emitter follower. Therefore, the DC output voltage is, bootstrapped to within one VBE drop of the zener voltage., The regulated dc output voltage will be,, Vout = VZ - VBE, , PD = VCE x IL = 8 x 300 mA = 2400 mw = 2.4 watts, , ........[1], , Because there will be quite a high dissipation depending, on load current requirement, medium to high power, transistors are used as pass transistors., Temperature effect on output voltage, When temperature increases, VBE decreases. Therefore,, Vout decreases by the change of current in VBE., Data sheets of transistors usually give information about, how much VBE changes with temperature., For all practical purposes, an approximate of 2 mV, decreases in VBE for each degree rise in temperature. For, instance when the temperature of the transistor rises from, 25°C (room temperature) to 75°C (due to power dissipation, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished, , 43

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at the transistor), VBE decreases approximately 100 mV., Hence, the output will increases by 100 mV. This is, relatively small, and hence, can be neglected., Temperature also has an effect on the voltage across the, zener. Any increase or decrease in the voltage across the, zener is reflected at the output. Hence, while choosing the, zener, it is equally important to know the temperature, coefficient of the zener, specially when the power supply, is connected to higher loads of the order of a few amperes., Classifications of amplifiers : An amplifier is an electronic, circuit which is used to amplify or increase the level of, weak input signals into very high output signals. Transistors, are used as amplifiers in most circuits. In addition,, resistors, capacitors and a biasing battery are required to, form complete amplifier circuits., Almost all electronic systems work with amplifiers. We, are able to hear the news or other programmes on our, radio, simply because the amplifier in the radio amplifiers, the weak signals received by its antenna., Classification of amplifiers: Linear amplifiers are, classified according to their mode of operation, i.e. the, way they operate according to a predetermined set of, values. Various amplifier descriptions are based on the, following factors., , 6 Based on the feedback, a current series feedback amplifier, b current parallel feedback amplifier, c voltage series feedback amplifier, d voltage parallel feedback amplifier, 7 Based on the biasing conditions, a Class A power amplifier, b Class B power amplifier, c Class AB power amplifier, d Class C power amplifier, Of the above mentioned, serial numbers one and two are, explained at this state. Some of the amplifiers dealt in this, book for detailed study the students can refer to any, standard books for the remaining portions depending on, their special interest., Common-emitter amplifier: This type of circuit is by far, the most frequently used. It has the greatest power gain,, substantial current and voltage gains, and is specially, advantageous in multistage application when a high gain, is a primary requirement. A common-emitter amplifier, stage with biasing from a single D.C supply battery is in, Figure 8., , 1 Based on the transistor configuration, a common emitter (CE) amplifier, b common collector (CC) amplifier, c common Base (CB) amplifier, 2 Based on the output, a voltage amplifier, b current amplifier, c power amplifier, 3 Based on the input, a small signal amplifier, b large signal amplifier, 4 Based on the coupling, a RC coupled amplifier, b transformer coupled amplifier, c impedance coupled amplifier, d direct coupled amplifier, 5 Based on the frequency response, a audio frequency (AF) amplifier, b intermediate frequency (IF) amplifier, c radio frequency (RF) amplifier, d VHF and UHF amplifiers, , 44, , The A.C. signal is applied between the base and the, emitter and the output is taken from the collector. For the, transistor to operate, the emitter base junction must be, forward-biased, the resistors R1 and R2 setting the base, voltage so that the emitter is forward-biased. The collector, current flows through the load resistors RL and Re and the, voltage developed by RL at the collector is the output., The voltage gain of a transistor is largely determined by, the value of this particular resistor since the voltage, developed across it due to change in the collector current, is far greater than that developed across the base resistor, from the input signal., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished

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Resistor Re is included to minimise the effect of temperature, changes in the collector current. To prevent Re from, reducing the signal gain by current feedback, a capacitor, C3 may be included in parallel with Re., The capacitors C1 and C2 are provided to prevent (block) the, flow of direct current so that the D.C. bias conditions are, in no ways affected by the signal circuit. In this way, the, D.C. conditions at one stage are prevented from affecting, the following stage, so that only D.C. signals are passed, from one stage to the next one., Common-collector amplifier : In this configuration, the, collector is the common point for the input and output, circuits, the input signal being applied between the base, and collector and taken off between the emitter and, collector, Fig 9. The notable feature is the large input, impedance virtually equal to that of the parallel circuit of R1, and R2. The output resistance is, however, low and, hence, it follows that the voltage gain is low, but a high current, amplification can be obtained., , between a high impedance source and a low impedance, load without excessive loss of power due to mismatching, or not suitable., Common-base amplifier: In this circuit the base is the, common terminal between the emitter terminal and the, collector terminal. The emitter current Ic is the input, current and the collector current Ic is the output current., (Fig 10) Since Ie = Ib + Ic and since in this circuit Ie is greater, than Ic, by the value of Ib, the current gain Ic/Ie will always, be slightly less than one. Therefore, there can be no, current gain in a common-base circuit. However, because, of the low impedance of the forward-biased emitter-base, junction and the high impedance of the reverse-biased, collector-base junction a sizable voltage gain is obtained., , For instance, if we assume that input resistance of 200Ω,, a load resistance of 50K and a current gain of 0.98, the, voltage gain is 0.98 x 50k/200 = 245, , The functions of the capacitors C1 and C2 are the same as, for the common-emitter stage, as the potential networks, R1 and R2 which provide forward bias for the emitter-base, junction. The main advantage of the common-collector, circuit is the readiness with which it may be directly, coupled to any point in a circuit regardless of voltage., The circuit is often called the emitter-follower because the, emitter voltage tends to follow the input voltage, the, difference between the two being only the AC voltage, across the base-emitter junction of the transistor which is, quite small. Hence the output gain is less than 1.The, current gain 50 to 500 is, however, high, being, approximately equal to that of the common-emitter circuit., The output resistance is very low (less than 100 ohms), since the emitter-to-collector resistance is low and there, is not resistance in the collector circuit., The external resistance of the collector circuit, that is, the, impedance presented by the transistor to the load is,, however, very high (300 KΩ) and hence the emitter, follower, circuit, transforms a very high input impedance, into a low output impedance; it is in fact an impedance, transformer. Hence its main application is as a buffer, i.e., an impedance matching device in which it can be connected, , The common-base circuit is not suitable for multi-stage, amplification because its current and power gain are low, when compared with the common-emitter. Also its low, input impedance shunts the load resistance of any previous, stage, thereby reducing the output voltage from that stage, causing a corresponding fall in overall gain., However, its ability to operate at high frequencies makes, it useful in v.h.f. amplifiers. At such frequencies this circuit, is more stable than the common-emitter amplifiers because, of the very small capacitance linking input and output, circuits (the emitter-collector capacitance)., Voltage amplifier: An amplifier is a circuit that incorporates, one or more transistors and is designed to increase an, alternating signal applied to the input terminals. It is called, a voltage amplifier. If the size or magnitude of the output, voltage is considerably greater than the input voltage, it is, called the voltage gain of the amplifier., The main function of a voltage amplifier is to produce a, given gain with the minimum of distortion, i.e. the output, voltages should have the same wave-form as the input, wave-form, but should of course be much higher in, magnitude. Examples for the voltage amplifier are the, common base and the common emitter amplifiers., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished, , 45

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Current amplifier: The function of the current amplifier is, when the current injected in the base, load can influence, to much greater current to flow in the emitter-collector, circuit., The remarkable result is that, if the base current is, increased by a certain proportion, the base current in the, collector current gives rise to a corresponding, but much, larger changes in the collector current. We have achieved, current amplification. The ratio of the output current to the, input current is called the current gain of the amplifier., , Fig 11 shows the complementary symmetry Class B, push-pull power amplifier circuit. In a complementary pair, of power amplifiers, one of them is an NPN type and the, other a PNP type. With no input signal, neither transistor, conducts and the output is zero. When the input signal is, positive going, the NPN transistor T1 conducts and the, PNP transistor T2 is cut off. When the signal is negative, going, T1 is tuned of while T2 conductors. The maximum, efficiency of this circuit is about 78%., , An example for the current amplifier is the commonemitter, common-collector amplifier. The current gain of, common-emitter amplifier is 50 to 300 and that of the, common-collector amplifier is 50 to 500., Power amplifier : Power amplifiers are used to drive the, output mechanism, e.g. a loudspeaker, a pair of earphones,, a moving coil meter or some other type of indicating, device. The main function of a power amplifier is to deliver, a good deal of undistorted power into the output device or, load circuit. Examples for the power amplifiers are class, A, class B, class AB and class C., , 46, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.166, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.167, , Function generator and cathode ray oscilloscope (CRO), Objectives: At the end of this lesson you shall be able to, • explain the use and control of function and AF (audio frequency) generator, • explain the function of CRO with block diagram, • state the functions of various controls in CRO, • state the use of CRO in electronic circuits., Introduction: A function generator is an equipment capable, of providing sine, square and triangular wave outputs at, different frequencies and amplitude. It has a maximum of, 20 volts peak to peak single amplitude. A function, generator finds applications in frequency modulations,, tone control, Audio electronic, other laboratory and research, work., , 9 Fine frequency dial: The output frequency of the, wave forms is given by the product of the setting of this, dial and the range selected., , Panel controls and features of function generator, , The desired frequency is set by depressing the frequency, range switch an positioning the fine frequency dial., , The front panel controls of function generator. (Fig 1), , Operating information: The function generator is powered, by 240V. AC mains. When the power ON switch is, depressed the LED will glow., , The desired wave from is selected by depressing the, appropriate function button from sine, square or triangle., The amplitude of the selected output signal is adjusted by, Amplitude control knob. A variation of the display amplitude, from 0-20 V peak is possible. The TTL output is not, affected by the amplitude control., , 1 Power ON-OFF switch: To turn on the function, generator this button should be depressed. To turn off, the same button should be pressed to release., , Audio Frequency (AF) Generator (Fig 2): Audio, frequency generators produce sine wave signals from 20, Hz to 20 kHZ. Certain type of AF generators produce sine, wave upto 100 kHZ. In addition to sine wave there may be, provision to produce square waves too., , 2 Range selectors: The range selection is of decade, frequency type. The output frequency is given by the, product of range selected and frequency dial indication., For example if the 10 K range button in depressed and, frequency dial is at 2, then the output frequency is 20, KHz., 3 Function selectors: These selectors select the desired, output waveform. (square, sine or Triangle), 4 Output jack: The wave forms selected by the function, switches are available at this jack., 5 VCO input jack: An external voltage (not exceeding ±, 20V peak) input will vary the output frequency. The, change in frequency is directly proportional to the input, voltages., 6 TTL JACK: A TTL (Transistor, Transistor logic) square, wave is available at this jack. This output is independent, of the Amplitude., 7 Amplitude control: This controls the amplitudes of, the output signal., 8 Offset control: This controls the DC offset of the, output., , These generators contain a variable amplitude control, which changes the signal amplitude from 10 mv to 20V., With the help of this generator the audio amplifier stages, in radio, TV recorders and audio amplifier could be tested., While the frequency range switch selects the desired, frequency range switch selects the desired frequency, range, the frequency dial is used to select the frequency, within the desired range., , Copyright @ NIMI Not to be Republished, , 47

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Cathode ray oscilloscope (CRO), Introduction: The oscilloscope is an electronic measuring, device which provides a visual presentation of any wave, form applied to the input terminals. Cathode ray tube, (CRT) like a television tube provides the visual display of, the signal applied as a wave form on the front screen. An, electron beam is deflected as it sweeps across the tube, face, leaving a display of the input signal., An oscilloscope usually consists of:, – Attenuator, – amplifiers, , Amplifier : The amplifiers of an oscilloscope consist of a, vertical amplifier and a horizontal amplifier. The vertical, amplifiers amplify the vertical input signal before it is, applied to the Y-plates. The horizontal amplifier amplifies, the signal, before it is connected to the X-plates., , – saw-tooth generator, – gate amplifiers or Z-amplifier, – Trigger, – CRT (cathode ray tube), – power supply, The block diagram of a simple cathode ray oscilloscope is, shown in Fig 3., Attenuator : The input signal should be attenuated to a, suitable magnitude before it is applied to the amplifier. The, attenuators are employed at the input of both vertical and, horizontal amplifiers., , saw-tooth signal is called the time base signal, and is, produced by the saw-tooth generator. The shape of the, saw-tooth signal is shown in Fig 4. The time-base signal, consists of trace, retrace and hold off period., , Saw-tooth generator: The measuring signal of any, shape is connected to the Y-input(plates) and then it, appears on the screen. The signal on X-plates should be, such that the image on the screen is similar to that on the, Y-plates. Hence a saw-tooth signal is required to be, connected to the X-plates which makes the image on the, screen like the signal connected at the vertical plate. The, 48, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.167, , Copyright @ NIMI Not to be Republished

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Gate amplifier or Z-amplifier: It is desirable that the, image seen on the screen of the CRT must be continuous,, that is, the electron beam is desired to appear only in the, trace period of the time-base signal. The retrace period of, the electron beam must not be visible on the screen., Therefore, the gate amplifier is required to control the, electron beam in order that it appears only in the trace, period., The signal from the gate amplifier is a square wave and is, related to the time-base signal. This is illustrated in Fig 5., , Line triggering : The signal which is supplied to the, trigger is the signal from the power supply of CRO. (Not, shown in the block diagram), Switches are provided to select the form of triggers as, required. In a CRO, suitable timing can be selected that, causes the image on the screen to be stationary., CRO (The Cathode ray tube): The constructional features, are explained later in this text., Power supply: Low voltage and high voltage DC supplies, which are required for the oscilloscope function are produced, by rectifier filters and switch mode power supply circuits., Controls and their functions in a CRO: The operating, controls on the front panel of a general purpose oscilloscope, is shown in Fig 7. The names of the controls and their, functions are listed below., , Trigger (Gate amplifier output) : As mentioned earlier,, the measuring signal-wave form is connected to Y-input,, which appears on the screen. In order to make the waveform stationary on the screen, it is required that the, starting point of the time base signal has to be fixed related, to the signal connected to the Y-input. This is known s, ‘synchronization’. The functional stage which performs, synchronization is the trigger., The trigger will produce a pulse or impulse for triggering the, time-base. Every time the time-base is triggered, one, saw-tooth wave-form is produced., There are three forms of triggering in an oscilloscope., Internal triggering : The signal which is supplied to the, trigger is the internal signal of the CRO produced by using, the signal from the vertical input signal. The sequence of, signal processing is shown in Fig 6., , General, Power-on (1): It is toggle switch meant for switching on, power. In the ON position, power is supplied to the, instrument and the neon lamp (3) glows., Intensity (2): It controls the trace intensity from zero to, maximum., It controls the sharpness of the trace. A slight readjustment, of this control may be necessary after changing the, intensity of the trace., , External triggering : The signal which is supplied to the, trigger is the external signal, produced by using the signal, from the external, sync., , X-Magnification (5): It expands length of the time-based, from 1 to 5 times continuously, and makes the maximum, time-base to 40ns/cm., Square wave (6): This provides a square wave of 2 V, (p-p) amplitude to enable the user of the scope to check, the Y-calibration of the scope., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.167, , Copyright @ NIMI Not to be Republished, , 49

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Saw-tooth wave (7): This provides a saw-tooth, waveform output coincident to the sweep-speed switch with an, output of 5V (p-p). The load resistance should not be less, than 10 k ohms., Vertical section, Y (10) : This control enables the movement of the display, along the y-axis., Y (13) : It connects the input signal to the vertical amplifier, through the AC-DC-GND coupling switch (14), AC-DC-GND coupling switch (14): It selects coupling to, the vertical amplifier, in DC mode, it directly couples the, signal to the input; in AC mode, it couples the signal to the, input through a 0.1 MF, 400-V capacitor. In GND position,, the input to the attenuator (12) is grounded, whereas the, Y-input is isolated., Volts/cm (Attenuator) (12): It is a 10-position attenuator, switch. It adjusts the sensitivity of the vertical amplifier, from 50 m V/cm to 50 V/cm in 1,2,5,10 sequence. The, attenuator accuracy is ±3%., x1 or x 0.1 switch (9), When switched in x 0.1 or position, it magnifies the basic, sensitivity to 5 m V/cm from 50 m V/ cm, CAL switch (8): When pressed, a DC signal of 15 m V or, 150 m V is applied to a vertical amplifier depending upon, the position of x1-x0.1 switch (9) position., DC bal (11): It is a preset control on the panel. It is, adjusted for no movement of the trace when either x1 - x0.1, switch (9) is pressed, or the position of AC-DC-GND, coupling switch (14) is changed., X-Position (21): This control enables the movement of, display along the X-axis., Trigger level (18): It selects the mode of triggering. In, AUTO position, the time-base line is displayed in the, absence of the input signal. When the input signal is, present, the display is automatically triggered. The span, of the control enables the trigger point to be manually, selected., , switch (16) selects whether the wave-form is to be triggered, on +ve or -ve step. NORM/TV switch (17) permits normal, or TV (line frequency ) frame., Stab (20): It is a preset control on the panel. It should be, adjusted so that you just get the base line in the AUTO, position of the trigger level control (18). In any other, position of the trigger level control, you should not get the, base line., Ext. Cap (23): This pair of connectors enables the timebase range to be extended beyond 50 ms/cm by connecting, a capacitor at these connectors., Hor. input (24): In connects the external signal to the, horizontal amplifier., Ext. sync. (25): It connects the external signal to the, trigger circuit for synchronization., Application of CRO, AC voltage measurement: The screen of the cathode, ray oscilloscope usually has a plastic gratitude overlay,, marked in centimeter divisions. The vertical amplitude of, any wave form indicates peak-to-peak voltage., To measure unknown AC voltages the main supply AC, should be isolated through a isolation transformer and the, attenuator is set to 50 V/ div. The AC-DC switch is set to, AC position (out). Voltage to be measured is connected, to the input and common terminal. Set the time base, switch to display several cycles of the wave form. Adjust, the V/div switch to get a wave form at a convenient height, such that the positive and negative peaks appears with-in, the screen., Measure the vertical amplitude (no. of divisions peak-topeak) of the voltage on the screen. Now multiply the, amplitude by the volts/div setting to find the peak-to-peak, voltage value., Example : Assume a vertical deflection of 6.4 divisions, as in Fig 8 and a volt/div setting of 5 volts., , Time-base (19): This sector switch selects sweep speeds, from 50 ms/cm to 0.2Ms/cm in 11 steps. The position, marked EXT is used when an external signal to be applied, to the horizontal input (24), Vernier (22): This control is a fine adjustment associated, with the time-based sweep-selector switch (19). It extends, the range of sweep by a factor of 5. It should be turned fully, clockwise to the CAL position for calibrated sweep speeds., Sync. selector (15, 16, 17): The INT/EXT switch (15), selects internal or external trigger signal. The +ve or -ve, 50, , Peak-to-peak voltage, , = 6.4 x 5 = 32 V, , therefore peak voltage, , = 16 V, , therefore RMS voltage, , = 16 x 0.707, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.167, , Copyright @ NIMI Not to be Republished, , = 11.31 V

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or RMS voltage =, , VPP, Peak to peak voltage, =, 2.83, 2x 2, , 32, =, =, 11.31v, 2x 2, , DC voltage measurement : The input selector switch is, set to DC position. Adjust the Y shift position to get the, trace at the centre of the screen. This line represents zero, DC volts. Connect the +ve of the DC voltage to be, measured to input terminal and the -ve to the common, terminal. Now the horizontal line will move up. (Down for, reverse polarity) the volts/div switch is set as required., , approximately two cycles of the wave-form to be measured., Adjust the Y-SHIFT control to move the trace so that the, measurement points are on the horizontal centre line. The, X-SHIFT control is adjusted to move the start of the, measurement points to a convenient reference line., The distance (divisions) between the points of one cycle, is measured as in Fig 10., , Now measure the vertical distance in divisions form the, zero reference line., The DC voltage can be found by multiplying the vertical, distance (division) with VOLT/DIV setting., An example is worked out with reference to Fig 9, , The product of the divisions of one cycle and the setting of, time/div switch gives the period of one cycle., The frequency can be determined by the formula, , Frequency =, , 1, Time period, , where frequency is in hertz and time in seconds., Example, Assume a vertical deflection of 2.6 division and a Volts/Div, setting of 20 V., DC voltage = 2.6 x 20 = 52V., Measurement of time and frequency : The wave-form, to be measured is connected to the V input. The volts/Div, switch is set to display a suitable vertical amplitude of the, wave-form. The Time/Div switch is set to display, , Time, , =, , Div x time base setting, , =, , 5 x 0.2 ms, , =, , 1 ms, , 1, 1, =, =, 1000 Hz, therefore frequency =, T 1 x 10 -3, Frequency, , = 1 kHz., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.167, , Copyright @ NIMI Not to be Republished, , 51

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.168, , Printed circuit boards (PCB), Objectives : At the end of this lesson you shall be able to, • state the types of etchants used for etching and preparation of etchant solution, • state the reasons for agitating the etchant solution while etching, • list the important points while drilling holes on PCBs, • list the advantages of marking component positions on PCBs., Introduction, Printed circuit board in which the connecting wires are, replaced by a thin conducting path called copper or silver, foil which is moulded in one side of the insulated board., The insulating board is generally made up of phonetic,, paper or fibre glass or epoxy., , prepared in a plastic tray of suitable size such that the, painted laminate to be etched can be fully immersed as, shown in Fig 1., , The moulded conducting path generally known as tracks, size depend on the power of the circuit. The width of, tracks are varied few millimeters to less than one millimeter, depend on the circuit., The thin tracks less than one millimeter made up with, silver tracks where IC circuits and micro controller circuits, are to be made. Several process moulded to make PCB, and it is explained below., Etching, Once the required portions on the copper foil side of the, laminate is painted/masked and dried, the next step is to, remove the copper present in the unmasked portions of, the laminate. This process is known as etching., Only after etching the unwanted areas of the copper foil,, the metal side of the laminate gets the actual shape of the, circuit connection required., Etching is done using any one of the following chemicals;, – Alkaline ammonia, – Sulpuric-hydrogen peroxide, , Since ferric chloride is an acid solution, although diluted,, it is harmful to the skin. Hence, rubber gloves are to be, used while working with this solution., The painted laminate to be etched is slid into the Fecl3, solution of required quantity, with the painted surface of, the laminate facing the top as in Fig 1, such that, as the, process of etching progresses, the extent of etching is, visible., To ensure speedy and uniform etching, the etchant solution, is agitated lightly by shaking and tilting the tray as shown, in Fig 2. Too much of agitation of the solution should be, avoided, as this may peel off the ends of the painted tracks, and remove those portions which were not intended to be, etched., , – Ferric chloride, – Cupric chloride, The most popular amongst beginners and economical way, of etching, is the manual etching process. This is done, generally using a solution of ferric chloride. Ferric chloride, is available in liquid, powder and crystal forms., While preparing the etching solution, concentrated ferric, chloride solution/powder is mixed with lukewarm, water(27°F) and stirred well using a glass rod. This forms, a diluted acid (FeCl3) solution., The ratio of ferric chloride and water decides the rate of, etching. The typical ratio is, 100mg of concentrated ferric, chloride powder/liquid for one litre of water. This Fecl3 is, 52, , Copyright @ NIMI Not to be Republished

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As the etching progresses, the copper in the unwanted, portion is gradually removed. When the etching is complete,, all the copper in the unwanted portion disappears and the, etched portion will have the colour of the insulator of the, laminate board., , Preparing and marking component lay out, A typical component side of a PCB with the components, marked on it is in Fig 4., , Once the unwanted portions of copper are completely, etched, the board is taken out of the solution and is, cleaned using fresh water to remove the remaining Fecl3, solution. This stops any further etching process., After cleaning the board using water and drying, the etchresistant ink/paint on the lay out pattern is removed using, solvents, such as, thinner or petrol. The cleaned board will, then have bright copper stripes and pads, only in the, required portions representing the circuit as in, Fig 3., , Marking the position of the components on the component, side of the PCB has two main advantages,, – Increases the speed of mounting the components as, the need of searching for the correct place for mounting, the component is eliminated., – Polarities of the components’ terminals can be marked, on the board itself such that the possibility of polarity, errors committed while assembling the board is, eliminated., , Drilling holes on PCBs, The next step after etching and removing the mask/paint, is to drill holes of required diameter at the pad centers for, inserting the components, input/output and Vcc &, ground(Gnd) connections. Extra care is to be taken while, drilling holes because carelessness while drilling may, peel off the pad area of the copper. Some hints for drilling, on PCB’s are given below;, – If the point where drilling is to be made is not clear,, punch the point again such that the drill bit sits at the, punched point before starting the drilling., , The standard procedure of component marking is to mark, either the symbol of the component along with its code, number or just the code number across the pads as shown, in Fig 4., A separate component list sheet, containing the component, code number along with its value as shown below, is, prepared for reference while collecting the components, and assembling the PCB., Component, , – Fix the PCB firmly on a vice using a wooden block so, that the PCB does not become loose while drilling and, peel of the pad area copper., – Ensure that all the points required are drilled because,, once the components are mounted, drilling holes on, the PCB may damage the mounted components due, to vibration., After drilling holes, clean the PCB such that it is free from, burr and dust. Apply varnish on the layout pattern, to, protect the copper pattern from corrosion., , Specification, , Resistors, , R1, R2,R3, , 1K Ohms,1W, 5%, 680 Ohms,1/4W,10%, , Capacitors, , C1, , 1000uF, 50V,, axial 0.01uF,, 100V, ceramic disc, , – Use a high speed drill gun/machine., – Use drill bits of the required size. If an exact size drill, bit is not available, use a drill bit one size smaller but, never one size larger., , Code, , C2 to C7, Diodes, , D1,D2,, D3,D4, , 1N4007, , For circuits using less number of components, instead of, a separate component list the component values are, marked directly on the printed circuit board as in Fig 5., To prepare manually the component side layout of the, PCB, the reverse of the pad positions of the PCB’s solder, side lay out is traced on to a graph sheet, and the, component positions and polarities indicated using standard, symbols. The components are numbered and a component, list is prepared., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.168, , Copyright @ NIMI Not to be Republished, , 53

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The component side layout is then traced on to the, insulator side (component side) PC board using a carbon, sheet and pencil. The traced portions on the board are, redrawn/touched using a permanent marker pen or using, paint and a thin brush., , 54, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.168, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.169, , Power electronic devices - UJT and FET, Objectives: At the end of this lesson you shall be able to, • state the construction and working characteristics of SCR and its testing, • state the use of UJT for triggering gate circuits, • explain the function of DIAC and TRIC, • state the FET principle working, biasing, applications, • state the JFET principle, biasing, application as an amplifiers., Introduction, Thyristors are four layer device which can be switched, ‘ON’ or ‘OFF’ electronically to control relatively large, amounts of current for motors and other electrical, equipment. The Silicon Controlled Rectifier (SCR) and the, Triac are examples of Thyristor. Almost all electronic, controls used in modern industries consist of electronic, circuits with Thyristors., Construction of SCR: The cross-sectional view of a, typical SCR and the symbol are shown in Fig 1. Basically,, the SCR consists of a four-layer pellet of P and N type, semiconductor materials. Silicon is used as the intrinsic, semiconductor to which the proper impurities are added., , In the ON-state, the current is limited by the external, impedance. If the anode-to cathode voltage is now, reduced, since the original depletion layer and the reversebiased junction J2 no longer exist due to the free movement, of the carriers, the device will continue to stay ON. When, the forward current falls below the level of the holding, current Ih, the depletion region will begin to develop around, J2 due to the reduced number of carriers, and the device will, go to the blocking state. Similarly, when the SCR is, switched on, the resulting forward current has to be more, than the latching current IL., This is necessary for maintaining the required amount of, carrier flow across the junctions; otherwise, the device will, return to the blocking state as soon as the anode-tocathode voltage is reduced. The holding current is usually, lower than, but very close to the latching current; its, magnitude is in the order of a few milliampere(mA). When, the cathode is made positive with respect to the anode,, junctions J1 and J3 are reverse-biased, and a small reverse, leakage current will flow through the SCR. This is the, reverse blocking state of the device., When the SCR is reversed biased the device will behave, in the same manner as two diodes connected in series, with the reverse voltage applied across them. The inner, two regions of the SCR will be lightly doped as compared, to the outer layers., , Working of SCR: The SCR is a four-layer device with, three terminals, namely, the anode, the cathode, and the, gate. When the anode is made positive with respect to the, cathode (Fig 1), junction J2 is reverse-biased and only the, leakage current will flow through the device., The SCR is then said to be in the forward blocking state, or off-state. When the anode-to-cathode voltage is, increased, the reverse-biased junction J2 will break down, due to the large voltage gradient across the depletion, layers. This is the avalanche breakdown. Since the other, junctions J1 and J3 are forward-biased, there will be free, carrier movement across all the three junctions, resulting, in a large anode-to-cathode forward current IF. The voltage, drop VF across the device will be the ohmic drop in the four, layers, and the device is then said to be in the conduction, state or on-state., , Hence, the thickness of the J2 depletion layer during the, forward-bias condition will be greater than the total thickness, of the two depletion layers at J1 and J3 when the device is, reverse-biased. Therefore, the forward break-over voltage, VBO will be generally higher than the reverse break-over, voltage VBR., SCR has two stable and reversible operating states. The, change over from off-state to on-state, called turn-on, is, achieved by increasing the forward voltage beyond VBO., There reverse transition, termed turn-off, is made by, reducing the forward current below Ih. A more convenient, and useful method of turning on the device employs the, gate drive., , Copyright @ NIMI Not to be Republished, , 55

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Characteristics of SCR, SCR voltage current characteristic: Fig 2 shows the, voltage current characteristic of an SCR whose gate is not, connected(open). When the anode-cathode circuit is, reverse biased a very small current in micro ampere called, reverse blocking current flows through the SCR. When the, reverse break over voltage reaches a value equivalent to, peak reverse voltage VBR, the SCR conducts due to reverse, avalanche breakdown and the current increases sharply, into ampere., , control method, is used as it is more efficient and easy to, implement for power control., Gate-current control: Injecting gate current into the SCR, lower the break over voltage, as shown in Fig 3. Here IGO, is for zero gate current. This situation is the same as that, shown in Fig 2, but the other examples in Fig 3 are for, increasing gate current. Note that, as gate current is, increased, the break over voltage is reduced., , In most of the cases the SCR gets damaged in this mode., The behaviour of the SCR at reverse bias mode is shown, by VI characteristic of Fig 2., When the SCR is forward biased, there is small forward, leakage current (as in Fig 2) called forward blocking, current which remains small, until the forward breakdown, voltage VBO is reached. This is the forward avalanche, region., When there is enough gate current, the break over voltage, becomes lower than the operating voltage or the forward, blocking voltage of the SCR. That is how the SCR is used., The injection of gate current lower the break over voltage, to a value below that of the applied voltage, thereby turning, the SCR on., Note that the ‘ON’ state is the same for all different values, of gate current in Fig 3. The gate current triggers the SCR, ‘on’; but when the SCR conducts the amount of forward, current is determined by the anode circuit impedance., At that point current increases suddenly to higher, conduction level. At this point the anode to cathode, resistance of the SCR becomes very small and the SCR, acts like a closed switch. The voltage across the SCR, drops to about 1.4V. Hence we can say that in forward bias, mode when the applied voltage is less than BFO the SCR, behaves as open switch and when the applied voltage, exceeds BFO the SCR behaves as closed switch. The, current through SCR is limited by the external load, resistance., Holding and latching currents: The holding current is, the +I value necessary in the anode circuit to keep the, SCR in conduction while it is ON. The latching current is, +I value needed to switch the SCR anode circuit ON from, the OFF condition. This I (current) is typically about three, times more than the holding current. When the SCR is, switched into conduction, the gate voltage must be on long, enough for the anode current to reach the value for, latching., Triggering of SCR: SCR can be switched into conduction, either by increasing the forward voltage beyond VBO or by, applying a positive gate signal when the device is forwardbiased. Of these two methods, the latter, called the gate56, , Applications: The following are the major applications of, SCR, – Power control, – Over voltage protection, – Time delay circuit, – Soft start circuit, – Logic and digital circuits, – Pulse circuits references, – Phase control in AC power control, – full-wave control circuit, – Speed control of motors, – Regulated DC power supplies, – DC motor control, Testing of SCR by multimeter, SCR can be tested in the multimeter in the following, sequence., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished

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Set the multimeter to a low range. Adjust to zero and, infinity with the adjustment knob. Connect the SCR as, shown in Fig 4. The meter will not indicate any reading., Even the test prods are interchanged because of the, junctions. The multimeter shows infinite resistance., Connect the SCR as in Fig 4. When the gate is touched, momentarily with the anode prods, the meter reads low, resistance between 30 and 40 ohm. When the gate is, removed, the meter still continues to read the same value, of 30 and 40 ohm., , This means that the SCR is in good working condition. If, the meter does not show any reading, the SCR is faulty., When the gate is given a small forward bias, the gate, switching the SCR and the internal resistance of the, junction is low, so the current can flow easily from the, cathode to the anode. Once the SCR is conducted, even, if the gate’s forward bias is removed, the SCR anode-tocathode current will flow through the meter, and the, multimeter will continue to read a low resistance, ie 30 to, 40ohm., The DIAC and TRIAC, Like UJTs, DIAC is a semi-conductor device used, extensively as a trigger device for triacs and thyristors gate, circuit. In its most elementary form, DIAC is a three layer, device as in Fig 5 without gate terminal., , As can be seen from Fig 5, DIAC is a three layer, two, terminal semi-conductor device capable of conducting, current in both directions., DIACs resembles an NPN or PNP bipolar transistor with, no base connection. Unlike bipolar transistor, the diac, possess uniform construction. This means, N-type and Ptype doping is essentially the same at both junctions. As, in Fig 5, diac may be constructed as either an NPN or PNP, structure., , Fig 6a shows the experimental setup for testing the diac., The isolation transformer is used to isolate the circuit from, the supply mains. The variable transformer is used to, apply the variable voltage to diac under test. The, characteristic curve of a typical diac is shown in Fig 6b., , As shown in the experimental setup at Fig 6a, when a, small voltage of either polarity is applied across a DIAC,, the current flow is very small as can be seen from its, characteristics in the first and the third quadrants. If the, applied voltage is steadily increased, the current will, remain at a low value until the applied voltage reaches a, value known as the breakover voltage of the DIAC as in, Fig 6b., Once this point is reached the diac current increases, rapidly and the diac voltage falls to a low value. At this, point, the diac exhibits negative resistance characteristics, (current conduction increases while the voltage across the, device decreases). The diac will continue to conduct, current as long as the current is greater than the holding, current of the device., A diac acts in a similar manner to two zener diodes that, are connected in reverse parallel and it therefore it is able, to rectify AC voltage during both half cycles. The symbol, used for DIAC is in Fig 5b., Application of DIAC: DIAC can be used to trigger triac or, SCR at specified voltage levels., DIAC testing: DIACs are similar to two diodes connected, back to back and break down in either direction once the, applied voltage reaches the breakdown voltage of the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished, , 57

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diode. While testing a diac using a ohmmeter, it should, show high resistance (infinite resistance) when checked, in either direction. The quick test only confirms that the, DIAC is not shorted; however this quick test is worth, carrying out before using the Diac in a circuit., TRIAC, TRIAC is a three terminal gated semi-conductor device for, controlling AC in either direction. The term TRIAC stands, for TRIODE AC semi-conductor. TRIAC is very similar to, that of two SCR connected in reverse parallel. A Triac is, able to conduct a large current in both directions, being, trigged ON in one direction or the other by a gate pulse of, the appropriate polarity., UJT and its applications of triggering circuits, UJTs are employed in a wide variety of circuits involving, electronic switching and voltage or current sensing, applications. These include, , The wave form developed across the capacitor is shown in, Fig 7 as VE, whereas the waveform produced across the, resistor RB1 is shown as a pulse VB1., The frequency of oscillation, 1, f= R C, E, , Where RE is the value of variable resistor in ohms and C is, the value of the capacitor in farad., By varying the value of RE, the frequency of the oscillator, can be varied. Although such an oscillator using a DC, supply voltage could be used to trigger a SCR, there would, be trouble in synchronizing the pulses with the cycles of, alternating current. Fig 8 shows a stable triggering circuit, for an SCR in which the firing angle can be varied from 0°, to 180°., , – triggers for thyristors, – as oscillators, – as pulse and sawtooth generators, – timing circuits, – regulated power supplies, – bistable circuits and so on., Let us analyse the waveform generated across the capacitor, and R1 with respect to the relaxation oscillator or free, running oscillator as in Fig 7., , The low output impedance of the UJT (39 ohms) is ideal for, driving the SCR, which has a relatively low input impedance, from gate to cathode., Resistor RD is used as a dropping resistor to restrict the, peak voltage across the UJT to within its specifications., By varying the variable resistor RE the oscillator frequency, can be varied thereby the frequency of trigger pulses which, are used to trigger the SCR. Time used for delay in, switching the SCR could be measured through a stop, watch from the time of switching on., Basic construction of a Triac, its symbol and a typical, Triac is shown in Fig 9a, 9b and 9c. As can be noticed in, Fig 9, the electrodes of a Triac are labelled as,, – Main terminal-1 (MT1), – Main terminal-2 (MT2) and, The negative - resistance portion of the UJT characteristic, is used in the circuit shown in Fig 7 to develop a relaxation, oscillator., , 58, , – Gate (G), The terminals are so labelled because, this device operated, in both directions and hence the terms anode and cathode, does not apply., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished

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TRIAC triggering : Triac can be triggered/turned-ON by,, 1 applying a gate current,, 2 applying a voltage exceeding the avalanche breakdown, voltage VBO, 3 allowing the MT1 - MT2 applied voltage to increase at a, rate in excess of the maximum dv/dt figure., Methods 2 and 3 above are not employed in normal Triac, operation but they may be considered as limiting factors, in circuit design. Hence, in all further discussion it is, restricted to triggering the Triac via the gate. Since Triac, is a bidirectional device, it can be triggered into conduction, by a negative or a positive gate signal. Triacs potentials, are considered with respect to main terminal - 1 (MT1)., This gives the following possible operating situations or, modes;, , From the Triac static characteristics. When MT2 is, positive with respect to MT1, the (Fig 6) Triac operates in, the first quadrant of its static characteristics, if it is not, triggered, the small forward current increases slowly with, increase in voltage until the breakdown voltage VBO is, reached and then the current increases rapidly. The, device can be, and usually is, turned ‘ON’ at a smaller, forward current by injecting a suitable gate current and the, characteristics shows the effect of increasing the gate, current from zero to 4mA., The gate current must be maintained until the main current, is atleast equal to the latching current. When terminal MT1, is positive with respect to MT2 the Triac operates in the, third quadrant and the current flows in the opposite, direction., Full wave control using a TRIAC: Fig 11a shows a Triac, used for controlling the current flowing in an AC circuit., Fig 11b shows the wave forms with different settings of, POT VR1., , – MT2 +ve with respect to MT1 - Gate signal +ve, (1st quadrant +), – MT2 +ve with respect to MT1 - Gate signal –ve, (1st quadrant –), – MT2 –ve with respect of MT1 - Gate signal +ve, +(3rd quadrant +), – MT2 –ve with respect to MT1 - Gate signal –ve, (3rd quadrant –), Unfortunately, Triac is not equally sensitive in all the above, said modes. It is least sensitive in 3rd quadrant mode (MT2, negative with respect of MT1 and triggered by a +ve gate, signal) so this mode is very rarely used in practice. When, a Triac is ON the current flowing between MT1 and MT2 is, known as principal current. The TRIAC will remain ON as, long as the current flowing through it is larger than the, holding current as in the static characteristics of a Triac in, Fig 10., Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished, , 59

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Note: In Triac the terms forward and reverse do, not arise since it is bidirectional., Quick testing TRIAC: A quick test can be carried out on, triac using an ohmmeter. If the readings taken are, comparable to the one shown in table below, the Triac can, be considered as satisfactory and can be used in circuit;, Meter polarities +, , Resistance, , MT2, , MT1 > 1M, , MT1, , MT2 > 1M, , MT2, , G > 1M, , G, , MT2 > 1M, , MT1, , G > 300Ω, , G, , MT1 > 300Ω, , Field-effect transistor (FET), , If the main current flow is only through the P-doped, material, then such a FET is referred as a P-channel or Ptype FET. The current through the P-doped material in the, P-type FET is only by Holes., Unlike in bipolar transistors in which the main current is, both by electrons and holes, in contrast in FETs depending, on the type(P or N type) the main current is either by, electrons or by holes and never both. For this reason FETs, are also known as Unipolar transistors or Unipolar device., There are a wide variety of FETs. In this lesson one of the, fundamental types called as Junction Field Effect Trasistor, (JFET) is discussed., Junction Field effect Transistor(JFET), It is a three terminal device and looks similar to a bi-polar, transistor. The standard circuit symbols of N-channel and, P-channel type FETs are shown in Fig 13., , The main difference between a Bi-polar transistor and a, field effect transistor is that,, Bi-polar transistor is a current controlled device, In simple terms, this means that the main current in a bipolar transistor (collector current) is controlled by the base, current., , The internal diagram of a N-channel FET is shown in, Fig 14., , Filed effect transistor is a voltage controlled device, This means that the voltage at the gate(similar to base of, a bi-polar transistor) controls the main current., In addition to the above, in a bi-polar trasistor (NPN or, PNP), the main current always flows through N-doped and, P-doped semiconductor materials. Whereas, in a Field, effect transistor the main current flows either only through, the N-doped semiconductor or only through the P-doped, semiconductor as in Fig 12., , If the main current flow is only through the N-doped, material, then such a FET is referred as a N-channel or Ntype FET. The current through the N-doped material in the, N-type FET is only by electrons., , 60, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished

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FET notation listed below are essential and worth, memorizing,, 1 Source terminal: It is the terminal through which, majority carriers enter the bar(N or P bar depending, upon the type of FET)., 2 Drain terminal: It is the terminal through which, majority carriers come out of the bar., 3 Gate terminal: These are two internally connected, heavily doped regions which form two P-N junctions., 4 Channel: It is the space between the two gates, through which majority carriers pass from source to, drain when FET is working(on)., Working of FET, Similar to Biploar transistors, the working point of, adjustment and stabilization are also required for FETs., Biasing a JFET, – Gates are always reverse biased. Therefore the gate, current IG is practically zero., – The source terminal is always connected to that end of, the supply which provides the necessary charge carriers., For instance, in an N-channel JFET source terminal S, is connected to the negative of the DC power supply., And, the posive of the DC power supply is connected, to the drain terminal of the JFET., Whereas in a P channel JFET, Source is connected to the, positive end of the power supply and the drain is connected, to the negative end of the power supply for the drain to get, the holes from the P-channel where the holes are the, charge carriers., Let us now consider an N channel JFET, the drain is made, positive with respect to source by voltage VDS as shown in, Fig 15a. When gate to source voltage VGS is zero, there is, no control voltage and maximum electron current flows, from source(S) - through the channel - to the drain(D). This, electron current from source to drain is referred to as Drain, current, ID., When gate is reverse biased with a negative voltage(VGS, negative) as shown in Fig 15b, the static field established, at the gate causes depletion region to occur in the channel, as shown in Fig 15b., This depletion region decreases the width of the channel, causing the drain current to decrease., If VGS is made more and more negative, the channel width, decreases further resulting in further decrease in drain, current. When the negative gate voltage is sufficiently, high, the two depletion layers meet and block the channel, , cutting off the flow of drain current as in Fig 15c. This, voltage at which this effect occurs is referred to as the, Pinch off voltage, VP., Thus, by varying the reverse bias voltage between gate and, source(-VGS), the drain current can be varied between, maximum current (with -VGS=0) and zero current(with VGS=pinch off voltage). So, JFET can be referred as a, voltage controlled devices., P channel JFET operates in the same way as explined, above except that bias voltages are reversed and the, majority carrier of channel are holes., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished, , 61

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Important specifications of typial JFETs, BF245B, , 4 they have low interelectrode capacity., BFW10, , Polarity of the device, (N-type/P-type), , Nj, , Nj, , Maximum drain-source, voltage, VDS, , 30 V, , 30 V, , Maximum gate-source, voltage, VGS, , 30 V, , 30 V, , Maximum drain current, ID, Maximum forward gate, , 25 mA, , 20 mA, , current, IG, Pinch-off Voltage, (at ID=0), VP, Maximum power, dissipation, Pmax, , 10 mA, , 10 mA, , 300 mW, , 300mW, , Package type, , TO92, , TO72, , Pin Diagram, (Refer 6605 data manual), , fig W141e fig W158b, , 8V, , The term Nj in the specification indicates that, it is a N-type junction FET., , Typical applications of JFET, One very important characteristic of JFET is its very high, input impedence of the order of 10 9 ohms. This, characteristic of FET, has made it very popular at the input, stage of a majority of electroinc circuits., As discrete components FETS are mainly used in,, •, , DC voltage amplifiers, , •, , AC voltage amplifiers(input stage amplifers in HF and, LF ranges), , •, , Constant current sources, , •, , Integtated circuits of both analog and especially in, Digital technology., , 1 FET AC voltage amplifier, In the circuit at Fig 17, the amplification is determined by, the design. it can be varied within certain limits of the drain, resistance and the source resistance are made variable., Potentiometer can be connected in series for this purpose., , As discussed earlier FETs also need a proper biasing, arrangement for it to work. Like transistors, FETs can also, be connected in different configuration. Fig 16 gives a, summary and comparision of basic FET configurations., Advantages of FET, 1 Since they are voltage controlled amplifier this makes, their input impedence very high, 2 They have a low noise output. This makes them useful, as preamplifiers where the noise must be very low, because of high gain in the following stages., 3 They have better linearity, , 62, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.169, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.170, , Power supplies-troubleshooting, Objectives: At the end of this lesson you shall be able to, • list the initial activities involved in troubleshooting, • list the three general steps involved in troubleshooting, • list and explain the two popular methods of troubleshooting, • list the possible defects in a power supply, • state the meaning and use of Problem Trees (PT) and service flow diagram (SFD)., Introduction, Troubleshooting in any equipment or in a circuit involves, the following activities:, – To identify the exact nature of the problem., – To identify the section causing the problem., – To isolate and arrive at the exact cause(s)., – To confirm the causes by necessary tests., – To replace the problem-causing parts., – To re-test and confirm the satisfactory working., The following are the general steps involved in, troubleshooting., i, , Physical and sensory tests, , – Look for the most common physical faults, such as, broken wires, cracked circuit boards, dry solders and, burnt out components., – Smell for hot or burning components., – Feel with the fingers for unduly hot components., ii Symptom diagnosis, Learn the operation of the system to be repaired with the, help of its block diagram and its input and output, specifications., , – Active low power components: These are the same, as in (a) but are physically small and can handle, smaller amounts of power., – High voltage/power passive components: Such, components are resistors, capacitors, transformers,, coils, etc. which handle large amounts of voltage/, power. They are found in power supplies and output, circuits., – Low power passive components: These are the, same as in (c) but are physically smaller and handle, comparatively less power and are low in value (ohm,, microfarad, microhenry, etc.), Note: This procedure may not turn out to be, true always. Hence, do not attempt to replace, common sense and meter measurements with, the procedure., While troubleshooting any electronic system, two main, methods are generally adopted. They are:, Step-by-step method of troubleshooting: This approach, is preferred by the beginners. In this approach, the, problem causing part or section is identified by testing the, parts or sections from the beginning to the end as shown, in Fig 1., , Observe the symptoms produced by the defective system,, and determine which section or function would produce, the symptoms., iii Testing and replacing defective components, When the probable defective section has been diagnosed,, check the probable components in that section of the, circuit that are most likely to go defective in the order given, below:, Components should be checked in the order given below, because that is the order in which they fall in most cases., – Active high power components: For example,, components such as transistors, ICs, and diodes., High power devices are physically large in size and are, used for handling the high power, generally in output, circuits., , Although this approach may take more time, this is the, most suited approach for the beginners., , Copyright @ NIMI Not to be Republished, , 63

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Shortcut or logical approach method of, troubleshooting: This method is used by the experienced, servicing people. In this method, the problem causing part, or section is identified from the nature of the problem, symptom. Divide and conquer procedure is adopted to, arrive at the exact cause. This method takes less time, comparatively., Troubleshooting power supplies: All electronic systems, can be broken down into blocks, generally based on their, function. Fig 1 shows the various blocks of a simple power, supply. Each block has a particular function to perform., Before carrying out the troubleshooting of power supplies,, the first thing to be done is to isolate the load connected, to the power supply. This is because the connected load, itself may be the cause of the problem as shown in the, problem tree (PT) in Fig 2., , Step 8: Test the capacitor(s) of the filter section., Step 9: Test the bleeder resistor, surge resistor and other, resistors, if any., Step 10: Test the output indicator lamps/LEDs., After completing all the above steps, from the defective, components identified, analyze the root cause for the, problem and confirm that the cause will not reoccur if the, identified components are replaced., Step 11: Replace the identified defective component(s)., Step 12: Switch the power ON and test the power supply,, first without load, and then connecting it to the load., Logical approach to troubleshoot power supply: In, this approach steps 1 to 4 of the step-by-step approach, are the same. The next step is to refer to the Logical, Service Flow Diagram (SFD) for the identified problem and, proceed with the troubleshooting as directed in the SFD., SFDs are very good tools in troubleshooting as they take, into account, the divide and conquer technique, thus, reducing the overall time taken to troubleshoot the defect, in the power supply., The possible types of defects that can occur in a simple, power supply consisting of a bridge rectifier and capacitance, input filter are listed below alongwith their SFD numbers., , Once it is confirmed that the power supply has the same, defect even with the load disconnected, you can follow, either the step-by-step approach or the logical approach, to troubleshoot the power supply., Step-by-step approach to troubleshoot power supply:, In the step-by-step approach of troubleshooting, the various, blocks of the power supply is in Fig 1 and the components, of the blocks are checked one by one, starting with block, 1 and in steps as given below., Step 1: Confirm the presence and satisfactory level of the, mains supply from which the power supply is powered., Step 2: Switch the power ON and test and note down the, exact nature of the problem. Although the nature of the, problem has been already told, it is essential to confirm, the exact nature of the problem. This is because, in a real, life situation, the customer may not be a technical person, to inform the exact nature of the problem., Step 3: Carry out physical and sensory tests., Step 4: Trace the circuit to identify any wrong polarity, connections., Step 5: Remove the power cord of the power supply from, the mains and test the power cord., , Possible defects in a power supply using bridge, rectifier and filter capacitor, i, , No output voltage, , This defect in the power supply may be due to one or more, component of the circuit. Problem Tree-1 (PT-1) given at, the end of this lesson for the causes of the problem., This PT shows the cause-effect relationship of the defective, components with the problem. The cause is given at the, top and the effect at the bottom for the only reason that it, is a normal tendency to read a page from the top to the, bottom., PT-1 shows two problem trees. The first in Chart 1,, indicated as Level-1 is a simple tree which gives the level1 causes of the problem. Level-2 is an extension of the, same problem tree, which gives one more level of the, causes for the causes given in the simple tree at level-1., Hints to Instructor: Instructor to discuss PT-1, and ensure that trainees clearly understand, the need and meaning of PTs., Chart 2 at the end of this lesson, shows the sequence to, be adopted while servicing a defective power supply. The, Service Flow Sequence - 1(SFS-1) at Chart 2 is selfexplanatory. However the following tips make it easy to go, through the SFS., , Step 6: Test the transformer., Step 7: Test the diode(s) of the rectifier section., 64, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.170, , Copyright @ NIMI Not to be Republished

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– The flow is from top to bottom., – Rectangular blocks indicate work to be done or action, to be taken., – Follow the path of the arrow., – Diamond blocks indicate a decision to be taken after, conducting a test or making a measurement. If the, answer to the question in the diamond block is YES,, follow the path of YES and continue. If the answer is, NO, follow the path of NO and continue., – Rounded rectangular ;block indicates the end of the, job., ii Low output voltage/increased ripple in output, Here, note that two defects are combined. The reason, being, that these two defects generally occur, , simultaneously. If the output voltage is low, the cause(s), for this also results in increased ripple and vice versa. Of, course with one exception that, if the mains level itself is, low or if the secondary voltage of the transformer itself is, low due to shorted windings, a low output voltage is not, associated with increased ripple. The cause for this defect, are given in problem tree PT-2 in Chart 3. Chart 4 shows,, the service flow diagram (SFS-2) for servicing the defect., NOTE: The SFSs and PTs for a fullwave rectifier, with a capacitance filter is almost similar to, that of a bridge rectifier. However, it is, suggested that the trainees shall make SFSs, and PTs for a fullwave rectifier power supply, on their own for practice and better, understanding of the method., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.170, , Copyright @ NIMI Not to be Republished, , 65

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Problem Tree - PT1, NATURE OF DEFECT, , :, , No Output voltage, , TYPE OF SYSTEM, , :, , Bridge rectifier with capacitor filter, , LEVEL 1, , Possibility, order, , Open wire connections, or, Dry solder points, , .............................................................................., , 1, , No voltage across Transformer...................................., Primary or Secondary winding, , 2, , ................................ 3, , Filter capacitor, shorted, , .......... 4, , Rectifier diodes, open, , No output, Voltage, , LEVEL 2, , Bad soldering, , Mishandling, , Open wire connections, or, Dry solder points, , Low capacitor, voltage rating, , Ageing, , Filter capacitor, shorted, , 66, , No Mains supply, , Defective transformer, , No voltage across, transformer Primary or, Secondary winding, , Shorted load, , Low IF/PIV rating, , Rectifier Diodes, open, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.170, , Copyright @ NIMI Not to be Republished

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Service flow sequence (SFS-2), NATURE OF DEFECT, , :, , Defective power supply with NO OUTPUT VOLTAGE, , Start servicing, , Carry out physical defect checkings, and rectify defects found., (Step 1 of Task 1), Carry out component polarity,, trace, check and rectify defects., (Step 2 of Task 1), , NO, , NO, , Tr. Pri., voltage, present, ?, , Tr. Sec, voltage, present, ?, , YES, , NO, YES, , Power-OFF PSU, , NO, Power cord may be, defective. Power-off,, Test, repair/replace, power cord., , Transformer may be, defective. Poweroff, Test, repair/, replace, transformer, , Filter, capacitor, OK, ?, , DC, output, of PSU, present, ?, , YES, , YES, , Replace capacitor, , Power ON, , Test diodes., Replace defective, diodes, , Power ON, , Equipment serviced, Report to Instructor, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.170, , Copyright @ NIMI Not to be Republished, , 67

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Problem Tree - PT2, NATURE OF DEFECT, , :, , Low Output DC/Increased ripple, , TYPE OF SYSTEM, , :, , Bridge rectifier with capacitor filter, , LEVEL 1, , Filter capacitor, open or leaky, , .........................................................................., One or pair of, Diode(s) open, , 1, , ..................................... 2, Tr. Sec. voltage, low, , .............. 3, , Low output voltage/, increased ripple in output, LEVEL 2, , Low capacitor, voltage rating, , Ageing, , Shorted load, , Filter capacitor, open or leaky, , Low IF/PIV rating, , One or pair of, Diode(s) open, , Mains voltage, low, , Some windings of, sec. shorted, , Transformer secondary, voltage low, , 68, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.170, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.171, , Power control circuit using SCR,DIAC,TRIAC & IGBT, Objectives : At the end of this lesson you shall be able to, • explain the construction and working of SCR,DIAC,TRIAC & IGBT, • explain power control circuits using SCR, • explain power control circuit using DIAC & TRIAC, • explain the construction and using of IGBT., Introduction to power electronics devices, Industrial electronics is concerned primarily with electronics, applied to industries such as industrial equipments,, controls and processes. An important application of, electronics in industries is in controlling of machinery., In communication electronics, domestic & entertainment, electronics, generally, the electronic devices operate with, currents in the order of Microamper to Milliamper. For, industrial applications, most frequently, devices are required, to handle currents in the range of ampere to several, thousands of ampere. This, therefore calls for high power, electronic devices. One such high power electronic device, frequently used in industrial electronic application is the, SCR,TRIAC,IGBT and DIAC for associate triggering, circuits., This devices can be used to run, dc motors from an ac, power source, control power tool speed,also to control, motor speeds of small appliances like, mixers and food, blenders, illumination control, temperature control and so, on., Silicon Controlled Rectifier (SCR), Before Silicon controlled rectifiers were invented(1956), a, glass tube device called Thyratron was used for high power, applications. Silicon Controlled Rectifier (SCR) is the first, device of the thyristor family. The term thyristor is coined, from the expression Thyratron-transistor.SCR is a, semiconductor device. SCR does the function of controlled, rectification. Unlike a rectifier diode, SCR has an additional, terminal called the gate which controls the rectification(gated, silicon rectifier)., The basic principle application of SCRs is to control the, amount of power delivered to a load(motor, lamp, etc.,).A, rectifier diode will have one PN junction. SCRs on the other, hand will have two PN junctions (P-N-P-N layers). Fig 1, shows the electrical symbol, basic construction and a, typical SCR packages., Basic operation of SCR, When a gate direct current is applied to the gate terminal,, forward current conduction commences in the SCR(latched, into conduction). When the gate current is removed, the, forward current through the SCR does not cut-off. This, , means, once the SCR is latched into conduction, the gate, loses control over the conduction. The current through the, SCR can be turned off only by reducing the current through, it(load current) below a critical value called the Holding, current., , Fig 2 shows how an SCR can be gated into conduction or, turned off., In Fig 2a, with switched S1 open the SCR is in OFF state, and no current is flowing through the load., In Fig 2b, when S1 is closed, a small gate current(around, 1/1000 or less compared to load current) turns-ON (fires), the SCR. A heavy load current starts flowing through the, SCR and load RL., In Fig 2c, when S1 is opened, gate current becomes zero., This will have no effect on the current through the SCR and, the heavy load current continues to flow through the SCR, in the DC gate supply., In Fig 2d, if a shorting wire is placed across the anode and, the cathode terminals, the current though the SCR gets, by-passed and all the current starts flowing through the, shorted wire instead through the SCR. This means the, current through the SCR is reduced below the rated, holding current(minimum current required through SCR to, keep it latched). This turns-OFF the SCR. Even when the, shorting wire is removed the SCR remains to be in OFF, state., Fig 2e shows an alternative method of turning-OFF the, SCR. In this instead of shorting the anode and cathode, terminals of the SCR, the load current is cut-off by opening, the Switch S2. This reduced current through the SCR, below the holding current and thus turns- OFF the SCR., Once the SCR is turned_OFF, the SCR does not turn-ON, even if the switch S2 is closed. To make the SCR fire again,, with the switch S2 closed, the gate current should be made, to flow by closing the switch S1., , Copyright @ NIMI Not to be Republished, , 69

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gate current IG can be suitably modified. Diode D1 prevents, negative voltage being applied to the gate when the ac, supply is in the negative half cycle., [X] During the +ve half cycle of the AC power source, as, the positive half cycle voltage increases, the gate, current IG increases. When IG reaches the trigger level,, SCR fires and allows current IL to flow through the load., From this point onwards the SCR impedance is low and, current IL continues to flow throughout the +ve half, cycle even though the gate current reduces below the, trigger value(recall: once SCR is fired it continues to, conduct even if the gate trigger is decreased or removed)., [Y] At the end of the +ve half cycle of AC power source, the, +ve voltage drops to zero and SCR ceases to, conduct(recall: one method of turning off SCR is to, reduce the current through the SCR to below the, holding current. This can be done by either opening the, load circuit or reducing the supply to zero). Thus the, SCR remains in off state throughout the negative half, cycle., Cycle [X] and [Y] repeats and current through the load, flows in pulses as in Fig 3d., Fig 3b,3c shows the voltage wave forms of source and, gate voltage., , Since the SCR does not conduct in the reverse direction,, the anode of the SCR should always be positive with, respect to cathode for conduction., Important features of SCR,, •, , A very small gate current will control the switching OFF, a large load current., , SCR operation with AC supply, Operation of SCR with AC circuit is similar to SCR, operation . Fig 3 illustrates working of SCR in AC control, circuits., The SCR gate circuit consists of resistor R1, potentiometer, R2 and silicon diode D1. Resistors R1 and R2 act as a, variable voltage divider. By adjusting the value of R2 the, 70, , If the value of R2 is varied, the point at which SCR triggers, also varies changing the firing point shown in Fig 3d. In the, circuit shown in Fig 3a, the firing of SCR can be adjusted, any where between almost 180 degrees(maximum) to 90, degrees(minimum)., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished

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This simple AC control circuit shown in Fig 3a using SCR, can be used to control the current through the load during, the +ve half cycle of AC. During the -ve half cycle the SCR, remains turned off. Thus, SCR can be used as an excellent, switching device in AC control circuits., The circuit in Fig 3 is useful only in limited, applications such as temperature control of, soldering iron etc.,, Power control using SCR, •, , DC Motor speed control, , •, , AC Motor speed control, , •, , Regulated DC power supplies, , •, , Power control, , •, , Circuit breakers, , •, , Time delay circuits, , •, , Soft start circuits, , •, , Pulse, logic and digital circuits and so on., , Speed control of DC motors: In this Related Theory, information only brief outline of power circuits is discussed., Due variation of motor load currents, inductance effect in, winding, the practical circuit should be modified to suit the, requirement. DC motors consists of field winding and, armature winding. The speed of DC motors can be varied, by two methods,, 1 controlling the field current, 2 controlling the armature voltage, The first method is used for controlling the motor speed, above the rated speed of the motor. The second method, is used for controlling the motor speed below the rated, speed of the motor., , There are few more details to be known, specially while designing and setting the firing, angles. For details refer reference books of, SCR., Fig 5a shows another simple circuit for speed control of DC, motors. The speed control is based on controlled full wave, rectified supply to the armature through an SCR. This, control circuit is applicable only to shunt or separately, excited motors. The voltage and current wave forms are, given in Fig 5b. Please note that DC series motor cannot, be controlled by this circuit. For reasons refer reference, books on motor control circuits., , Speed control of DC shunt motor by controlling the, armature voltage: This is the most popular method of, controlling the speed of DC shunt motors. Fig 4a illustrates, the speed control of a DC shunt motor with separate field, excitation. The DC supply to the field winding is given from, a full wave bridge rectifier. The DC supply to the armature, is given using a ‘symmetrical half controlled bridge rectifier’., By controlling the SCRs 1 and 2, the DC voltage to the, armature can be varied by varying the motor speed. The, principle of operation of the circuit at Fig 4a can be, understood by examining the current and voltage wave, forms shown in Fig 4b. SCR-1 and 2 are fired in half cycles., During the positive ;half cycle, SCR1 and D3 will conduct., The SCR firing angle is set to desired angle as in Fig 4b., Hence the reduced applied armature voltage is shown, shaded (Fig 4b). This applied voltage to the armature can, be varied by changing the firing angle using a suitable, phase control circuit thus controlling the motor speed. A, similar operation will take place during the negative half, cycle as in Fig 4b when SCR2 and D1 conduct., , Fig 6 shows a speed controller by armature control, method for a separately excited 415volts DC motor., Other DC motor's speed control circuits are discussed in, further lessons after learning a few more components that, go along with SCR in motor speed control., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished, , 71

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Speed control of AC motors: Phase control can be very, conveniently used for speed control of AC motors also., This is achieved by applying a variable voltage to the motor, whose speed is to be controlled. As the speed of the, synchronous motors does not change when the input, voltage is varied, this method is useful only for commutator, or induction motors., For AC motors, full wave phase control circuits are, required. Fig 7 shows a schematic arrangement for speed, control of single phase and three phase induction motors., When the firing angle of SCR are varied the RMS input, voltage to the motor can be changed thus changing the, speed of the motor., , This circuit features a double time constant phase-shift, network. This reduces hysteresis in firing of the triac,, thereby making the manual adjustment of dimmer operation, or control off speed more repeatable., The DIAC used as trigger device, adds to the reliability of, the circuit. The elemental low-pass filter comprising LF, and CF attenuates much of the radio-frequency interference, (RFI) that gets generated and tries to get into the power, line. This high frequency RF1 energy is generated by the, extremely rapid turn-on time of the TRIAC. Which should, be eliminated to avoid radio interference due to higher, frequency content of the rectified wave form Otherwise,, the frequency may interfere with reception at nearby, places or in the main line circuit elsewhere., Lamp dimmers: Lamp dimmer is a circuit which controls, as AC power supplied to an incandescent lamp thereby, controlling the intensity of light emitted by the lamp from, almost zero to full brilliance., Conventional and soft-start dimming of incandescent, lights: Advantage of semi-conductor based light dimmers, over the auto transformer connected light dimmers, , Power circuit using TRIAC and DIAC, TRIAC or SCR for speed control of AC motors: Compared, to SCR, Triac is most popular and works satisfactorily for, lamp dimmer circuits and speed control of universal, motors. Although both SCR and TRIAC can be used to, phase control and vary the current through the lamp or, motor, TRIAC being a full wave device, symmetrically, controls the phase of both half cycles of the applied AC., The resultant full wave current format then produces, smooth lamp or motor operation that can be attained from, the half wave rectification using SCRs. This is particularly, noticeable during low/dim light requirement or low speed, for motors., The circuit at Fig 8 shows a TRIAC phase control circuit for, controlling the brightness of the lamp or speed of universal, motors., The load shown in circuit at Fig 8 is a general load rather, than a motor symbol because, this circuit can also be, used for light dimmers and for the control of heaters., 72, , Old technology light dimmers used high wattage rheostats, adjustable auto-transformers or saturable reactors, which, were large, expensive generated considerable heat and, power loss. Present day semi-conductor light dimmers, have overcome these difficiencies and have therefore, become very popular for many applications., Modern semi-conductor dimmers are inexpensive, reliable,, small generate little heat, and are easy to control remotely., These properties have not only permitted semi-conductor, dimmers to supersede older types in theatres and, auditoriums with excellent results, but have made dimmers, practical for built-in home lighting, table and floor lamps,, projection equipment and other uses., Semi-conductor based light dimmers: Two light, dimmers for incandescent light bulbs are discussed below., Both these dimmer circuits control light intensity by, adjusting the angle of conduction of a triac connected in, series with the bulb. The first dimmer uses a very simple, circuit that is ideal for highly compact applications requiring, minimum cost. The second dimmer features soft starting, for low in rush current and consequent long lamp life. Soft, start lamp dimmers are especially useful with expensive, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished

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lights with short lives, such as projection lamps and photographic bulbs., Simple light dimmer: The circuit shown in Fig 9 is a wide, range light dimmer using very few parts. The circuit can, be operated using any mains supply source (240V, 50Hz), by choosing appropriate value of circuit components. The, circuit can control upto 1000watts of power to incandescent, bulbs., , begin to charge, but because the voltage is low, C2 will, have adequate voltage to trigger Q1 only near the end of the, half cycle. Although the lamp resistance is low at this, time, the voltage applied to the lamp is low and the inrush, current is small. Then the voltage on C1 rises, allowing C2, to trigger Q1 earlier in the cycle., At the same time the lamp is being heated by slowly, increasing applied voltage and by the time the peak, voltage applied to the lamp has its maximum value, the, bulb has been heated sufficiently so that the peak inrush, current is kept to a reasonable value., Resistor R4 controls the charging rate of C2 and provides, the means to dim the lamp. Power to the load can be, adjusted manually by varying the resistance of R4. T1 is, a pulse transformer. In addition to supplying the trigger to, Triac, this transformer isolates the high current load circuit, from the low power triggering circuit (gate isolation methods, for Triac is discussed in further paragraphs)., , The power to the bulbs is varied by controlling the, conduction angle of Triac. Many circuits can be used for, phase control, but the single Triac circuit used is the, simplest and is therefore chosen for this particular, application., The control circuit for this Triac must function as shown in, Fig 9b. The control circuit must create a delay between, the time voltage is applied to the circuit and the time it is, applied to the load. The Triac is triggered after this delay, and conducts current through the load for the remaining, part of each alteration. This circuit can control the, conduction angle from 0° to about 170° and provides better, than 97% of full power control., Light dimmer with soft-start option: The circuit at Fig 10, is a light dimmer with soft start option. Soft starting is, desirable because of the very low resistance of a cold lamp, filament compared to its hot resistance. At the time of, initial switching ON, the low resistance of the lamp causes, very high inrush currents which leads to short filament/, lamp life. Lamp failures caused by high inrush currents is, eliminated by the soft start feature, which applies current, to the bulb slowly enough to eliminate high surges., Operation of the circuit at Fig 10 begins when voltage is, applied to the diode bridge consisting of D1 through D4. The, bridge rectifies the input and applies a DC voltage to, resistor R1 and zener diode D5. The zener provides a, constant voltage of 20volts to unijunction transistor Q1,, except at the end of each alternation when the line voltage, drops to zero. Initially the voltage across capacitor C1 is, zero and capacitor C2 cannot charge to trigger Q1. C1 will, , A simple lamp dimmer cum Universal motor speed, controller: In the lamp dimmer cum universal speed, controller circuit is in Fig 11, a Triac is used as control, device. Phase control technique is used to control, conduction angle of the triac which inturn control the power, fed to the lamp., , A lamp L is connected in series with AC mains supply to, the Triac. The trigger pulses to Triac gate is given through, Diac. The Diac is triggered at the same breakover voltage, level (30V) during both positive and negative half cycles., Potentiometer R4 provides the facility for varying the, intensity of light or speed of a universal motor., Snubber circuit: One problem with the Triac control is the, sudden application of reverse voltage across the triac, immediately after it has stopped conduction. This is a, serious problem when the load is a highly inductive as in, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished, , 73

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motors. This reapplied voltage denoted by dv/dt can, trigger-on (unwanted or false triggering) the device losing, the phase control., To avoid this false triggering, an R and C series network is, placed across the circuit R4 and C4 as shown in Fig 11., This RC network slows down the rate of rise of voltage, applied across the Triac. This RC circuit connected, across the Triac circuit is called snubber circuit., , Structure of IGBT, The structure of IGBT is similar to that of MOSFET. Fig 13, show the vertical cross section of IGBT . In this structure, observe that there is additional P+ layer. This layer is, collector (Drain) of IGBT., Fig 13, , The inductance L and capacitor C1 forms a low pass filter, to substantially reduce the radio frequency interference, (RF) generated by the rapid turn-on and turn-off the triac., , ELN411711D, , Fan speed regulator: The lamp dimmer circuit at Fig 11, can be used equally well as a fan speed regulator. The, only change to be made is to connect a fan in place of the, lamp shown in the circuit at Fig 11. The speed can be, varied from almost zero to full speed by just rotating, POT R3., IGBT (Insulated Gate Bipolar Transistor), The insulated Gate Bipolar Transistor (IGBT) is the latest, device is power electronics. It is obtained by combining, the properties of BJT and MOSFET. We know that BJT, has lower on - state losses for high values of collector, current. But the drive requirement of BJT is little, complicated. The drive of MOSFET is very simple (i.e only, voltage is to be applied between gate and source). But, MOSFET has high on - state losses., The gate circuit of MOSFET and collector emitter circuits, of BJT are combined together to form a new device. This, device is called IGBT. Thus IGBT has advantages of both, the BJT and MOSFETs. Fig 12 shows the symbol of IGBT., Observer that the symbol clearly indicates combination of, MOSFET and BJT., , This P+ injection layer is heavily doped. It has the doping, intensity of 1019 per cm3. The doping of other layer is, similar to that of MOSFET. n+ layers have 1019 per cm3., P-type body region has doping level of 1016 per cm3. The ndrift region is lightly doped (1014 per cm3)., Punch through IGBT, The n+ buffer layer is not necessary for the operation of, IGBT. The IGBTs which have n+ buffer layer are called, punch through IGBTs. Such IGBTs have asymmetric, voltage blocking capabilities. Punch through IGBTs have, faster turn-off times. Hence they are used for inverter and, chopper circuits., , Fig 12, , Non - punch through IGBT, , ELN411711C, , The IGBTs without n+ buffer layer are called non-punch, through IGBTs. These IGBTs have symmetric voltage, blocking capabilities. These IGBTs are used for rectifier, type applications., , The IGBT has three terminals : Gate (G), collector (C) and, emitter (E), Current flows from collector to emitter whenever, a voltage between gate and emitter is applied. The IGBT, is said to have turned 'ON'. When gate emitter voltage is, removed, IGBT turns - off. Thus gate has full control over, the conduction of IGBT. When the gate to emitter voltage, is applied, very small (negligible) current flows. This is, similar to the gate circuit of MOSFET. The on - state, collector to emitter drop is very small like BJT., , 74, , Operation of IGBT, When VGS > VGS(threshold), then the channel of electrons, is formed beneath the gate as in Fig 14. These electrons, attract holes from p+ layer. Hence, holes are injected, from p+ layer into n- drift region. Thus hole / electron, current starts flowing from collector to emitter. When, holes enter p-type body region, they attract more electrons, from n+ layer. This action is exactly similar to MOSFET., Fig 15 shows the structure of IGBT showing how internal, MOSFETs and transistors are formed. The MOSFET is, formed with input gate, emitter as source and n- drift, region as drain. The two transistors T1 and T2 are formed, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished

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as in Fig 15. The holes injected by the P+ injecting layer, go to the n- drift region. This n- drift region is base of T1 and, collector of T2. The holes in the n- drift region further go to, the p - type body region, which is connected to the emitter., The electrons from n+ region (which is emitter) pass, through the transistor T2 and further in the n- drift region., Thus holes and electrons are injected in large amounts in, n- drift region. This reduces the resistance of the n- drift, region. This is called conductivity modulation of n- drift, region. Note that such conductivity modulation does not, exist in MOSFET. The connection of T1 and T2 is such that, large amount of hole/electrons are injected in n- drift, region., , is base of T2. Therefore T2 also turns ON. The collector of, T2 is base of T1. Thus the regenerative loop begins and, large number of carriers are injected in n- drift region. This, reduces the on- state loss of the IGBT just like BJT. This, happens due to conductivity modulation of n- drift region., Fig 16, , ELN411711E, , ELN411711G, , Fig 14, , Fig 15, , When the gate drive is removed, the IGBT should turnOFF. When gate is removed, the induced channel will be, vanished and internal equivalent MOSFET will turn-OFF., Hence T1 will turn -OFF if T2 turns-OFF T2 will turn - OFF if, the p- type body region resistance R1 is very very small., Under such situation, its base and emitter will be virtually, shorted. Hence T2 turns - OFF. Therefore T1 will also turn, - OFF. Hence structure of IGBT is organizes such that, body region resistance (R1) is very very small., If R1 is very very small, than T2 will never conduct and the, equivalent circuit of IGBT will be as in Fig 17. IGBTs are, thus different than MOSFETs because of conduction of, current from collector to emitter. For MOSFETs, on state, losses are high since resistance of drift region remains, same. But in IGBTs, resistance of drift region reduces, when gate drive is applied. This resistance reduces, because of P+ injecting region. Hence, on state loss of, IGBT is very small., , The action of T1 and T2 is like SCR which is regenerative., The gate serves as trigger for T1 through internally formed, MOSFET. Fig 16 shows the equivalent circuit. In this, figure observe that when gate is applied (VGS > VGS(th)), the, internal equivalent MOSFET turns ON. This gives base, drive to T1. Hence T1 starts conducting. The collector of T1, Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished, , ELN411711H, , ELN411711F, , Fig 17, , 75

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Merits, Demerits and Applications of IGBT, , 2 IGBTs are costlier than BJTs and MOSFETs., , Merits of IGBT, , Applications of IGBTs, , 1 Voltage controlled device. Hence drive circuit is very, simple., , 1 AC motor drives, i.e. inverters., , 2 On - state losses are reduced., , 3 UPS systems., , 3 Switching frequencies are higher than thyristors., , 4 Harmonic compensators., , 4 No commutation circuits are required., , Comparison of Power Devices, , 5 Gate have full control over the operation of IGBT, 6 IGBTs have approximately flat temperature coefficient., Demerits of IGBT, 1 IGBTs have static charge problems., , 2 DC to DC power supplies, i.e choppers, , The power devices can be compared on the basis of, switching frequency, gate drive circuit, power handling, capacity etc. Table 1 shows the comparison of SCR, BJT,, MOSFET and IGBT., , Table 1, S.No., , Parameter, , SCR, , BJT, , MOSFET, , IGBT, , 1, , Symbol, , 2, , Triggered i.e, latching or linear, , Triggered or latching, device, , Linear trigger, , Linear trigger, , Linear trigger, , 3, , Type of carriers in, device, , Majority carrier device, , Bipolar device, , Majority carrier, device, , Majority carrier, device, , 4, , Control of gate or, base, , Gate has no control, once turned on, , Base has full control Gate has full, control, control, , Gate has full, control, , 5, , On-state drop, , < 2 Volts, , < 2 Volts, , < 4-6 Volts, , < 3.3 Volts, , 6, , Switching, frequency, , 500 Hz, , 10 kHz, , up to 100 kHz, , 20 kHz, , 7, , Gate drive, , Current, , Current, , Voltage, , Voltage, , 8, , Snubber, , Unpolarized, , Polarized, , Not essential, , Not essential, , 9, , Temperature, coefficient, , Negative, , Negative, , Positive, , Approximately, flat, but positive, at high current, , 10, , Voltage and current 10 kV/4kA, ratings, , 2 kV/4kA, , 1 kV/50 A, , 1.5 kV/400 A, , 11, , Voltage blocking, capability, , Symmetric and, , Asymmetric, , Asymmetric, , Asymmetric, , 12, , Application, , AC to DC converters,, AC voltage controllers,, electronic circuit, breakers, , DC to AC converters,, induction motor, drives, UPS, SMPS,, Choppers, , DC choppers, low, powers, UPS,, SMPS, brushless, DC motor drives, , DC to AC, converters, AC, motor drivers,, UPS choppers,, SMPS etc,., , 76, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.171, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.172, , Integrated circuit voltage regulators, Objectives: At the end of this lesson you shall be able to, • explain integrated circuit, • state the classification of integrated circuit, • state the types of IC voltage regulators, • design voltage regulator for a required output voltage, • modify fixed voltage regulator to variable output regulator, circuit., IC introduction, , iii Complementary metal oxide semiconductor (CMOS), - electron or hole current., , Integrated circuit, Electronic circuits invariably consist of a number of discrete, components connected to each other in a specific way., For instance, the series regulator circuit discussed in, earlier lessons, consists of transistors, zener diodes,, resistors and so on, connected in a defined way for it to, function as a regulator. If all these components instead of, building on a board, if they are built on a single wafer of a, semiconductor crystal, then, the physical size of the, circuit becomes very small. although small, this will do, the same job as that of the circuit wired using discrete, components. Such miniaturised electronic circuits, produced within and upon a single crystal, usually silicon,, are known as Integrated circuits or ICs. Integrated circuits, (ICs) can consists of thousands of active components like, transistor, diodes and passive components like resistors, and capacitors in some specific order such that they, function in a defined way, say as voltage regulators or, amplifiers or oscillators and so on., Classification of Integrated circuits: Integrated circuits, may be classified in several ways. However the most, popular classifications is as follows:, 1 Based on its type of circuitry, i, , Analog ICs - Example: amplifier ICs, voltage regulator, ICs etc., , ii Digital ICs - Example: Digital gates, flip-flops,, address etc., 2 Based on the number of transistors built into IC, i, , Small scale integration (SSI) - consists of 1 to 10, transistors., , ii Medium scale integration (MSI) - consists of 10 to, 100 transistors., iii Large scale integration (LSI) - 100 to 1000 transistors., iv Very large scale integration (VLSI) - 1000 and, above., 3 Based on the type of transistors used, i, , Bipolar - carries both electron and hole current., , Note: The terms MOS and CMOS are another, type of transistor and the trainees are requested, to refer any standard electronic book for further, reference., ICs are available in different packages and shapes. The, usual packages are:, – dual in the packages DIP, – single in line package SIP and, – metal can packages., ICs handling power more than IW are provided with heat, sinks., Advantages of integrated circuits over discrete circuit, (Refer Table 1), Table 1, Integrated circuits, , Discrete circuits, , Advantages, 1 All in a single chip, , All are separate discrete, components, , 2 Requires less space, due to smaller size, , Requires more space, , 3 Cheaper due to mass, manufacture, , Costlier due to individual, components, , 4 More reliable due to, specific construction, , Less reliable, , 5 Easy for servicing and, repairs, , Difficult for servicing and, repairs, , Disadvantages, 1 ICs are manufactured, Discrete devices can be, for specific applications used for any circuit, having specific circuits, 2 If any part of IC is, defective, the entire, IC is to be replaced, , Only particular defective, component requires, replacement, , ii Metal oxide semiconductor (MOS) - electron or, hole current., , Copyright @ NIMI Not to be Republished, , 77

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When the advantages are considered, the disadvantages, of IC are negligible. They are widely used for different, applications such as voltage regulators, audio amplifiers,, TV circuits, computers, industrial amplifiers etc. ICs are, available in different pin configurations in different outlines, suitable for different circuits., Integrated circuit (IC) voltage regulators: The series, voltage regulators discussed in earlier lessons are available, in the form of integrated circuits (ICs). They are known as, voltage regulator ICs., There are two types of voltage regulator ICs. They are,, – Fixed output voltage regulator ICs, – Adjustable output voltage regulator ICs., Fixed output voltage regulator ICs: The latest generation, of fixed output voltage regulator ICs have only three pins as, in Fig 1. They are designed to provide either positive or, negative regulated DC output voltage., , The capacitor C2 is used to improve the transient response, of the regulated output voltage. C2 bypasses these, transients produced during the ON/OFF time. Typical, values of C2 range from 0.1μF to 10μF., Fixed voltage three terminal regulators are available from, different IC manufacturers for different output voltages, (such as 5V, 9v, 12V, 24V) with maximum load current, rating ranging from 100mA to more than three amps., The most popular three terminal IC regulators are,, 1 LMXXX-X series, Example: LM320-5, LM320-24 etc., 2 78XX and 79XX series, Example: 7805, 7812, 7912 etc., A list of popular three terminal regulators is given in IC data, book., Specifications of three terminal IC regulators: For, simplicity in understanding, let us consider the specification, of a three terminal IC μA7812. The table 2 given below lists, the specifications of μA7812., Table 2, Parameter, , Min., , Type., , 11.5, , 12, , 12.5, , V, , 4, , 120, , mV, , Short-circuit, output current, , 350, , mA, , Drop out voltage, , 2.0, , V, , Output voltage, Output regulation, , These ICs consist of all those components and even more, in the small packages in Fig 1. These ICs, when used as, voltage regulators, do not need extra components other, than two small value capacitors as in Fig 2., , Ripple rejection, Peak output, current, , 55, , Max., , Units, , 71, , dB, , 2.2, , A, , Output voltage: This specification indicates the regulated, DC output voltage that can be obtained from the IC. As can, be seen from the sample specification table given above,, the manufacturer specifies minimum, typical and maximum, output voltage. While using this IC take the typical value, as this value corresponds to the output voltage at IC under, normal input and load conditions., Output regulation: This indicates the amount by which, the output voltage may vary at rated maximum load, condition. For example, in μA7812 IC, the output voltage, may vary by 4mV from its rated 12V DC when the rated, typical load current is 2.2A., The reason behind using capacitor C1 is when the voltage, regulator IC is more than a few inches from the filter, capacitors of the unregulated power supply, the lead, inductance may produce oscillations within the IC., Capacitor C1 prevents setting up of such oscillations., Typical value of bypass capacitor C1 range from 0.220μF, to 1μF. It is important to note that C1 should be connected, as close to the IC as possible., 78, , Short circuit output current: This indicates the shorted, current ISC, if the output gets shorted. In μA 7812 the, output current is limited to 350mA when the output, terminals are shorted., These regulators also canbe used fold back current, limiting., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.172, , Copyright @ NIMI Not to be Republished

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Drop out voltage: For instance, in μA7812 in which the, output voltage is +12V, the input unregulated DC voltage, to the regulator must be higher than the output voltage., The specification drop out voltage indicates, the minimum, positive different between the input and output voltages for, the IC to operate as a regulator. For example, in, μA7812, the unregulated input voltage should be atleast 2 volts, more than the regulated DC output of 12V. This means for, μA7812 the input must be atleast 14V., The difference between the voltage across the input and, output of the IC should also not to be very high as this, causes unwanted dissipation. As a thumb rule, the input, voltage to the regulator shall be restricted to a maximum, of twice the output voltage of the regulator. For example,, for μA7812, the unregulated input voltage should be more, than 14V, but less than 24V., – Ripple rejection, This indicates the ratio of ripple rejection between the, output to input, expressed in decibels,, – Peak output current, This indicates the highest output or load current that can, be drawn. Above this rated maximum current the safety, of the IC is not guaranteed., Identification of output voltage and rated maximum, load current from IC type number, – 78XX and 79XX series are 3 Terminal voltage regulators., , 78SXX, , -, , S indicates rated maximum load, current is 2amp., , Example, μPC 78 M 15H, Indicates positive, , Indicates, , Fair Child, (Manufacturer’s, code), , Regulated output, voltage is 15V, , Positive regulator, , Rated maximum, load current is, 500mA, , LM 3XX series of 3 terminal voltage regulators: In LM, series of three terminal regulators, to find the specifications,, it is suggested to refer to its data manual. However, the, following tips will help in identifying whether the IC is a fixed, positive or fixed negative regulator., LM320-X and LM320-XX, , t Fixed –ve voltage, regulators., , LM340-X or LM340-XX, , t Fixed +ve voltage, regulators., , Examples, LM 320 - 5, RCA, (Manufacturer), , Output, voltage -5V, , – All 78XX series are positive output voltage regulators, , Fixed negative, voltage regulator, , – All 79XX series are negative output voltage regulators, , LM 340 - 15, , The term XX indicates the rated output regulated voltage., Example, Indicates output, voltage is +5V, 7912, Indicates negative, output regulator, , Output, Fixed positive, voltage regulator, , 7805, Indicates positive, output regulator, , RCA, , Practical 78XX and 79XX voltage regulator: Fig 3, shows the circuit connections of a 12V, 1A regulated, power supply using 7812., , Indicates output, voltage is –12V, , It is important to note that, different manufacturers of 78, XX/ 79XX series such as Fair Child (MA/Mpc), Motorola,, Signetics (SS) adopt slightly different coding schemes to, indicate the rated maximum current of the three pin, regulated. ICs. One such scheme is given below., 78LXX, , -, , L indicates rated maximum load, current as 100mA., , 78MXX, , -, , M indicates rated a maximum load, current as 500mA, , 78XX, , -, , Absence of an alphabet between 78, and XX indicates that the rated, maximum load current is 1A., , The output voltage of a 3-terminal regulator IC is with, reference to the IC’s common terminal (COM). When the, COM terminal is grounded, the output voltage of the, regulator will be the specified output voltage of the IC as in, Fig 3. But the output voltage of the IC can be increased, above the specified value by rising the voltage at the COM, terminal as in Fig 4. Because of 6.1V zener, the output, voltage of the IC can be increased above the specified, value by raising the voltage at the COM terminals, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.172, , Copyright @ NIMI Not to be Republished, , 79

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as in Fig 4. Because of 6.1V zener, the output voltage will, be 6.1V + 12V = 18.1V or approximately 18V as in Fig 4., , When the COM terminal of the IC is grounded as in Fig 2,, the quiescent current flowing from the COM terminal to, ground in 78 series is around 8μA. This current decreases, as the load current increases. When a zener is connected, at COM terminal as in Fig 4, to ensure that the zener is, always in the reverse ON condition, resistor R1 is used. If, R1 = 1.8K, Iz will be 7mA which is sufficient to keep the, zener ON always., Fig 5 shows a variable output voltage regulator. The, variable reference voltage at COM terminal is obtained, using a POT., , Four-terminal regulators: These are adjustable output, voltage regulators and are also available as +ve and -ve, regulators. These ICs have internal reference voltages and, are protected internally for thermal overload, short circuit, etc. Table 1 provides important specifications for most, common ICs., Fig 6 to 8 shows the common ICs used as voltage, regulators with their terminal marking and Fig 9 to 11, shows the circuit configuration., , 80, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.172, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.173, , Binary numbers, logic gates and combinational circuits, Objectives : At the end this lesson you shall be able to, • explain the digital electronics principle and positional notation and weightage, • explain decimal to binary conversion, binary odometer, • explain hexadecimal number system, • convert decimal to hexa, hexa to decimal and BCD system, • explain logic gates principle - NOT, OR and AND gates with truth table, • explain combinational gates - NAND, NOR with truth table and logic pulser., Introduction, When we hear the word 'number' immediately we recall the, decimal digits 0,1,2....9 and their combinations. Digital, circuits do not process decimal numbers. Instead, they, work with binary numbers which use the digits '0' and '1', only. The binary number system and digital codes are, fundamental to digital electronics. But people do not like, working with binary numbers because they are very long, when representing larger decimal quantities. Therefore, digital codes like octal, hexadecimal and binary coded, decimal are widely used to compress long strings of binary, numbers., , This decimal number system is an example of positional, notation. Each digit position has a weightage. The positional, weightage for each digit varies in the sequence 100, 101,, 102, 103 etc starting from the least significant digit., The sum of the digits multiplied by their weightage gives, the total amount being represented as shown above., In a similar way, binary number can be written in terms of, weightage., To get the decimal equivalent, then the positional weightage, should be written as follows., , Binary number systems consists of 1s and 0s. Hence this, number system is well suited for adopting it to the digital, electronics., , [1010]2 = 1(23) + 0(22) + 1(21) + 0(20), , The decimal number system is the most commonly used, number system in the world. It uses 10 different characters, to show the values of numbers. Because this number, system uses 10 different characters it is called base-10, system. The base of a number system tells you how many, different characters are used. The mathematical term for, the base of a number system is radix., , [1010]2 = [10]10, , The 10 characters used in the decimal number systems, are 0,1,2,3,4,5,6,7,8,9., , =8+0+2+0, , Any binary number can be converted into decimal number, by the above said positional weightage method., Decimal to Binary conversion, Divide the given decimal number by 2 as shown below and, note down the remainder till you get the quotient - zero., Example, , Positional notation and weightage, A decimal integer value can be expressed in units, tens,, hundreds, thousands and so on. For example decimal, number 1967 can be written as 1967 = 1000 + 900 + 60 +, 7. In powers of 10, this becomes., —————————————, , 1 x 10 = 1000, , 10, , 9 x 10 = 900, , 3, , 10, , 2, , 10, , 1, , 10, , 0, , 3, , 2, , —————————————— 6 x 10 = 60, 1, , 1, , 9, , 6, , 7, , 2, , 1, , 1, , 2, , 2, , 0, , 2, , 4, , 0, , 2, , 8, , 0, , 2, , 17, , 1, , 2, , 34, , 0, , →, , MSB, , → LSB, , ———, , The remainder generated by each division form the binary, number. The first remainder becomes the LSB and the last, remainder becomes the MSB of binary number., , 1967, , Therefore, [34]10 = [100010]2, , 7 x 100 =, , ——————————————, , 0, , 7, , i.e. [1967]10 = 1(10 ) + 9(10 ) + 6(10 ) + 7(10 ), 3, , 82, , 2, , 1, , 0, , Copyright @ NIMI Not to be Republished

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Counting binary number, , Decimal, , Binary, , To understand how to count with binary numbers, let us, see how an odometer (KM indicator of a car) counts with, decimal numbers,, , 10, , 1010, , 11, , 1011, , 12, , 1100, , The odometer of a new car starts with the reading 0000., , 13, , 1101, , After traveling 1KM , reading becomes 0001., , 14, , 1110, , Successive KM produces 0002, 0003 and so on upto 0009, , 15, , 1111, , At the end of 10th KM , the units wheel turns back from 9, to 0, a tab on this wheel forces the tens wheel to advance, by 1. That is why the number changed from 0009 to 0010., That is, the units wheel is reset to 0 and sent a carry to the, tens wheel. Let us call this familiar action as reset and, carry. The other wheels of odometer also reset and carry., For instance, after covering 999KM , the odometer shows, 0999., After the next KM , the unit wheel resets and carries, the, tens wheel resets and carries, the hundreds wheel resets, and carries and the thousands wheel advances by 1 to get, the reading 01000., , Sum, , Carry, , 0+0=0, , 0, , 1+0=1, , 0, , 0+1=1, , 0, , 1+1=0, , 1 (one plus one is equal, to zero with carry one), , Ex: 1, , Ex: 2, , 10, , 1+1+1= 1, , + 11, , Binary odometer, Visualize a binary odometer, a device whose wheels have, only two digits 0 and 1. When each wheel turns, it displays, 0 then 1 and then back to 0 and the cycle repeats. A four, digit binary odometer starts with 0000., After 1km, it indicates - 0001., The next km forces the units wheel to reset and sends, carry. So the number changes to 0010., The third km results in 0011., After 4km, the units wheel resets and sends carry, the, second wheel resets and sends carry and the third wheel, advances by 1. Hence it indicates 0100., Table below shows all the binary numbers from 0000 to, 1111 equivalent to decimal 0 to 15., Decimal, , Addition of binary numbers, , Binary, , +1, , (One plus one plus, one is equal to one, with carry one), , 10, +1, 101, , 11, , Hexadecimal number system: In hexadecimal system, there are 16 characters. They are 0,1,2,3,4,5,6,7,8,9,, A,B,C,D,E,F where A=10, B=11, C=12, D=13, E=14,, F=15 in decimal. In this system, the base is 16. This, system is mainly used to develop programmes for, computers., For Example, [23]16 = [35]10 ; 161 X 2 + 160 X 3 = 32 + 3 = 35;, [2C]16 = [44]10 ;161 x 2 + 160 x 12 = 32 + 12 = 44;, Decimal to hexadecimal conversions, The conversion of decimal to hexadecimal is similar to, binary conversion. Only difference is that divide the decimal, number successively by 16, and note down the remainder., 0, , 0, , 0000, , 1, , 0001, , 2, , 0010, , 3, , 0011, , 16 1, , 1, , 4, , 0100, , 16 27, , 11 or B, , 5, , 0101, , 16 432, , 0, , 6, , 0110, , 7, , 0111, , 8, , 1000, , 9, , 1001, , →, , MSB, , → LSB, , [432]10 = [1B0]16, Hexadecimal to Decimal, This conversion can be done by putting it into the positional, notation., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.173, , Copyright @ NIMI Not to be Republished, , 83

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Ex: 223A16 = 2 x 163 + 2 x 162 + 3 x 161 + A x 160, = 2 x 4096 + 2 x 256 + 3 x 16 + 10 x 1, = 8192 + 512 + 48 + 10, = 876210, BCD (Binary Coded Decimal), Binary Coded Decimal (BCD) is a way to express each of, the decimal digits with a binary code, since there are only, ten code groups in the BCD system, it is very easy to, convert between decimal and BCD. Because decimal, system is used for read and write, BCD code provides an, excellent interface to binary systems. Examples of such, interfaces are keypad inputs and digital readouts., 8421 code, The 8421 code is a type of binary coded decimal (BCD),, binary coded decimal means that each decimal digit, 0, through 9 is represented by a binary code of four bits. The, designation 8421 indicates the binary weights of the four, bits (23, 22, 21, 20). The ease of conversion between 8421, code numbers and the familiar decimal numbers is the, main advantage of this code. All you have to remember are, the ten binary combinations that represents the ten, decimal digits as shown in the Table., Decimal, digit, , 0, , 1, , 2, , 3, , BCD, , 0000, , 0001, , 0010, , 0011 0100, , Decimal, digit, , 5, , 6, , 7, , 8, , BCD, , 0101, , 0110, , 0111, , 1000 1001, , 4, , The table summarizes the operation, Vin, , Vout, , Low(0), , High(1), , High(1), , Low(0), , The logic expression for the inverter is as follows: Let the, input variable be ‘A’ and the output variable be Y, then the, output Y = A ., OR and AND gate circuits, OR Gate, The output of an OR will be in 1 state if one or more of the, inputs is in 1 state. Only when all the inputs are in 0-state,, the output will go to 0-state. Fig 3 shows the schematic, Symbol of an OR Gate :, , 9, , The 8421 code is the pre-dominant BCD code, and when, we refer to BCD, we always mean the 8421 code unless, otherwise stated., , The boolean expression for OR gate is Y=A+B., The equation is to be read as Y equals A ORed B. Twoinput truth table given below is equivalent to the definition, of the OR operation., Truth table for OR gate, , Inverters (NOT Gate), An inverter is a gate with only one input signal and one, output signal. The output state is always the opposite of, the input state. Logic symbol is shown in Fig 1., , Transistor inverter, The Fig 2 shows the transistor inverter circuit. The circuit, is a common emitter amplifier which works in saturation or, in cut off region depending upon the input voltage. When, Vin is in low level, say less than the transistor cut in voltage, 0.6V in silicon type, the transistor goes to cut off condition, and the collector current is zero. Therefore, Vout = +5V, which is taken as high logic level. On the other hand, when, Vin is in high level, the transistor saturates and Vout = Vsat, = 0.3V i.e low level., 84, , A, , B, , Y=A + B, , 0, , 0, , 0, , 1, , 0, , 1, , 0, , 1, , 1, , 1, , 1, , 1, , Electrical equivalent circuit, The Fig 4a shows the electrical equivalent circuit of an OR, gate. It is evident that if any one of the switch is closed,, there will be output., 2 in-put OR gate using diode, The Fig 4b shows one way to build a 2-input OR gate,, using diodes. The inputs are labeled as A and B, while the, output is Y., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.173, , Copyright @ NIMI Not to be Republished

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Even if one of the inputs is low, the output becomes low., AND gate symbols for 2 input and 3 input gates are shown, in Fig 5a and 5b., , Truth table, Assume, , logic 0 = 0V (low), logic 1 = +5V (high), , Since this is a 2 input OR gate, there are only four possible, cases,, Case 1: A is low and B is low. With both the input voltage, low, both the diodes are not conducting. Therefore the, output Y is in low level., Case 2: A is low and B is high, The high B input voltage, (+5V) forward biases the lower diode, producing an output, voltage that is ideally +5V (actually +4.3V taking the diode, voltage drop 0.7V into consideration). That is, the output, is in high level. During this condition, the diode connected, to input A is under reverse bias or OFF condition., , Two input AND gate, A, , B, , Y=AB, , 0, , 0, , 0, , 0, , 1, , 0, , 1, , 0, , 0, , 1, , 1, , 1, , Three input AND GATE, A, , B, , C, , Y=ABC, , 0, , 0, , 0, , 0, , 0, , 0, , 1, , 0, , 0, , 1, , 0, , 0, , Case 3: A is high and B is low, the condition is similar to, case 2. Input A diode is ON and Input B diode is OFF and, Y is in high level., , 0, , 1, , 1, , 0, , 1, , 0, , 0, , 0, , 1, , 0, , 1, , 0, , Case 4: A is high, B is high. With both the inputs at +5V,, both diodes are forward biased, since the input voltages, are in parallel, the output voltage is +5V ideally [+4.3V to, a second approximation]. That is, the output Y-is in high, level., , 1, , 1, , 0, , 0, , 1, , 1, , 1, , 1, , OR gates are available in the IC form. IC7432 is a T.T.L OR, gate IC having 4 OR gates inside it., Simple application of OR gate, Intrusion detection, Simplified portion of an intrusion detection and alarm, system is two windows and a door. The sensors are, magnetic switches that produce a high(1) output when, windows and doors are opened and a low(0) output when, closed. As long as the windows and the door are secured,, the switches are closed and all three of the OR gate inputs, are in low(0). When one of the windows or the door is, opened, a high(1) output is produced on that input of the, OR gate and the gate output goes high. It then activities, an alarm circuit to warn of the intrusion., AND gates, , Electrical equivalent circuit of an AND gate, The output is available only when both the switches are, closed. IC7408 is a T.T.L quad AND gate IC. (Refer data, book for pin diagram). The electrical equivalent of AND, gate and AND gate using diodes are shown in Fig 6a, and 6b., , Two input AND gate using diode, I condition, , The AND gate has two or more inputs but only one output., All input signals must be held high to get a high output., , A=0, B=0, Y=0 as in Fig 7., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.173, , Copyright @ NIMI Not to be Republished, , 85

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AND gate as an Enable/Inhibit device, A common application of the AND gate is to enable (i.e to, allow) the passage of a signal (pulse waveform) from one, point to another at certain times and to inhibit (prevent) the, passage at other times., During the above condition I/P A and B are connected to, ground to make logic low inputs. During this condition,, both the diodes conduct, and pulls the O/P Y to logic-0., II condition, A=0, B=1, Y=0 as in Fig 8., , In the II condition shown in the figure above, diode D1 is, connected logic-0 input and diode D2 is connected to +5V, [Logic high]. Diode D1 is in forward bias and conducts., Diode D2 is having equal potential (+5V) at anode and, cathode. So potential difference between anode and, cathode is 0. Hence diode D2 does not conduct. The, output Y is pulled down to logic zero, since D1 is conducting., III condition, A=1, B=0, Y=0 as in Fig 9., , In Fig 11a AND gate controls the passage of a signal, (waveform A) to a digital counter. The purpose of this, circuit is to measure the frequency of waveform ‘A’. The, enable pulse has a width of precisely 1 second. When the, enable pulse applied at B is high, waveform A passes, through the gate to the counter, and when the enabled, pulse is low, the signal is prevented (inhibited) from, passing through. Refer Fig 11b for the waveforms of the, above process., , During the 1 second interval of the enabled pulse, a certain, number of pulses in waveform A pass through the AND, gate to the counter. The number of pulses counted by the, counter is equal to the frequency of the waveform A. For, example, if 1000 pulses pass through the gate in the 1, second interval of the enabled pulse, there are 1000, pulses/sec. That is, frequency is 1000Hz., Combinational gate circuits - NOR and NAND, NOR Gate, , The III condition is similar to the II condition. D2 is forward, biased. D1 is reverse biased. Hence output Y is pulled to, logic-0., IV condition, , In Fig 12a the output y of the circuit equals to the, complement of A OR B, because the circuit is an OR gate, followed by a NOT gate. To obtain high output [Logic-1],, both the inputs should be tied to low input [Logic-0]. For, the rest of the other three possibilities, output will be zero,, the combination of this OR and NOT gate is called as NOR, gate., , A=1, B=1, Y=1 as in Fig 10., , Symbol (Fig 12b) :, , In this condition both the diodes are reverse biased. So, both the diodes act as open circuit. Therefore output y is, +5V i.e y is in logic-1 condition., 86, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.173, , Copyright @ NIMI Not to be Republished

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We can define a NOR gate as follows:, The output of a NOR gate is 0, even if one of the inputs is, in logic-1. Only when both the inputs are in logic-0, the, output is in logic-1., Truth table, A, , B, , A+B, , 0, , 0, , 1, , 0, , 1, , 0, , 1, , 0, , 0, , 1, , 1, , 0, , IC7402 is a T.T.L NOR gate IC. It contains 4 NOR gates., For pin details, refer data book., NAND gate, An AND gate followed by a NOT gate forms the NAND gate, as in Fig 13a. In this gate to get a low output (logic=0), all, the inputs must be in high state and to get high output, state, any one of the inputs or both inputs must be in low, state., , Fig 13b is the standard symbol for a NAND gate. The, inverter triangle has been deleted and the bubble is moved, to the AND-gate output., Truth table for NAND gate, A, , B, , Y = AB, , 0, , 0, , 1, , 0, , 1, , 1, , 1, , 0, , 1, , 1, , 1, , 0, , Pulsed operation, Output waveform Y is low only for the time intervals when, both inputs A and B are high as shown in the timing, diagram Fig 14., Logic pulser, Fig 15 shows the circuit diagram of logic pulser, the circuit, essentially consists of NAND gates connected debouncer, circuit and its output is Double inverted. The LED indicates,, pulses ON or OFF status., , When switch S1 is not pressed, (OFF position) B input of, , NAND gate No.2 is grounded, hence its output Y is forced, to go logic HIGH. This HIGH output is feedback to NAND, gate 1, A input of NAND gate 1 is also held HIGH through, R1 resistor (820Ω) and thus the output of NAND gate-1 'Y', is at low. This logic low output keeps LED in OFF condition, and this logic low is again double inverted at the logic, pulser tip through NAND gate 3 and 4 to get logic low level, at pulser tip., When S1 is pressed to ON, A input of NAND gate is forced, to go logic-low. Hence the output of this NAND gate is, forced to go logic-HIGH. Therefore the 'Y' output is at logic1, so LED glows and a logic-HIGH appears at probe tip., Also note that with HIGH at Y output, the inputs of NAND, gate 2 are also at logic-HIGH and the output of NAND, gate-2 is forced to go low. As long as switch S1 is at ON, position the probe tip is HIGH. When it is released it, springs back to OFF position, and the output returns to a, logic-LOW condition., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.173, , Copyright @ NIMI Not to be Republished, , 87

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Electrical, Electrician - Electronic Practice, , Related Theory for Exercise 4.1.174, , Wave shapes - oscillators and multivibrators, Objectives: At the end of this lesson you shall be able to, • state the working principle and gain of oscillator, • explain the RC phase-shift oscillator and frequency calculation, • state the features, gain and frequency of Hartley, colpitts and crystal oscillators, • state the working principle and frequency calculation of bistable and monostable multivibrator using, CRO., Oscillator: An oscillator is a circuit for producing voltages, that vary in a regular fashion with respect to time. The, output wave forms of oscillators are repeated exactly in, equal successive intervals of time as in Fig 1a and Fig 1b., , To build an oscillator, the following are essential;, – An amplifier, – A circuit which provides positive feedback from output, to input., The gain of an amplifier with feedback is given by,, Avf =, , AV, 1 − kA V, , kAv is known as the loop gain of the amplifier. In the case, of the amplifiers when the sign associated with kAv is, negative, the denominator has value more than 1. And,, hence the value of Avt will always be less than Av (negative, feedback). But, if the value of kAv is made larger, such, that, it approaches unity, and, if the sign associated with, kAv is negative then the value of the denominator decreases, to less than 1, and hence, Avf will be larger than Av., In case of oscillators, if the loop gain kAv is made positive,, i.e. by feeding back signal which is in-phase with the input, signal, then there will be an output signal even though, there is no external input signal. In other words, an, amplifier is modified to be an oscillator by positive feedback, such that it supplies its own input signal., The output wave-form of an oscillator may be sinusoidal as, in Fig 1a. Such oscillators are known as sine wave, oscillators or harmonic oscillators., The output of oscillators may be square, triangular or sawtooth wave forms as in Fig 1b. Such oscillators are known, as non-sinusoidal oscillators or relaxation oscillators., It was discussed earlier that positive feedback results in, converting an amplifier into an oscillator. To provide, positive feedback the feedback signal should be inphase, with the input signal such that it adds up with the input, signal., In practice, an oscillator will have no input AC signal at all,, but it still generates AC signal. An oscillator will have only, a DC supply. The oscillator circuit, makes use of the noise, generated in resistors at the switching on time of dc supply, and sustains the oscillations., , 88, , Example, An amplifier has a voltage gain of 40 without feedback., Determine the voltage gains when positive feedback of the, following amounts is applied., i) k = 0.01, ii) k = 0.02, iii) k = 0.025, Solution, i) Avf =, , AV, 40, 40, =, =, = 66.7, 1 – kA V 1 – 0.01 x 40 0.6, , ii) Avf =, , AV, 40, 40, =, =, = 200, 1 – kA V 1 – 0.02 x 40 0.2, , Copyright @ NIMI Not to be Republished

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(iii), , Avf =, , AV, 40, 40, =, ==, ∞ (Infinity), 1 – kA V 1 – 0.025 x 40 0, , In (iii) the gain of the amplifier become infinite when the, loop gain kAv = +1. This is known as the critical value of, the loop gain kAv. It is important to note that the output, voltage cannot be infinite. Instead the amplifier will start, working as an oscillator without the need of any separate, input. If the feedback path contains a frequency selective, network, the requirement of kAv = 1 can be met at only one, particular frequency, such that, the output of the oscillator, will be a sinusoidal signal of a particular frequency. Such, oscillators are known as sine wave oscillators., One of the simplest form of sine wave oscillators is the, phase shift oscillator. Fig 2 shows the principle behind an, RC phase shift oscillator., , f=, , 1, 2πRC 6, , The other condition to be satisfied oscillations to occur is, that the loop gain KAv should be equal to unity. To satisfy, this condition, using classical network analysis, it can be, found that, the value of K should be, k = 1 29 . Therefore,, the voltage gain of the amplifier Av stage must be greater, than 1 k or greater than 29 so that kAv becomes equal, to 1., , Transistor RC phase shift oscillator: Fig 3 shows a, single transistor phase shift oscillator using resistors and, capacitors in a feedback network., There are three sections of R and C in the feedback, network. Each RC section provides a 60° phase shift at, a specific frequency, resulting in a 180° phase shift as, required for positive feedback. This satisfies one of the two, required conditions for oscillations., In Fig 3, the feedback signals coupled through a feedback, resistor R1 in series with the amplifier stage input Resistance, Rin. resistor R1 can be made variable for adjusting the, oscillator frequency. For each of three sections of RC, phase shift network to produce 60° phase shift, it is, necessary that C1 = C2 = C3 and R1 = R2 = R' + Rin., The other required condition for oscillation, i.e. loop gain, kAv to be unity is satisfied by the circuit at Fig 2, when β, of the transistor used in the circuit is,, , The feedback network shown in Fig 3 consists of resistors, and capacitors which provide the required phase shift of, 180°. Due to the presence of capacitors in the feedback, network, the feedback network can be so designed to, provides the required phase shift of exactly 180° at a, particular frequency f given by,, , R, R, =, + 4 C ......(2), 23 + 29, hfe = β =, RC, R, , where, R1 = R2 = R, When β is atleast the value given by equation (2) or greater, than, the circuit at Fig 2 it will oscillate., Practical transistor RC phase shift oscillator, Fig 4 shows a practical transistor RC phase shift oscillator, which is similar to that shown in Fig 2., In Fig 4 note that resistor R3 (in Fig 2 it is denoted as R’), used for frequency adjustments is connected in series, with one of the resistors of the RC section. Resistor R4, provides the necessary bias stabilisation for the transistor, operation. Note that a small value capacitor C4 is connected, in parallel with the input. The purpose of C4 is to bypass the, unwanted high frequency oscillations to ground. The value, of R3 can be varied to adjust the frequency of oscillations., However, the variation that can be obtained by R3 is, limited., For the circuit at Fig 3, the frequency of oscillation is given, by,, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished, , 89

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When switch S is put into position B, as in Fig 5b, the, capacitor starts discharging through the inductor, creating, an expanding magnetic field around L. Since the inductor, has the property of opposing any sudden change in current, through it, the current builds up slowly., Once the capacitor gets fully discharged, the magnetic, field around L begins to collapse. The collapsing magnetic, field, induces a voltage (back-emf) in L. This back emf, tends to maintain the electron flow through L in the same, direction as when C was discharging. Hence, this back, emf in the inductor starts charging the capacitor with, opposite polarity as in Fig 5c. After the magnetic field has, totally collapsed, C would have got charged in the opposite, direction as in Fig 5c., , f=, , 1, , ......(3), , 2, , 2πC 6R1 + 4R1R C, , Sinusoidal wave form: However, owing to the resistance, in a practical inductor and the losses in the capacitor due, to resulting I2R (heat loss) the amplified of the oscillation, decreases gradually (damped) and ultimately the, oscillations die down as in Fig 5d., , where, C = C1 = C2 = C3, The minimum value of hfe or β of the transistor used in the, circuit at Fig 3 should be,, R1, RC, h=, = β 23 + 29 R + 4 R1, fe, C, , using the component values at Fig 3, the β of the transistor, used should be a minimum of,, β= 23 + 29, , 1.2K, 5.6K, +4, =, 47.89, 5.6K, 1.2K, , The frequency of oscillations can be increased, by decreasing the value of R or by decreasing, the value of C., In the practical circuit at Fig 3, collector feedback bias is, employed to ensure that the transistor will never go to, saturation. Other biasing techniques such as voltage, divider bias can also be used for DC biasing of the, transistor. Since the frequency of oscillations is decided, only by the feedback phase shift network, biasing resistors, will not have any effect of the frequency of oscillations. The, important point to be noted is that the β of the transistor, should be higher than the minimum β given in equation 2, to have sustained oscillations., Hartley oscillator, Principle of sinusoidal or harmonic oscillations:, Fig 5a shows an inductor and a capacitor connected in, parallel as a parallel LC resonant circuit. A parallel LC, circuit is also known as tuned circuit or tank circuit., In Fig 5a, when switch S is put into position A, the, capacitor gets charged with the bottom plate being negative, and the top plate positive. This means, energy is stored, in the capacitor in the form of an electric charge., 90, , The frequency of oscillation produced by the resonant, frequency is given by,, f=, , 1, 2π LC, , Overcoming losses in tank circuit for sustained, oscillations: To avoid the damping of oscillations, when, the energy fed into the circuit has been used up, it is, necessary to supply more energy by charging the capacitor, again. As shown in Fig 5a, by switching S between A and, B at proper time, the oscillations can be maintained thus, obtaining sinusoidal waveform of constant amplitude and, frequency., Another method of making the LC tank circuit to give, undamped oscillations is, to connect the tank circuit in the, output of an amplifier as in Fig 6., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished

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The signal induced in the base thus eliminates the need, for an external input to the oscillator and the LC tank will, oscillate as long as the DC power to the circuit is ON., The feedback given to the amplifier in Fig 7 in the proper, phase so as to sustain (keep going) oscillations is referred, to as positive feedback or regenerative feedback., Barkhausen criterion: The mathematical analysis for an, amplifier to oscillate on its own is given below:, , The amplifier is kept at cut-off by the dc supply VBB which, reverse-biases the base-emitter circuit. A sine wave is, injected to the base circuit with such an amplitude that the, collector current flows at the peak of the negative alterations, of the input sine wave. This excites the LC circuit in the, collector of the transistor and the tank keeps oscillating., If the input sine wave has the same frequency as the, frequency of oscillations of the tank circuit, the oscillations, in the LC tank is maintained., , •, , In the amplifier shown in Fig 7, assume that the gain of, the amplifier is A and the feedback factors is β. If the, product of Aβ is less than 1 (Aβ<1), then the output, signal will be a damped oscillations which will die down, as is shown in Fig 8a., , •, , If Aβ>1, the output voltage builds up as shown in Fig 8b., Such oscillations are called growing oscillations., , •, , If Aβ=1, the output amplitude of oscillations remains, constant as in Fig 8c., , Fig 7 shows a modified form of circuit at Fig 6. In Fig 5a, transistor amplifier connected in such a way that it will, cause undamped oscillations without requiring any external, signal. Such a circuit is known as an oscillator., , The oscillator circuit at Fig 7 is known as tickler-coil, oscillator. Here L1 is inductively coupled to L. When, power is first switched ON to the circuit, current flows in, the transistor. As the current flows through L, it induces, a voltage in L1 which is coupled to the base of the, transistor and is amplified., If the phase of the feedback voltage is adding, then there, is an increase in the collector current. This action builds, up a large current pulse which excites the LC tank into, oscillations. The signal fed by L1 to the base of the, transistor is a sine wave of the same frequency as that in, the LC circuit and of proper phase to sustain the oscillations., , When the feedback is positive (regenerative), the overall, gain of the amplifier with feedback (Af) is given by,, Af =, , A, 1 – Aβ, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished, , 91

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When Aβ = 1, the denominator of the equation will be zero,, and hence Af = Infinity. The gain becoming infinity means,, there is output without any input. i.e. the amplifier becomes, an oscillator. This condition Aβ = 1, is known as Barkhausen, criterion for oscillations., Summarizing, the basic requirements for an oscillator are;, •, , A stable DC power supply source, , •, , An amplifier, , •, , A regenerative (positive) feedback from output to input, , •, , A LC tank circuit to determine the frequency of, oscillations, , Starting signal for oscillators: As discussed above an, oscillator gives alternating output voltage without an input, signal once the amplifier is given a regenerative feedback., But in a practical oscillator circuit, to start off oscillations,, no starting input signal is provided. However, the starting, signal of an oscillator is generated by the noise voltage, while switching on the oscillator circuit. Such noise, voltages are produced due to the random motion of, electrons in resistors used in the circuit., Noise voltage contains almost all the sinusoidal frequencies, of small amplitude. However, it gets amplified and appears, at the output terminals. The amplified noise now drives the, feedback network, which is a resonant tank circuit., Because of this tuned tank circuit, the feedback voltage, Aβ is maximum at a particular frequency fr, which will be, the frequency of oscillations., Further more, the phase shift required for positive feedback, is correct at this frequency fr only. Thus although the noise, voltage contains several frequency components, the output, of the oscillator will contain a single sinusoidal frequency, fr the resonant frequency of the tank circuit., To summarize, the following are the requirements of an, oscillator circuit to take-off with oscillations and have, sustained oscillations,, •, , there must be positive feedback., , •, , Initially the loop gain product Aβ must be >1., , •, , After the circuit starts oscillating, the loop gain product, Aβ must decrease to 1 and remain at 1., , Hartley oscillator: One of the simplest of sinusoidal, oscillators is the Hartley oscillator shown in Figs 9a, and 9b., As in Fig 9a is a series fed Hartley oscillator. This circuit, is similar to the tickler coil oscillator shown in, Fig 7, but the tickler circuit coil L1 is physically connected, to L, and is hence a part of L (like an auto-transformer)., This oscillator is called series-fed because, the high, frequency oscillations generated and the DC paths are the, same, just as they would be in a series circuit. Series fed, Hartley oscillators are not preferred due to their poor, stability of oscillations., 92, , Fig 9b is parallel fed Hartley oscillator commonly used in, radio receivers. Parallel fed Hartley oscillators are known, for their high stability of oscillations., The circuit at Fig 9b is actually an amplifier with positive, (regenerative) feedback to have sustained oscillations., The capacitor C2 and inductor L2 form the path for RF, current in the collector to ground circuit., RF current through L2 induces a voltage in L1 in proper, phase and amplitude to sustain oscillations., The position of the tap at the junction of L1 and L2, determines how much signal is fed back to the base, circuit., The capacitor C and the inductors L1 + L2 forms the, resonant tank circuit of the oscillator which determines the, frequency of oscillations. Capacitor C can be made, variable capacitor for tuning the oscillator to different, frequencies. C1 and R1 form the RC circuit which develops, the bias voltage at the base., The RF choke at the collector keeps the high frequency ac, signal out of the Vcc supply. In cheaper oscillator circuits, the RF choke is omitted and is replaced by a resistor., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished

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Resistor R2 connected in the emitter provides DC, stabilization. R2 is by-passed by C3 to prevent AC, degeneration., , The transistor used is a silicon high frequency transistor, (BF series) as the oscillator frequency is in the range of 1, MHz., , The Hartley oscillator coil has three connections. These, are usually coded on the coil. If they are not, it is generally, possible to identify them by a resistance check. The, resistance between the taps T and P as in Fig 10, is small, compared with the resistance between T and G., If the coil, connections are not made properly, the oscillator will not, work., , The divider biasing is provided to make the DC conditions, such that the amplifier works as Class A. With the heavy, feedback (large β), the large feedback signal drives the, base of the transistor into saturation and cut-off. This large, feedback signal produces negative DC clamping at the, base, changing the operation from Class A to Class C., This negative clamping automatically adjusts the value of, Aβ to 1. If the feedback is too large, it may result in loss, of some of the output voltage because of the stray power, loses., When you build an oscillator, you can adjust the amount, of feedback to maximize the output voltage. The trick is, to use enough feedback to start under all conditions, (different transistors, temperature, voltage etc.), but not so, much that you lose more output than necessary., The frequency of oscillations of the oscillator circuit at, Fig 10 can be varied by varying the position of the shaft of, the gang of the gang capacitor (C4)., , Checking oscillator frequency: The frequency of an, oscillator can be computed if the values of L (L = L1 + L2), and C are known using the formula,, f=, , 1, 2π LC, , where, f is in hertz, L in henry, and C in farad., The frequency of an oscillator may be measured in two, ways,, •, , Using a direct read-out frequency meter also known as, frequency counter which is most accurate, popular and, easy to use., , •, , Using an oscilloscope with a calibrated time base to, measure the period of the wave-form. From the, measured period, ‘T’ frequency is calculated using the, formula, f=, , Colpitt's oscillator: Colpitt's oscillator is another type of, sinusoidal oscillator or harmonic oscillator which uses a, tank circuit for oscillations. Colpitt's oscillators are very, popular and are widely used in commercial signal, generators and communication receivers., A typical Colpitt's oscillator is in Fig 11 is similar to a, Hartley oscillator. The only difference is that the Colpitt's, oscillator uses a split capacitor for the tank instead of a, split inductor used in Hartley oscillators., The parallel-fed or shunt-fed Colpitt's oscillator is in Fig 11,, uses the common emitter configuration. The capacitors, C1A & C1B from the voltage divider used to provide the, feedback signal. The voltage drop across C1B determines, the feedback voltage. All other components in this circuit, have the same function as in the Hartley circuit., , 1, T, , where, f is the frequency in Hz and ‘T’ the time period in, seconds., A practical Hartley oscillator circuit using medium-wave, oscillator coil as L is shown in Fig 10., The advantage of using a medium wave oscillator coil for, L is that the output can be taken out of the secondary, winding (4 and 5) of the coil., Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished, , 93

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The frequency of oscillations of the Colpitt's oscillator is, given by,, f=, , 1, 2π LC, , where,, f is the frequency of oscillation in hertz,, L is the inductance of the coil in henry, C is the total capacitance in farad given by,, C1A x C1B, C =C +C, 1A, 1B, , The problem of frequency drift can be largely overcome by, using high Q coils and good quality capacitors. But, with, ordinary inductors and capacitors, Q-values in excess of, a few hundred is very difficult or impossible to achieve., Large improvements in frequency stability can be achieved, by using a quartz crystal in the place of the conventional, tuned circuit. Such oscillator circuits are referred to as, crystal controlled oscillators., Piezo-electric effect: It was discovered that certain, crystals such as quartz and Rochelle salt, exhibit a, special property known as piezo-electric property. A, quartz crystal looks like a piece of thin frosted glass, usually cut into 1/4 to 1 inch squares as in Fig 13., , The frequency of oscillations can be changed by using a, miniature ganged capacitor for C1A & C1B., By varying the shaft of the ganged capacitor, both the, capacitances C1A and C1B get varied, and hence, the, frequency of oscillations of the oscillator varies., Colpitt's oscillators are generally used for generating, frequencies above 1 MHz., A practical Colpitts oscillator circuit using a ganged, capacitor for C1A and C1B and a medium wave oscillator, coil for L is in Fig 12., , When such a crystal is held between two flat metal plates, and pressed together, a small emf will be developed, between the plates as if the crystal became a battery for, an instant. When the plates are released, the crystal, springs brings back to its original shape and an emf of, opposite polarity is developed between the two plates. In, this way, mechanical energy/force is converted to electrical, energy by the crystal., Crystal oscillators: The LC oscillator circuits such as, Hartley and Colpitts have the problem of frequency instability. The most important reason for the frequency drift, in LC oscillators is, the change in value of capacitance and, inductance of the tank circuit that occurs when temperature, changes., As the temperature increases or decreases, the values of, L and C deviate causing the circuit to oscillate at a, frequency different from the desired resonant frequency., Other reasons for frequency deviation are, the leads of, transistor, inter electrode and wiring capacitances., , 94, , This property is made use of in the pick-ups for gramophone, records. In a gramophone record, small mechanical, vibrations are produced when the stylus tracks the groove, on the gramophone plate. This vibrating force gives rise to, corresponding voltages representing the recorded sound, at the pick-up terminals., In addition to the above property of the crystal, when an, emf is applied across the two plates of the crystal, the, crystal will distort from its normal shape. If an opposite, polarity emf is applied, the crystal will reverse its physical, distorted shape. In this way, these crystals also convert, electrical energy into mechanical energy., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished

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The above two reciprocal actions of a crystal are known as, piezo-electric effect. Such crystals are housed in crystal, holders as in Fig 13., Amongst several crystals having this piezo-electric, property, the quartz crystal is most popular because,, mechanical oscillations are started in this crystal it takes, a long time for the oscillations to die away. Quartz, crystals therefore, have a very high mechanical Q., , of the transistor determines the oscillating frequency. As, in a colpitts oscillator, capacitors C1 and C2 form a, capacitive voltage divider for feedback. The ac voltage, across C2 provides the necessary positive feedback to the, base., , So far as the electrical properties are concerned, a quartz, crystal is equivalent to the LC resonant circuit is in, Fig 14., , In Fig 15, the crystal acts like an inductor that resonates, with C1 and C2. In the base circuit, the R1R2 divider supplies, forward bias voltage from the VCC. Bias stabilization is, provided by the RECE combination in the emitter circuit., , The values of L,R,C and Cm depend upon the physical size, of the crystal and how the crystal is cut from the original, mass. Capacitance C m represents the mounting, capacitance. For using the crystal in electronic circuits,, two conducting electrodes are placed onto its two faces., Connecting leads are then joined to these electrodes., When the leads are connected to a source of oscillating, voltage, mechanical vibrations are set up within the crystal., If the frequency of the oscillating voltage is close to a, resonant frequency of the crystal, then the crystal forces, the oscillating voltage to coincide with the oscillating, frequency of the crystal. Hence, in an oscillator, by using, the crystal in the place of an LC resonant circuit, the, frequency of oscillation is determined almost entirely by, the crystal. Q values in excess of 20,000 are easily, obtained with readily available crystals resulting in highly, stable oscillating frequency., Hence, when accuracy and stability of the oscillation, frequency are important, a quartz crystal oscillator is used, instead of Hartley or Colpitt's oscillators. The frequency, range of crystals is usually between 0.5 to 30 MHz., Pierce crystal oscillator: The pierce crystal controlled, oscillator is in Fig 15 is often used because it requires very, few components and has good frequency stability., The pierce crystal oscillator is similar to the Colpitts, oscillator but for the inductance coil replaced by a crystal., Here the crystal across the collector and the base terminals, , In Fig 15, if the crystal resonant frequency is, say, 3579.545 Hz, then the oscillator oscillates at the same, frequency and gives a sinusoidal output of 3579.545 Hz., Crystal oscillators are generally used in,, •, , mobile radio transmitters and receivers, , •, , broadcast transmitters, , •, , test equipments such as signal generators where, exact frequency and very high frequency stability are of, utmost importance. The frequency drift in crystal, controlled oscillators will be less than 1 Hz per 106 Hz., , Multivibrator, It is a free running oscillator which gives repetitive pulse, wave form output, and other types of multi-vibrators which, are classified depending upon the manner in which the two, stages of the multi-vibrator interchange their ON and OFF, states. They are:, •, , Mono-stable multivibrator (having one stable state)., , •, , Bistable multivibrator (having two stable states)., , Mono-stable Multivibrator, Fig 16 shows a typical mono-stable multi-vibrator also, known as mono-shot or one-shot., A mono-shot has one stable state with one transistor, conducting and the other off. This state can be changed, only temporarily by giving an input pulse generally known, as trigger pulse to the transistor which is off. But this, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished, , 95

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changed state returns back to its original stable state after, a period decided by the values of R and C., , Fig 17 shows a practical mono-stable multi-vibrator with, trigger input. Fig 17 also shows the wave-forms at different, points of the circuit., , Bistable multivibrator, An astable multi-vibrator automatically switches from one, state to other (ON-to-OFF or OFF-to-ON...). Whereas, a, bistable multi-vibrator will change the state(ON to OFF or, OFF to ON) when triggered and remain in the new state, (ON or OFF). This means, a bistable multi-vibrator has two, stable states. Fig 18 shows a typical bistable, multi-vibrator circuit., The circuit at Fig 18 is completely symmetrical. The, potential dividers R1, R2 and R3, R4 form identical bias, network at the base of transistors. Each transistor is, biased from the collector of the other transistor. Due to the, slightest difference in parameters of the transistor, when, the circuit is switched ON, any one of the two transistors, will turn-ON, and the other remain in OFF condition., In the circuit at Fig 18, the two identical CE amplifier, stages are so connected that the output of one is fed to the, input of the other, through resistors R1, R3 and shunted by, capacitors C1, C2. The purpose of the capacitor is nothing, but to speed up the switching characteristic of the circuit, to get distortion-less output wave-form. Capacitors C1 & C2, are also known as commutating capacitors., , A bistable multi-vibrator is also known as a flip-flop. The, output terminals are generally identified as Q & Q (Q-bar), as in Fig 19., When Q is in high state (also known as Logic-1 state in, , The period t for which Q2 is kept off temporarily is given by,, t = 0.69 RC., Mono-stable multi-vibrators are extensively used as timers, in electronic timing control circuits., , 96, , digital electronics), Q (Q-bar) will be in low state (also, known as Logic-0 state), and vice versa. This circuit is, known as a flip-flop circuit because, if one output flips(high/, logic-1) the other output automatically flops(low/logic-0)., A flip-flop can be switched from one state to the other by, applying a suitable triggering input. Flip-flops are used as, a basic memory cell in digital computers for storing, information. Flip-flops are used in various forms in almost, all digital system as counters, frequency dividers and so, on., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished

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Practical bistable multi-vibrators with unsymmetrical and, symmetrical triggering arrangement are shown in, Fig 20a and 20b., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.1.174, , Copyright @ NIMI Not to be Republished, , 97

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Electrical, Related Theory for Exercise 4.2.175 to 4.2.177, Electrician - Control Panel Wiring, Control elements, accessories - layout of control cabinet, Objectives: At the end of this lesson you shall be able to, • explain the layout marking methods and necessity, • state the methods of marking, cutting, drilling, fixing of accessories and components, • explain the methods of mounting and wiring the accessories, • state the various control elements used for control panel board, • list the different wiring accessories used in control panel wiring., Introduction, Preperation of layout drawing and marking on control, cabinet is very much essential, we must have a clear, vision of mounting components and their location on panel, board/ control cabinet., There is no such important method inpratice to make the, layout on control cabinet. However a neat layout on control, cabinet is very much required., The display and indicating instruments should be selected, on the top position of the cabinet. Heavy and rare operated, devices such as fuse breaker etc; are to be fixed on the, bottom of the cabinet., The components and fixtures should have sufficient space, in between to carryout future repair (or) replace, requirements. But too much space should not be provided,, that will increase the size of the cabinet unnecessarily., While finalising the layout plan the relevent IE rulers to be, followed for better result., , wiring accessories required for said wiring should be, obtained or fabricated., While selecting the control and protective accessories of, the control panel the full load current of the individual load,, total load and duty cycle, simultaneous operation of the, load and 25% additional load capacity of the motors have, to be considered., The over load and short circuit protection may be given, either ahead of the control panel by calculating the highest, rating of the branch circuit or individual motors depends, on space available, cost factor and sensitiveness of the, operation., The finalized layout may vary depends the individual design, and mind application. However a sample layout marking, for the above starter is given in the Fig 1., , Layout marking, Wiring diagrams for power and control circuit should be, developed for sequence of operation of automatic star delta starter with forward and reverse. Types of protection,, control, indication and measuring accessories needed, should be finalized., To wire up the above starter in a control panel the well, designed and easily understandable layout should be, finalized. Layout of the finalized wiring diagram should, developed keeping important features of the control panel, in mind. While designing the control panel the outside, dimensions, the swing area of cabinet doors and area, required for maintenance and tools kit have to be, considered., , Once the panel layout is designed we must find out where, and how to fit the accessories., , Control panel may be often used near the process area, with high temperature, humidity and dust hence the, arrangement for cooling fan and dehumidifier along with, filters and intake and exhaust vents should be needed., , The finalized layout of accessories can be marked in the, control panel using suitable marking device., , Suitable size of control panel which can accommodate, all the controlling, protective, measuring, indicating and, , The mounting or fixing holes along with necessary tap or, die in suitable size (if any) can be prepared in the front, door and inside of the control panel as in Fig 2., , 98, , Cutting and drilling, , Copyright @ NIMI Not to be Republished

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Race way is one form of cable ducting used to carry the, wiring between components and keeping the wires neat., The leads wires and cables are laid inside the raceways, brought out through the holes / slots in the sides and can, be inspected by removing the cover of the raceways., The minimum spacing between components and raceways, should be 100 mm for 415V systems and 50 to 75 mm for, less than 415V system. The next stage is to clip the, accessories to the rail and wire them., Mounting and wiring the accessories in control panel, The accessories can be mounted on the DIN rails allowing, sufficient space for easy maintenance, wiring and, troubleshooting. The mounting should not move or lean in, the DIN rail due to vibration or strain due to cables., Contactor can be either flush mounted to the chassis or, DIN rail - mounted . Contactor mounting type over load, relay which have three pin connectors engage into the, contactor terminals may be used to reduce the mounting, and wiring time and labour., , Din rail is a metal rail made from cold rolled carbon steel, sheet with zinc plated or chromate bright surface finish, used to mount the circuit breakers and control accessories, without using screws as in Fig 2. DIN rail being fixed to, the chassis before fitted the contactors and other, accessories as in Fig 3., The standard specification of widely available DIN rail is, top hat rail EN 50022 which dimension is 35 mm width, and a 15 mm or 7.5 mm depth. They can be cut in to the, required length and then screwed or bolted inside the panel, before mounting any accessories and wiring begins as, in Fig 4., , To mount the contactor on rail first place the back top, groove on the top of rail and turn it downwards against the, lower rail which will cause the spring of the contactor to, retract and snap into place behind the rail. There is a slot, in the spring clip of the contactor so that the clip can be, retracted using small screw driver or connector to remove, the contactor if required. To avoid fouling the underneath, of the accessories use screws with low profile heads., The contactor arrangements and terminals are usually, labeled which conforms to BS 5583. For example 1 and 2, for NC contacts, 3 and 4 for NO contacts, odd numbers, like 1, 3 and 5 for incoming terminals and even numbers, like 2, 4 and 6 for outgoing terminals of the main contacts, of contactors and OLR., The conductor should be trimmed OFF to that the conductor, does not insert more than the half way through the, connectors. Single strand wire should be folded back to, give additional thickness. The over tightening of screw, have to be avoided otherwise this can crush the strand, and give a weak connection., All the internal wiring should be terminated in the top and, external wiring in the bottom of the connectors to avoid, the crossover of both wirings. Flexible conduit and cables, have to be installed in such a way that the liquid or water, if any can drain away from the fitting and grommets., An earth terminal usually green or green yellow to be, clamped to the rail and ensure the cabinet and door are, earthed properly., An insulated separator can be used to isolate the high, voltage connections from others. End stops are used to, clamps the connectors together and close the open, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 99

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terminals on one end, sometimes the earth terminal will, do the same job as in Fig 5., The control panel should be grounded properly so that, control panel should have proper earthing bolts / nuts. If, more ground points are used a common earth plate should, be fixed inside the cabinet as in Fig 5., , Routing and bunching, Routing, Conductors and cables should run from terminal to, terminal without any intervening joins and cross over. Extra, length should be left at connector / terminals where, assembly needs to be disconnected for maintenance and, servicing. Multi core cable terminations have to be, adequately supported to avoid undue strain on the, terminals., Different colour may be used to aid identification of group, of controls and functions., The associated earth and neutral conductor should be, routed close to the respective live conductors to avoid, undue loop resistance., Select the race ways to leave some slacks or looping of, the cable inside it. The wires inside the race way should, not more than the half fill., Bunching and tying, , U loops of the cables as long as possible facing down, and anchored on each side of the hinged doors and panel, with screws or bolts and do not use adhesive. Place the, sleeve and spiral flexible conduits of suitable size over, the cables running between the hinged doors and panel, as in Fig 6., , Run the wires in horizontal and vertical lines avoid diagonal, runs as possible. Do not run the wire over the other, devices or race ways. Uses of spring cage terminals, instead of standard screw terminals can reduce the, termination error, the wiring and maintenance time which, in turn reduce the cost and labour., To connect the accessories, cut the individual control, wires to the proper lengths, strips the insulation, mark, wire identification, insert ferrules at the ends of wires,, use suitable lugs or thimbles., The wires should be neatly bundled, run in the race ways, and routed with smooth radius bends., All the terminals, wires and components should have, identification marks and labels. A good labelling and, identification will reduce the errors in termination, testing,, maintenance and repairs. A legible and durable label in, an efficient and cost effective manner may be chosen., , The care to be given to the bundle of wires which is, mounted on the hinged doors should not restrict the, opening and closing of the door or the doors should not, damage the wires., Minimize the use of cable ties if the raceways are used., They may be cut OFF during troubleshooting and rarely, replaced., , To the possible extent the power and control wiring should, be run in separate race way or cable management which, will reduce the radio interference, trouble shooting time, and make the future alteration if any is easier., By taking some extra cares like pest control, dust control,, adequate terminal pressure, selection of proper wires and, accessories, it can be ensured that the control panel has, no failure time and with moderate maintenance it will be, trouble free panel for entire life., Where the multiple earths are used it is necessary to, use a common earth terminal or connectors as in Fig 5., , 100, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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Tests, Before energizing the control panel all necessary tests, should be carried out like open, short, earth continuity, and earth soundness etc. The supply voltage and, frequency are also to be checked., Control elements, Difference between control panel and switch board, A panel board contains a single panel or a group of, panel units as single panel that includes bus-bars,, protective devices and control switches, instruments and, more starters etc., In a panel board, the interior are designed to place the, accessories and wires in a cabinet or cut out box or, partition and accessible only from the front., , 2 Push button switch (Fig 8), , A switch board consists of a large single panel or frame, or assembly of switch gears, with or without instruments,, but the term switch board does not apply to a group of, local switches in the final circuit. Unlike panel boards,, switch boards are generally accessible from the rear as, well as from the front and are not intended to be installed, in cabinets. However the terms, panel board and switch, board, are used normally without much discrimination., For wiring of control panel board the following control, elements / components and accessories are required., They are, -, , Isolating switch, , -, , Push button switch, , -, , Indicating lamp, , -, , MCB (Miniature Circuit Breaker), , -, , Contactors, , -, , Electro mechanical relays, , -, , Thermal over load relays, , -, , Time delay relay (timers), , -, , Rectifiers, , -, , Limit switches, , -, , Control transformers etc., , Push button is a simple push switch mechanism for, making or breaking the circuit as and when required. It is, made out of hard plastic or metal. An indicating lamp is, incorporated with the push button switch to indicate start, or stop is also available., 3 Indicating lamp (Fig 9), , Control elements for control panel, 1 Isolating switch (Fig 7), Isolating switch (Isolator) is a manually operated, mechanical switch which isolates/disconnects the circuit, which are connected with it from the supply system as, and when required. It should be normally operated at, “OFF” load condition., , It is a low voltage, low wattage filament or neon or LED, lamps used to indicate the various indication like, availability of supply or motor ON/OFF, mains/motors, fails or trip etc., It is available in different size, colour and wattage. It should, be generally fitted in the front side of the control panel, with suitable holder., , It is available in different current, voltage rating and size., Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 101

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4 MCB (Fig 10), , Electromechanical relays are electrically operated, switches used to control a high powered circuit, accessories using low power signal. When an electric, current passes through its coil it produces a magnetic, field that activates the armature to make or break a, connection., current passes through its coil it produces a magnetic, field that activates the armature to make or break a, connection., 8 Thermal overload relays (Fig 13), , Miniature circuit breaker (MCB) is an electro mechanical, protective device which protect an electrical circuit from, short circuit and over load . It automatically turns off, when, the current flowing through it exceeds the maximum, allowable limit., 5 Fuses, It is a protective device which is connected is series with, the live wire to protect the circuit from short circuit and, earth fault., 6 Contactors (Fig 11), , It is a thermally operated electromechanical device that, protects motors from over heating and loading., 9 Time delay relay (timers) (Fig 14), , A contactor is an electrically controlled double break, switch used for switching ON / switching OFF the electrical, circuit, similar to a relay with higher current ratings. It is, controlled by a circuit which has a much lower power, level than the switched circuit., 7 Electro mechanical relays (Fig 12), , Time delay relays are simply the control relays in - built, with a time delay mechanism to control the circuit based, an time delay., In time delay relays its contact will open or close after, the pre-determined time delay either on energising or on, de-energising its no volt coil. It can be classified into two, types as ON delay timer and OFF delay timer., 10 Rectifiers (Fig 15), , 102, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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A rectifier is a static device consists of one or more, diodes that converts alternating current (AC) to direct, current (DC). A diode is like a one -way valve that allows, an electrical current to flow in only one direction., , It protects the wires from dust, humidity, corrosion, water, intrusion, heat, mechanical damage and physical threats., 2 DIN rail (Fig 18), , 11 Limit switches (Fig 16), , Limit switch is a switch with an actuator which is operated, by the motion of a machine part or an object., When an object or parts comes into contact with actuator,, it operates the contacts of the switch to make or break, an electrical connection. They are used to control the, distance or angles of movement of any machine parts or, axis or objects., , It is a zinc - plated or chromated metal rail which is used, for mounting the control accessories like MCB, contactors, and OLR etc, with out using screws inside the control, panel., 3 G Channel (Fig 19), , 12 Control transformer, It is a transformer which is used to supply the power to, the control or auxiliary circuit or equipment which does, not intend for direct connection to the main supply., 13 Panel meter (voltmeter and ammeter), They are the measuring instruments used to measure, the various electrical parameter of the circuits such as, voltage and current etc., , It is a zinc - coated metal channel which is especially, used for mounting the feed through or spring load or double, deck terminal connectors without using screw inside the, control panel., 4 Terminal connectors (Fig 20), , Wiring accessories for control panel wiring, 1 PVC channel / Race ways (Fig 17), , It is an inspection type PVC enclosed channel which, provides a pathway for electrical wiring inside the control, panel. It has the opening slots on both sides to facilitate, the good ventilation and visual inspection., , It is the set of insulated screw terminals at both sides, used to connect the accessories of the control panel with, external control switches, limit switches, input supply, and motor terminals etc., Terminal connectors with barrier strips and clamping plates, provide a tight and electrically sound termination. It is, available in various size, current and voltage ratings., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 103

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5 Wire ferrules (Fig 21), , It is a small circular ring made up of polymer plastics or, rubber or fibre, used to easily identify the ends of wires, which are to be connected into a particular terminals or, accessories. It should be inserted on the both ends of a, wire as collar or bracelet., , 8 Nylon cable ties (Fig 24), , It is available is different size like 1 sq.mm, 1.5 sq.mm, and 2.5 sq.mm etc generally in yellow colour printed with, either numerical or alphabet letters on it., 6 Lugs and thimbles (Fig 22), , It is a cylindrical barrel along with circular rings or, cylindrical rod or U shape or flat surface made up of, aluminum or copper or brass, used to ensure the sound, electric connection of the cable / wire on to the terminals., It prevent flare out of stripped and stranded cable, increase, the conductivity of the connection, support the cable /, wire and avoid the loose connection and sparking. Suitable, crimping tool has to be used to connects them with cables, / wires. It is available in different size like 1 sq.mm, 4, sq.mm, 25 sq.mm, 70 sq.mm, 125 sq.mm and so on., •, , •, , It is a type of fastener used to hold or tie or bunch the, wires / cable or group of cables., , •, , It is made of nylon tape or belt which has teeth that, will engage with head of the pawl to form a ratchet and, tightens the wires., , •, , In general the tie can not be loosened, or removed or, reused. However some reusable ties are also available., , •, , it is available in different colour, length and width., , •, , Because of its low cost and easy to use, it is widely, used in general purpose application also., , 9 Sleeves (Fig 25), , Thimbles may also be referred as sockets., , 7 Cable binding straps and button (Fig 23), It is made up of PVC or polymer belt with a small holes at, regular intervals, used to tie up, bunching, binding and, dressing the cable / wires with help of buttons., It is reusable and good insulator to the heat and electricity., It is generally available 8mm, 10 mm and 12 mm width., , 104, , •, , It is flexible tubular / cylindrical insulator into which, the electric wire or cable or group of cables can be, inserted., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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•, , Apart from the electrical insulation and easy, identification of wires, it also protect the wires from, abrasion, heat, chemical, physical damage and radio, interference., , •, , It is available is different colour, style, materials like, carbon fibre, fabrics, Teflon, fibre glass, nylon, poly, ethylene (PET) wrap, braided metal and heat shrink, sleeves., , 10 Grommets (Fig 26), , and easiness in operation. These switches are operated, by levers or knobs which in turn operate cams inside the, switch to contact various terminals in sequence by the, internal contact blocks. These cams and blocks are made, of hard P.V.C. and are designed to withstand many, operations. It is possible to get many circuit combinations, by combining various cams and contact blocks. As the, contact blocks, terminals and cams are spring-loaded,, these switches should not be opened by inexperienced, persons for repairs. Fig 28 shows 250V AC 15 Amps 2pole three position flush mounting coin-slot operator., Function: This switches can do a number of functions,, depending upon the cover and contact block combinations., According they can be used for ON/ OFF switch, manual, Forward / Reverse operation, Manual star delta switches,, Pole changing switches, Selection switch for meaning, instrument etc.., , It is a type of bushing which is used to insulate and hold, the cables when they pass through a punched / drilled, holes of panels or enclosures. It is generally made of, rubber, plastic, plastic coated metal and protect the cable, from twist, tug, cut, break, strain, vibration etc and prevent, the entry of dirt, dust, water, insects and rats into the, panel. It may also called as glands., 11 Wire clips (Fig 27), It is a type of fixing or fastening device which is used to, fix and hold the cables or punch of cables in a secure, manner., Rotary type switches (Fig 28), Rotary switches are most commonly used in lathes, milling, and drilling machines due to their exact visual position, , Power and control circuits for three phase motors, Objectives: At the end of this lesson you shall be able to, • state the necessity of starters for a 3-phase induction motor to start and name the types of starters, • explain the basic contactor circuit with a single push-button station for start and stop, • state the function of DOL starter, semi and fully automatic start - delta strater, • explain the function of jogging inching forward and reverse control circuit, • explain the remote station control circuit, • explain the sequential control of motors., Necessity of starter: A squirrel cage induction motor just, before starting is similar to a polyphase transformer with, a short-circuited secondary. If normal voltage is applied to, the stationary motor, then, as in the case of a transformer,, a very large initial current, to the tune of 5 to 6 times the, normal current, will be drawn by the motor from the mains., This initial excessive current is objectionable, because it, , will produce large line voltage drop, which in turn will affect, the operation of other electrical equipment and lights, connected to the same line., The initial rush of current is controlled by applying a, reduced voltage to the stator winding during the starting, period, and then the full normal voltage is applied when the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 105

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motor has run up to speed. For motors, up to 3 Hp, full, normal voltage can be applied for starting. However, to, start and stop the motor, and to protect the motor from, overload currents and low voltages, a starter is required in, the motor circuit. In addition to this, the starter may also, reduce the applied voltage to the motor at the time of, starting., , windings U V & W of the motor are connected to the supply, terminals R Y B via the ICTP switch, contactor and OL, relay., , Types of starters: Following are the different types of, starters used for starting squirrel cage induction motors., •, , Direct on-line starter, , •, , Star-delta starter - semi and fully automatic, , •, , Step-down transformer starter, , •, , Auto-transformer starter., , In the above starters, except for the direct on-line starter,, reduced voltage is applied to the stator winding of the, squirrel cage induction motor at the time of starting, and, regular voltage is applied once the motor picks up the, rated speed., Selection of starter: Many factors must be considered, when selecting starting equipment. These factors include, starting current, the full load current, voltage rating of, motor, voltage (line) drop, cycle of operation, type of load,, motor protection and safety of the operator., Contactors: The contactor forms the main part in all the, starters. A contactor is defined as a switching device, capable of making, carrying and breaking a load circuit at, a frequency of 50 cycles per second or more. It may be, operated by hand (mechanical), electromagnetic,, pneumatic or electro-pneumatic relays., The contactors shown in Fig 1 consist of main contacts,, auxiliary contacts and no-volt coil. As per Fig 1, there are, three sets of normally open, main contacts between, terminals 1 and 2, 3 and 4, 5 and 6, two sets of normally, open auxiliary contacts between terminals 23 and 24, 13, and 14, and one set of normally closed auxiliary contact, between terminals 21 and 22., Auxiliary contacts carry less current than main contacts., Normally contactors will not have the push-button stations, and O.L. relay as an integrated part, but will have to be, used as separate accessories along with the contactor to, form the starter function.The main parts of a magnetic, contactor are in Fig 1, and Fig 2 shows the schematic, diagram of the contactor when used along with fused, switches (ICTP), push-button stations and OL relay for, connecting a squirrel cage motor for starting directly from, the main supply. In the same way the direct on-line starter, consists of a contactor, OL relay and push-button station, in an enclosure., Functional description, Power circuit: As in Fig 2, when the main ICTP switch is, closed and the contactor K1 is operated, all the three, 106, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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The overload current relay (bimetallic relay) protects the, motor from overload (`motor protection'), while the fuses, F1/F2/F3 protect the motor circuit in the event of, phase-to-phase or phase-to-frame short circuits., Control circuits, Push-button actuation from one operating location:, As shown in the complete circuit Fig 2, and the control, circuit Fig 3, when the `ON' push-button S3 is pressed, the, control circuit closes, the contactor coil is energised and, the contactor K1 closes. An auxiliary, a normally open, contact 13,14 is also actuated together with the main, contacts of K1. If this normally open contact is connected, in parallel with S3, it is called a self-holding auxiliary, contact., , After S3 is released, the current flows via this self-holding, contact 13,14, and the contactor remains closed. In order, to open the contactor, S2 must be actuated. If S3 and S2 are, actuated simultaneously, the contactor is unaffected., In the event of overloads in the power circuit, the normally, closed contact 95 and 96 of overload relay `O' opens, and, switches off the control circuit. Thereby K1 switches `OFF', the motor circuit., Once the contact between 95 and 96, is opened due to the, activation of the overload relay `O', the contacts stay open, and the motor cannot be started again by pushing the `ON', button S3. It has to be reset to normally closed position by, pushing the reset button. In certain starters, the reset, could be done by pushing the `OFF' button which is in line, with the overload relay `O'., Push-button actuation from two operating locations, (remote control): If it is desired to switch a contactor OFF, and ON from either of the two locations, the corresponding, OFF push-buttons should be connected in series, and the, ON push-buttons in parallel, as in the complete diagram, Fig 4 and the control diagram Fig 5., , Tripping of starters: A starter may trip due to the, following reasons., •, , Low voltage or failure of power supply, , •, , Persistent overload on the motor, , No-volt coil: A no-volt coil consists of generally more, number of turns of thin gauge of wire., Coil voltages: Selection of coils depends on the actual, supply voltage available. A wide variety of coil voltages like, 24V, 40V, 110V, 220 V 230/250 V, 380V 400/440V AC or, DC are available as standard for contactors and starters., Troubleshooting in contactor: Table 1 gives the common, symptoms their causes and remedies., , If either of the two ON push-buttons is actuated, K 1 is, energised and holds itself closed with the help of, normally-open contact 13 & 14 which is closed by contactor, K1. If either of the two OFF push -buttons is actuated, the, contactor opens., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 107

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Table 1, Symptoms, , Causes, , Remedies, , Motor does not start when the, 'start' button is pressed. However on, pressing the armature of the, contactor manually, motor starts, and runs., , Open in no-volt coil circuit., , Check the main voltage for lower, than acceptable value. Rectify the, main voltage. Check the control, circuit wiring for loose connection., Check the resistance of the no-volt, coil winding. If found incorrect, replace the coil., , Motor starts when `ON' button is, pressed. It however stops, immediately when `ON' button is, released., , Auxiliary contact in, parallel with the start-button, is not closing., , Check the parallel connection from, `ON' button terminals to the auxiliary, contact of the contactor., Rectify the defect., Check the auxiliary contact points, of the contactor for erosion and, pittings., Replace, if found defective., , Motor does start when the startbutton is pressed. However, a, humming or chattering noise comes, from the starter., , Movable armature and fixed, limb of electromagnet are, not stably attracted., , Dust or dirt or grit between the mating, surfaces of the electromagnetic core., Clean them., Low voltage supply. Find the cause, and rectify the defect., Break in the shading ring in the case, of AC magnet., , Failure of contactor due to too much, heating of the `No' volt coil., , Higher incoming supply rating., No-volt coil rating is not high., , Higher supply voltage than normal., Reduce the incoming voltage., Voltage rating of the no-volt coil is, less. Replace with standard rating,, according to the main supply., , Motor does not restart immediately, after tripping of OL relay even, though OL relay was reset., , It takes a little time for the thermal, bimetal to cool and reset., , Wait for 2 to 4 minutes before restarting., , Coil does not get energised even, though supply voltage is found, across the no-volt coil terminals., , Open-circuited NVC., NVC burnt out., , Check the nylon strip on relay., Check the nylon button below the, start button, Replace, if necessary., , Relay coil has been changed., However motor does not start, when the start-button is pressed., , Control circuit of relay open., , Check the control circuit for open., Clean the control station contacts., Overload relay not reset., , Humming or chattering noise., , Low voltage., Magnetic face between yoke, and armature is not clean., Shading ring on iron core missing., , Feed the rated voltage., Clean the surfaces of yoke and, armature., Provide shading ring in the iron core., , D.O.L. starter, A D.O.L. starter is one in which a contactor with no-volt, relay, ON and OFF buttons, and overload relay are, incorporated in an enclosure., Construction and operation: A push-button type, direct, on-line starter, which is in common use, is in, Fig 6. It is a simple starter which is inexpensive and easy, to install and maintain., 108, , There is no difference between the complete contactor, circuit explained in Exercise 4.2.175(i) and the, D.O.L.starter, except that the D.O.L. starter is enclosed, in a metal or PVC case, and in most cases, the no-volt coil, is rated for 415V and is to be connected across two, phases as in Fig 6. Further the overload relay can be, situated between ICTP switch and contactor,or between, the contactor and motor as in Fig 6, depending upon the, starter design. Trainees are advised to write the working of, the D.O.L. starter on their own by going through the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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explanation given in Exercise 4.2.175(i) which is for a, complete contactor circuit., , Forward and reversing of 3 phase induction motors, In many machines like large milling machine, it is, essential to run the motor in both directions in forward &, reverse. In lift also the forward & reverse operation is, essential., By changing the phase sequence of any two phases the, direction of rotation of a 3 phase motor can be changed but, it is not practically possible of interchanging any two, phases of 3 phase supply when even needed. It consumes, time and also damages the equipments., So it is necessary to have a circuit for forward and reversing, of 3 phase induction motors. (Fig 7), The supply terminal L1 is connected with motor terminal A1, in both direction of runing (Fig 7), Supply terminal L2 & L3 are connected with motor terminal, B1 & C1 in forward direction. While the reverse contact, energiser supply terminal L2 connected with motor terminal, C1 and L3 terminal connected with B1 thus the sequence of, phase changed the direction of rotation also changed., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 109

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The inter locking protection is in corporated by normally, closed (NC) contacts of forward and reverse contactors, (Fig 7b) By this when forward contactor is working, if, reverse push button is wrongly pressed, without any break, the motor run in same direction continuously., , The direction only can be changed by switch OFF and, press the reverse direction push button., , Table of relay ranges and back-up fuses for motor protection, Sl., No., , Motor ratings, 240V 1-phase, hp, , kW, , Full load, current, , 1, 2, , 0.05 0.04, , 3, 4, , Motor ratings, 415V 3-phase, , 0.125 0.11, , hp, , Relay range, A, , Nominal back-up, fuse recommended, , a, , c, , kW, , Full load, current, , 0.05 0.04, , 0.175, , 0.15 - 0.5, , 1A, , 0.1 0.075, , 0.28, , 0.25 - 0.4, , 2A, , 0.25 0.19, , 0.70, , 0.6 - 1.0, , 6A, , 0.50 0.37, , 1.2, , 1.0 - 1.6, , 6A, , 5, , 0.5, , 0.18, , 2.0, , 1.0, , 0.75, , 1.8, , 1.5 - 2.5, , 6A, , 6, , 0.5, , 0.4, , 3.6, , 1.5, , 1.1, , 2.6, , 2.5 - 4.0, , 10A, , 2.0, , 1.5, , 3.5, , 2.5 - 4.0, , 15A, , 2.5, , 1.8, , 4.8, , 4.0 - 6.5, , 15A, , 3.0, , 2.2, , 5.0, , 4.0 - 6.5, , 15A, , 6.0 - 10, , 20A, , 9.0 - 14.0, , 25A, , 10.0 - 16.0, , 35A., , 7, 8, , 0.75 0.55, , 9, 10, , 1.0, , 0.75, , 7.5, , 5.0, , 3.7, , 7.5, , 11, , 2.0, , 1.5, , 9.5, , 7.5, , 5.5, , 11.0, , 12, , 3.0, , 2.25, , 14, , 10.0, , 7.5, , 14, , Semi-automatic star-delta starter, The standard squirrel cage induction motors with both, ends of each of the three windings brought out (six, terminals) are known as star-delta motors. If the starter, used has the required number of properly wired contactors,, the motor can be started in star and run in delta., The proper use of manual star-delta starter demands a, special skill in handling the starter. The sluggish operation, of the manual lever often causes damage to the moving, and fixed contacts in a manual star-delta starter., The contactors are employed for making and breaking the, main line connections. Figure 8 shows the wiring diagram, and Fig 9 shows the line diagram of power circuit and the, control circuit., Operation: Refer to the control circuit and power circuit, diagrams shown in Fig 9a,9b. When the start button S2 is, pressed the contactor coil K3 energises through P4, P3 and, K1 normally closed contact 12 and 11. When K3 closes,, it opens the normally closed contact K3 between 11 and 12, and makes contact between 10 and 9 of K3. The mains, contactor K1 energies through P4, 10 and 9 of K3. Once K1, energises the NO contact of K1 point 8 and 7 establishes, a parallel path to K3 terminals 10 and 9., 110, , The star contactor K3 remains energised so long as the, start button is kept pressed. Once the start button is, released, the K3 coil gets de-energised. The K3 contact, cannot be operated because of the electrical interlock of, K1 and normally closed contacts between terminals 12, and 11., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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In star-delta motors all the winding are used and there are, no limiting devices such as resistors or auto-transformers., Star-delta motors are widely used on loads having high, inertia and a long acceleration period., Overload relay settings : Three overload relays are, provided on star-delta starters. These relays are used so, that they carry the motor winding current. This means that, the relay units must be selected on the basis of the, winding current, and not the delta connected full load, current. The motor name-plate indicates only the delta, connected full load current, divide this value by 1.73 to, obtain the winding current. Use this winding current as the, basis for selecting and setting the motor winding protection, relay., Operation : Fig 10a, 10b & 10c shows the line diagram, of the power circuit and the control circuit and alternative, form of control circuit of the automatic star-delta starter., Pressing the start button S-energises the star contactor, K3. (Current flows through K4 T NC terminals 15 & 16 and, K2 NC terminals 11 & 12). Once K3 energises the K3 NO, contact closes (terminals 23 & 24) and provide path for the, current to close the contactor K1. The closing of contactor, K1 establishes a parallel path to start button via K1 NO, terminals 23 & 24., Fig 11 shows the current direction and closing of contacts, as explained above., , When the K3 contactor get de-energised the normally, closed contact of K3 between terminals 11 and 12, establishes contact in the contactor K2 - coil circuit. The, delta contactor K2 closes., The operator has to observe the motor starting and, reaching 70% of the synchronous speed for satisfactory, starting and running of the induction motor., Figure 9c shows the alternative form of drawing control, circuit., Automatic star-delta starter, Applications : The primary application of star-delta motors, is for driving centrifugal chillers of large central airconditioning units for loads such as fans, blowers, pumps, or centrifuges, and for situations where a reduced starting, torque is necessary. A star-delta motor is also used, where a reduced starting current is required., Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 111

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Similarly Fig 12 shows the action taking place after the, timer relay operating the contact K4T., , Automatic star - delta starter with forward and, reverse control, Fig 13 shows the connections established while the motor, is running in delta with the contactors K1 and K2 closed., , 112, , It is a starter which is used to start the three phase motor, in star and after some pre-determined time it, automatically runs in delta either in forward or reverse, direction depends upon the requirement. Like all other, starters it reduces the starting current, protects the motor, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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from over load and disconnects the motor from supply, during power failure., The Fig 14 and 15 shows the power and control circuit of, the automatic star-delta starter with forward and reverse, operation., Its main components are, five numbers of power, contactors, one ON-delay timer, three numbers of push, buttons and one thermal over load relay (OLR). The five, power contactors are intended one each for forward, direction (C1), reverse direction (C2), main contactor (C3),, star contactor (C4) and delta contactor (C5)., Six numbers of indicator lamps are also used to indicate, the availability of the three supplies, availability control, voltage and to indicate whether the motor is running either, in forward or reverse direction. These neon indicators lamps, are to be mounted in the front door of the control panel, along with three push buttons., Three push buttons are intended one each for stop push, button with one NC (Normally Closed) contact, for forward, and for reverse operation with one NO (Normally Opened), contact., , The choosing of control circuit voltage and power depends, on the no volt coil rating of the contactor, whether it needs, AC or DC. Here a separate 415/240V, 200 VA control, transformer is used for control circuits., , The choice of contactor depends upon the type of supply, voltage, load power, load characteristics and duty cycles., The standed duty cycles of the contactors is given below., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 113

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For AC loads, AC1 - Resistive load switching example heaters and, furnace., AC2 - Resistive and inductive load starting and stopping, example slip ring induction motor., AC3- High inductive load switching and breaking for, continuous running operation., AC4- High inductive load switching and breaking with, frequent and short time operation i.e., intermediate, operation like inching and jogging examples cranes, lifts, and hoists., , 4 After some pre-determined time delay, the timer NC, get open causes the C4 to de-energize and the delta, contactor (C5) is getting energized though the NC, contact of C4. Now the motor is running in delta, connection in forward direction., 5 When the motor is running in the forward direction,, even by a mistake if the reverse push button (R) is, pressed the reverse contactor (C2) will not get the, control voltage because of the interlock NC contact of, C1 is connected in series with C2., , DC2- Starting and stopping of shunt motors., , 6 If the stop bush button (OFF) is pressed the C1, C3, and C5 contactors get de-energized simultaneously, and the motor stops. In other hand if either the OLTC, open due to over load or the supply fails, the motor, will stop. Then the motor could be started only by, pressing either forward or reverse push button as, required after resetting the OLTC and it could not get, started automatically even if the OLTC getting reset, after cooling down or the power resumes., , DC3- Starting and stopping with inching and braking, , Sequence of operations for reverse direction, , DC4- Starting and stopping of series motors., , 1 If the reverse push button (R) is pressed, the NVC (No, Volt Coil) of the reverse contactor (C2) get control voltage, through over load relay trip contact (OLTC), stop push, button and NC contact of the C1. Now the C2 energized, and get self holding through its own NO contact. So, even after releasing the "R" push button the C2 will, continuous in energized condition., , For DC loads, DC1- Resistive loads except motor load, , DC5- Starting and stopping of series motor with inching, and plugging., The auxiliary contact can be fitted to the top or to the, sides of the contactors depend its design., Working of starter : When the three phase supply is, switched ‘ON’ by the isolator switch (S) the indicator lamps, (L1, L2 and L3) will indicate the availability of supply, (Fig 14), the control transformer gets the supply through, MCB2 and the indicator lamp (L4) indicates the availability, of control voltage., Sequence of operations for forward direction, 1 If forward push button (F) is pressed, the NVC of the, forward contactor (C1) gets control voltage through over, load relay trip contact (OLTC), stop push button and, NC contact of the C2. Now the C1 energized and get, self holding through its own NO contact. So even after, releasing the 'F' push button the C1 will continuous in, energized condition., 2 The one more NO contact of C1 is closed, so the NVC, of the star contactor (C4) and timer get the control, supply simultaneously through the delta and timer NC, contact hence the C4 and timer (T) getting energized., 3 The NO contact of C4 closes and the NVC of the main, contactor (C3) getting energized. Now the motor is, started in star in forward direction and the main, contactor (C3) is getting self holding through its own, NO contact whereas the delta contactor (C5) will not, energize because of the NC contact of C4 which, connected in series with C5 is already in open, condition., , 114, , 2 The one more NO contact of C2 is closed, so the NVC, of the star contactor (C4) and timer get the control, supply simultaneously through the delta and timer NC, contact hence the C4 and timer (T) getting energized., 3 The NO contact of C4 closes and the NVC of the main, contactor (C3) getting energized. Now the motor is, started in star in reverse direction and the main, contactor (C3) is getting self holding through its own, NO contact whereas the delta contactor (C5) will not, energize because of the NC contact of C4 which, connected in series with C 5 is already in open, condition., 4 After some pre - determined time delay, the timer NC, get open causes the C4 to de-energize and the delta, contactor (C5) is getting energized through the NC, contact of C4. Now the motor is running in delta, connection in reverse direction., 5 When the motor is running in the reverse direction even, by a mistake if the forward push button (F) is pressed, the forward contactor (C1) will not get the control, voltage because of the interlock NC contact of C2 in, series with C1., 6 If the stop push button (OFF) is pressed the C2, C3, and C5 contactors get de-energized simultaneously, and the motor stops. In other hand if either the OLTC, open due to over load or the supply fails, the motor, will stop. Then the motor could be started only by, pressing either forward or reverse push button as, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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required after resetting the OLTC and it could not get, started automatically even if the OLTC getting reset, after cooling down or the power resumes., Jogging (inching): In some industrial applications, the, rotating part of a machine may have to be moved in small, increments. This could be done by a control system called, jogging (inching). Jogging is defined as the repeated, closure of the circuit to start a motor from rest, producing, small movements in the driven machine. By pressing the, jog push-button the magnetic starter is energised and the, motor runs; when the jog push-button is released, the, motor stops., When a jogging circuit is used, the motor can be energised, only as long as the jog-button is depressed. This means, the operator has instantaneous control of the motor drive., , The motor can be started or stopped by jogging/inching, the start button. The motor will operate as long as the, start-button is held pressed., , Purpose of jogging/inching controls: Normally jogging, (inching) controls are incorporated in the following machines, for operational convenience shown against each., , Jogging control using a push-button: Fig 18 shows the, control circuit of a D.O.L. starter connected to a, start-jog-stop push-button station. When the `ON', push-button is pressed, coil K is energised as the no-volt, coil circuit is complete through the normally closed `jog', button contacts 30 & 31, thereby closing the main contactor,, and the motor runs. The self-holding auxiliary contact K1, between terminals 13 and 14 gets closed, and keeps the, no-volt coil circuit in function though the `ON' button is, released., , •, , Lathe machine controls - for checking the trueness of, the job and setting the tool initially., , •, , Milling machine controls - for checking the concentric, running of the cutter at initial setting and also to set the, graduated collar for depth of feed of the cutter., , •, , Grinding machine controls - for checking proper, mounting of the wheel., , •, , Paper cutting machine - for adjusting the cut., , Apart from the above, the inch control is the prime control, in cranes, hoists and conveyor belt mechanism so that, incremental movements either vertically or horizontally, could be achieved in the driven machinery., Jogging may be accomplished by the following methods., •, , Selector switch, , •, , Push-button, , •, , Push-button with a jog relay, , Jogging control using a selector switch: By using a, selector switch, the existing start button can be used as, a jogging push-button in addition to its function as a, starting push-button. The holding contacts of the contactor, which are in parallel to the start-button are disconnected, and the selector switch is placed in the jog position as, shown by the circuit in Fig 16 and the panel layout in, Fig 17., , As soon as the jog push-button is pushed, as the circuit, of the no-volt coil opens initially, the contactor is, de-energised and the motor stops if it is running. Then the, jog-button closes the bottom contacts 32 & 33, thereby, the no-volt coil circuit closes and the motor runs as long, as the jog-button is held pressed. By pushing and releasing, the jog-button repeatedly, the motor starts and stops, causing the driven machinery to `inch' forward to the, desired position. On the other hand, pressing the, start-button will make the motor to run normally., Jogging control using a relay: Fig 19 shows the control, circuit of a D.O.L. starter connected to a control relay with, the other usual components. When the start button is, pressed, the control relay coil CR is energised and closes, the contacts R1 and R2, thereby momentarily completing, the no-volt coil `K' circuit through relay contact R2. This in, turn closes the self-holding auxiliary contact K1 of the, no-volt coil relay K, and the motor runs continuously even, though the pressure on the start-button is released., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 115

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Fig 20 show a typical industrial agitator used to remove, the sludge and improve the chemical properties of the, liquid or chemical before feeding to the process reactor. It, has the feeding pump, agitator and discharge pump. The, liquid to be treated is fed into the agitator tank through, the feed pump which is started manually., , When the motor is not running, if the jog-button is pressed, the no-volt coil, K circuit, is completed, and the motor runs, only as long as the jog-button is held pressed as the, holding circuit through R1 is not completed for the starter, coil as the control relay CR is not energised., For a 3-phase, D.O.L. starter having the jog control, through relay, four normally open contacts (3 for main and, 1 for auxiliary) are required and the control relay should, have two normally open contacts as in Fig 19., Sequential control of motors, It is a kind of multiple motor's control in a specified manner, by means of timer or limit switches or sensor depend the, requirements of industries or application., , After some time lapse the agitator motor starts by means, of timer and stir the liquid continuously till the level of the, liquid reaches the minimum level. When the liquid level in, agitator reaches the maximum level, the sensor or limit, switch installed in the tank is switched off the feed pump., , In this method generally the operation of two or more, individual motors are controlled with respect to the, specified time lapse or reaching of the specified level or, completion of the specified operation. The operation of, first motor will control the operation of the second or other, motors and operation of second motor will control the, operation of other motors and so on., , After specified time lapse of starting the agitator motor, the discharge motor is started by means of one more, timer and discharge the liquid to further process. When, the liquid level in agitator reaches the minimum level, the, sensor or limit switch installed in the tank is switched, OFF the discharge pump., , This type of the control system reduce the error due to, human and man power, increase the accuracy of the, operation cycle, minimize the ideal time of the machines, and increase the efficiency and production of the, industries., The example of such sequential control system might be, found in some of the industrial agitator system which, explained in details below., Industrial agitator, It is the machine consists of an electric motor along with, impeller in its long shaft and fitted in the agitator tank, which used in the chemical, food and pharmaceutical, process industries to, , The agitator also have the submerged aerator through, which the air is fed, a sludge discharge line with valve to, discharge unwanted sludge, minimum and maximum level, sensor or limit switches to maintain the liquid level in the, tank., A control panel with necessary wiring and protection are, designed and installed to control the sequential control of, all the three motors. The Fig 21 and 22 show the power, and control circuit of the sequential control of the typical, agitator system with three motors., All the three motors have individual power circuit of DOL, starter with over load and short circuit protection. The, total control panel has an isolation switch to ON and OFF, the supply. It has indicator lamps to indicate the availability, of the power supply and control supply and also indicates, the running status of feed pump, agitator motor and, discharge pump., , •, , Mix the different type of liquid or chemical, homogeneously., , •, , Improve the chemical properties of the liquid or, substance., , Sequence of operations of the sequential control of, the agitator system having three motors, , •, , Keep and stir the stored liquid in the specified heat, and properties., , When the start push button is pressed the NVC of the, feed pump motor contactor (C1) and timer 1 (T1) is getting, the control voltage through the stop push button, OLTC of, OLR1 and NC contact of the maximum level limit switch., , 116, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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Now the C1 and T1 energized and get self holding through, the NO contact C1. So even after releasing the 'start' push, button the C1 and T1 will continuously be in energized, condition., , After some pre-determined time lapse the NO contact of, the timer 1 closes and the NVC of the agitator motor, contactor (C2) and timer 2 (T2) get control voltage through, the minimum level limit switch and OLTC of OLR 2. Now, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished, , 117

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the C2 energized and get self holding through its own NO, contact. So even if the C1 if get de-energized due to, maximum level limit switch, the C2 will continuously be in, energized condition., , When the all the three motors are working, in case if the, OLTC of OLR1 opens the C1 will only get de-energized, and C2 and C3 continuously in energized condition through, the self holding contact of C2., , After the some time lapse the NO contact of the timer 2, closes and the NVC of the discharge pump motor, contactor (C3) is getting the control voltage and get, energized., , In case if the OLTC of OLR 2 opens due to over load the, C2 will only get de-energized if the C1 is in energized, condition. In other hand if the C1 is already of OFF condition, due to activation of maximum level limit switch, the C3, also will get de-energized., , If the liquid level of the agitator reduces to the minimum,, the NO contact of the minimum level limit switch open, causes C2 and C3 get de-energized., , 118, , In case if the OLTC of the OLR3 opens due to over load, the C3 alone will get de-energized., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.175 to 4.2.177, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.2.178 & 4.2.179, Electrician - Control Panel Wiring, Installation of instruments and sensors in control panel and its performance, testing, Objectives: At the end of this lesson you shall be able to, • state the sensor main specification, application necessity and types, • state the specification and types of sensors required in panel board, • explain the performance testing of panel control board., Instruments in panel board, Industrial operation for any process requires many, machines, apparatus for usual supply and maintain, continuous production. Some machines requires operator, always to operate many control on process for example a, lathe machine is required always its operator assistance, to do different job, turning, shaping etc, but in some cases, the machine not required continuous manual operator for, single job operations., In a workshop AC motor or DC motor is to operate for many, of its intended job. Once the machine starts it will continue, to work for its assigned job and requires only ON and OFF, operation. This operation may need many job completion, in different places located in the work shop. This operation, has to be controlled and monitored in time intervels and a, constant watch also may require., The instruments are used to measure the electrical, quantities, which in turn gives the feed back of load, conditions and performance. A motor draws a constant, current, which can monitor by a ammeter connected to, them similarly the rated voltage, frequency, power factor, etc, are also to be checked through the meters. If number, of machines and meters are more it is difficult to watch the, parameters individual places. A panel board having this, meters are installed helps to collect the data at one place, where different machines are working., Selection of meters are in accordence with the machine, ratings and working voltage limits. A low range meter, cannot be connected in a heavy load machine for its, readings it may damage the meter and its wiring., Sensors types, classification and its application, Sensors is a device that detects/measures a physical, quantity. A motor is running with its rated rpm but some, cases load variations on motor affects the rpm. The quality, of the product may depend on the machine accuracy, then, it is very important to run the motor at its rated rpm., Automatic rpm correction is possible with relevant circuits, but a sensor has to feed back the working rpm to the, control circuit. In this case a Tacho generator is the device, to produce the feed back of rpm of motor. Tacho generator, can be fixed on the shaft of the motor and the resultant feed, back quantity(V or I) can be brought to the control panel, board., , Similarly, the temperature measurement also can be done, by suitable sensors. Since the temperature is the big, problem for all electrical applications, a constant watch on, the temperature helps to increase the life of the machine, and a uniform production with specified quality. In this way, temperature can be controlled by installing suitable sensor, preferably with a thermistor-PTC or NTC will help to control, the temperature within safe limits. The sensor element will, kept in the winding and the cable is brought up in the, control panel, to connect the temperature indicating unit, for indication., A sensor is a special kind of transducer which is used to, generate an input single to a measurement,, instrumentation or control system. The signal produced, by a sensor in an electrical analogy of a physical quantity,, like acceleration, temperature, pressure, distance,, velocity, light, level etc., Types of sensors: There are two types of sensors, a) Passive sensor, b) Active sensor., a) Active sensor: Self generating sensor is that one can, generate a signal without any external power source., Eg. photovoltaic cell, thermo couple, piezoelectric, device ., b) Passive sensor: It requires external power supply to, generate the signal. Eg. Diaphragm used to convert, pressure or velocity, oscillations, or sound wave's into, movements of a solid sheet., Classification of sensors: It is classified into many, categories according to the output, application etc. It is, mainly divided into two groups, they are; a) Digital sensor, and b) Analog sensor., Digital sensor: The resolution of this sensor is most, accurate and maximum speed. Its ability to detect a, change in the sensed quantity is excellent. The output is, always taken as 180, high and low, or yes or no., Analog sensor: The resolution of this sensor in less, accurate corporate to digital and it records very small, changes or variations resulting more error. It is usually, used to record very small changes, or variations., , Copyright @ NIMI Not to be Republished, , 119

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Further, the sensors are mainly used to measure, temperature and RPM in the electrical circuits. The, following sensors are used to measure temperature. They, are;, a) Thermo couple, b) RTD (Resistance Temperature Detector), c) Thermistor, d) IR sensors (Infra Red), e) Semi conductor sensors - VDR, LDR, Photo diode, etc.,, The sensors used to measure RPM of motor; are in, different types; they are, a) Shaft encoders (rotary type) 1-5000 pulses, b) Photoelectric (optical type), c) Magnetic rotational speed (proximity type) - medium, or low RPM., d) Photo sensor reflection target- Tachometer - 20-20,000, range, Sensor assembly and measurements, Temperature measurement using resistance temperature, detector (RTD) and 1 assembly with position adjustment,, tachometer sensor assembly and a AC tachometer, generator is in Fig 1. The AC is rectified by a bridge circuit., The amplitude and frequency of the induced emf are, equivalent to the speed of the shaft. Thus either amplitude, or frequency is used for measuring the angular velocity., Performance testing of panel board, , The panel board should be earthed properly and all metal, parts have to be connected to earth. If the current in the, panel board is heavy; a separate earthing has to be, provided and maintained within the standard., Connection to machine from panel board has to be made, on short as possible. If the machine draws less current,, line drop will be minimum and resultant power is low hence, in cable is also low and even negligible. If the connecting, cable length is much more than line loss will be too high, and it will turn shorten the life of machine and cables, connected. Running of cable can be made as per the, situation and facilities. Keep away from direct sun light wet, condition, and near fire or any other polluted areas., A simple model panel board to the load power is given for, your guidance in Fig 2., , It is important to see that the panel board is to install, carefully as it carrys a number of connection and controls., Any loose connection or wrong connection to any device, will affect the performance and it may cost more., While testing the performance make sure that all, connections and wiring are correct and as per IE rules., Wrong connection and substandard materials will cause, heavy damage to the panel board. The continuity of cable,, earth resistance values are to be kept in the safe level as, per IE rule normal., , 120, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.2.178 & 4.2.179, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - AC/DC Motor Drives, , Related Theory for Exercise 4.3.180, , AC/DC drives, Objectives: At the end of this lesson you shall be able to, • state the classification and working of AC & DC drives, • state the applications of AC & DC drives, • describe the block diagram, parts of DC drive and advantages and disadvantages of DC drives., Electrical drives, , -, , An electric drive can be defined as an electromechanical, device for converting electrical energy into mechanical, energy to feed motion to different machines and, mechanisms for various kinds of process control., Motion control is required in large number of industrial, and domestic applications like transportation, systems,, rolling mills, paper machines, textile mills, machine tools,, fans, pumps, robots, washing machines etc., Systems employed for motion control are called Drives,, and may employ any of prime movers such as diesel or, petrol engines, gas or steam turbines, steam engines,, hydraulic motors and electric motors; Supplying, mechanical energy for motion control Drives employing, electric motors are known as Electrical drives., Classification of electric drives, i, , According to mode of operation, , -, , Continuous duty drives, , -, , Short time duty drives, , -, , Intermittent duty drives, , Reversible and non - reversible smooth speed control, , Advantage of electrical drives, 1 They have flexible control characteristics., 2 Drives can be provided with automatic fault detection, systems. Programmable logic controller (PLC) and, computers can be employed to automatically control, the drive operation in a desired sequence., 3 They are available in wide range of torque, speed and, power., 4 They are suitable to almost any operating conditions, such as explosive and radioactive environments., 5 It can operate in all the four quadrants of speed - torque, plane., 6 They can be started instantly and can immediately be, fully loaded., 7 Control gear requirement for speed control, starting, and braking is usually simple and easy to operate., Choice (or) selection of electrical drives, -, , Choice of an electric drive depends on the important, factors are., , -, , Manual, , -, , Semi automatic, , 1 Steady state operating conditions requirements., Nature of speed torque characteristics, speed, regulation, speed range, efficiency, duty cycle,, quadrants of operation, speed fluctuations if any, rating, etc., , -, , Automatic, , 2 Transient operation requirements, , ii According to means of control, , iii According to number of machines, -, , Individual drive, , -, , Group drive, , -, , Multi - motor drive, , 3 Values of acceleration and deceleration, starting,, braking and reversing performance., , iv According to dynamics and transients, , 4 Requirements related to the source. Types of source, and its capacity, magnitude of voltage, voltage, fluctuations, power factor, harmonics and their effect, on other loads, ability to accept regenerative power., , -, , Uncontrolled transient period, , 5 Space and weight restriction if any., , -, , Controlled transient period, , 6 Environment and location., , V According to methods of speed control, , 7 Reliability, , -, , Reversible and non - reversible uncontrolled constant, speed, , Group electric drive, , -, , Reversible and non - reversible step speed control, , -, , Variable position control, , This drive consists of a single motor, which drives one or, more line shafts supported on bearings. The line shaft, may be fitted with either pulleys and belts or gears, by, means of which a group of machines or mechanisms, , Copyright @ NIMI Not to be Republished, , 121

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may be operated. It is also some times called as shaft, drives., Advantages, , Special machines, Brush less DC motors, stepper motors, switched, reluctance motors are used., , A single large motor can be used instead of number of, small motors., , Power Modulators (Controller), , Disadvantages, , •, , It modulates flow or power from the source to the, motor is imparted speed - torque characteristics, required by the load., , •, , During transient operation, such as starting, braking, and speed reversal, it reduces the motor current with, in permissible limits., , •, , It converts electrical energy of the source in the from, of suitable to the motor., , •, , It selects the mode of operation of the motor (i.e), motoring and braking., , There is no flexibility. If the single motor used, develops, fault, the whole process will be stopped., , Functions, , Individual electric drive, In this drive each individual machine is driven by a separate, motor. This motor also imparts motion to various parts of, the machine., Multi motor electric drive : In this drive system, there, are several drives, each of which serves to actuate one of, the working parts of the drive mechanisms., , Types of power modulators (Controllers), -, , In the electric drive system, the power modulators can, be any one of the following., , Paper making industries., , -, , Controlled rectifiers (AC to DC converter ), , Rolling machines etc., , -, , Inverters (DC to AC converters), , A modern variable speed electrical drive system has the, following components, , -, , AC voltage controllers (AC to DC converters), , -, , DC choppers (DC to DC converters ), , -, , Electrical machines and loads, , -, , Cyclo converters (Frequency conversion), , -, , Power modulator, , -, , Sources, , -, , Control unit, , -, , Sensing unit, , e.g : Complicated metal cutting machine tools, , Electrical sources, , Electrical machine, Most commonly used electrical machines for speed control, applications are the following., , Very low power drives are generally fed from single phase, sources. Rest of the drives is powered from a 3-phase, source. Low and medium power motors are fed from a, 415V supply. For higher ratings, motors may be rated at, 3.3KV, 6.6 KV and 11 KV. Some drives are powered from, battery., Sensing unit, , DC machines, , -, , Speed sensing (from motor), , Shunt, series, compound, DC motors and switched, reluctance machines., , -, , Torque sensing, , -, , Position sensing, , AC machines, , -, , Current sensing and voltage sensing (from lines or from, motor terminals from load), , Induction, wound rotor, synchronous, permanent magnet, synchronous and synchronous reluctance machines., , -, , Temperature sensing, , Control unit, Control unit for a power modulator are provided in the, control unit. It matches the motor and power converter to, meet the load requirements., , 122, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.180, , Copyright @ NIMI Not to be Republished

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Comparison between DC and AC drives, DC Drives, , AC Drives, , The power circuit and control circuit are simple, , The power circuit and control circuit are complicated, , It requires frequent maintenance, , Less maintenance, , The commutator makes the motor bulky, costly,, and heavy, , These problems are not there in these motors and, are inexpensive, particularly squirrel motors, , Fast response and wide speed range of control, can, be achieved smoothly by conventional and solid, state control, , In solid state control the speed range is wide and, conventional method is stepped and limited, , Speed and design ratings are limited due to, commutations, , Speed and design ratings have upper limits, , Applications, , And also, the armature current is proportional to the motor, , •, , Paper mills, , •, , Cement mills, , Eb, torque. N ∝ I and Ia ∝ T Therefore, by increasing or, f, , •, , Textile mills, , •, , Sugar mills, , •, , Steel mills, , •, , Electric traction, , •, , Petrochemical industries, , •, , Electrical vehicles, , reducing the applied voltage, the speed of the motor is, varied. However, it is possible up to the rated voltage. If, the speed greater than the base speed is required, the, field current of the motor has to be reduced., , Another one type of electric drive is ‘Eddycurrent drive’, Eddy current drives, An eddy current drive consists of a fixed speed motor, and an eddy current clutch. The clutch contains a fixed, speed rotor and an adjustable speed rotor separated by a, small air gap. A direct current in a field coil produce a, magnetic field that determines the torque transmitted from, the input rotor to the output rotor. The controller provides, closed loop speed regulation by varying clutch current,, only allowing the clutch to transmit enough torque to, operate at the desired speed. Speed feedback is typically, provided via an integral AC tachometer., Eddy current drives are slip - controlled systems the slip, energy of which is necessarily all dissipated as heat. Such, drives are therefore generally less efficient than AC/DCAC conversion based drives. The motor develops the, torque required by the load and operates at full speed., The power is proportinoal to torque multiplied by speed., The input power is proportional to motor speed and times,, operating torque while the output power is output speed, and times operating torque. The difference between the, motor speed and the output speed is called the slip, speed. Power proportional to the slip speed times, operating torque is dissipated as heat in the clutch., Working principle of DC drives, In DC motors, the speed is proportional to the armature, voltage and inversely proportional to the field current ., , By reducing the field current, the flux in the motor reduces, and it reduces the armature counter emf. Further, this, armature current increases the motor torque and the speed, will increase. These are the two basic principles employed, in DC drives to control the speed of the motor., In armature controlled DC drives, by varying the armature, voltage, variable speed is obtained as in Fig 1., , Generally, a fixed field supply is provided in these DC, drives. As the torque is constant (which describes a load, type) over the speed range, the motor output horse power, is proportional to the speed. The motor characteristics of, this drive are in Fig 1., Constant torque operation, In case of armature and field controlled drives, the armature, voltage to the motor is controlled for constant torquevariable HP operation up to the base speed of the motor., And for the above base speed operation, drive switches, to the field control for constant HP- reduced torque, operation up to maximum speed as in Fig 2 In this case,, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.180, , Copyright @ NIMI Not to be Republished, , 123

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reducing the field current increases the speed of the motor, up to its maximum speed as in Fig 2., , with a three phase incoming supply is used. During each, quadrant operation, SCRs are triggered at a phase angle, in order to provide required DC voltage to the motor., Drive operation, The drive applications can be categorized as single quadrant, two - quadrant, three-quadrant or four- quadrant;, the chart’s four quadrants (Fig 3) are defined as follows., , In most instances the shunt field winding is excited, with, a constant - level voltage from the controller . The SCR, (silicon controller rectifier), also known as thyristor, which, converts the alternating current (AC) of the power source, to variable DC output which is applied to the armature of, a DC motor. Speed control is achieved by regulating the, armature voltage to the motor., A thyristor bridge is a technique commonly used to control, the speed of a DC motor by varying the DC voltage., Important to note that the voltage applied to a DC motor, can not be greater than the rated name plate voltage., The tachometer ( feedback device) converts actual speed, in to an electrical signal that is summed with the desired, reference signal. The output of the summing junction, provides an error signal to the controller and a speed, correction is made., In modern DC drives, SCRs are completely replaced, by MOSFET s and IGBTs in order to achieve high speed, switching so that distortion to the AC incoming power, and currents during switching is eliminated. Hence, the, drive becomes more efficient and accurate., Silicon controlled rectifier (SCRs) are widely used, thyristors for large DC motor drives in its power conversion, unit. An SCR conducts when a small voltage applied to, its gate terminal. Its conduction continues till the starting, of negative cycle and it turned OFF automatically once, the voltage across the SCR goes through natural zero till, next gated signal., The purpose of using these SCRs in DC drives is to convert, the fixed AC supply to variable DC supply that controls, the motor speed. Some SCR DC drives are supplied, from single phase AC supply and use four SCRs in the, form of bridge for the DC rectification. In case of high, power DC drives, a three phase supply with six SCRs is, used for DC rectification., In case of four quadrant operation (forward motoring,, forward braking, reverse motoring and reverse braking) of, the DC drive, a bridge rectifier consisting of 12 SCRs, 124, , Quadrant I : Driving or motoring forward accelerating, quadrant with positive speed and torque, Quadrant II : Generating or braking, forward brakingdecelerating quadrant with positive speed and negative, torque., Quadrant III: Driving or motoring, reverse accelerating, quadrant with negative speed and torque., Quadrant IV : Generating or braking, reverse braking decelerating quadrant with negative speed and positive, torque., Most applications involve single quadrant loads operating, in quadrant I, such as in variable - torque (e.g. centrifugal, pumps or fans. etc., Certain applications involve two - quadrant loads operating, in quadrant I and II where the speed is positive but the, torque changes polarity Some sources define two quadrant drives as loads operating in quadrants I and III, where the speed and torque is same (positive or negative), polarity in both directions., Certain high - performance applications involve four quadrant loads (Quadrants I to IV) where the speed and, torque can be in any direction such as in hoists, elevators, and hilly conveyors. Regeneration can occur only in the, drive’s DC link bus when inverter voltage is smaller in, magnitude than the motor back - EMF and inverter voltage, and back - EMF are the same polarity., The connection of SCRs for four quadrant operation of, the drive) from incoming three phase AC supply to the DC, output is in Fig 4. In this, the motoring SCR bridge and, regeneration SCR bridge achieve the drive four quadrant, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.180, , Copyright @ NIMI Not to be Republished

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operation by receiving the appropriate gate signals from, (analog or digital) controller., , If the SCRs were gated with a phase angle of zero, degrees, then the drive function as a rectifier which feeds, the full rectified rated DC supply to the motor and by, varying the firing angle to the SCRs, a variable DC supply, is applied to the motor., The DC output voltage waveform is related to the AC, waveform for above circuit is in Fig.5. This average DC, output voltage is obtained for 40°, 32° and 24° firing phase, angles. By this way, the average output is controlled by, varying the firing phase angles to the SCRs., , Rectifier Bridge : The power component of a controlled, DC drive is a full wave bridge rectifier which can be driven, by three phase or single phase supply. As mentioned, above the number of thyristor may vary depends on the, supply voltage., A six - thyristor bridge (in case of three phase converter), rectifies the incoming AC supply to DC supply to the motor, armature. The firing angle control of these thyristors varies, the voltage to the motor., Field Supply Unit (FSU) : The power is to be applied to, the field winding is much lower than the armature power., In many cases a two - phase supply is drawn from the, three phase input (that supplies power to the armature), and hence the field exciter is included in the armature, supply unit., The function of the field supply unit is to provide a constant, voltage to the field winding to create a constant field or, flux in the motor. In some cases, this unit is supplied, with thyristors to reduce the voltage applied to the field, so as to control the speed of the motor above the base, speed incase of permanent magnet DC motors, the field, supply unit is not included in the drive., , As the field winding also requires the regulated DC supply,, only four SCRs are used in the field bridge converter. This, is because field never requires a negative current and, hence another set of SCRs is not required, which were, used in armature for reversing the motor., Block diagram of DC drive, The block diagram of a DC drive system is in Fig 6, DC drive input : Some thyristor based DC drives operate, on a single phase supply and use four thyristors for full, wave rectification. For larger motors 3 phase power supply, is needed because the waveforms are much smoother. In, such cases, six thyristors are needed for full wave, rectification., , Speed Regulation unit : It compares the operator, instruction (desired speed) with feedback signals and, sends appropriate signals to the firing circuit. In analog, drives, this regulator unit consists of both voltage and, current regulators. The voltage regulator accepts the, speed error as input and produces the voltage output, which is then applied to the current regulator., The current regulator then produces required firing current, to the firing circuit. If more speed is required, additional, current is drawn from the voltage regulator and hence, thyristors conduct for more periods. Generally, this, regulation (both voltage and current) is accomplished with, proportional -integral- derivative controllers., The field current regulator is also provided where speed, greater than the base speed is required., Parts of DC drive, DC drives of various brands with different ratings are, available in the market. It is generally assembled in a, metallic enclosure. The front panel has the power terminals,, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.180, , Copyright @ NIMI Not to be Republished, , 125

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control terminals, keypad for controlling the drive etc. It, has provision for connecting to PC for programming the, drive., , B0 & B1 are meant for armature and field connections, respectively. Names and locations are illustrated in Fig 8, , The main parts of DC drive are given below.(Fig 7), , Advantages of DC drive, 1 Main drive assembly, 2 Terminal cover, 3 Terminal cover retaining screw, 4 Blank cover, , •, , DC drives are less complex with a single power, conversion from AC to DC., , •, , DC drives are normally less expensive for most, horsepower ratings., , •, , DC motors have a long tradition of use as adjustable, speed machines and a wide range of options have, evolved for this purpose., , •, , Cooling blowers and inlet air flanges provide cooling, air for a wide speed range at constant torque., , •, , Accessory mounting flanges and kits for mounting, feedback tachometers and encoders., , •, , DC regenerative drives are available for applications, requiring continuous regeneration for overhauling loads., AC drives with this capability would be more complex, and expensive., , •, , Properly applied brush and commutator maintenance, is minimum., , •, , DC motors are capable of providing starting and, accelerating torques in excess of 400% of rated value., , •, , Some AC drives may produce audible motor noise, which is undesirable in some applications., , 5 Keypad, 6 COMMS technology box (optional), 7 Speed feedback technology card ( optional), 8 Gland plate, 9 Power terminal shield, 10 Power terminals, 11 Control terminals, 12 Earthing / grounding points, 13 Keypad part, 14 Programming part, 15 Auxiliary power, external contactor, blower and isolated, thermistor terminals, Power and control terminals, In DC drive, the front panel has the power terminals L1,, L2 and L3 where 3 phase input supply of 415V can be, connected., , Disadvantages of DC drive, •, , More complicated because of commutators and, brushes., , There are control terminals given for speed adjust, potentiometer, Torque adjust potentiometer, START/RUN/, STOP switch, JOG/RUN/ switch, AUTO/MAN switch,, FORWARD/REVERSE switch etc. Terminal A1 & A2 and, , •, , Heavier than AC motors., , •, , High maintenance is required., , •, , Large and more expensive than AC drive., , •, , Not suitable for high speed operation., , 126, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.180, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.3.181 & 4.3.182, Electrician - AC/DC Motor Drives, Speed control of 3 phase induction motor by VVVF/AC drive, Objectives: At the end of this lesson you shall be able to, • state about AC drives (VFD/VVFD) and changing of speed of AC motor by AC drive, • explain the operation of AC drive with block diagram, • list out the advantages and disadvantages of AC drive, • explain the components / parts and power and control terminals of AC drive, • state the parameter setting - speed control changes of direction of AC & DC drives / VFD/VVVFD (variable, frequency drive/ variable voltage variable frequency drive), • state the speed control of universal motor., Variable Voltage Variable Frequency Drive (VVVFD), , Constant V/F ratio operation, , The AC drive industry is growing rapidly and it is now, more important than ever for technicians and maintenance, personnel to keep AC drive installations running smoothly., AC drives change the speed of AC motor by changing, voltage and frequency of the power supplied to the AC, motor. In order to maintain proper power factor and reduce, excessive heating of the motor, the name plate volts /, hertz ratio must be maintained. This is the main task of, VFD (Variable frequency drive)., , If the same voltage is applied at the reduced frequency,, the magnetic flux would increase and saturate the, magnetic core, significantly distorting the motor, performance. The magnetic saturation can be avoided by, keeping the φm constant., , Applications of AC drives, 1 AC drives are used to stepless speed control of squirrel, cage induction motors mostly used in process plants, due to its ruggedness and maintenance free long life., 2 AC drives control the speed of AC motor by varying, output voltage and frequency through sophisticated, microprocessor controlled electronics device., 3 AC drive consists of rectifier and inverter units. Rectifier, converts AC to DC voltage and inverter converts DC, voltage back to AC voltage., Changing of speed of AC motors by using AC drive, From the AC motor working principle, that the synchronous, speed of motor Ns in rpm, is dependent upon frequency., Therefore by varying the frequency of the power supply, through AC drive, it can control the synchronous speed., Speed (rpm) = Frequency (Hertz) x 120 / No. of poles., Where, Frequency = Electrical frequency of the power supply in, Hz., No. of poles = Number of electrical poles in the, motor stator. Thus the speed of AC motor can conveniently, be adjusted by changing the frequency applied to the, motor. There is also another way to make the AC motor, work on different speed by changing the no. of poles, but, this change would be a physical change of the motor., The VFD provides the controls over frequency and voltage, of motor input to change the speed of a motor. Since the, frequency is easily variable as compared with the poles, variation of the motor. AC drives are frequently used., , All AC drives maintain the voltage -to- frequency (V/F), ratio constant at all speeds for the reason that follows., The phase voltage V, frequency F and the magnetic flux φ, of motor are related by the equation., V=4.444 f N φm, or, V/f = 4.444x N φm, Where N = number of turns per phase, φm = magnetic flux, Moreover, the AC motor torque is the product of stator, flux and rotor current. For maintaining the rated torque at, all speeds the constant flux must be maintained at its, rated value, which is basically done by keeping the voltage, - to - frequency (V/f) ratio constant., An AC drive is capable of operating a motor with constant, flux (Φ) from approximately zero (0) to the motor’s rated, nameplate frequency (typically 50Hz). This is the constant, torque range. As long as a constant volts per hertz ratio, is maintained the motor will have constant torque, characteristics. AC drives change frequency to vary the, speed of a motor and voltage proportionately to maintain, constant flux. The Fig1 is the graph illustrates the volts, per hertz ratio of a 415 volt, 50 hertz motor. To operate, the 415 volt motor at 50% speed with the correct ratio,, the applied voltage and frequency would be 207.5V volts,, 25 Hz. The voltage and frequency ratio can be maintained, for any speed up to 50Hz. This usually defines the upper, limits of the constant torque range., Some applications require the motor to be operated above, base speed. The nature of these applications requires, less torque at higher speeds. Voltage, however, cannot, be higher than the available supply voltage. This can be, , Copyright @ NIMI Not to be Republished, , 127

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illustrated as in Fig 2. Voltage will remain as 415 volts for, any speed above 50Hz. A motor operated above its rated, frequency is operating in a region known as a constant, horsepower. Constant volts per hertz and torque is, maintained up to 50Hz. Above 50Hz the volts per hertz, ratio decreases. The V/Hz ratio at 25 Hz is 8.3, at 50Hz, is 8.3, at 70Hz is 5.93 and at 90Hz is 4.61. Flux (Φ) and, torque (T) decrease. Operation of the motors above rated, nameplate speed (base speed) is possible, but is limited, to conditions that do not require more power than the, nameplate rating of the motor. This is sometimes called, “field weakening” and, for AC motors, means operating at, less than rated V/Hz and above rated nameplate speed., , prevent the device from turning on. So the gate can control, the switching on/off operation of an IGBT., Fig 3 shows the block diagram of AC drive and Fig 4, shows the internal connection diagram. There are three, basic sections of the AC drive; the rectifier, DC bus, and, inverter., , The rectifier in an AC drive is used to convert incoming, AC power into direct current (DC) power. Rectifiers may, utilize diodes, silicon controlled rectifiers (SCR), or, transistors to rectify power . An AC drive using transistors, in the rectifier section is said to have an “active front end., , Block diagram of AC drive, The Insulated - Gate - Bipolar- Transistor (IGBT) is in the, past two decades come to dominate VFD as an inverter, switching device., IGBTs (insulated gate bipolar transistor) provide a high, switching speed necessary for PWM (Pulse width, Modulation) inverter operation. IGBTs are capable of, switching ON and OFF several thousand times a second., An IGBT can turn on in less than 400 nanoseconds and, off in approximately 500 nanoseconds. An IGBT consists, of a gate, collector and an emitter. When a positive voltage, (typically +15 VDC) is applied to the gate the IGBT will, turn on. This is similar to closing a switch. Current will, flow between the collector and emitter., An IGBT is turned off by removing the positive voltage, from the gate. During the off state the IGBT gate voltage, is normally held at a small negative voltage (-15 VDC) to, 128, , After the power flows through the rectifiers it is stored on, a DC bus. The DC bus contains capacitors to accept, power from the rectifier, store it, and later deliver that power, through the inverter section. The DC bus may also contain, inductors, DC links, chokes, or similar items that add, inductance, thereby smoothing the incoming power supply, to the DC bus., Inverter : An inverter is a device which converts DC into, AC. The inverter contains transistors that deliver power, to the motor. The “Insulated Gate Bipolar Transistor” (IGBT), is a common selection in modern AC drives. The IGBT, can switch on and off several thousand times per second, and precisely control the power delivered to the motor., The IGBT uses a method named “Pulse Width Modulation”, (PWM) to simulate a current sine wave at the desired, frequency to the motor., The following example, explains how one phase of a threephase output is developed and controlled. Switches, replace the IGBTs for convenience. A voltage that, alternates between positive and negative is developed by, opening and closing switches in a specific sequence. For, example, during steps one and two A+ and B- are closed., The output voltage between and A and B is positive. During, step three A+ and B+ are closed. The difference of, potential from A to B is zero. The output voltage is zero., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished

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During step four and five A- and B+ are closed. The output, voltage from A to B is negative. During step 6. A- and Bclosed. The difference of potential A to B is again zero., The same action from step 1 to 6 is repeated from step 7, onwards. This will continue. The Fig 5 shows the internal, connection of inverter which converts DC into AC. The, Fig 6 shows the output wave form of inverter. Only one, single waveform due to switching action between A and B, is shown. There are other two waveforms between B & C, and A & C together which form a 3 phase AC supply. The, magnitude and frequency of output voltage is dependent, on the speed of the switching action of IGBTs., , Special AC motor enclosure types are more readily, available at lower prices., •, , Multiple motors in a system must operate, simultaneously at a common frequency/speed., , Disadvantages, •, , A standard motor can not adequately cool its winding, at slow speed or handle the irregular electrical, waveform from the AC drive., , •, , An AC drive requires installation of motor with heavier, windings., , •, , AC drive has complicated electronics circuit, so fault, rectification is costly., , •, , AC drives produce a simulated waveform, not a perfect, sine wave. That degrade the power equality., , Components of AC drive, A variable frequency drive is a device used in a drive system, consisting of the following three main sub-systems. AC, motor, main drive controller assembly, and drive / operator, interface as in Fig 7., , AC motor, , Advantages and disadvantages of AC drive, Advantages, •, , They use conventional low cost 3 phase AC induction, motors for most applications, , •, , AC motors require virtually no maintenance and are, preferred for application where the motor is mounted, in an area not easily reached for servicing or, replacement., , •, , AC motors are smaller, lighter, more commonly, available and less expensive than DC motors., , •, , AC motors are better suited for high speed operation, (over 2500 rpm) since there are no brushes, and, commutation is not a problem., , •, , Whenever the operating environment is wet, corrosive, or explosive, special motor enclosures are required., , The AC electric motor used in a VFD system is usually, three - phase induction motor. Some types of single phase motors can be used, but three - phase motors are, usually preferred. Various types of synchronous motors, offer advantages in some situations, but three - phase, induction motors are suitable for most purposes and are, generally the most economical motor choice. Motors that, are designed for fixed - speed operation are often used., Elevated - voltage stresses imposed on induction motors, that are supplied by VFDs require that such motors are, designed for definite - purpose inverter-fed duty., Controller, The VFD controller is a solid - state power electronics, conversion, system consisting of three distinct subsystems, a rectifier bridge converter, a direct current (DC), link, and an inverter. Voltage - source inverter (VSI) drives, are the most common type of drives. Most drives are AC, to AC drives in that they convert AC line input to AC inverter, output. However, in some applications such as common, DC bus or solar applications, drives are configured as, DC-AC drives. The most basic rectifier converter for the, VSI drive is configured as a three -phase, six -pulse, fullwave diode bridge., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished, , 129

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In a VSI drive, the DC link consists of a capacitor which, smooths out the converter’s DC output ripple and provides, a stiff input to the inverter. This filtered DC voltage is, converted to quasi-sinusoidal AC voltage output using the, inverter’s active switching elements. VSI drives provide, higher power factor and lower harmonic distortion than, phase- controlled current - source inverter (CSI) and load, - commutated inverter (LCI) drives., In variable -torque applications suited for volts - per- Hertz, (V/Hz) drive control. AC motor characteristics require that, the voltage magnitude of the inverter’s output to the motor, be adjusted to match the required load torque in a linear, V/Hz relationship. For example, 415V, 50Hz motors, this, linear V/Hz relationship is 415/50=8.3V/Hz., Although space vector pulse- width modulation (SVPWM), is becoming increasingly popular, sinusoidal PWM, (SPWM) is the most straight forward method used to vary, drives motor voltage ( or current) and frequency. With, SPWM control quasi- sinusoidal, variable - pulse-width, output is constructed from intersections of a saw-toothed, carrier signal with a modulating sinusoidal signal which, is variable in operating frequency as well as in voltage (or, current)., , a motor to develop 150% of its rated torque while the, VFD is drawing less than 50% of its rated current from, the mains in the low - speed range. A VFD can be adjusted, to produce a steady 150% starting torque from standstill, right up to full speed. However, motor cooling deteriorates, and can result in overheating as speed decreases such, that prolonged low -speed operation with significant torque, is not usually possible without separately motorized fan, ventilation., With a VFD, the stopping sequence is just the opposite, as the starting sequence. The frequency and voltage, applied to the motor are ramped down at a controlled, rate. When the frequency approaches zero, the motor is, shut off. Additional braking torque can be obtained by, adding a braking circuit (resistor controlled by a transistor), to dissipate the braking energy., Part of AC drive (Fig 8a & 8b), , An embedded microprocessor governs the overall, operation of the VFD controller. Basic programming of, the microprocessor is provided as user - inaccessible, firmware. User programming of display, variable, and, function block parameters is provided to control, protect,, and monitor the VFD, motor, and driven equipment., Operator interface, The operator interface provides a means for an operator, to start and stop the motor and adjust the operating, speed. Additional operator control functions might include, reversing, and switching between manual speed, adjustment and automatic control from an external, process control signal. The operator interface often, includes an alphanumeric display and /or indication lights, and meters to provide information about the operation of, the drive., An operator interface keypad and display unit is often, provided on the front of the VFD controller shown in the, Fig 7. The keypad display unit can often be cable connected and mounted a short distance from the VFD, controller. They are also provided with input and output (I/, O) terminals for connecting push buttons, switches, and, other operator interface devices or control signals. A serial, communications port is also often available to allow the, VFD to be configured, adjusted, monitored, and controlled, using a computer., Operation of AC drive, When the VFD is started the applied frequency and voltage, are increased at a controlled rate or ramped up to, accelerate the load. This starting method typically allows, 130, , AC drives of various brand with different ratings are, available in the market. It is generally assembled in a, metallic enclosure. The front panel has the power input, and output terminals, control terminals, keypad (operator, interface) for controlling the drive etc. It has provision for, connecting to PC for programming the drive., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished

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The main parts are given below and shown in Fig 8a and, 8b., 1 Mounting screw holes, 2 Name plate label, 3 Bottom cover, , inversly proportional to the field current(If) and also the, armature current (Ia) is proportional motor torque., In armature controlled DC drives, the drive unit provides a, rated current and torque at any speed up to rated speed., The Fig 10 shows Basic Operator Panel (BOP) keypad, provided on the front panel meant for controlling the drive., , 4 Digital keypad, 5 Upper cover, 6 Ventilation hole, 7 Input terminals, 8 Control Input/Output terminals, 9 External brake resistor terminal, 10 Output terminals, 11 Grounding, Power and control terminals, In AC drive, the front panel has the input power terminals, viz R/L1, S/L2 and T/L3 where 3 phase AC 415V, 50Hz, supply is connected. The 3 phase induction motor is, connected of output power terminals viz. U/T1, V/T2 and, W/T3., There are control terminals viz M0, M1, M2, M3, GND,, +10V, AV1 etc. for starting/stopping/ reversing and speed, control actions. Names and locations are given in Fig 9, , The LCD is used to monitor the parameter. To start the, motor, 'ON' key is to be pressed, and to stop the motor, 'OFF' key is to be pressed. There is 'JOG' key provided, for inching operation., There is a key 'P' given for operator interface, changing, over the parameter setting can be done by using this key, in association with (Δ) key and key (∇). Parameters like,, voltage current, Torque etc will be displayed turn by turn, on each pressing of 'P' key /button., The (Δ) or (∇) keys are used to increase or decrease the, values. Numeric keys are also can be used to enter the, values directly., LED indicators are provided to indicate the status of drive., Green LED indicates the system running where as Red, LED indicates when fault is occurred., Programming of DC drive is possible through, personal, computer (PC) also. For this purpose a connector for, connecting PC through interfacing cable is provided at, the rear panel., There may be variations in terms of names of, key, display setting etc for different brands., Operation of motor through DC drive, Fig 11 shows the operation of controls arrangement which, is called as basic operator panel (BOP) ., , Parameter settings of DC drive, As discussed in previous chapter, the speed of DC motor, is directly proportional to the armature voltage (Eb) and, , The input supply connections and armature and field, connections are well illustrated in Fig 11. Input 3 phase, AC, 415V, 50Hz supply can be connected L1, L2 and L3., The armature is connected across A1 and A2 where as the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished, , 131

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field is connected across B0 and B1 (The terminal names, may vary depends on the type and make) an equipment, ground conductor ( Ground wire) must be connected to, the controller mounting panel. Separate equipment, grounding conductors from other major components Viz,, motor, drive enclosure isolation transformer case (if used), in the system must also be connected continuously to a, control connection point., , Inching operation, For inching operation the ‘JOG’ position should be, selected. Then the controller will operate only as long as, the “ON” button is held pressed., Changing the direction of rotation, In some model a ‘reversing switch’ is provided to change, the direction of rotation of the motor. This switch is, responsible for changing the polarity at the motor armature, connection. First start the motor by pressing ‘ON’ button., The motor will run in forward direction. To change the, direction of rotation, press “OFF” button and ensure that, the motor is completely stopped. Now press the reversing, button and then press the “ON” button. The motor will, now run in the reverse direction. The reversing key has a, provision which prevents direct transfer from one direction, to the other., Precautions during installation, connection and, operation of DC drive, , The AC input supply is provided should match the voltage, and frequency given on the controller's name plate., Improper voltage may damage the equipment and, insufficient current will cause erratic operation of the drive., The shielded cable is recommended for the tachometer, and all low level signal circuit to eliminate the possibility, of electrical interference., In some DC drives a speed adjusting potentiometer is, provided to vary motor speed by controlling armature input, voltage after the controller has been started. Some time, a torque adjusting potential meter is used in place of, speed adjusting potentiometer. It controls motor torque, by controlling the DC current in the motor armature., Starting and controlling the speed of DC motor, When the ‘ON’ button in BOP is pressed, the motor will, start running. The desired speed can be attained by using, ‘P’ button and Δ & ∇ buttons., When the “OFF” button is pressed the motor will stop but, AC line voltage remains connected to the controller and, full field voltage is present. Armature voltage is reduced, to zero. When pressing the “ON” button again the motor, will accelerate to the preset speed., , 132, , •, , Ensure all screws are tightened to the proper torque, rating., , •, , During installation, follow all local electrical and safety, codes., , •, , Ensure that appropriate protective devices (circuit, breaker MCB or fuses) are connected between the, power supply and DC drive., , •, , Make sure that the drive is properly earthed., , •, , Do not attach or remove wiring when power is applied, to the DC drive., , Parameter setting of AC drive, As explained earlier the speed (N) of AC induction motor, is directly proportional to the voltage (V) and frequency (f), of the applied power supply. Within the base speed limit,, the torque (T) can be kept constant by maintaining a, constant voltage / frequency (V/F) ratio. By increasing of, speed to above base speed limit is also possible but at, the cost of the torque., (VFD /VVVFD (Variable Voltage Variable Frequency Drive), drives are used for efficient speed control of AC motors., The advantages of using drives to control the speed is, already explained., The AC drive has a front panel which includes two parts., Display panel and keypad. The display panel is provided, with the parameter display and shows operation status of, the AC drive. Keypad provides programming interface, between users and AC drives. The Fig 12. shows the, location of buttons and display unit on the front panel of, AC drive., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished

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Frequency setting knob, By using this knob, the frequency variation can be done., ‘RS 485’ communication port, Programming of AC drive can be done through personal, computer (PC) also. For this, the drive should be interfaced, with PC through ‘RS 485’ port., LED displays are also given in the display unit to indicate, the status of drive like ‘RUN’, ‘FWD’ and ‘REV’., Operation of AC motor through drive, The motor and drive connections are well illustrated in, Fig 13. A 3∅ , 415V, 50Hz AC supply is connected to the, drive input terminals R/L1, S/L2 & T/L3. Similarly output, terminals of this drive is such as U/T1, V/T2 & W/T3 are, connected to 3 phase induction motor. (The terminal, names may vary depends on the type and make), , Mode /Reset button, By pressing this button repeatedly the display will show, status at the AC drive such as the reference frequency, and output current. If the drive stops due to a fault, correct, the fault first, then press this button to reset the drive., Prog/Data button, By pressing this button will store the entered data or can, show factory stored data., Run/Stop button, To ‘start’ or ‘stop’ the AC drive operation this button is to, be pressed., This button can only be used to ‘stop’ the AC drive, when, it is controlled by the external control terminals., , Both input end and output ends are earthed separately., , UPΔ, Δ / down ∇ button, , Changing of speed, , By pressing the ‘Up’ or ‘Down’ button momentarily, parameter setting can be changed. These key may also, be used to scroll through different operating values or, parameters. Pressing the ‘Up’ or ‘Down’ button, momentarily it will change the parameter setting in single, unit increments. To quickly run through the range of, settings, press ‘Down’ and hold the button., , The AC input supply provided, should match the voltage, and frequency given on the nameplate. Improper voltage, may damage the drive., Programming can be done through ‘MOD/RESET’ button, in association with Δ and ∇ button and the drives speed, can be changed by using these buttons. The drive is started, through ‘RUN’/STOP’ button., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 4.3.182, , Copyright @ NIMI Not to be Republished, , 133

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The motor can be run at different speed by programming, for the required speed., Changing the direction of rotation, , whose amplitude is dependent in the phase control of the, SCR. The operation of the circuit shown in Fig 14 is as, follows., , The direction of rotation can be changed. To do this,, press ‘RUN/STOP’ button. When the motor is completely, stopped, select ‘rev’ parameter and press ‘RUN/STOP’, button again. Now the motor will run in opposite direction., Same procedure can be followed to change, the direction of rotation of double cage, induction motor also., Precautions to be observed during installation,, connection and operation of AC drive, •, , Do not connect the AC power to the U/T1, V/T2, W/T3, terminals, as it will damage the AC drive., , •, , Ensure all screws are tightened to the proper torque, rating., , •, , During installation, follow all local electrical and safety, codes., , •, , Ensure that the appropriate protective devices (circuit, breaker or fuses) are connected between the power, supply and AC drive., , •, , Make sure that the leads are connected correctly and, the AC drive is properly grounded. (Ground resistance, should not exceed 0.1Ω), , •, , Use ground leads that comply with standards and keep, them as short as possible., , •, , Multiple VFD-L units can be installed in one location., All the units should be grounded directly to a common, ground terminal., , -, , Assuming that the motor is running, the voltage at, point A in the circuit must be larger than the forward, drop of diode D1, the gate to cathode drop of the SCR,, and the emf generated by the residual mmf in the motor,, to get sufficient forward flow to trigger the SCR., , -, , The wave form at point A (VA) for one positive half cycle, is in Fig 14b and with VSCR, VD and motor generated, emf VM. The phase angle at which the SCR would, trigger is shown by the vertical dotted line., , -, , For any reason if the motor speed increases, then VM, will increase, the trigger would move upwards and to, the right along the curve so that the SCR would trigger, later in the half - cycle thus providing less power to, the motor, causing it to slow down. Similarly, if the, motor speed decreases, the trigger point will move to, the left and down the curve, causing the SCR to trigger, earlier in the half cycle providing more power to the, motor thereby speeding it up., , -, , •, , Make sure that the power source is capable of, supplying the correct voltage and required current to, the DC drive., , •, , Do not attach or remove wiring when power is applied, to the AC drive., , Resistors R1, R2, R3 along with diode D1 and C1 forms, a ramp generator. Capacitor C1 is charged by the, voltage divider R1, R2 and R3 during the positive half, cycle. Diode D2 prevents negative current flow during, the negative half cycle, therefore C1 discharges through, R2 and R3 during negative half cycle. Varying the value, of R2 varies the trigger angle α., , •, , Do not monitor the signals on the circuit board while, the AC drive is in operation., , A practical version of the circuit for controlling the speed, of universal motors is in Fig 15., , •, , If filter is required for reducing EMI (Electro Magnetic, interference), install it as close as possible to AC drive., , Speed control of universal motors using SCR : Majority, of domestic appliances like electric drilling machine, mixer, etc., incorporate universal electric motors. Any of the half, wave or full wave controls discussed earlier can be used, to control speed of universal motors. Universal motors, have some unique characteristics which allow their speed, to be controlled very easily and efficiently with a feedback, circuit is in Fig 14., The circuit at Fig 14a provides phase controlled half wave, power to the motor; that is, one the negative half cycle,, the SCR blocks current flow in the negative half cycle,, the SCR blocks current flow in the negative direction, causing the motor to be driven by a pulsating direct current, 134, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 182, , Copyright @ NIMI Not to be Republished

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As can be seen, the circuit at Fig 15 is quite similar to, that at Fig 14 but for the addition of two transistors and a, few resistors., In Fig 6, the action of Q1 - Q2 is to provide adequate gate, current to trigger the SCR into conduction., Q1 - Q2 and their associated resistors acts as a voltage, sensitive switch. In each half cycle, C2 is able to charge, via R1. As soon as voltage across C2 rises to suitable, value. Q1 and Q2 both switch- on and partially discharge, C2 into the gate of the SCR, thus delivering a pulse of, , high current to the SCR gate, independent of any current, drive limitations of RV1. The Q1 - Q2 and C2 network thus, enables virtually any SCR to be used in the circuit almost, irrespective of its sensitivity characteristics., The universal motor speed control circuit is in Fig 15, enables the motor speed to be smoothly varied from zero, to 75% of maximum via a single control. It also, incorporates built - in feedback compensation to maintain, the motor speed virtually constant at any given speed, setting, regard-less of load changes., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.3.181 & 182, , Copyright @ NIMI Not to be Republished, , 135

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Electrical, Electrician - Inverter and UPS, , Related Theory for Exercise 4.4.183, , Voltage stabilizer and UPS, Objectives: At the end of this lesson you shall be able to, • state the basic concept of stabilizer, • draw the block diagram and explain the function of each blocks, • state the working various types of voltage stabilizers, • state the basics of UPS system, • explain the block diagram of OFF line UPS and its various controls and functions, • explain the block diagram ON line UPS and advantages and disadvantages., Voltage stabilizer, It is an electrical supply device controlled by electronic, circuit which gives the constant output voltage irrespective, of the variation in the high input supply voltage or disconnect, the output circuit if the input voltage is very low or very high., Sl.No., , Name of the equipment, , Every electrical device is designed to operate at a certain, rated voltage for optimum efficiency and maximum length, of service. Power supply voltages should not drop or rise, by more than 5% of rated voltage as per IS., The effect of voltage variations in commonly used electrical, appliances are given below., , Low voltage, , High voltage, , 1, , Incandescent lamp, , Lamp efficiency decreases, if the voltage is decreased., , Life of the lamp decreases or the, lamp fuses in extreme cases., , 2, , Fluorescent lamp, , If voltage is too low, lamp, will not light up., , Life of the tube/choke, decreases., , 3, , Electric stove, electric, iron, water heaters,, toasters etc., , Increases the heating time, as heat produced is low., , Shortens the life of heating, elements or heating elements, burnt out., , 4, , Fans, vacuum cleaners, , Efficiency decreases., , Life of the equipment is, decreased, , 5, , Washing machines,, refrigerators and, air-conditioners, , Motor of the machine will draw, The motor insulation may fail and, more current from the line that, draw excess current which can, results in overheating of the, lead to burn out., motor which may lead to burn out., , 6, , Radios and television sets, , Poor quality of reception,, picture will not be clear in the, television sets., , Life of the equipment is decreased, , Some of the electronic equipment such as colour television sets are designed by the manufacturers with, built in electronic stabilizers like Switch Mode Power Supplies (SMPS). Hence there is no need to, provide an additional external stabilizers for these equipments., Types of AC voltage stabilizers, 1 Stepped voltage stabilizer, a) Manual, b) Automatic relay type, , switch as in Fig 1 regulates the output voltage in the, manual type. In automatic relay type stabilizers a sensing, circuit actuates the relays which regulates the output, voltage. The schematic diagram is in Fig 2 is for an, automatic relay type stabilizer., , 2 Servo voltage stabilizer, 3 Constant voltage transformer, Stepped voltage stabilizer, In the stepped voltage stabilizer, an auto-transformer is, used for regulating the output voltage. A manually operated, 136, , Copyright @ NIMI Not to be Republished

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Stepped voltage stabilizer - manual type : Fig 4 shows, an auto-transformer in which the output voltage increases, as the tap changing switch S1 is turned clockwise. The, output voltage can be seen by connecting a voltmeter in, the output side as in Fig 4. Increasing or decreasing the, output voltage near to the set value is possible by rotating, the tap changing switch S2 in the appropriate direction, within ±10% of the desired output voltage. A push-button, switch S1 enables to measure the incoming voltage., , Mains Tx, This transformer supplies two level voltage i.e, low voltage, and high voltage, which is to be supplied according to the, needs. Some stabiliser working in buck boost operation to, meet special application for load requirements. The auxiliary, supply also provides for control circuit requirements by the, mains transformer., Control circuit, In the ordinary voltage stabilisers, control circuit regulate, the relay operation, irrespect or output voltage. When, input voltage falls below the set voltage H.T side relay will, operate and incase high voltage condition LT side relay will, operate and maintain the stipulated operate voltages. The, relay operation controls by controlling relay coil supply, which is set for separate DC regulated voltage levels., Relays, It is a electromagnetic relay which operates two different, coil voltage. the DC coil voltage decides which relay has, to be operate depends on the input AC voltage supplied, to the transformer. Fig 3 shows an automatic relay type, stabilizer., , Feed back, In non automatic voltage stabiliser DC voltage are taken on, the feed back quantity, which operates the relay coil. The, coil DC voltage will be two different voltage to activate the, relay in case of low and high voltage AC input conditions., Load, Load can be anything connected to the stabiliser. Some, electrical equipments requires a constant input voltage to, operate. such case a stabiliser is required. But in automatic, stabiliser have the disadvantage of transient line (Change, over to one voltage to other voltage level) which may cause, the stabiliser to OFF condition few milli seconds., , Stepped voltage stabilizer - automatic type : Fig 5, shows a stepped voltage stabilizer of the automatic type, operated by relays. T1 is an auto-transformer with multiple, tappings. S1 and S2 are two secondaries for relay operation., The secondary voltage of S1 is rectified and filtered for the, use of the sensing circuit while voltage S2 is rectified and, filtered for the use of the relay operation. P1 and P2 are preset resistors (variable resistors) used for adjustment. R 1,, P1 and R2 provide sensing voltage to the zener diode. DZ1, and R3P2 and R4 to the zener diode DZ2. Q1 and Q2 are two, transistors used as switches. RL1 and RL2 are two relays., , When the input voltage is low, say less than 200V, both, DZ1 and DZ2 do not conduct as the voltages at the preset, tappings are less than their zener diode voltages. This, causes both transistors to cut off and the relays are in the, off position. At the off position of the relays, NO contacts, of both the relays connect terminal R of the auto-transformer, to output which results in booster output voltage., When the input voltage increases above 210V, but below, 240V voltage across S1 increases proportionally. This, increases the pre-set tap voltage, thereby the zener diode, DZ1 conducts and hence make the transistor Q1 to ON., The relay RL1 operates and connects the supply voltage, directly to the output through NO. contact of RL1 and NC, contact of RL2. By this operation the output voltage will be, the same as the input voltage., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished, , 137

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When the input supply voltage increases above 240V the, zener diode DZ2 gets voltage from P2 and hence conducts, which makes Q2 to ON. This results relay RL2 energise, and output is taken from NO. point of RL2. The output, voltage reduces or bucks., Usually 12V DC relays with the required current ratings of, contacts are preferred for stabilizers. Diodes or capacitors, are used across the relay coil to protect the transistors, from reversed induced emf when the relays become OFF., LED indicators are sometimes used to indicate the mode, of operation such as buck, normal, boost etc., Stepped voltage stabilizers are available with different, types of electronic circuits with one to three relays to, provide an output voltage of 200-240V. They are specified, for maximum input voltage variation and for their output,, KVA ratings say 170 to 270 volts 1 KVA or 135 to 260 volts, 0.5 KVA., Some of the stabilizers are provided with over-voltage and, under-voltage cut off to protect the connected equipment., Applications : Stepped voltage stabilizers are used along, with refrigerators, air conditioners, TVs, VCRs etc. Colour, TVs with self-contained switch mode power supplies do, not require voltage stabilizer as they are designed to, operate from 130 to 260 volts., Servo - voltage stabilizer, The servo voltage stabilizer employs a toroidal autotransformer and a servo motor driven by a sensing circuit, which senses the voltage. The difference between the, output and nominal voltage is sensed by a sensing circuit, which drives the servo motor. Any variations in mains, cause the motor to move clockwise or anticlockwise thus, correcting the voltage., , When the output voltage is less than the reference voltage,, the electronic circuit senses the difference, drives the, motor in one direction which results in increase in the, output voltage., When the output voltage increases above the ratings, the, motor is driven in the opposite direction so that the output, voltage increases. When the voltage difference in output, and the reference are equal, the servo motor is switched, off by the circuit., A servo stabilizer provides constant voltage to an accuracy, around ±1% or ±0.5% and a correction range 10 to 30 volt/, sec., A servo stabilizer is more accurate and also costlier, and,, therefore, used with costlier equipments such as, computers, xerox machines, medical electrical equipments, etc., Constant voltage transformer, A constant voltage transformer works on ferro-resonant, principle. The variation in the primary flux with an, unsaturated iron core does not affect the secondary flux, with saturated iron core. Thus, the secondary induced, voltage remains relatively independent of the voltage, impressed upon the primary winding., In an ordinary transformer, the primary and secondary, coils are closely coupled. Any change in primary voltage, is directly transferred to the secondary in the ratio of the, number of turns. In a CVT, the primary and secondary coils, are loosely coupled. These are wound on separate sections, of the transformer core as in Fig 7. In between the coils,, a separate shunt path is provided for the flux to flow but an, air gap is provided in the shunt path. A capacitor is, provided in parallel with the secondary., , A servo voltage stabilizer is provided with three transformers, function along with control circuits and a servo motor as in, Fig 6. T1 is a continuously variable toroidal auto-transformer, (variac) driven by a servo motor M., , The output from the variac, drives a series buck/boost, transformer T2 so that boost takes place when the variable, tap arm moves down and bucks the voltage when the arm, moves up. The transformer T3 provides the required reference, voltage and sensing voltage for the electronic circuit which, drives the motor., 138, , Now imagine what will happen when voltage is applied to, the primary. Starting from zero, if the voltage increases, slowly, initially, all the flux generated by the primary, voltage will pass through the lower half of the transformer, core because the air gap in the shunt path will prevent it, from taking this path. This is shown by bold arrows in Fig, 6. As a result, the rise in secondary voltage is proportional, to the primary. But as voltage in the secondary coil rises,, at a certain point the impedance of the coil will become, equal to the impedance of the capacitor, i.e., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished

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π, , =, , C, 1 f, 2, , C, , L, f, 2, r, o, , X, , L, , X, , =, , π, , This is the condition of resonance, and at this point a high, current will flow in the LC circuit. This high current will, result in a sudden rise of voltage across the secondary, (Fig 6), and the core in this section of the transformer will, saturate., Once the core gets saturated, it prevents the entry of, further flux coming from the primary side. Therefore, any, increase in flux due to increase in primary voltage has to, take an alternate shunt path as in Fig 7. Hence, very little, increase in the secondary voltage takes place. This little, increase can also be nullified by a feedback-FB winding, connected as in Fig 8. The output winding can be separated, from the capacitor circuit if the voltage required is low or, tappings can be taken out of the capacitor., , CVT may not be suitable for an instrument in which SCR, power supply is used or an inductor or a capacitor is, coming in the AC circuit or a motor drawing a heavy in -rush, current is used inside the instrument. But it is suitable for, electronic machines such as TVs, computers, FAX, machines etc., Testing a stabilizer : To test a stabilizer for its operating, range, a variac and rated load along with voltmeters/, ammeters are necessary. A simplified circuit for testing, the stabilizer is given in Fig 9., , inherent defects and the danger posed to sophisticated, and sensitive electronic instruments. For ordinary household, appliances such as incandescent lamps, tubes, fans, TV, and fridge, the mains AC supply does not make much of a, difference, but when used for computers, medical, equipments and telecommunication systems, a clean,, stable, interruption-free power supply is of utmost, importance., As more and more personal computers, word processors, and data terminals find their way into small business, UPS, systems that meet the power requirements and price range, needs for small business and offices are being manufactured., The ever increasing importance of computers in industry, and commerce will increase the need for quality, high, stability and interruption-free power supplies., Earlier Data Operating System (DOS) does not have any, shut- down procedure. So in case power failure it does not, affect the operating system. Latest operating system, Windows 9x and application softwares require proper, shuting down and exit procedures. This procedures requires, time which is provided by UPS in case of mains power, failure., UPS (Uninterrupted Power Supply) is the only solution, available to an individual customer faced with the problem, of ensuring high quality of power for critical loads. All UPS, designs contain a battery charger to keep the battery fully, charged by the power from mains. Small UPS normally, comes with a sealed maintenance free (SMF) batteries, which can provide 10 to 15 minutes of power backup, the, backup time increases with the capacity of the battery., Tubular batteries or automotive batteries are used in, medium and large capacity UPSs., UPS classification, There are two broad categories of UPS topologies - OFF, line, and ON line . These topologies differ in the way they, serve the load when the mains is present and is healthy., They vary in features & pricing., OFF-Line and ON-Line, , By connecting the stabilizer as shown in the figure above, and varying the input voltage to the range specified in the, name-plate detail such as 170 to 260V or 130 to 270V etc., The output voltage should be satisfied with the specified, voltage such as 200 to 240V. There should not be any, undue heating or failures with the rated load for a continuous, working., Basics of UPS systems, Most people take the mains AC supply for granted and use, it almost casually without giving the slightest thought to its, , OFF-Line UPS filters the mains and feeds it directly to the, load for most of the time. When the mains is unhealthy,, perhaps due to a slight drop in voltage, the load is switched, by a fast relay, in typically less than half a cycle, to an, inverter deriving its power from a battery. The inverter, generates a square or stepped waveform to emulate the, mains-satisfactorily for most computers. This particular, technique represents the lowest cost solution., Online UPS converts AC mains into DC before inverting, again to AC to power the load with a synthetic sine wave., A battery connected across the DC link acts as the backup, power source., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished, , 139

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This gives a supply for the computer that totally isolates the, input mains from the load, removing all mains noise and, with no break when the mains fails., Standby/OFF Line block diagram (Fig 10), In the off line UPS, the load is connected directly to the, mains when the mains supply is available. When working, over voltage/under voltage conditions are detected on the, mains, the off line UPS transfers the load to the inverter., When the line is present, the battery charger charges the, battery and the inverter may either be shut down or will be, idling. Thus in an off line UPS, there is a load transfer, involved every time, the mains is interrupted and restored., This transfer is effected by change- over relays or static, transfer switches. In any case there will be a brief period, during which the load is not provided with voltage.If the load, is a computer and the transfer time is more than 5ms, then, there is a chance that the computer will reboot., , Some modified designs incorporate a limited range of, voltage regulation by transformer tapping and a certain, degree of transient protection by using RF filters and, MOV’s (Metal Oxide Varistor). Off line UPS is an economical, and simple design and hence it is preferred for small rating,, low cost units aimed at individual PC user’s market. When, the load is really a critical one an off line UPS is not, acceptable. Usually square wave output off line UPS are, available in market with lower loading capacities., Advantages of OFF line UPS: High efficiency, small, size, low cost., Disadvantages: There can be change over complaint in, offline UPS. Off line very much depends on battery. If, battery fails entire system fails. Sometimes during changeover computer re-boots which causes loss of files. Another, disadvantage is that output voltage will be a varying one., Usually in the range of 200V-240V and hence not suitable, to all electronic gadgets., , Front panel indications and rear panel sockets/, switches used in UPS, All UPS systems have, •, , Fuse/Fuse holder, , •, , Switches, , •, , Sockets, , •, , Panel indicator (LED and Neon lamp), , •, , Meters (Volt/Ampere), , Fig 11 and 12 shows the front and rear panel controls/, sockets., Switches: On/Off switch and reset switch are commonly, used in UPS. Reset switch is used to cut off an overload, circuit and restart the supply. This is a push to off switch., In normal position this switch keeps the circuit on and, when pushed, it cuts off the circuit., 140, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished

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Power factor specification will be different for different, manufactures. Suppose for 1 KVA UPS with a power factor, 0.6 the load will be 1000 x0.6 = 600 watts., Normally a single PC takes around 180 watts. There are, sine wave, square wave and quasi square wave output, UPS. Usually sine wave out UPS is better than square, wave output UPS., General specifications, Output capacity = Output capacity will be in volt amperes, (VA), Input voltage = 230V AC ±20%, 50 Hz single phase sine, wave, Socket: A common 5 Amp. or 15 Amps. three pin power, output socket is used in UPS to provide UPS output to the, various devices. One can connect an ordinary 5/15Amp., plug to the UPS output., Different LED indications/buzzers that are used in, UPS, Mains ON indication: It indicates mains input is present, and UPS is working on mains., Mains Low indication: It indicates that mains input is low, and is below a rated value., Mains high indication: It indicates mains input is high., Inverter ON indication: It indicates that UPS is working, in the battery mode and mains is absent., To get the output from UPS switch ON the ‘Inverter, ON’ switch., UPS Trip indication: It indicates that UPS output is Off, or tripped., Overload indication: Which indicates that the load, current is above a pre-determined value., Overload buzzer: It beeps whenever overload occurs., Low battery warning: It indicates battery voltage is below, a pre-determined value along with a buzzer ., Battery charging indication: It indicates that battery is, charging properly., Output voltage low indication: It indicates that output, voltage is below a pre-determined value., General specifications & UPS protections, UPS are available from 500VA to 20KVA or above.VA is, voltampere., , Output voltage = 230V AC ±10%, 50 Hz square wave or, sine wave, = 230V AC ±2%, 50 Hz (for ON-Line), Battery = 7 AH, 12V Sealed Maintenance Free (SMF) for, OFF-Line (depends on the capacity of the UPS), = Tubular batteries from 40 AH to 160 AH (12V to 120V) for, ON-Line (depends on the capacity of the UPS)., Availability of Automatic Voltage Regulation (AVR) feature., Typical recharge time to charge 90% of the full capacity of, the battery is 5 hours., Different types of protection in UPS, Input fuse on mains: It protects the system from high, voltage inputs, line disturbances and short circuiting etc., MOV (Metal Oxide varistor) protection: MOV conducts, when high input voltage appears thereby blowing the fuse, Polyester capacitor for lightening protection: This is, connected across the transformer winding. It burns when, lightening occurs and protects the transformer., Fuses to protect the MOSFETS: MOSFETS are highly, sensitive to rapid changing currents. These fuses are used, to protect the MOSFET., Charger fuse to protect the charger circuit: If any fault, in charger circuit occurs, fuse blows to protect SCRs., Output high voltage protection MOV: This MOV is, connected across output sockets phase and neutral. If, feedback circuit fails the output voltage will jump to more, than 300 volts. In such situation the MOV conducts to, protect the load., Overload protection: It protects the UPS especially, MOSFET/IGBT when output current exceeds a preset, value (overloading the UPS). When this occurs, UPS, output becomes OFF along with an indication., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished, , 141

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Battery over charge/discharge protection: It protects, the battery from charging to a high value (SMF batteries will, charge upto 15.8V) and tubular batteries upto 14.1V. It, also protects the battery from getting discharged below a, level (low battery protection). If the battery voltage is, discharged below 10.5V, then the UPS gets automatically, switched OFF., General tips for testing a UPS, •, , Connect the battery to the terminals using a fuse wire., If any fault occurs in testing the fuse will blow to protect, the UPS., , •, , Do the testings on no load condition., , •, , Check the gate voltages of the two MOSFET banks it, should be the same. If PWM gate pulses are not, present gate voltage will be around 5.6V. If the PWM, gate pulses are present then the gate voltage will be, around 2-2.5 volts., , •, , Some frequency meters are designed to measure pure, AC frequency only. If the UPS output is square wave,, then the reading will not be correct. To mea- sure the, correct frequency connect a 60/100W load at the, output of the UPS. Then the frequency meter shows a, near correct frequency., , •, , For overload setting in ON-Line UPS, the load current, is calculated by dividing the maximum load with the, output voltage. This can also be measured using a, clamp meter on the output terminal. Overload is set at, this value of load current., , •, , While using extension boxes either in the input or on, the output of an UPS, ensure proper earth connection., Improper earthing may lead to poor line filtering and, shock hazards., , •, , If number of MOSFETs are connected in parallel,care, should be taken to see that all the MOSFETs are of the, same Rds. For MOSFET Rds value (drain to source, resistance) and current rating are important., , Changeover in OFF-Line UPS system, In this type of UPS, the relay controls the battery voltage, which is applied for relay coils. If the battery voltage is too, low then relay coil will not get sufficient supply to trigger, the switch.This may lead to the absence of mains voltage,, even if mains is present and is healthy. This type of OFFLine systems are battery dependent., Some OFF-Line systems are battery independent. The, coil supply is provided by the mains itself. Mains supply, is reduced and rectified. This rectified supply is given to, the changeover relay coil . Battery low voltage does not, affect the relay coil supply. This type of OFF-Line UPS, provides mains output irrespective of the battery condition., , 142, , Isolation of inverter, Another important point is that the isolation of the inver ter, section during the presence of mains , this is done by the, change over relay. For inverter side isolation a switching, transistor is used . This switching transistor controls the, shut down pin voltage of oscillator IC. This transistor makes, this pin high when mains is present., Once shut down pin becomes high, oscillator IC stops, generating pulses to MOSFETs. MOSFEET becomes, OFF and inverter section becomes inactive. When mains, failure occurs this pin voltage is changed by the transistor, to generate gate pulses., The inverter section of OFF-Line and ON-Line UPS are, almost same expect in the mains section., OFF-Line UPS employs a mains delay capacitor. This is, a prevention to fast varying mains input voltage. If mains, condition is changing rapidly (Mains ON/OFF) then the, UPS has to switch alternately to battery mode and mains, mode. Since MOSFET cannot respond to these fast, varying currents it will burn.To avoid this, a delay capacitor, in mains mode (.1Mf) to delay the mains input. As soon as, mains is sensed by the opto coupler, mains on indication, glows. Changeover relay will respond after a few seconds, to mains because of this capacitor. Removing this capacitor decreases changeover time. But this may cause, damage of MOSFET., ON line UPS, In an ON line UPS, the inverter always supplies the load, irrespective of whether mains power is available or not. The, load is always left connected to inverter and hence there is, no transfer process involved. When the mains power is, present, it is rectified and applied in parallel with the, battery. Hence all the supply system transients are isolated, at the battery and the inverter always delivers pure sine, wave of constant amplitude to the load., Fig 13 represents a basic block diagram of an ON Line, UPS., In the block diagram (Fig 13), the mains input is stepped, down to a lower level and applied to a thyristor based phase, controlled AC to DC converter, employing firing angle(α), control. The PWM inverter which usually employs pulse, width modulation using triangular/square wave carrier runs, in battery mode. The output is filtered and given to the load., The PWM inverter is switched in the frequency range, (50Hz) depending on the power rating and hence the DC, side current drawn by the inverter will contain switching, frequency components., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished

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Along with the charging current the second harmonic, component of DC side current of the inverter also flows into, the battery. This second harmonic is quite large in value, and this represents unnecessary strain on the battery. This, is one of the major disadvantages of this design since it, affects the battery life adversely., , Advantages, , When the mains is present the load power flows though the, converter, reaches the battery node and from there flows, into the inverter i.e there is double conversion of power. The, converter, Inverter and the two level shifting transformers, incur power losses in this process. Hence the efficiency, of this design is lower than the OFF line design., , Disadvantages, , In a properly designed control system the battery voltage, is measured and compared with a set float voltage. The, error is processed in a proportional controller and the, processed error decides the charging current that should, flow into the battery. Charging current will be a constant, one for ON line UPS., Often it is found that the battery is in discharge mode even, when mains is present i.e the battery shares the load, current with the mains. This happens when the mains, voltage is low and/or the output is loaded to above 75%. The, efficiency of ON line UPS can be increased by using boost, type power factor correction circuit., , •, , Constant output voltage (No AVR card) free from, changeover problem., , •, , Constant charging current., , •, , complex in design, lower efficiency, higher cost, bigger, in size and strain on the battery., , Presets of an ON-Line UPS, The presets of ON Line UPS are different from the OFF, Line., ON-Line UPS presets, Output high cut preset: Suppose there occurs a failure in, PWM or feedback section. The output voltage will jump, above 300V AC. This much output voltage causes harm to, the output load. To prevent this output high cut preset is, used. When the output voltage reaches set limit, this, preset cuts the output. To set this limit, increase the output, voltage using the PWM output voltage control preset till it, reaches 265V and set the output high cut preset to shut, off the output., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.183, , Copyright @ NIMI Not to be Republished, , 143

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Electrical, Electrician - Inverter and UPS, , Related Theory for Exercise 4.4.184, , Emergengy light, Objectives: At the end of this lesson you shall be able to, • explain the block diagram of emergengy light, • explain the emergency light circuit diagram and charging of battery., Emergency light, Emergency lighting system is commonly used in public, building, work places, residences etc., The main function, of the emergency lamp in the industry are, •, , to indicate ESCAPE routes, , •, , to provide illumination to path ways and exit, , •, , indicate the location of the fire fighting equipments., , The block diagram of an emergency light is in Fig 1. The, circuit is discussed here are basic circuits without over, charging protection for battery or trickle charging facility., Modern emergency lights have these facilities., , and the other is green are provided in the circuit to indicate, the presence of AC and the lighting of the lamp through the, battery supply respectively., One 1000 microfarad capacitor is used in the rectifier, circuit to smoothen the output D.C. supply and one 10, microfarad capacitor is used across the relay to increase, the efficiency of relay operation., Emergency tube light circuit: The emergency light, which is connected to an ordinary incandescent lamp will, give less light. If the fluorescent tube is used in emergency, light it will give about 3 times more light consuming same, wattage. Hence most of the emergency lights are, incorporated with fluorescent tube lights., The inverter circuit is incorporated with the ordinary, incandescent lamp could be replaced by a tube light as, shown in the block diagram, (Fig 3). The tube light requires, a high voltage for its operation. The inverter is used to, convert DC supply to AC and then it is stepped up to light, the fluorescent tube. The inverter circuit is made operative, by the sensor (relay). When AC supply is not available,, during power failure battery voltage operates the inverter, in, which DC is converted to AC and then stepped up to high, voltage to enable the fluorescent tube to light up., , As shown in the block diagram AC main supply is fed to the, step down transformer, then it is rectified to charge the, battery through a sensor relay. A lamp is connected in the, battery circuit through the relay. When AC supply fails the, relay enables the battery to the connected lamp circuit, through the normally closed contact and the lamp will glow., When the AC supply is restored, the battery will be getting, charged through the normally open contact of the relay., The charging current is regulated by the series resistances, of 2.2 ohm, 5 watt. as in Fig 2. The two LEDs, one is red, , 144, , Copyright @ NIMI Not to be Republished

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Inverters are basically transistorised oscillators as in Fig 4., They can be made to oscillate at the frequency of about 6.6, kHz. The frequency of the circuit can be changed by, changing the value of resistor and capacitor in the circuit, which is connected in the base of the transistor., When the AC supply is resumed the sensor relay connects, the battery terminals to the rectified DC circuit for charging, , and the inverter circuit is disconnected from the circuit by, the relay., For keeping the temperature of the power transistor within, its temperature range suitable heat sink should be mounted, over the power transistor., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.184, , Copyright @ NIMI Not to be Republished, , 145

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Electrical, Electrician - Inverter and UPS, , Related Theory for Exercise 4.4.185, , Battery charger and inverter, Objectives: At the end of this lesson you shall be able to, • explain the working of battery charger with the help of block diagram, • describe various batteries and its maintenance, rating, methods of charging, • explain the battery charging circuit and its auto-cut-off, • state the principle of inverter with the help of block diagram, • explain power inverter and input output voltage, frequency, power relations., Battery charger, Proper selection and maintenance of the battery is very, essential for the proper working of battery wherever is used:, such as inverter,UPS etc, Many types of battery used for different purpose.Each have, more advantages and disadvantages., Commonly the following four types of batteries are used, with the inverter systems, UPS etc., •, , Automobile batteries, , •, , Tubular/Industrial lead acid batteries, , •, , Sealed maintenance free (smf )batteries, , •, , Nickel cadmium batteries, , It is more expensive when compared to the other batteries., It is more sensitive than other batteries. If the operating, temperature is more than 40 degree centigrade half the, capacity and life of batteries are reduced to half., Nickel cadmium batteries, These are very expensive batteries and used in defence,, space, nuclear science etc applications.It has extra any, life operation ., Rating of battery, Commonly the batteries are available in 6V,12V,24V,48V,, and 120V and so on. Normally 6 ,12 and 24 V rating are, mostly available. The capacity of the battery is rated the, Ampere/Hour(AH), The back up time depends on the AH capacity of the battery., higher the AH capacity more the back up time., , Automobile batteries, This type of batteries are commonly used in automobile,, cars, trucks etc. It is cheapest of the other batteries used., It has many draw backs one major draw back with these, batteries are during stand by use.(i.e) In long duration under, float charger they develops positive grid corrosion, which, will reduce the back up time provided by it., , Charging of battery, The life of battery is very much depends on the charging, method used to charge the battery., Three types of charging used to change the batteries., , A good quality of automobile lead acid battery has a life, an of only about 250-300 full charge /discharge cycle., , •, , Constant voltage, , Tubular/Industrial lead acid battery, , •, , Constant current, , •, , Constant voltages- constant current, , This type of batteries are designed for the heavy duty, charge required ., The operating life is more than 1000 charge/discharge, cycles. These type of battery requires regular maintenance., Because of the acid in these batteries irritating smell gases, and It can not be kept in computer rooms and other AC, rooms., Sealed maintenance free (SMF)batteries, These batteries are completely sealed, so they do not, require any kind of regular maintenance. In side of battery,, do not contain any wet acid, (ie) lead paste batteries. It is, small in size, and it can be kept in the ac room along with, inverter., 146, , Constant voltage, This type of charging method using series regulators is, suitable for the SMF batteries but not useful in automobile, and tubular lead acid batteries., Constant current, This charging method using shunt regulators, is useful for, automobile and tubular /Industrial lead acid batteries, but, it can damage the SMF batteries by overcharging them., , Copyright @ NIMI Not to be Republished

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A simplified block diagram of battery charger, is explained to understand the function of, battery charger. (Fig 1), , Constant current, This charging method using shunt regulators, is useful for, automobile and tubular /Industrial lead acid batteries, but, it can damage the SMF batteries by overcharging them., Constant voltage and constant current, This charging method contains more advantages .This, method is suitable for automobile and tubular /Industrial, lead acid batteries and also for SMF batteries., This method provide regulated charging to improve the, battery life., , Transformer, The mains transformer primary is connected through auto, transformer and the supply to auto transformer controlled, through relays. The automatic charge control supply is, always present at the primary of charge control unit, transformer., , Charging operation of battery, , Relay unit, , The transformer works on step down which has 0-240 V,, taping at the primary and 12-0-12 V at the secondary., , The relay unit supplies the DC rectifier input supply to the, required DC input to the battery for charging. This relay unit, also cut-off the rectifier input AC in case of the battery is, fully charged., DC rectifier, This rectifier unit always is a full wave bridge rectifier to, handle heavy charging current. High current metal rectifiers, are found mostly used in this circuit, but high current, capacity semi conductor diode are in use., Charging unit, This indicates the charging current taken by the battery, and it is controlled by ON-OFF switches. A test switch is, provided to test the charging condition of the battery., Battery section, The battery under charger is always to kept in a well, ventilated room and also open the vent plug for easy, evaporation of exhausted gases from cells., Charge control unit, Once the battery fully charged; then the DC supply to, battery to be cut-off automatically. The voltage sensing, circuit enables the control unit to trip the AC input to the, rectifier unit thereby stop the charging voltage., Constant voltage, This type of charging method using series regulators is, suitable for the SMF batteries but not useful in automobile, and tubular lead acid batteries., , When the mains A.C is available, the mains supply is, connected to 0-240V taping of auto transformer through a, relay., , The voltage at the secondary is used to charge the batteries, connected., Trickle charging, In an inverter, when the mains A.C is available the battery, get charged. After the battery is fully charged the charger, is cut-off. After the battery get fully charged if the charger, is not cut off then the battery will get damaged., Trickle charging is a special charging method used to keep, the battery constantly in full charge position by keeping, the battery charged constantly., This method of charging is slightly different from the normal, charging method., For trickle charging 100th part of the normal charging current, is provided to the battery., A Simple battery charger, The charger can charge 6V,12Vand 24V battery at Suitable, current rate. This circuit has many protection built in it to, protect the battery from overcharge and reverse polarity, etc., The charger consist of an auto transformer X2,(Fig 2) for, supplying constant current and voltage., A charger transformer ‘X 1’ is connected to the auto, transformer and the secondary of the X1 (Fig 2)is rectified, through full wave bridge rectifier and supplied to the battery, under charger through. Ammeter voltmeter and a, potentiometer (Fig 2), , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.185, , Copyright @ NIMI Not to be Republished, , 147

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A step down transformer X3 is used to keep cut off relay is, energised condition when the mains AC supply is cut off, to the charger circuit. Relay RL1 used to cut off the AC, mains supply to the charger circuit. Pole P1of relay RL1 is, connected to AC mains supply and pole P2 is connected, to cut off circuit., Relay is energised by the centre tapping of potentiometer,, which is set such that, the current in the charger circuit, exceeds then it is energised and poles P1& P2 are, connected to normally opened (NO)pin, switching ‘Off’ A/, C mains supply to the circuit., The test switch S3 is connected to check battery polarity,, reset switch S4 is used to reset the charger, when any, fault occurs. Then the charger is cut off and the Switch, ‘S1’ is mains ON/OFF switch., A fully charged lead acid battery must be 2.1 volt/cell during, on charge.It will increase upto 2.7V/cell.The voltage of a, battery is multiple of the number of cells., , 148, , In discharged condition the voltage is 1.8V/cell,it should, not be further discharged in this condition as it may, permanently damage the cell., E.g A 100AH (ampere hour)battery requires (100 AH/, 10Hr=10 Amp) 10 Amp. Charging current for 10 hours for, fully charged. To get complete discharge at the rate of, 5Amps will require 20 Hrs., The fully discharged battery requires about 11/2 times more, to get charged .If the battery is in dead (or )not in use for, long time even in normal changing current is passed. These, dead batteries require higher charge voltage to start the, charging current., Checking of battery, Acid level and specific gravity of electrolyte, will indicate, the condition of battery whether it requires charging or, not., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.185, , Copyright @ NIMI Not to be Republished

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The hydro meter is used for checking the acid level in a, battery .The scale in marked in the hydrometer from 1100, to 1300.when it is inserted in the battery, the reading, i) 1100-1150 -indicates battery is down, ii) 1200-1250- indicates battery is o.k., iii) 1250-1300 indicates excess acid, Voltage testing, By using high rate discharge tester, the voltage the each, cell must be 2.1V, If it indicates below than 1.8V, then it, shows the battery is in fully discharged. It is still below, 1.8V.Then the battery becomes dead condition., Never connect the high rate discharge tester for long duration while checking voltage, it will load the battery heavily, and the cell, will discharge., If the electrolytic level down in the container shell of the, battery, top up with distilled water. Never add electrolyte, prepared separately to the battery., In a lead acid battery the electrolyte level of the battery, should be checked and maintained every 15 days in, summer season., Inverter, It is an electronic device, which converts a D.C potential, (voltages) normally derived from a lead-acid battery into a, stepped-up AC potential (voltage) which is similar to the, domestic AC voltage., Locating the fault and troubleshooting of an inverters which, provide sine wave outputs or the use of PWM(Pulse Width, Modulation) technology is very difficult. (Fig 3), , Switching circuits, It is the input stage of a inverter. This circuits supplying the, power to further stages and connected to battery. The DC, supply of battery in this supplies to the switching circuits, for various needs., Oscillator, It is an electronic circuit which generates the oscillating, pulses either through an IC circuit or a transistorized, circuit. This oscillations are the production of alternate, pulse of positive and negative (ground) voltage peaks of a, battery and at a specified frequency (No.of positive peaks, per second). These are generally in the form of square, waves and the inverters are called square wave inverters., The complete circuit diagram of a static 50Hz static inverter, is in Fig 4., The oscillator section of the inverter used a IC circuit to, produce control signal frequency to the control and driner, section. The received oscillating frequency is amplified to, a high current level using power transistor or MOSFET.IC, 7473(JK Flip type) used to power amplification and control, the frequency to the driver transistors T1 and T2 driving the, power transistor to the required level as in the Fig 4., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.185, , Copyright @ NIMI Not to be Republished, , 149

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The two parallel connected power transistor T5, T6 and T7,, T8 are connected to the output transformer which is used, to step up the low level AC from the amplifies stage into the, specified level., The transformer secondary is supplied the required level of, AC 240V. The generation of the oscillations due to which, the process of voltage induction is able to take place, across the windings of the transformer., The inverter does not produce any power and the power, produced by DC source. The inverter requires a relatively, , 150, , stable power source capable of supplying of enough, current for the intended power demands of the system., An inverter can produce square wave, modified sine wave,, pulsed sine wave, pulse width modulated wave (PWM) or, sine wave depending on circuit design., The inverters more than three stages are more complex, and expensive. Most of the electric devices are working, with pure sine wave and AC motors directly operated on, non-sinusoidal power may produce extra heat, and have, different speed-torque characteristics., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.185, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.4.186 & 4.4.187, Electrician - Inverter and UPS, Stabiliser, battery charger, emergency light, inverter and UPS, Objectives: At the end of this lesson you shall be able to, • state the general precaution to carryout for preventive maintenance, • explain the steps to follow the break down maintenance, • service the voltage stabilizer, emergency light, battery charger, inverter and UPS, • analyse the trouble shooting chart and find the problem/ repair the equipment., Use of flow chart and troubleshooting charts for fault, location : The circuit diagram is in Fig 1 is given for your, reference. The working of the mains cord, fuse, relay, contacts, windings of the auto-transformer etc. can easily, be ascertained by using a test lamp and/or a series lamp, or by a voltmeter for checking the electronic circuit and, relay coil winding. A multimeter in appropriate range is a, must to localise the fault. A series lamp or test lamp, should not be used to test these as they are liable to spoil, while testing., , When one of the relay circuit is only not operating that, particular function will be absent i.e. either back or boost, function will be absent., , Method of trouble shooting : Referring to Fig 1, we find, that the absence of control voltage from S1, S2 or DC, voltages will make both the relays inoperative, and, hence,, will be in the off position resulting in higher output voltage, than input voltage with boost indication. The same result, also occurs when both transistors are open., , While removing the components from PCB, the component, position with respect to the PCB, the terminal connections, and hook up wire connections should be noted to enable, the electrician to reconnect the component properly., When replacing the components procure the component, of the same specification or equivalent so that the, performance of the equipment is not affected after repair., , When both the transistors are short i.e. collector to emitter, is short or both zener diodes are short the relays are, energised and the output voltage will be lower than input, voltage., , When a component mounted on PCB is suspected to be, defective, first ascertain from all possible tests with in the, circuit and then remove the component from PCB only, when it is absolutely necessary. Even removing, components for testing should be done as rarely as, possible., , Troubleshooting chart given in Table 1 illustrates the, problem, section to be suspected possible cause and, action required for a stepped automatic voltage stabilizer., , Copyright @ NIMI Not to be Republished, , 151

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General precautions for preventive maintenance, Maintenance for any equipment needs a working knowledge, of that machine is very much essential to the person, concerned. For example the volt ampere rating of voltage, stabilizer is very important to carryout the preventive, maintenance. Low quality, substandard components or, materials never be used or recommended for use. Necessary, steps to taken for safe temperature controlling and over, loading conditions. Proper operating sequence or working, steps to follow of all the equipments under maintenance., Steps to follow break down maintenance, Break down can happen anytime, anywhere. Adequate, protection might have provided to all equipments, for its, smooth working. However continuous running or usage,, , lack of maintenance, human error and some unexpected, reasons break down is happening., Once break down maintenance or repair is required a, detailed study of that equipment is essential. Always, involve more persons pertain to the repair work or, maintenance work for achieving a good result. A collective, and competitive effort only will produce good results. Give, value for everyones suggestion, expertise and workmanship., There must be a clean idea and vision to finalise the, maintenance and repair. Ensure the services of experts,, availability of spares, details of past records, diagrams and, past history of the equipment such as its installation date,, service records, number of break downs and its frequency, etc; Servicing of voltage stabilizer by trouble shooting, method., , Table 1, Trouble shooting chart for stepped automatic stabilizer, Sl., No., , Problem, , Section to be, suspected, , Possible cause for, defective, , Action, , 1, , No output voltage, at output socket., , Input, buck/boost relays., , Mains cord, switch,, fuse, transformer and relays, , Locate and repair, or replace, , 2, , The output voltage is, more, do not regulate., , Electronic circuit or, relays., , Open/shorted rectifier, / diodes, or open zener, diodes, , Locate the defective part and, replace., , 3, , Output voltage is same, as input. Do not regulate., , Transformer or, Electronic circuit, , Transistor or held up, relay contacts or, Partial open transformer, / leads., , Test, repair, or replace., , 4, , Output voltage is low., Do not regulate., , Electronic circuit, , Shorted zener diode or, transistor or open resistors, , Test and, replace., , 5, , Chattering in relays, , Electronic circuit/relays, , Leakage capacitors, , Replace., , Trouble shooting of UPS, The trouble shooting and repair of UPS is difficult as this, circuit is so complicated with so many functions. A step by, step trouble shooting approach with a reasonable analysing, , is very important to carryout the troubleshooting in the UPS, circuit., A trouble shooting chart of UPS is given for your reference, in table - 2., , Table 2, Troubleshooting chart of UPS, Sl.No., 1, , Fault, , Possible Reason, , UPS works on 240V VAC mains, but does not operate on battery, , 1 Battery fuse is blown out, 2 Battery is discharged, , Troubleshooting, 1 Check the battery fuse. If fuse is, blown, replace it, if it is loose,, tighten, 2 Recharge the battery, also check, the polarity of battery, , 2, , 152, , When UPS is switched on,, charger does not turn on, , 1 Mains input fuse may be, blown, , 1 Change mains fuse, if fuse blown, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.186 & 4.4.187, , Copyright @ NIMI Not to be Republished

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Sl.No., , Fault, , Possible reason, 2 Charger input fuse, blown out, , Troubleshooting, 2 Check the battery polarity and, conditions, correct it if wrong,, replace the fuse, 3 Check the supply from mains, if, OK, then check relay wiring, check, relay coil., , 3, , 240 VAC mains supply NOT, available, , 1 Mains supply fails, 1 Check the supply of mains, 2 Input AC mains is very, 2 Check the voltage, low, 3 Tight the connection of wiring, 3 Loose connection in input, coming from distribution board, wiring, , 4, , DC voltage is OK, but UPS shows, DC under voltage and trips, , 1 Inverter fuse is blown, 2 Rust/loose connection in, battery, , 1 Replace fuse, 2 Check the connection, , 5, , When the UPS is switched ON, with out load but DC under voltage, indicator turns ON at load., , 1 Load too high, , 1 Check the load, add loads, gradually., 2 Tight the connections and check, the polarity of battery, , 2 Loose connection of, battery terminal, 3 Short or earth fault in, load, , 3 Check the load circuit wiring, , 6, , Where there is no AC mains supply, and the UPS is operating on, battery, DC under voltage indicator, turns ON, , 1 Battery is discharged, 2 Battery terminal dust, or loose, , 1 Recharge the battery, use proper, current capacity cable in the, battery circuit., 2 Check the connection, , 7, , DC fuse blows OFF, , 1 Overload or short circuit, , 1 Change DC fuse, 2 Reduce the overload. If power, transistors are short or leaky,, replace them., , 8, , UPS does not switch ON, , 1 Supply fails due to blown 1 Replace fuse, check the cables, out fuse or some break in 2 Check and correct dry soldering, cable, and de-soldering, 2 No DC supply in the, 3 Check control card wiring, control card due to dry, soldering or desoldering, , 9, , UPS trips when full load is, connected, , 1 Overload setting is wrong 1 Adjust the overload setting, check, the power consumption of the load., Gradually increase the load., , 10, , UPS output is high, , 1 Some connection is, broken in the feedback, loop, 2 Control card is not, functioning properly, , 1 Check feedback transformer wiring, and adjust feedback voltage preset., 2 Check /Replace control card, 3 Check overload sensing circuit, , 3 Over voltage sensing is, faulty, 11, , UPS does not switch on in, battery mode, , 1 Mains earthing is not, 1 Check the earth connection, proper, 2 Check battery, MOSFET, oscillator, 2 Problem in inverter circuit, section, driver section, output, section, , 12, , Battery wire getting burned, , 1 The relay points are, joined together, , 1 Check / Replace relays, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.186 & 4.4.187, , Copyright @ NIMI Not to be Republished, , 153

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Sl.No., , Fault, , Possible reason, , Troubleshooting, , 13, , Change over time high, computer, connected to the UPS reboots, during change over., , 1 Check oscillator circuit, , 1 Check /replace IC and other, components of oscillator section, , 14, , Low backup time, , 1 Main filter capacitor, problem, 2 Battery get short, circuit/discharge, , 1 Check and replace capacitor, 2 Check battery, replace if required, , Trouble shooting of battery charger and emergency, light, As you have seen that the battery charger is a simple, circuit compare to UPS. The main function of the charger, circuit is to feed the DC voltage to battery at a prescribed, , level we discuss only the trouble shooting of charger circuit, and its repair. Battery maintenance is not discussed in the, trouble shooting chart., Analyse the fault in battery charging circuit (Fig 1) with the, help of trouble shooting chart given in Table 3 and 4., , Table 3, Sl., No., 1, , 2, , 3, , Problems, No DC voltage, at charging, terminal, , Section to be, suspected, , Possible cause, for defects, , Action, , 1 Faulty Ammeter, (open circuit), , Aged/over, current, , Replaced, Ammeter, , 2 Blown fuse, , Over current, , Replace fuse, , 3 Faulty rectifies diode, , Aging/over loading, , Replace all diodes, , 4 Defective transformer, , Aging/over loading, , Replace transformer, , 5 Faulty Relay contacts, , Repeated closed open, , Replace contact, , 6 Open Relay coil, , Over voltage/current, , Replace relay, , 7 Main fuse blown, , Over loading, , Replace fuse, , 8 No link between, meter to battery, , Loose connection, , Tighten the connection, , 9 Defective auto transformer Over loading, , Replace transformer, , Low terminal, voltage, , Anyone pain diode, open circuited, Partial short in transformer, , Ageing, , Replace all four diodes, , Over heat, , Replace transformer, , No automatic, charging voltage, cut off, , Defective, potentiometer, , Long use, , Replace new, potentiometer, , Driver diode open, , Ageing, , Replaced 2 diodes(D7), , Defective electrolytic, capacitor, , Ageing, , Replace capacitor (C1), , Defective bleeder resistor, , Over current, , Replaced same value, resistor(R1), , Control circuit rectifier, diode open, , 154, , Ageing, Over current, , Replace both, diodes(D5 & D6), , LT winding transformer open Ageing / over current, , Replace new transformer (x3), , LT fuse open, , Over current, , Replace fuses (F2), , Defective auxiliary relay, terminal, , Repeated operation, , Replace contact RLI(B), , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.186 & 4.4.187, , Copyright @ NIMI Not to be Republished

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Table 3 contd..., Sl., No., 4, , Problems, Irregular over, voltage cut off, , Section to be, suspected, , Possible cause, for defective, , Action, , Defective, potentiometer, , Loose contact, in the disc (track), , replace new, potentiometer (VP1), , Shorted driver diode, , ageing/over current, , replace new diode (d7), , Loose in relay contacts, leaky electrolytic capacitor, , Repeated contacts, ageing, , replace contacts, replace electrolytic capacitor, , Table 4, Trouble shooting chart for emergency light, Sl, No, , Problems, , Section to be, suspected, , Possible cause, for defective, , Action, , 1, , Lamp dead, in both condition, lamp, , Defective tube, , Ageing, , Replace tube lamp, , Defective inverter, transformer, , Over loading/ageing, , Replace inverter, transformer, , Defective driver, , Over loading/ageing, transistor, , Replace transistor, (213055), , Low/ dead battery, , Ageing, , Replace New, battery, , 2, , Lamp out, glowing if AC fails, , Servicing of equipment are discussed based on a sample, circuits. When servicing of other equipments with different, circuits may differ from the troubleshooting sequences., However the basic principle based on the block diagram, may be taken for guidance to service/repair the equipment., , taken from the output transformer to regulate the output, through the control circuits., , Trouble shooting of inverter, , A constant DC source; either from a converter or battery is, very much essential to keep the power output in a constant, stage. DC to AC conversion with a specified frequency and, a particular wave is difficult., , DC to AC inverter is quite complicated circuit, it consists, of many functions. The switching circuit, oscillator circuit,, control circuit power amplifier circuit, driver, finally the, output circuit through the transformer. A feed back is also, , Analyse the fault in a inverter is explained (Fig 2) with the, help of trouble shooting chart is given in Table 5. However, the fault and problem are discussed while considering the, 50Hz static inverter circuit is in Fig 2., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.186 & 4.4.187, , Copyright @ NIMI Not to be Republished, , 155

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Table 5, Sl, No, , Problems, , Section to be, suspected, , Possible cause, for defects, , Action, , 1, , Output - Dead, , - Output transformer, , - Transformer open or short, , Rectify transformer, , - DC source, , - CT & transformer open, , Rectify the CT, connection, , - No DC from battery, , Replace battery, , - Battery dead, 2, , 3, , 4, , 156, , Low or high, frequency, , Low voltage, frequency ok, , Frequent cut-off, the output, , - Oscillator IC (555), , - Faulty IC, , Replace IC, , - Control IC JK Flip-Flop, , - Faulty IC, , Replace IC, , - No supply to IC, (series resistor open), , Replace resistor, , - Capacitor connected, to IC 555 shorted, , Charge faulty, capacitor, , - Driver transistor, , Fault in driver transistor, , Charge the transistor, , - Power transistor, (output transistor), , Fault in power transistor, , Replace the, power transistor, , Fault in output transformer, Partial short in winding / cave, , Rectify the transformer, fault or Replace the, transformer, , - Battery, , - Low A/H capacitor, of battery, , Replace Battery, , - Fault in IC, , - Over heat in IC, , Provide heat, , - Fault in power, transistor, , - Over heat in power, transistor, , Sink to IC, Sink to transistor, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.186 & 4.4.187, , Copyright @ NIMI Not to be Republished

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Electrical, Electrician - Inverter and UPS, , Related Theory for Exercise 4.4.188, , Installation of inverter in domestic wiring, Objectives: At the end of this lesson you shall be able to, • enumerate the important points to be kept in your mind to select the inverter to be installed, • state how to select the place to install the inverter and battery, • explain how to install the inverter with battery and load, and check for its performance, • state the rating of inverter and its sample calculation., Important points to be considered before installing, an inverter, Many time when a new inverter is not giving proper service,, the fault is due to improper installation only, not in inverter., Another most important point is when connecting an, inverter to the line is, the total load connected to the, inverter should not exceed 80% of capacity of inverter., Before providing points to connect the loads to the inverter,, the total connected load must be considered., If over load occur, then the overload protection will ‘cut, OFF’ the output and reduce the load then the reset key, must be pressed, and if the inverter is not provided with, overload protection, it may get damaged at the time of, over load than the capacity of the inverter., , Selection of place for installation of inverter, To connect inverter to the supply line, suitable place for, the inverter is to be located. That place must be nearer to, the service energy meter and ICDP switch and provide a, 3 pin output socket from the mains supply line for the, inverter and connect the inverter to the socket as in, (Fig 1)., Installation of inverter, Collect the suitable inverter with sealed free maintenance, battery to be installed, and check for their proper function, Place the inverter’s battery to a suitable place near the, inverter and connect the battery to the inverter.(Fig 1), , Copyright @ NIMI Not to be Republished, , 157

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Keep the battery as close as possible to the inverter, so, that the wire connecting the battery terminals to the inverter, can be small and current loss is reduced. Make sure the, battery is fully charged before installation., The positive terminals of battery (red wire) is connected, to the place provided for the positive terminal on the inverter, and the negative terminal of the battery (blue or black, wire), which is to be connected to the place provided for, the negative terminal on the inverter., When connecting battery terminals to the inverter, use, special auto wires do not use common mains wiring with, wires such as ‘3/20’ and 7/20 etc.connecting battery using, these wires will not provide proper connection between, the battery and the inverter., After connecting the battery, put some grease (or) vaseline on the battery terminals, which reducing the terminal, corrosion., All the connection is completed take the output from the, inverters output socket and use it to power the load. Use, 1/18 copper wire to the output of the load. Do not use, 3/20, 3/22 or 7/20 wires, commonly used in house wiring., The output is taken from the phase out ‘pin of inverter’, output socket, and is provided to the ON/OFF switches, on the wall pause.(Fig 1), The neutral line is common for both the inverter output, and the mains A/C line. So, only one wire for the phase, , 158, , line can be drawn from the inverter output socket to the, switches., In Fig 1, one bulb, one fan and a 2 pin output socket are, connected to the inverter output and the other devices in, the room. (ie) the tube light, fan (2) and a 3 pin output, socket are directly connected to the mains A/C line., In the two pin socket, should not be connected with heavy, load during power ‘OFF’ only small load like mosquito, repeller can be connected., As in (Fig 1) the load connected to the inverter will get the, mains A.C supply. If the mains supply is ‘On’ at the same, time, other devices will also work on the main supply,, because they are connected directly to the mains A.C, supply., But at the time of power shut down, the devices directly, are connected to the mains A.C will stop functioning and, the devices, which are connected to the inverter output, will keep on working on the inverter output., Later, if the mains A.C supply returns, the inverter will, once again connect the load, which are connected to its, output to the main supply. This process is in, Fig 2., Inverter rating calculation, Generally, the inverters are available with ratings such as, 200w,300w,400w,500w,600w,1000w,1200w,1500w and so, on., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.188, , Copyright @ NIMI Not to be Republished

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The cost of the inverter is proprotional to their capacity in, wattage (or) VA. It must be considered before buying the, Inverter., , Device, time, , Approx, Watts, , P.f-0.8, (app), VA, , Running, for 1 unit of, consumption, (approx.), Hrs. - Min., , Hot plate, , 1000W, , 800, , 1-00, , Oven, , 1000W, , 800, , 1-00, , Electric kettle 1000W, , 800, , 1-00, , Iron, , 360, , 2-15, , Calculation of power consumption, True power = Apparent power x power factor, Let us assume,, The loads are - 2 tube lights,(ie) 2x40W = 80W, - 1 fan (ie ), 1x60W = 60W, - 1 bulb (ie), 1x40W = 40W, Total load = 180 W, , 450W, , Water heater: 3000W, (a)Instant, geysers, 1.5 - 2 liter), , 2400, , 0-20, , If the total load is 180W, the inverter capacity is to be, selected for 300W, giving some safe margin., Always, the inverter with high rating must be purchased, by considering the future the household appliances may, be added., , Water heater: 2000W, (b)Storage type, (10-12 liter), , 1600, , 0-30, , Power consumption Table, , Water heater: 1000W, (c) Immersion, rod, , 800, , 1-00, , Vacuum, cleaner, , 700W, , 560, , 1-25, , Washing, machine, , 325W, , 260, , 3-00, , Water pump, , 750W, , 600, , 1-20, , TV, , 60W, , 48, , 16-00, , Radio, , 15W, , 12, , 66-00, , Video, , 40W, , 32, , 25-00, , Tape recorder 20W, , 16, , 50-00, , Stereo system 50W, , 40, , 20-00, , PC Cop., , 120W, , 150, , 8-20, , PC/XT cop., , 185W, , 230, , 5-25, , Device, time, , Approx, Watts, , P.f-0.8, (app), VA, , 20, , Running, for 1 unit of, consumption, (approx.), Hrs. - Min., , Incandecent, bulbs, (B.C bulbs), , 25W, , Incandecent, bulbs, , 40W, , 32, , 25-00, , Incandecent, bulbs, , 60W, , 48, , 16-40, , Incandecent, bulbs, , 100W, , 80, , 10-00, , Fluorescent, tube 61 cms, , 20W, , 16, , 50-00, , Fluroescent, 40W, tube 122 cms, , 32, , 25-00, , PC/AT Cop., , 255W, , 320, , 3-55, , 320W, , 400, , 3-08, , 4 feet, night lamp, , 15W, , 12, , 66-40, , 386& Higher, Cop., , 55, , 22-45, , Mosquito, repellent, , 5W, , 200-00, , Mono chrome 44W, monitor, CGA monitor, , 64W, , 88, , 15-35, , Fans, , 60W, , 48, , 16-40, , EGA monitor, , 80W, , 100, , 12-30, , Air - coolers, , 170W, , 136, , 5-50, , VGA monitor, , 120W, , 150, , 8-20, , Airconditioners, (1 to 1.5 ton), , 1500W, , 1200, , 0-40, , 80-column, dot-matrix, printer, , 64W, , 80, , 15-40, , Refrigerators, (165 liters), , 225W, , 180, , 4-30, , 160-240 cps, printer, , 100W, , 125, , 10-00, , Mixer/blender 450W, /juicer, , 360, , 2-15, , 140W, , 175, , 7-08, , Toaster, , 640, , 1-15, , 132- column, dot matrix, printer, , 4, , 800W, , 40-00, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.188, , Copyright @ NIMI Not to be Republished, , 159

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Device, time, , Approx, Watts, , P.f-0.8, (app), VA, , Running, for 1 unit of, consumption, (approx.), Hrs. - Min., , e ensures all equipment safe in good conditions, , The unplanned preventive maintenance is nothing but a, routine maintenance work. For example lubricating,, cleaning, tightening of nuts and bolts etc, are same of, the maintenance. This not involves any predetermined work, associated. The following is the draw backs of unplanned, preventive maintenance., , Image writer II 80W, , 80, , 12-30, , Laser write, plus, , 880W, , 1100, , 1-08, , HP Laser jet, Printer, , 840W, , 1050, , 1-11, , External, Hard Disks, , 80W, , 100, , 12-30, , 175, , 7-08, , Tape Back up 140W, , Preventive and breakdown maintenance, Preventive maintenance : It improves the performance, safety of a business instead of a large repairs being needed, and major problems arising. Consistent maintenance is, carried out to reduce these risks. This improves the, performance of all equipment. It also helps to avoid, unplanned repairs and unexpected maintenance needs., Preventive maintenance further divided into two parts they, are;, a Planned preventive maintenance and, b Unplanned preventive maintenance, a Planned preventive maintenance, , f, , If meets safety and environment standards, , g Improves the safety and health of workers., b Unplanned preventive maintenance, , a Increases overall material cost, b Improper usage of manpower, c Not guaranteed of quality or quality or quantity in, production, d No guarantee of machine condition, e Increased risk of problems, f, , Unexpected problems in production and quality., , Breakdown maintenance is a form of material or equipment, remediation that is performed after the equipment or, material has lost its functioning capabilities or properties., Breakdown maintenance is maintenance performed an, equipment that has broken down and is unusable. It is, based on a breakdown maintenance trigger., Demerits of breakdown maintenance, a Loss of production and business unexpected, , A planned preventive maintenance cut-down maintenance, cost and ensure the long life of equipment and a steady, quality output. The following is the benefits of planned, preventive maintenance., , b Huge expenses for restoration, , a overtime costs reduced, , e Leads to major accidents loss of life, , b reduced risk of problems, , f, , c reduced no. of repairs, , A well planned preventive maintenance can avoid, breakdown of machines and keep maintain steady quality, production and maintain company standards., , d small repairs can be carried out regularly, , 160, , c Non availability of spares and experts, d Accidents, environmental problems, Wastage of raw material if time based supply, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.4.188, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.5.189, Electrician - Power Generation and Substation, Sources of energy - Thermal power generation, Objectives: At the end of this lesson you shall be able to, • explain conventional and non-conventional energy source, • state the various source of energy, • state the type of fuels used for power generation, • explain the working principle of thermal power station - cool and nuclear based, • explain schematic arrangement and constituents of thermal, diesel and gas turbine power plants., Introduction of power generation, Energy is the basic necessity for the economic, development of a country and it exists in different forms, in nature. But the most important form is the electrical, energy . The modern society is fully depend on the, electrical energy and it has close relationship with, standard of living. The per capita consumption of energy, is the measure of standard of living of people., Sources of electrical energy, Since electrical energy is produced from energy available, in various forms in nature, it is desirable to look into the, various sources of energy. The natural sources of energy, which are used to generate the electricity are :, i, , Sun, , ii Wind, iii Water, iv Fuels, v Nuclear energy, vi Tidal, Out of these sources, the energy due to Sun and wind, has not been utilized on large scale due to a number of, limitations. At present, the other three sources viz, water,, fuels and nuclear energy are primarily used for the, generation of electrical energy., i, , Sun : The Sun is the primary source of energy. .Solar, cells are the one of the methods which uses the heat, energy of the sun to generate the electrical energy in, present days. this method came into large application, of solar cells to produce electricity.however, than the, limitations as:, , a) It requires a large area for the generation of even a, small amount of electric power., b) It cannot be used in cloudy days or at night, c) It is an uneconomical method compared to conventional, method, ii Wind: This method can be used where wind flows for, a considerable length of time. The wind energy is, used to run the wind mill which drives a small generator., , In order to obtain the electrical energy from a wind mill, continuously, the generator is arranged to charge the, batteries which supply the energy even the wind stops., This method has the advantages that maintenance and, generation costs are negligible. However, drawbacks, of the method are that it is unreliable because of, uncertainly about wind pressure and power generated, is quite small., iii Water: When water is stored at a suitable place, it, possesses potential energy because of the head, created. This water energy can be converted into, mechanical energy with the help of water turbines. The, water turbine drives the alternator which converts, mechanical energy into electrical energy. This method, of generation of electrical energy has become very, popular because it has low production and, maintenance costs., iv Fuels: The main sources of energy are fuels viz. solid, fuel as coal, liquid fuel as oil and gas fuel as natural, gas. The heat energy of the fuels is converted into, mechanical energy by suitable prime movers such as, steam engines, steam turbines, internal combustion, engines etc. The prime mover drives the alternator, which coverts mechanical energy into electrical energy., Although fuels continue to enjoy the place of chief, source for the generation of electrical energy, yet their, reserves are diminishing day by day. Therefore, the, present trend is to harness water power which is more, or less a permanent source of power., v Nuclear energy: Towards the end of Second world, War, it was discovered that large amount of heat energy, is liberated by the fusion of uranium and other, fissionable materials. It is estimated that heat, produced by 1 Kg of nuclear fuel is equal to that, produced by 27,50,000 kg of coal. The heat produced, due to nuclear fission can be utilized to raise steam, with suitable arrangements. The steam can run the, steam turbine which in turn can drive the alternator to, produce the electrical energy., Comparison of energy sources, The main sources of energy used for the generation of, electrical energy are water, fuels and nuclear energy. Below, is given their comparison in a tabular form in Table 1., , Copyright @ NIMI Not to be Republished, , 161

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Table 1, Sl.No, , Terms, , Water Power, , Fuels, , Nuclear Energy, , 1, , Initial cost, , High, , Low, , Highest, , 2, , Running cost, , Less, , High, , Least, , 3, , Reserves, , Permanent, , Exhaustible, , Inexhaustible, , 4, , Cleanliness, , Cleanest, , Dirtiest, , Clean, , 5, , Simplicity, , Simplest, , Complex, , Most complex, , 6, , Reliability, , Most reliable, , Less reliable, , More reliable, , Types of fuels used for power generations, Fuels are categorized into Three; They are, 1 Solid fuels, , ii Liquid fuel plant can be started quickly and can pick, up the load in a short time., iii There are no stand by losses., iv The overall cost is much less than that of coal., , 2 Liquid fuels, , v The thermal efficiency is higher than that of a coal., , 3 Gaseous fuels, , vi If requires less operating staff., , Solid Fuels, This can further be classified an, a Natural solid fuel, b Artificial soild fuel, The natural solid fuels are wood and different variation of, coal, while the artificial solid fuels are charcoal, coke and, pulverized fuel., , Disadvantages, i, , ii The plant can generate only low power., Advantage and disadvantage of solid fuel :Advantages, i, , Liquid Fuels, This can replace coal for the production of steam. The, major petroleum products, considered an liquid fuels are, the following., , The plant where liquid fuel is used has high running, cost as the fuel (i.e. diesel) used is costly., , The fuel (i.e coal) used in quite cheap., , ii The coal can be transported to the site of plant by rail, or road., Iii Solid fuel plant requires less space as compared to, the hydro-electric power station., , 1 Gasoline (Petrol), , v The cost is lesser than that of diesel., , 2 Kerosene, , Disadvantages, , 3 Gas oil, , i, , 4 Diesel, , It pollutes the atmosphere due to the production of, large amount of smoke and fumes., , ii It’s handling cost is high., , Gaseous Fuels, This fuel can be divided in the following categories., , Types of electrical power generation, , 1 Natural Gas - It is obtained from soil by mean of dup, wells and it is pumped out., , a Conventional power generation, , 2 Producer Gas - This is a mixture of CO and H2 with a, little CO2., 3 By product gases - This gas is obtained from blast, furnace and coke ovens., Advantages and disadvantages of liquid fuel, Advantages, i, , The design and layout of the plant where liquid fuel, is used are quite simple and it occupies less space, as the number and size of the auxiliaries are small., , 162, , Basically power generation are of two types, , Power generations by using non- renewable sources of, energy through various methods such as hydro, thermal, and nuclear etc is called conventional power generation., It contributes to the major power requirement., b Non conventional power generation, Power generation by using renewable energy sources, such as wind, Tide and sun etc, is called nonconventional power generation. They are small scale power, generation used for specific purpose., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished

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Generating stations, Bulk electric power is produced by special plants known, as generating station or power plants. A generating station, employs a prime mover coupled with an alternator or, generator for the production of electric power. The, generated power is further transmitted and distributed to, the customers., Depending upon the form of energy converted into, electrical energy the generating station are classified into,, 1 Steam power stations /Thermal power stations, 2 Hydro - electric power stations, 3 Diesel power stations, 4 Nuclear power stations, 5 Gas - turbine power stations, 1 Thermal /steam power station, A generating station which converts the heat energy of, coal combustion into electrical energy is known as a, steam power station., The scheme of generation can be divided into two phases, (i) Formation of steam in the boiler house (ii) Generation, of electrical power in the generator room., , The initial cost of harnessing water and converting the, potential energy into electrical energy is quite high but, recurring expenses etc. are quite less. So, the overall, system will be very economical., 3 Nuclear Power Station, A generating station which converts the nuclear energy, into the electric energy is called as nuclear power station., The nuclear power obtained by nuclear fission is fast, entering into arena of energy sources. The heat produced, by nuclear fission of atomic material is utilized in special, heat exchangers to produce steam to run steam turbines., The atomic materials utilized for nuclear fission are thorium, and uranium. Another reason of fast development of, nuclear power is that the natural resources of coal and, petroleum will exhaust early if the pace of industrial, development remained so fast., 4 Non conventional energy, It is evident that all energy resources based on fossil, fuels has limitations in availability and will soon exhaust., Hence the long term option for energy supply lies only, with non-conventional energy sources. These resources, are in-exhaustible/do not deplete for the next hundreds of, thousands of years., , In the boiler the fuel is burnt and the water is converted, into high pressure steam which is further super heated in, a super - heater. The super - heated steam is passed in, to the turbine to rotate the turbine blades, thus it converts, the heat energy into electrical energy., , For example electrical energy from solar energy, Bioenergy, Wind energy, Geothermal energy, Wave, Tidal, and Micro-hydro., , The turbine is the generation room acts as a prime mover, of the alternator which generates electric energy. The, alternator is connected through the circuit breaker to the, bus bars., , In order to achieve overall economy, the following points, should be considered while selecting a site for a steam, power station., , This type of power station is suitable where coal and water, are available in abundance and a large amount of electric, power is to be generated., 2 Hydro - electric power station, A generating station which converts the energy posses, by the water into the electrical energy is known as hydroelectric power station., Water is a great source of energy. There are two types of, energies which the water can posses. The flowing water, in stream may have only kinetic energy. The flowing steam, of water may have both kinetic as well as potential energy, or simply potential energy at some elevation with respect, to a lower datum level. The practical examples of which, are water - falls or water stored at the back of a dam. The, water stored in the reservoir is allowed to fall on the blades, of a water turbine placed at the foot of the dam., , Choice of site for steam power stations, , i, , Supply of fuel : The steam power station should be, located near the coal mines so that transportation, costs of fuel is minimum. However, if such a plant is, to be installed at a place where coal is not available,, then care should be taken that adequate facilities, exists for the transportation of coal., , ii Availability of water : As huge amount of water is, required for the condenser, therefore, such a plant, should be located at the bank of a river or near a canal, to ensure the continuous supply of water., iii Transportation facilities : A modern steam power, station often requires the transportation of materials, and machinery. Therefore, adequate transportation, facilities must exist. i.e., the plant should be well, connected to other parts of the country by rail, road, etc., iv Cost and type of land : The steam power station, should be located at a place where land is cheap and, further extension, if necessary is possible. Moreover,, the bearing capacity of the ground should be adequate, so that heavy equipment could be installed., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished, , 163

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v Nearness to load centers: In order to reduce the, transmission cost, the plant should be located near, the center of the load. This is particularly important if, DC supply system is adopted. However, if AC supply, system, is adopted, this factor becomes relatively, less important. It is because AC power can be, transmitted at high voltages with consequent reduced, transmission cost. Therefore, it is possible to install, the plant away from the load centers, provided other, conditions are favourable., , Conclusion : It is clear that all the above factors cannot, be favorable at one place. However, keeping in view the, fact that now- a -days the supply system in AC and more, importance is being given to generation than transmission,, a site away from the towns may be selected. In particular,, a site by river side where sufficient water is available and, fuel can be transported economically, may perhaps be, an ideal choice., , vi Distance from populated area : As huge amount of, coal is burnt in a steam power station, therefore, smoke, and fumes pollute the surrounding areas. This, necessitates that the plant should be located at a, considerable distance from the populated areas., , Although steam power station simply involves the, conversion of heat of coal combustion into electrical, energy, yet it embraces many arrangements for proper, working and efficiency. The schematic arrangement of a, modern steam power station is in Fig.1. The whole, arrangement can be divided into the following stages for, the sake of simplicity., , 164, , Schematic arrangement of steam power station, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished

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1 Coal and ash handling arrangement, , metre of furnace which implies high furnace temperature., , 2 Steam generating plant, , iii Super heater : A super heater is a device which super, heats the steam (i.e) it further raises the temperature, of steam. This increases the overall efficiency of the, plant. A super heater consists of a group of tubes, made of special alloy steels such as chromiummolybdenum. The steam produced in the boiler is led, through the super heater where it is superheated by, the heat of flue gases. Super heaters are mainly, classified into two types according to the system of, heat transfer from flue gases of steam viz., , 3 Steam turbine, 4 Alternator, 5 Feed water, 6 Cooling arrangement, Constituents in steam power station, A modern steam power station is highly complex and, has numerous equipment and auxiliaries. However, the, most important constituents of a steam power station, are :, 1 Steam generating equipment, 2 Condenser, 3 Prime mover, 4 Water treatment plant, 5 Electrical equipment, 1 Steam generating equipment, This is an important part of steam power station. It is, concerned with the generation of superheated steam and, includes such items as boiler, boiler furnace, super heater,, economizer, air pre-heater and other heat reclaiming, devices., , a Radiant super heater, b Convection super heater, iv Economiser : It is a device which heats the feed water, on its way to boiler by deriving heat from the flue gases., This results in raising boiler efficiency, saving in fuel, and reduces stresses in the boiler due to high, temperature of feed water. An economizer consists of, a large number of closely spaced parallel steel tubes, connected by headers of drums. The feed water flows, through these tubes and the flue gases flow outside. A, part of heat of flue gases is transferred to feed water,, thus raising the temperature of the latter., , a Water tube boilers, , v Air Pre-heater : Super heaters and economizers, generally cannot fully extract the heat from flue gases., Therefore, pre - heaters are employed which recover, some of the heat in the escaping gases. The function, of an air pre-heater is to extract heat from the flue, gases and give it to the air being supplied to furnace, for coal combustion. This raises the furnace, temperature and increases the thermal efficiency of, the plant. Depending upon the method of transfer of, heat from flue gases to air, air pre-heaters are divided, into the following classes., , b Fire tube boilers, , a Recuperative type, , In a water tube boiler, water flows through the tubes and, the hot gases of combustion flow over these tubes. On, the other hand, in a fire tube boiler, the hot products of, combustion pass through the tubes surrounded by water., Water tube boilers have a number of advantages over fire, tube boilers viz. require less space, smaller size of tubes, and drum, high working pressure due to small drum, less, liable to explosion etc. Therefore, the use of water tube, boilers has become universal in large capacity steam, power stations., , b Regenerative type, , i, , Boiler : A boiler is closed vessel in which water is, converted into steam by utilizing the heat of coal, combustion. Steam boilers are broadly classified into, the following two types., , ii Boiler furnace : A boiler furnace is a chamber in which, fuel is burnt to liberate the heat energy. In addition, it, provides support and enclosure for the combustion, equipment i.e burners. The boiler furnace walls are, made of refractory materials such as fire clay, silica,, kaolin etc. These materials have the property to, resist change of shape, weight or physical properties, at high temperatures., The size of furnace has to be limited due to space, cost, and other considerations. This means that furnace of a, large plant should develop more kilo calories per square, , 2 Condensers, A condenser is a device which condenses the steam and, the exhaust of turbine. It serves two important functions., Firstly, it creates a very low pressure at the exhaust of, turbine, thus permitting expansion of the steam in the, prime mover to a very low pressure. This helps in, Converting heat energy of steam into mechanical energy, in the prime mover. Secondly, the condensed steam can, be used as feed water to the boiler. There are two types, of condensers, namely, a Jet condenser, b Surface condenser, 3 Prime movers, The prime mover converts steam energy into mechanical, energy. There are two types of steam prime mover viz.,, steam engines and steam turbines. A steam turbine has, several advantages over a steam engine as a prime mover, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished, , 165

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viz., high efficiency, simple construction, higher speed,, less floor area requirement and low maintenance cost., Therefore, all modern steam power stations employ steam, turbines as prime movers., Steam turbines are generally classified into two types, according to the action of steam on moving blades viz., a Impulse turbines, b Reaction turbines, In an impulse turbine, the steam expands completely in, the stationery nozzles (or fixed blades), the pressure over, the moving blades remaining constant. In doing so, the, steam attains a high velocity and the impulsive force on, the moving blades which sets the rotor rotating., In a reaction turbine, the steam is partially expanded in, the stationery nozzles, the remaining expansion take, place during its flow over the moving blades. The results, is that the momentum of the steam causes a reaction, force on the moving blades which sets the rotor in motion., 4 Water treatment plant, , =, , 1.008, 6.03 x 10 23, , = 1.67 x 10-24 gm = 1.67 x 10-27 kg................ (1), The mass of 1 electron, , Boilers require clean and soft water for longer life and, better efficiency. However, the source of boiler feed water, is generally a river or lake which may contain suspended, and dissolved impurities, dissolved gases etc. Therefore,, it is very important that water is first purified and softened, by chemical treatment and then delivered to the boiler, The water from the source of supply is stored in storage, tanks. The suspended impurities are removed through, sedimentation, coagulation and filtration. Dissolved gases, etc, are removed by aeration and degasification. The water, is then ‘softened’ by removing temporary and permanent, hardness though different chemical processes. The pure, and soft water thus available is fed to the boiler for steam, generation., Nuclear based thermal power stations, Composition of an atomic nucleus, A matter is said to be composed of small particles called, atoms and the atom itself is composed protons, neutrons, and electrons, arranged in a particular fashion. The centre, of the atom consists of a very dense nucleus formed by, protons and neutrons. Around the nucleus the electrons, revolve in orbit. The system so formed is similar to that of, planetary system as shown in Fig 2. The radius of the, nucleus is about 10-12 cm. While that of electron orbit is, about 10-5 cm., , =, , 1.67 x 10 −27, = 9.10 x 10 − 31 kg .......... ........( 2), 1840, , It has been practically observed that, to deposit 1 molecule, gram of hydrogen 96,493.7 coulombs of electricity are, required., So, charge on each electron, , =, , 96.493.7, 6.03 x 1023, , = 1.602 x 10-19 coulombs ............................... (3), The charge of proton is the same as that of electron, = 1.602 x 10-19 coulombs ............................... (4), The charge and mass of an electron, proton and neutron, can be summarized as., Name of, atomic, ingredient, , Electric, charge in, coulomb, , Mass in, kilogram, , Mass in, atomic, mass unit, (a.m.u)*, , 1. Electron, , -1.602 x 10-19 9.10x10-21, , 0.000, 548, , The important properties of the atomic structure are:, , 2. Proton, , +1.602x10-19, , 1.67x10-27, , 1.00,758, , The mass of proton and neutrons is almost same while the, mass of each electron is 1/1840 times that of a proton or, neutron which shows that the mass of an atom is only due, to the nucleus. From avogadro’s hypothesis, the number, of atoms in a gram atom is 6.03 x 1023 (actually its mass, is 1.008 gm), , 3. Neutron, , 0, , 1.67x10-27, , 1.00,898, , 166, , *1 a.m.u = 1.6597 x 10-19 kg., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished

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Atomic number and mass number: The chemical, properties of an atom depend on the number of protons, present in the nucleus., The atomic number of an atom is defined as the number of, protons present in the nucleus of an atom and is represented, as Z., Let, N be equal to number of neutrons in the nucleus. The, mass number (A) is given as., A= Z +N, The advantage of atomic number and mass number is that, this represents an atom uniquely. Thus, for example, sodium atom is represented as 12Na23, where, the prefix, represents the atomic number (Z) and suffix represents, mass number (A), i .e 12 is atomic number and 23 is mass, number., , Advantages, i, , The amount of fuel required is quite small. Therefore,, there is a considerable saving in the cost of fuel, transportation., , ii A nuclear power plant requires less space as compared, to any other type of the same size., iii It has low running charges as a small amount of fuel is, used for producing bulk electrical energy., iv This type of plant is very economical for producing bulk, electric power., v It can be located near the load centers because it does, not requires large quantities of water and need not be, near coal mines. Therefore, the cost of primary, distribution is reduced., , The number of neutron (N) presents in the atom can be, determined by, , vi There are large deposits of nuclear fuels available all, over the world. Therefore, such plants can ensure, continued supply of electrical energy for thousands of, years., , N = A - Z = 23-12, , vii It ensures reliability of operation., , = 11, , Disadvantages, , The atomic number, mass and number of neutrons for, some elements are listed in Table 1., , i, , Table 1, Element, , Symbol, , Atomic, number, =Z, , Mass Neutrons, No =A A - Z, , Hydrogen, , 1, , H1, , 1, , 1, , 0, , Helium, , He4, 2, , 2, , 4, , 2, , Oxygen, , 8, , O16, , 8, , 16, , 8, , Uranium, , 92, , U238, , 92, , 238, , 146, , Nuclear power station, A generating station in which nuclear energy is converted, into electrical energy is known as a Nuclear power station., In nuclear power station, heavy elements such as Uranium, (U235) or Thorium (Th232) are subjected to nuclear fission in, a special apparatus known as a reactor. The heat energy, thus released is utilized in raising steam at high temperature, and pressure. The steam runs into the steam turbine, which converts steam energy into mechanical energy., The turbine drives the alternator which converts mechanical, energy into electrical energy., The most important features of a nuclear power station is, that huge amount of electrical energy can be produced, from a relatively small amount of nuclear fuel as compared, to other conventional types of power station. Although the, extracting of the nuclear fuels (i.e Uranium and Thorium), is difficult and expensive, yet the total energy content are, considerably higher than those of conventional fuel, viz., coal, and gas., , The fuel used is expensive and is difficult to extract., , ii The capital cost on a nuclear plant is very high as, compared to other types of plants., iii The erection and commissioning of the requires greater, technical know - how., iv The fission by products are generally radio - active and, may cause a dangerous amount of radioactive pollution., v Maintenance charges are high due to lack of, standardization. Moreover, high salaries of specially, trained personnel employed to handle the plant further, raise the cost., vi Nuclear power plants are not well suited for varying, loads as the reactor does not respond to the load, fluctuations efficiently., vii The disposal of the waste, which are radioactive, is a, big problem. They should either be disposed off in a, deep trench or in the sea away from the sea- shore., Schematic arrangement of nuclear power station, The schematic arrangement of a nuclear power station is, in Fig 3. The whole arrangement can be divided into the, following main stages., i, , Nuclear reactor, , ii Heat exchanger, iii Steam turbine, iv Alternator, i, , Nuclear reactor : It is an apparatus in which nuclear, fuel (U235) is subjected to nuclear fission. It controls the, chain reaction that starts once the fission is done. If, the chain reaction is not controlled, the result will be an, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished, , 167

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explosion due to the fast increase in the energy, released., A nuclear reactor is a cylindrical stout pressure vessel and, houses fuel rods of Uranium, moderator and control rods, (Fig 4)., The fuel rods constitute the fission material and release, huge amount of energy when bombarded with slow moving, neutrons. The moderator consists of graphite rods which, enclose the fuel rods. The moderator slows down the, neutrons before they bombard the fuel rods. The control, rods are of cadmium and are inserted into the reactor., Cadmium is strong neutron absorber and thus regulates, the supply of neutrons for fission., , ii Heat exchanger : The coolant gives up heat to the, heat exchanger which is utilized in raising the steam., After giving up heat, the coolant is again fed to the, reactor., , 168, , When the control rods are pushed in deep enough, they, absorb most of fission neutrons and hence few are, available for chain reaction which, therefore, stops. However,, as they are being withdrawn, more and more of these, fission neutrons cause fission and hence the intensity of, chain reaction (or heat produced) is increased. Therefore,, by pulling out the control rods, power of the nuclear reactor, is increased whereas by pushing them in, it is reduced., In actual practice, the lowering or raising of central rods, is accomplished automatically according to the, requirement of rod. The heat produced in the reactor is, removed by the coolant, generally in a sodium metal. The, coolant carries the heat to the heat exchanger., , iii Steam turbine : The steam produced in the heat, exchanger is led to the steam turbine through a valve., After doing a useful work in the turbine, the steam is, exhausted to condenser. The condenser condenses, the steam which is fed to the heat exchanger through, feed water pump., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished

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iv Alternator : The steam turbine drives the alternator, which converts mechanical energy into electrical, energy. The output from the alternator is delivered to, the bus- bars through transformer, circuit breaker and, isolators., Selection of site for nuclear power station, , sea or river and away from thickly populated areas., Nuclear reactors, Nuclear reactors may be classified on the following basis., A) On the basis of neutron energy, 1 Thermal reactors, , The following points should be kept in view while selecting, the site for a nuclear power station., , 2 Fast breeder reactors, , i, , 1 Natural uranium, , Availability of water : As sufficient water is required, for cooling purposes, therefore, the plant site should be, located where ample quantity of water is available e.g., across a river or by sea - side., , ii Disposal of waste : The waste produced by fission in, a nuclear power station is generally radioactive which, must be disposed off properly to avoid health hazards., The waste should either be buried in a deep trench or, disposed off in the sea quite away from the sea shore., Therefore, the site selected for such a plant should, have adequate arrangement for the disposal of, radioactive waste., iii Distance from populated areas : The site selected, for a nuclear power station should be quite away from, the populated areas as there is a danger of presence, of radio - activity in the atmosphere near the plant., However, as the precautionary measure, a dome is, used in the plant which does not allow the radioactivity, to spread by wind or underground waterways., iv Transportation facilities : The site selected for a, nuclear power should have adequate facilities in order, to transport the heavy equipment during erection and to, facilitate the movement of the workers employed in the, plant., From the above mentioned factors it becomes apparent, that idel choice for a nuclear power station would be near, , B) On the basis of fuel used, 2 Enriched uranium, C) On the basis of moderator used, 1 Graphite reactors, 2 Beryllium reactors, D) On the basis of coolant used, 1 Water cooled reactors (ordinary or heavy), i, , Boiling water reactor, , ii Pressurized water reactor, iii Heavy water cooled and moderated reactor, 2 Gas cooled reactors, 3 Liquid metal cooled reactors, 4 Organic liquid cooled reactors, E) On the basis of type of core used, 1 Homogenous reactors, 2 Heterogeneous reactors, Boiling water reactor (BWR), In this reactor fuel used is enriched uranium. Water is, used as both the moderator and coolant. As is clear from, its name it utilizes light water as a coolant. In this case the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished, , 169

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steam is generated in the reactor itself. Feed water enters, the reactor tank at the bottom and takes up the heat, generated due to the fission of fuel and gets converted into, steam., Steam leaves the reactor at the top and flows into the, turbine. Uranium fuel elements are arranged in a particular, lattice form inside the pressure vessel containing water., Feed water passes through fuel elements in the core as, coolant and also as moderator. Fig 5 shows a boiling water, reactor., Advantages, 1 Heat exchanger circuit is eliminated and as a result, there is reduction in cost and gain in thermal efficiency, (30% to 20% for a pressure water reactor (PWR))., 2 As water is allowed to boil inside the reactor the, pressure inside the reactor vessel is considerably, lower than in the case of a PWR. As a result the reactor, vessel can be made much lighter reducing its cost, considerably., 3 The BWR cycle is more efficient than the PWR cycle, since for a given containment pressure the outlet, temperature of steam is appreciably higher in a BWR., 4 The metal surface temperature is lower than in the, case of a PWR since boiling of water is inside the, reactor., 5 A BWR is more suitable than a PWR, (In fact BWR is, commonly known as a self - controlled reactor), Disadvantages, 1 There is a possibility of radio - active contamination in, the turbine mechanism should there occur any failure, of fuel elements. Therefore more elaborate safety, measures are needed. This increases the cost., , 170, , 2 There is wastage of steam resulting in lowering of, thermal efficiency on part load operation., Pressurized Water Reactor (PWR), A pressurized water reactor is in Fig 6. The line arrangement, of such a reactor with heat exchanger in circuit is in Fig 7., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished

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5 The reactor lacks flexibility; this requires the reactor to, be shut down before recharging and there is difficulty, in fuel element design and fabrication., 6 The thermal efficiency of a PWR is as low as 20%, Less compared with that required for PWRs and BWRs., Amongst disadvantages are : the extremely high cost of, heavy water, problem of leakage and very high standard of, design etc., Nuclear fission and fusion, The fuel used is enriched uranium clad with stainless steel, or zirconium alloy and water under pressure is used as, both moderator and coolant. This type of reactor is, designed to prevent the boiling of the water coolant in the, uranium core. A pump circulates water at high pressure, (as high as 140 Kg/cm2) round the core so that water in, liquid state absorbs heat from the uranium and transfer it, to the secondary loop-the boiler. The boiler has a heat, exchanger and a steam drum., A pressuriser and surge tank tapped into the pipe loop, maintains constant pressure in the water system throughout, the load range. An electric heating coil in the pressuriser, boils the water to form steam which is collected in the, dome; this steam pressurizes the entire coolant circuit., Water spray is used to condense the steam when, pressure is desired to be reduced., , Nuclear fission : When an uranium nucleus is bombarded, with a slow moving neutron, it exploded into two nearly, equal fragments of Barium and Krypton., The process of breaking up of the nucleus of a heavy atom, into two fragments with the release of large amount of, energy is known as fission. The fission is accompanied by, the release of three neutrons and energy in the form of γrays., Fig 8 shows that the compound nucleus undergoes, distortion due to the excitation energy to attain the shape, of a dumb-bell and finally splits up into fission products, Ba141 and Kr92 with the release of three neutrons., , Since water is passing through the reactor becomes radio, - active the entire primary circuit including heat exchanger, has to be shielded., Advantages, 1 A PWR is relatively compact in size compared with, other types., 2 There is a possibility of breeding plutonium by providing, a blanket of U-238., 3 The reactor has a high power density., 4 Due to use of heat exchanger containment of fission, products is possible., 5 An inexpensive substance (light water) can be used as, moderator - cum-coolant-cum-refractor., 6 The reactor responds to supply more power when the, load increases. (The positive power demand co-efficient, makes this almost automatic), Disadvantages, 1 The moderator remains under high pressure; a strong, pressure vessel is required., 2 Expensive cladding material is required to prevent, corrosion., 3 There is heat loss due to use of heat exchanger., 4 In comparison to other types more elaborate safety, devices are required., , It was observed that Barium and krypton were not the only, products of fission, the isotopes of different elements in, the atomic number range from 34 to 58 were also obtained, as the fission products., Chain reaction, The process of nuclear fission usually results in the, emission of two or three free neutrons per fission besides, the other fission fragments., When 92U235 nucleus splits up, it generally release three, neutrons. One of the neutrons may escape without hitting, any other uranium nucleus and thus get lost. The other two, may strike against other fissionable nuclei to produce, further fission, accompanied by the release of still more, neutrons and so on. Thus more than one neutron per, fission is produced on the average., The number of fissions taking place at each successive, stage goes on increasing at a rapid rate, giving rise to what, is called chain reaction. A chain reaction can be set up, only if the mass of the fissionable material is greater than, a critical mass., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.189, , Copyright @ NIMI Not to be Republished, , 171

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Electrical, Related Theory for Exercise 4.5.190, Electrician - Power Generation and Substation, Hydel power plants, Objectives: At the end of this lesson you shall be able to, • state the types of hydro- electric power station, • state the advantage & disadvantage of hydro electric power station over thermal power station, • list out the reason for selecting the site of a hydro electric power station, • explain the schematic arrangement of hydro electric power station, • state the turbines used in hydro electric power station with suitable reasons, • state the classification of hydro electric power station., Hydro - electric power stations, A generating station which utilizes the potential energy of, water at a high level for the generation of electrical energy, is known as "Hydro-electric power station"., A basic model of a H.E.P generation is illustrated in, Fig 1 is known as hydro - electric power station., , v It does not requires a long starting time like a steam, power station. In fact, such plants can be put into, service instantly., vi It is robust and has a longer life., vii Such plants serve many purposes. In addition to the, generation of electrical energy, they also help in, irrigation and controlling floods., viii Although such plants require the attention of highly, skilled persons at the time of construction, yet for, operation, a few experienced persons may do the job, well., Disadvantages, i, , It involves high capital cost due to construction of dam, , ii There is uncertainly about the availability of huge, amount of water due to dependence on weather, conditions., iii Skilled and experienced hands are required to build the, plant, , Hydro - electric power stations are generally located in, hilly areas where dams can be built conveniently and large, water reservoirs can be obtained. From the dam, water is, led to a water turbine. The water turbine captures the, energy in the falling water and changes the hydraulic, energy (i.e product of head and flow of water) into, mechanical energy at the turbine shaft., The turbine drives the alternator which converts mechanical, energy into electrical energy. Hydro electric power stations, are becoming very popular because the reserves of fuels, (i.e coal and oil) are depleting day by day., Advantages, i, , It requires no fuel as water is used for the generation of, electrical energy, , ii It is quite neat and clean as no smoke or ash is, produced, iii It requires very small running charges because water, is the source of energy which is available free cost., iv It is comparatively simple in construction and requires, less maintenance., 172, , iv It requires high cost of transmission lines as the plant, is located in hilly areas which are away from the, consumers., Choice of site for hydro - electric power stations, The following points should be taken into account while, selecting the site for a hydro - electric power station, i, , Availability of water : Since the primary requirement, of a hydro - electric power stations is the availability, of huge quantity of water, such plants should be built, at a place (e.g. river, canal) where adequate water is, available at the good head., , ii Storage of water : There are wide variations in water, supply from a river or canal during the year. This makes, it necessary to store water by constructing a dam in, order to ensure the generation of power throughout the, year., iii Cost and type of land : The land for the construction, of the plant should be available at a reasonable price., Further, the bearing capacity of the ground should be, adequate to withstands the weight of heavy equipment, to be installed., , Copyright @ NIMI Not to be Republished

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vi Transportation facilities : The site selected for hydro, - electric plant should be accessible by rail and road so, that necessary equipment and machinery could be, easily transported, Schematic arrangement of hydro - electric power, station : (Fig 2), , include booms and racks for diverting floating debris,, sluices for by - passing the debris and sediments and, valves for controlling the flow of water to the turbine. The, flow of water into and through head works should be as, smooth as possible to avoid the head loss and, cavitation. For this purpose, it is necessary to avoid, sharp corners and abrupt contractions or enlargements., iv Surge tank : Open conduits which leading the water, to the turbine require no protection. However, when, closed conduits are used, protection becomes, necessary to limit the abnormal pressure in the conduit., For this reason, closed conduits are always provided, with a surge tank. a surge tank is a small reservoir or, tank (open at the top) in which water level rises or fails, to reduce the pressures swings in the conduit., , The schematic arrangement of a modern hydro - electric, plant is shown in Fig. 2. The dam is constructed across a, river or lake and water from the catchment area collects at, the back of the dam to form a reservoir. A pressure tunnel, is taken off from the reservoir and water brought to the valve, house at the start of the Penstock., The valve house contains main sluice valves and automatic, isolating valves. The former controls the water flow to the, power house and the latter cuts of supply of water flow to, the power house when the penstock bursts. From the valve, house, water is taken to water turbine through a huge steel, pipe known as penstock . The water turbine converts, hydraulic energy into mechanical energy. The turbine, drives the alternator which converts mechanical energy, into electrical energy., Constituents of Hydro - Electric Plant, The constituents of hydro - electric plant are (1) hydraulic, structures (2) water turbines and (3) electrical equipment., 1 Hydraulic Structures, Hydraulic structures in a hydro electric power station, include dam, spillways, headworks, surge tank, penstock, and accessory works., i, , Dam : A dam is a higher barrier which stores water and, creates water head. Dams are built of concrete or, stone masonry, earth or rock fill. The type and, arrangement depends upon the topography of the site., The type of dam also depends upon the foundation, conditions, local materials and transportation available,, occurrence of earthquakes and other hazards., , ii Spillways : There are times when the river flow, exceeds the storage capacity of the reservoir. Such a, situation arises during heavy rainfall in the catchment, area. In order to discharge the surplus water from the, storage reservoir into the river on the down - stream, side of the dam, spillways are used., iii Headworks : The headworks consists of the diversion, structures at the head of an intake. They generally, , A surge tank is located near the beginning of the conduit., When the turbine is running at a steady load, there are no, surges in the flow of water through the conduit is just, sufficient to meet the turbine requirements. However,, when the load on the turbine decreases, the governor, closes the gates of turbine, reducing water supply to the, turbine., The excess water at the lower end of the conduit rushes, back to the surge tank and increases its water level. Thus, the conduit is prevented from bursting. On the other hand,, when load on the turbine increases, additional water is, drawn from the surge tank to meet the increased load, requirement. Hence, a surge tank overcomes the abnormal, pressure in the conduit when load on the turbine falls and, acts a reservoir during increase of load on the turbine., (v) Penstocks : Penstocks are open or closed conduits, which carry water to the turbines. They are generally, made of reinforced concrete or steel. The thickness of, the Penstock increases with the head or working, pressure, Various devices such as automatic butterfly valve, air, valve and surge tank are provided for the protection of, penstocks. Automatic butterfly valve shuts off water flow, through the penstocks promptly of its ruptures. Air valve, maintains the air pressure inside the penstock equal to, outside atmospheric pressure., When water run out of a penstock faster than it enters, a, vacuum is created which may cause the penstocks to, collapse. Under such situations, air valve opens and, admits air in the penstock to maintain inside air pressure, equal to the outside air pressure. A typical penstock, protective device is in Fig 3., (vi) Tail race : The tail race is the channel which carries, water (known as tail water) away from the power house, after it has passed through the turbine. It may be the, natural stream channel or a specially excavated channel, entering the natural stream at some point down stream, from the power house. The water surface in the tail race is, known as tail race level or simply the tail race., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.190, , Copyright @ NIMI Not to be Republished, , 173

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partly with velocity head. The important types of reaction, turbine are., , (vii) Draft tube : In the case of a reaction turbine there is, a pressure difference existing between water in the turbine, and atmosphere. Therefore this type turbine must be, completely enclosed. Accordingly it is necessary to, connect the turbine outlet by means of a pipe or a passage, of gradually increasing cross sectional area up to tail race level., A draft tube has two important purposes to serve., 1 It permits a negative or suction head to be established, at the runner exit thus making it possible to install the, turbine above the tail race level without loss of head., 2 It converts a large proportion of the velocity energy, rejected from the runner into useful pressure head i.e, it acts as a recuperator of pressure energy., , a. Francis turbines, b. Kaplan turbines, A fancies turbine is used for low to medium heads. It, consists of an outer ring of stationary guide blades for to, the turbine casing and an inner ring of rotating blade, forming the runner. The guide blades control the flow water, to the turbine. Water flows radically inwards and changes, to a downward direction while passing there the runner., As the water passes over the rotating blade of the runner,, both pressures and velocity of water reduced. This, causes a reaction force which drive turbine., , Water turbines are used to convert the energy of falling, water into mechanical energy. The principal types of water, turbines are :, , A Kaplan turbine is used for low heads and large quantities, of water. It is similar to Francis turbine except that the, runner of Kaplan turbine receives water axially. Water, radially inwards through regulating gates all round sides,, changing direction in the runner to axial flow causes a, reaction force which drives the turbine., , i, , 3 Electrical equipment, , 2 Water turbine, , Impulse turbines, , ii Reaction turbines, i, , Impulse turbines : Such turbines are used for high, heads. In an impulse turbines, the entire pressure of, water is converted into kinetic energy in a nozzle and, the velocity of the jet drives the wheel i.e, pelton wheel, as in Fig 4. It consists of a wheel fitted with elliptical, buckets along it periphery. The force of water jet, striking the bucket on the wheel drives the turbine. The, quantity of water jet falling on the turbine is controlled, by means of needle or spear (not shown in the figure), placed in the tip of the nozzle., , The movement of the needle is controlled by the governor., If the load on the turbine decreases the governor pushes, the needle into the nozzle, there reducing the quantity of, water striking the bucket. Reverse action takes place if, the load on the turbine increases., ii Reaction turbines : Reaction turbines are used for, low and medium heads. In a reaction turbine water, enters the runner partly with pressure energy and, 174, , The electrical equipment of a hydro - electric power, includes alternators, transformers, circuit breaker and, switching and protective devices., Types of hydro - electric plants, There are three different methods of classifying the electric, plants. The classification may be based on,, a Quantity of water available, b Available head, c Nature of load, Classification of Hydro - electric plants according to, quantity of water available., According to this classification, the plants may be divided, into., i, , Run - off river plants without pondage, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.190, , Copyright @ NIMI Not to be Republished

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ii Run - off river plants with pondage, iii Reservoir plants, i, , Run off river plants without pondage, , As the name indicates this type of plant does not store, water. The plant uses water as it comes. The plant can, use water only as and when available., ii Run- off river plants with pondage, Usefulness of a run - off river plant is increased by, pondage. Pondage permits storage of water during the off, - peak periods and use of this water during the peak, periods., iii Reservoir plants, Water is stored behind the dam and is available to the plant, with control as required. Such a plant has better capacity, and can be used efficiently throughout the year., , Classification of hydro - electric plants according to, available head, Hydro - electric plants may be classified into high - head,, medium - head and low head plants. A plant may be, classified as high - head if operating on a head above 300, meters. Low - head plants work under heads below 30, metres. Medium - head plants are those lying between the, above two classes., In the case of high - head plants water in due to rains or, melting of snow is stored at high elevation. A low - head, plant stores water by the construction of a dam across a, river and the power plant is installed near the base of the, dam of the down - stream side. The medium - head plant, is similar to the low - head plant but works on a head of, about 30 to 300 m., Classification of Hydro- electric plants according to, nature of load, Hydro - electric plants may be classified in to base load, peak load and pumped storage plants for peak load., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.190, , Copyright @ NIMI Not to be Republished, , 175

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Electrical, Related Theory for Exercise 4.5.191 & 4.5.192, Electrician - Power Generation and Substation, Visiting of electrical substation, Objectives: At the end of this lesson you shall be able to, • state the initial preparatory work before commencing the visit, • explain the individual trainees main areas and its importance for preparation, • list out the supporting materials to carry for visit, • prepare a list of do’s and dont’s during visit., Introduction, A industrial visit is a very important step to tap actual, working environments. During practical exercises practicing, in the lab or workshop never provides actual working, condition because it is a part of structure training planned, to complete within a stipulated time and a assessment at, later stage., Initial preparatory work, The trainees should be in a position to interact well at the, actual site. Every industry technical experts execute the, work on a team and produce better results. The technician, or operator concerned will be able to give a clear idea of, working or procedure of a particular work and you have to, extract it fully, To understand the whole process from the concerned, technician or operator, you must have a sound knowledge, of that particular abject or process. You should prepare, well to meet the challenge whenever you go industrial visit, in a factory or work place., Preparation areas and its importance, If the process is complicated or multi level procedure, involved; in that case trainees should be made small, batches to interact or involve the whole process. In such, cases each batch should be formed in advance and, decided the section or part to be interacted. Finally all the, batches together to make the end result., , When the visit is at generating stations, have must collect, the following:, 1 Installed capacity of the plant., 2 Maximum load demand ., 3 Load factor ., 4 Distance of the nearest sub station., Total number of alternators installed and its working, conditions., , 176, , 7 Solutions to meet extra fuel in case of environmental, emergency., 8 Location Map of the plant and its surroundings., 9 Gather maximum information regarding generation and, distribution techniques other than guided or studied., 10 Maximum hazardous Area - PPE facility Emergency, root in case of emergency., Do’s & Dont’s, Do’s, 1 Wear uniform with name badge., 2 Ensure the protective gadgets are available otherwise, carry them., 3 Follow the safety norms imposed in the particular, areas, listen the instruction carefully., 4 Carry materials to record your findings and assessments, to make then and their., 5 Follow strict discipline and punctuality ., 6 Obey all the instructions and rules., 7 Walk in the prescribed areas only., Dont’s, 1 Avoid wearing loose clothes and ornaments., 2 Not to carry any bag or attachments., 3 Do not cross-over any prohibited areas ., , Supporting materials, , 5, , 6 Details of the fuel used (Coal- Nuclear - Its availability,, quality etc) and the daily expenditure for fuel., , 4 Do not operate, touch or play with any part or machine, you pass over., 5 Do not sit or learn over any machine or place you come, accross., 6 Do not shout or make any unusual noices when the, visit is in progress or inside the factory., 7 Do not involve any kind of horse play at the time of, visiting various sections, areas., 8 Do not avoid or neglect any instruction passed on you, at any time., , Copyright @ NIMI Not to be Republished

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9 Do not indulge any horse play or encourage others to, do. The person responsible for leading the visit has to, arrange the programme well in advance and informs all, concerned. Taking permission to visit and arrange, transportation to reach in time. Arrangement may also, be done to carry or provide hospitality is also the, responsibility of the person concerned., Fig 1 shows a typical single line layout diagram of a, transmission and distribution substation., , Electrical substations, Objectives: At the end of this lesson you shall be able to, • state the functions and purpose of electrical substations, • classify the different types of substation, • list out the equipment and components used in substation, • state the single line diagram of electrical substation with symbols., Substations, , Classification of substation, , Electric power is produced at the power generating stations,, which are generally located far away from the load centers., Between the power generating station and consumers a, number of transformations and switching stations are, required. These are generally known as substations., , The substations may be classified in according to service, requirements and constructional features. According to, service requirements they are classified in to transformer, substations, switching substations and converting, substations., , Substations are important part of power system and form, a link between generating stations, transmission systems, and distribution systems. It is an assembly of electrical, components such as bus-bars, switch gear apparatus,, power transformers etc., , 1 Transformer substations : Majority of the substations, in the power system are in this type. They are used to, transform the power from one voltage level to another, voltage level. Transformer is the main component in, such substations. Transformer substations are further, classified into step-up substations, primary grid, substations, secondary substations and distribution, substations., , Function, Their main functions are to receive power transmitted at, high voltage from the generating stations and reduce, voltage for switching operations of transmission lines., Substations are provided with safety devices to disconnect, equipment or circuit at the time of faults., Substations are the convenient place for installing, synchronous condensers for the purpose of improving, power factor and it provides facilities for making, measurements to monitor the operation of the various, parts of the power system., , a Step - up substations : These substations are usually, located at the generating stations. Generating voltage, of the order of 11KV needs to be stepped up to a, primary transmission voltage level of the order of, 220KV or 400KV., b Primary grid substations : These substations are, located at the end of primary transmission lines and, the primary voltage is stepped down to suitable, secondary voltages of the order of 66KV or 33KV., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished, , 177

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c Secondary substations : The voltage is further stepped, down to 11KV. Large consumers ar supplied with, power at 11KV., d Distribution substations : These substations are, located near the consumer localities to supply power, at 415V three phase or 240V single phase to the, consumers., 2 Switching substations : These substations are meant, for switching operations of power lines without, transforming the voltage. Different connections are, made between the various transmission lines., 3 Converting substation : Such substations are meant, for either converting AC to DC or vice versa. Some are, used to change the frequency from higher to lower or, vice versa for industry utilizations., According to constructional features substations are, classified into indoor substations, outdoor substations,, under ground substations and pole mounted substations., 1 Indoor substations : All equipment of the substation, are installed within the station buildings., 2 Outdoor substations : All equipments such as, transformers, circuit breakers, isolators, etc, are, installed outdoors., , These are also referred to EHV substations., •, , Secondary substation : Along secondary transmission, line. It receive the power at 66/33KV which is stepped, down usually to 11KV., , •, , Distribution substation: Created where the, transmission line voltage is stepped down to supply, voltage., , •, , Bulk supply and industrial substation : Similar to, distribution substation but created separately for each, consumer., , •, , Mining substation : Needs special design, consideration because of extra precaution for safety, needed in the operation of electric supply., , •, , Mobile substation : For emergency replacement of, transformer etc., , •, , Distribution substations : It receive power at 11KV,, 6.6 KV and step down to a volt suitable for LV, distribution purposes, normally at 415 volts., , The parts, equipment and components installed in, substation, Each substation has the following parts and equipment., 1 Outdoor switchyard, , 3 Underground substations : In thickly populated areas, where the space is the major constraint, and cost of, land is higher, under such situation the substations are, laid underground., , •, , Incoming lines, , •, , Outgoing lines, , •, , Busbar, , 4 Pole mounted substations : This is an outdoor, substation with equipment installed overhead of a H, pole or 4 pole structure., , •, , Transformers, , •, , Bus post insulator & string insulators, , •, , Substation equipment such as circuit-breakers,, isolators, earthing switches, surge arresters, CTs,, PTs neutral grounding equipment, , •, , Station earthing system comprising ground mat, risers,, auxiliary mat, earthing strips, earthing spikes & earth, electrodes., , •, , Overhead earthwise shielding against lightning strokes., , •, , Galvanized steel structures for lower equipment, supports., , •, , PLCC equipment including line trap, tuning unit, coupling, capacitor, etc., , •, , Power cables, , •, , Control cables for protection and control, , •, , Road, cable trenches, Station illumination system, , The substations can also be classified in several ways, including the following., 1 Classification based on voltage levels : eg. AC, substation : EHV, HV, MV, LV : HVDC substation., 2 Classification based on outdoor or indoor : Outdoor, substation is in open air. Indoor substation is inside a, building., 3 Classification based on configuration, •, , Conventional air insulated outdoor substation or, , •, , SF6 Gas insulated substation (GIS), , •, , Composite substations having combination of the above, two., , 4 Classification based on application, •, , Step up substation : Associated with generating, station as the generating voltage is low., , •, , •, , Primary Grid substation : Created at suitable load, centre along primary transmission lines. It receive the, power from EHV lines at 400KV, 220 KV, 132KV and, transform the voltage to 66KV, 33KV or 22KV ( 22KV, is uncommon) to suit the local requirements in respect, of both load and distance of ultimate consumers., , •, , Administrative building, , •, , Conference room etc., , 178, , 2 Main office building, , 3 6.6/11/22/33/66/132 KV switch gear LV, •, , Indoor switch gear, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished

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4 Switchgear and control panel building, •, , Low voltage AC switchgear, , •, , Control panels, protection panels, , 5 Battery room and DC distribution system, •, , DC battery system and charging equipment, , •, , DC distribution system, , 6 Mechanical, electrical and other auxiliaries, •, , Fire fighting system, , •, , D.G (Diesel Generator) set, , •, , Oil purification system, , An important function performed by a substation is, switching, which is the connecting and disconnecting of, transmission lines or other components to and from the, system. A transmission line or other component may, need to be de-energized for maintenance or for new, construction, for adding or removing a transmission line or, a transformer. All work to be performed, from routine, testing to adding new substations, must be done while, keeping the whole system running., , A fault may develop in a transmission line or any other, component. Some examples of this a line is hit by, lightning and develops an arc, or a tower is down by a high, wind. The function of the substation is to isolate the faulty, portion of the system within the shorted possible time., Substation layout and their components, Fig 1 shows the typical substation layout. It consists of the, following components and explained below., Power transformer : Power transformers are used for, generation and transmission network for stepping-up the, voltage at generating station and stepping down the, voltage for distribution. Auxiliary transformers supply, power to auxiliary equipment at the substations. (Fig 2)., Current transformers (CT) : The lines in substations, carry currents in the order of thousands of amperes. The, measuring instruments are designed for low value of, currents. Current transformers are connected in lines to, supply measuring instruments and protective relays. For, example a 100/1A CT is connected in a line carrying 100A,, and then the secondary current of CT is 1A. (Fig 3)., , Fig 2, , OIL LEVEL INDICATOR, DEHYDRATING BREATHER, OIL FILTER PLUG, CONSERVATOR, CONTANCT THERMOMETER, BUCHHOLZ RELAY, RATING PLATE, TERMINAL BOX, CORRUGATED TANK, , ELN4519122, , WHEEL, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished, , 179

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Lightning arresters (LA) : Ligtning arresters are the, protective devices used for protection of equipment from, lightning strokes. They are located at the starting of the, substation and also provided near the transformer terminals., , Fig 3, , HV TERMINAL, , TANK, , Wave trap : This equipment is installed in the substation, for trapping the high frequency communication signals, sent on the line from remote substation and diverting them, to the telecom panel in the substation control room., , SECONDARY, TERMINAL BOX, , ELN4519123, , PORCELAIN, INSULATOR, , Earth switch : It is a switch normally kept open and, connected between earth and conductor. If the switch is, closed it discharges the electric charge to ground, available, on the uncharged line., , Potential transformers (PT) : The lines in substations, operate at high voltages. The measuring instruments are, designed for low value of voltages. Potential transformers, are connected in lines to supply measuring instruments, and protective relays., These transformers make the low voltage instruments, suitable for the measurement of high voltages. For, example a 11KV/110V PT is connected to a power line and, the line voltage is 11KV then the secondary voltage will be, 110V. (Fig 4)., Fig 4, , Coupling capacitor : A coupling capacitor is used in, substations where communication is done by AC power, line. It offers very low impedance to high frequency carrier, signal and allows them to enter the line matching unit and, blocks the low frequency signals., Bus - bar : When number of lines operating at the same, voltage levels needs to be connected electrically, bus bars are used. Bus - bars are conductors made of copper, or aluminium, with very low impedance and high current, carrying capacity. Different types of bus - bar arrangements, are single bus bar arrangements, single bus - bar with, sectionalization, double bus- bar arrangements,, sectionalized double bus - bar arrangement, double main, and auxiliary bus - bar arrangement, breaker and a half, scheme /1.5 Breaker scheme, and ring bus - bar scheme., , ELN4519124, , Single bus-bar arrangement : It consists of single bus, - bar. Both incoming and outgoing lines are connected to, the single bus - bar (Fig 5). The advantages of this, arrangement are low maintenance, low initial cost and, simple operation. The drawback of this arrangement is if, any repair work is to be done on bus-bar, complete system, get interrupted., , Circuit breaker (CB) : Circuit breakers are used for, opening or closing a circuit under normal as well as, abnormal (faulty) conditions. Different types of CBs which, are generally used are oil circuit breaker, air - blast circuit, breaker, vacuum circuit breaker and SF6 circuit breaker., Isolators for isolating switches : Isolators are employed, in substations to isolate a part of the system for general, maintenance. Isolator switches are operated only under, load condition. They are provided on each side of every, circuit breaker., , 180, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished

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Single bus-bar with sectionalization: Single bus-bar is, divided into sections. Any two sections are connected by, circuit breaker and isolators. During fault or maintenance, particular section can be de-energized. This eliminates, complete shutdown of the system. Fig 6 shows that two, incoming and two outgoing lines are connected bus, section I and other two incoming and two outgoing lines, are connected bus section. 2 by using bus coupler., , representation of substation the electrical components, such as power transformers, incoming and outgoing lines,, bus- bars, switching and protecting equipments, are, represented by standard symbols and their, interconnections between them are shown by line. Single, line diagrams are useful in planning a substation layout., , Double bus - bar arrangements : This arrangement is, also known as duplicate bus-bar system. It consists of two, bus -bars ‘main’ and a ‘spare’ of same capacity. Incoming, line and outgoing lines can be connected to either bus by, means of bus coupler breaker and isolators. Continuity of, supply of the circuit can be maintained during maintenance, of main bus-bar or fault occurring on it., Single line diagram for substation, Any complex power system even though they are three, phase circuits, can be represented by a single line, diagram, showing various electrical components of power, system and their interconnection. In single line, Standard symbols used for single line diagram of substation, Sl. No., , Electrical components, , Symbosl, , 1, , AC Generator, , 2, , Bus bar, , 3, , Power transformer - Two winding, , (or), , 4, , Three winding transformer, , (or), , 5, , Current transformer (CT), , 6, , Voltage transformer or Potential transformer (PT), , (or), , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished, , 181

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Sl. No., , Electrical components, , 7, , Circuit Breaker (CB), , 8, , Circuit breaker with isolator, , 9, , Isolator or Group Operating Switch (GOS), , 10, , Lightning Arrester (LA), , 11, , Earth Switch (ES), , 12, , Wave or Line trap, , 13, , Coupling Capacitor (CC), , Fig 7 & 8 show the examples ( 1 & 2) of substation layout, drawings with all equipments represented by symbols., Example 1, Draw the single line diagram of substation having the, following equipment., i, , Incoming lines : Two, 110KV, , ii Outgoing lines : (a) One, 110KV (b) Four, 11KV, iii Transformers : (a) Two, 100MVA, 110/11KV, Δ/Y (b), one, 2MVA, 11KV/ 415V, Y/Y, , 182, , Symbosl, , iv) Bus-bars : 110KV- Duplicate bus - bar, 11KV single, bus - bar shows the positions of CTs, PTs isolators,, lightning and arresters, circuit breakers., Fig 7 shows the single line diagram of the substation., Example - 2, Draw the single line diagram of a pole mounted substation., Fig 8 shows the typical single line diagram of pole, mounted substation., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished

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Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.191 & 4.5.192, , Copyright @ NIMI Not to be Republished, , 183

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Electrical, Related Theory for Exercise 4.5.193, Electrician - Power Generation and Substation, Electrical power generation by non conventional methods, Objectives: At the end of this lesson you shall be able to, • state the non - conventional energy, • explain the methods of generators power from, bio-gas, micro-hydel, tidal, magnetic hydro dynamic power, generation, • list out the merits and demerits of non-conventional power generation., Non - conventional energy, , Bio-gas, , Energy generated by using wind, tides, solar, geothermal, heat and biomass including farm and animal waste is, known as non-conventional energy. All these sources are, renewable or inexhaustible and do not cause environmental, pollution., , Biogas is a good fuel. Bio mass like animal excreta,, vegetable wastes and seeds undergo decomposition in, the absence of oxygen in a biogas plant and form a mixture, of gases. This mixture is the biogas. Its main constituent, is methane. This is used as a fuel for cooking and lighting., , Mertis of non - coneventional over conventional, sources of energy, , Aerobic and anaerobic bio- conversion process, , 1 Provide more energy, 2 Reduce security risk associated with the use of, nuclear energy., 3 Reduce pollutants, 4 Less running and maintenance cost, 5 Never destroyed, 6 Despite the high initial investment and several, limitations, use of solar energy to meet our ever, increasing energy demand seems to be the only, answer., 7 Green house effect and global warming is avoided, 8 Less environment problems., Demerits of non conventional over conventional, sources of energy, 1 Many non- conventional sources are still in their infant, stages and required a lot of development efforts. The, use of solar energy is a completely a very gentle /, minutes operation. Cadmium is used in fabricating thin, film solar cells, which is both poisonous and radio, active., But it is very small quantity of cadmium is released, from discarded PV panels, Carbondioxide produced, while forming silicon from silica increases atmospheric, temperature., 2 High initial cost, 3 Less reliable and efficiency, 4 Can not be used for base load demand., Bio-gas power generation, The method of generating the electrical energy by using, bio-gas is termed as bio-gas power generation., 184, , There are mainly three aerobic and anaerobic bio conversion, process for the biomass energy applications. There are;, Bio products : Converting biomass into chemicals for, making products that typically are made from petroleum., Bio fuels : Converting biomass into liquid fuels for, transportation., Bio power : Burning biomass directly, or converting it into, a gaseous fuel or oil, to generate electricity., Properties of biogas, Main properties of biogas are :, 1 Comparatively simple and can be produced easily., 2 Burns without smoke and does not leave any ash as, residues., 3 Household wastes and bio-wastes can be disposed, off, usefully and in a healthy manner., 4 Reduces the use of wood and to a certain extent, prevents deforestation., 5 The slurry from the biogas plant is excellent manure., Biogas plant technology & status, The important parts of biogas plant are :, 1 The tank where biomass undergoes decomposition, (digester), 2 The tank where biomass is mixed with water (mixing, tank), 3 The tank where slurry of biomass is collected (out flow, tank), 4 Arrangement to store gas., , Copyright @ NIMI Not to be Republished

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Due to the action of bacteria in the absence of oxygen,, biogas is produced in the plant. This is collected in the, tank. In the gasholder type plant, the cylinder rises up as, the gas fills the tank and the storage capacity increases., The gas storage capacity of dome type will be less than, that of gasholder type. Residue of biomass (slurry) can be, used as good manure., Biogas plants are built in several sizes, small ( 0.5 m3/day), to very large (2500 m3/day). Accordingly, the configurations, are simple to complex., Biogas plants are mainly classified into following two, types., -, , Continuous type and batch type, , -, , Drum type and dome type, , Continuous type, , discharged in a sequential manner to obtain the output, biogas continuously., 3 Batch type biogas plants have longer digestion time, and are therefore more suitable for materials which are, difficult for anaerobic digestion (e.g. harder, fibrous, biomass)., 4 Batch type biogas plant needs initial seeding to start, the anaerobic fermentation., 5 Batch type biogas plant needs larger volume of the, digester to accommodate larger volume of the batch., Hence initial cost is higher., 6 Operation and maintenance is relatively more complex., Batch type biomass plants need well organized and, planned feeding. Such plants are preferred by European, farmers. Such plants are not yet popular in India., Fixed dome type digester (Fig 1), , Continuous type biogas plant delivers the biogas, continuously and is fed with the biomass regularly., Continuous type biogas plant is of two types., (A) Single stage continuous type biogas plant, In such a plant phase - I (Acid formation) and phase -II, (methanation) are carried out in the same chamber without, barrier. Such plants are simple, economical, easy to, operate and control. These plants are generally preferred, for small and medium size biogas plants. Single stage, plants have lesser rate of gas production than the two, stage plant., (B) Two stage continuous type biogas plant, In such a plant phase - I (Acid formation) and phase -II, (methane formation) take place in separate chambers., The plant produces more biogas in the given time than the, single stage plant. However, the process is complex and, the plant is costlier, difficult to operate and maintain. Two, stage plant is preferred for larger biogas plant systems., Batch type biogas plant, The infeed biomass is fed in batches with large time, interval between two consecutive batches. One batch of, biomass infeed is given sufficient retention time in the, digester (30 to 50 days). After completion of the digestion,, the residue is emptied and the fresh charge is fed. The, fresh biomass charge may be subjected - to aeration or, nitrogenation after feeding and then the digester covers, are closed for the digestion process. Thereafter, the, biogas is derived from the digester after 10 to 15 days., Fermentation continues for 30 to 50 days., Salient features, 1 Batch type biogas plant delivers gas intermittently and, not continuously., 2 Batch type biogas plant may have several digesters, (reactors) which are fed in a sequential manner and, , In the fixed dome type digester biogas plant, the digester, and gas collector (gas dome) are enclosed in the same, chamber. This type of construction is suitable for batch, type biogas plant. The digester is conveniently built at or, below ground level in comparatively cooler zone. The, construction of the digester is with locally available materials, like, bricks, terracotta., The pressure inside the digester increases as the biogas, is liberated. The biogas gets collected in the upper portion, of the digester in a dome shaped cavity. The outlet pipe is, provided at the top of the fixed dome. Alternatively, the gas, collector (gas holder) is a separately installed chamber., The digester tank and gas collector chamber are separated, by a water seal tank., The arrangement of a separate gas collector is preferred, as the tapping of gas from the gas holder does not affect, the pressure and the digestion process in the main, digester. The water seal tank prevents the return of the gas, from the gas collector to the digester chamber., An additional displacement chamber may be provided for, providing space to the displacement slurry in the digester,, due to gas pressure in the upper dome of the fixed type, digester. The fixed dome type digester can be fed on daily, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished, , 185

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basis with small quantities of the slurry. The excess slurry, in the digester gets accommodated in the displacement, chamber., The level of the slurry in the main digester and the, displacement collector can vary in accordance with the, pressure and volume of the biogas in the fixed type of, dome. The pressure in the fixed dome and the displacement, gas collector are almost the same as they are connected, by the outlet from the main digester., Floating gas holder type (Fig 2), , Co - generation, Because of the poor energy conversion efficiencies of, biomass fuels, practical generating systems often employ, a co-coal generation to achieve reasonable utilization of, the generating plant., Environmental issues, While biomass crops provide an environment friendly fuel, source for generating electrical energy. The land used for, disposing the slurry (waste) may be better employed for, cultivation., Micro hydel power generation, Micro-Hydel Power (MHP), The method of generating electrical power by using low, head or small flow rate of water is termed as micro hydel, power generation., , In this design a dome made floats above the slurry in the, disaster. In the Fig 2 the digester tank is of cylindrical, masonry construction. The floating dome is of fabricated, steel construction. The dome guide shaft provides the, axial guide to the floating dome., , Small -scale micro hydro power is both an efficient and, reliable form of energy, most of time. However, there are, certain disadvantages that should be considered before, construction a small hydro power system. With the right, research and skills, micro hydro can be excellent method, of harnessing renewable energy from small streams., Advantages, a Efficient energy source, , As the gas is collected in it, the sliding bearing provides, smooth sliding surface and guide to the floating dome. The, gas generated in the slurry gets collected in the dome and, the dome arises. The water seal tank provides separation, between the gas in the dome and the outlet gas., , It only takes a small flow rate of water (as little as two, gallons per minute) or a head as low as two feet to generate, the electricity with micro hydro., , Electricity generating plant, , Hydro produces a continuous supply of electrical energy, in comparison to other small - scale renewable, technologies. The peak energy season is during the, winter months when the large quantities of electricity are, required., , Generating plant fuelled by biomass uses conventional, steam turbine as used in thermal power stations with, modifications to the combustion chamber and fuel handling, systems to handle the bulkier fuel. The schematic, arrangement is in Fig 3., , b Reliable electricity source, , c No reservoir required, Microhydro is considered to function as a ‘run- of-river’, system, meaning that the water passing through the, generator is directed back into the stream with relatively, little impact on the surrounding ecology., d Cost effective energy solution, Building a small -scale hydro - power system can cost, less amount depending on site electricity requirements, and location. Maintenance cost are relatively small in, comparison to other technologies., , 186, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished

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e Power for developing countries, Because of the low-cost versatility micro hydro, the, developing countries can adopt and implement the, technology to help supply much needed electricity to, small communities and villages., f, , Integrate with the local power grid, , If your site produces a large amount of excess energy,, some power companies will buy back your electricity, overflow., g Suitable site characteristic required, In order to take full advantage of the electrical potential of, small streams, a suitable site is needed. Factors to, consider are; distance from the power source to the, location where energy is required, stream size ( including, flow rate, output and head), inverter, batteries, controller,, transmission line and pipelines., , •, , Metering, , •, , Main DC disconnect, , •, , Inverter, , •, , AC breaker panel, , Intake, Intakes can be as simple as a screened box submerged, in the water course, or they can involve a complete, damming of the stream. The goal is to divert derbis and airfree water into a pipe line. Effectively getting the water into, the system’s pipe line is a critical issue that often does not, get enough attention. Poorly designed intake often become, the focus of maintenance and repair effort for hydroelectric systems., Pipe line, , The size and flow of small streams may restrict the future, site expansion as the power demand increases., , Most hydro turbines require at least a short run of pipe to, bring the water to the machine, and some turbines require, piping to move water away from it. The length can vary, widely depending on the distance between source and the, turbine. The pipeline’s diameter may range from 1 inch to, 1 foot or more, and must be large enough to handle the, design flow. Losses due to friction need to be minimized, to maximize the energy available for conversion into, electricity., , b Low - power in the summer months, , Turbine, , In many locations stream size will fluctuate seasonally., During the summer months there will likely be less flow, and therefore less power output. Advanced planning and, research will be needed to ensure adequate energy, requirements are met., , The turbine converts the energy in the water into electricity., Many types of turbines are available, so it is important to, match the machine to the site’s conditions of head and, flow., , Disadvantages, a Energy expansion not possible, , c Environmental impact, The ecological impact of small - scale hydro should be, minimal. Stream water will be diverted away from a portion, of the stream, and proper caution must be exercised to, ensure there will be no damaging impact on the local, ecology or civil infrastructure., Micro-hydel electric system basic components, Here are some brief descriptions of the common equipment, used in grid- intertied and off- grid micro hydro electric, systems. The basic components of the systems may, vary, where all the following equipment is not necessary for, every system., •, , Intake, , •, , Pipe line, , •, , Turbine, , •, , Controls, , •, , Dump load, , •, , Battery bank, , Controls, The function of a charge controller in a hydro system is, equivalent to turning on a load to absorb excess energy., Battery-based micro hydro systems require charges, controllers to prevent the overcharging of the batteries., Controllers generally send excess energy to a secondary, (dump) load, such as an air or water heater. Unlike a solar, - electric controller, a micro hydro system controller does, not disconnect the turbine from the batteries. This could, create voltages that are higher than some components, can withstand, or cause the turbine to over speed, which, could result in dangerous and damaging over voltages., Dump load, A dump load is an electrical resistance heater that must, be sized to handle the full generating capacity of the micro, hydro turbine. Dump loads can be air or water heaters, and, are activated by the charge controller whenever the batteries, or the grid cannot accept the energy being produced, to, prevent damage to the system. Excess energy is “shunted”, to the dump load when necessary., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished, , 187

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Battery Bank, By using reversible chemical reactions, a battery bank, provides a way to store the surplus energy when more is, being produced than consumed. When demand increases, beyond what is generated, the batteries can be called on, to release the energy to keep your household loads, operating., Metering, System meters measure and display several different, aspects of microhydro - electric system’s performance, and status - tracking the condition of battery, amount of, electricity produced and used / consumed., Main DC disconnect, In battery-based systems, a disconnect between the, batteries and inverter is required. This disconnect is a DCrated breaker mounted in a sheet-metal enclosures. It, allows the inverter to be disconnected from the batteries, for services and protects the inverter to battery wiring, against the electrical faults., Inverter, Inverter transform the DC electricity stored in battery into, AC electricity for powering household appliance. Grid tied, inverters synchronize the system’s output with the, utility’s AC electricity, allowing the system to feed hydro, , electricity to the utility grid. Battery- based inverters for, off -grid or grid - tied systems often include a battery, charger, which is capable of charging a battery bank from, either the grid or a backup generator., Micro hydel power working principle, Hydro power is based on simple concepts. Moving water, turns a turbine, the turbine spins a generator, and, electricity is produced. Many other component’s may be, in a system, but it all begins with the energy already within, the moving water., Water power is the combination of head and flow. Both, must be present to produce electricity. Consider a typical, hydro system. Water is diverted from a stream into a, pipeline, where it is directed downhill and flow through the, turbine. The vertical drop (head) creates pressure at the, bottom end of the pipeline. The pressurized water drives, the turbine. More flow or more head produces more, electricity. Electrical power output will always be slightly, less than water power input due to the turbine and system, efficiencies., Flow is water quantity, and is expressed as “volume per, time”. such as gallons per minute (gpm), cubic feet per, second (cfs) or litres per minute (lpm). Design flow is the, maximum flow for which your hydro system is designed., It will likely be less than the maximum flow of your stream, (especially during the rainy season), more than your, minimum flow, and a compromise between potential, electrical output and system cost., , Tidal power generation, Objectives: At the end of this lesson you shall be able to, • explain the features of tidal power generation, • state the system on which the tidal power generation works, • state the advantages and disadvantages of tidal power generation., The generation of electricity using tidal power is termed as, tidal power generation. It is basically the transformation of, tidal power found in tidal motion of water in seas and, oceans into electrical energy., Tidal power, , This potential energy will then be used in creating kinetic, energy as doors in the barrage are opened and the water, rush from the high level to the lower level. This kinetic, energy will be converted into rotational kinetic energy that, will rotate turbines giving electrical energy. Fig 1 shows, the process in very simple terms., , Tidal power is the power inherent in tides at sea or oceans,, that is power of motion of water actuated by tides. Tides, are defined as the increase and decrease in water levels, due to the motion of water from one place to the other. Thus, there is a renewable source of energy in the tidal motion, of water at seas and oceans. This source of energy could, be used to generate other types of energy that could be, useful in industrial applications., This is done using a very basic idea involving the use of a, barrage or small dam built at the entrance of a bay where, tides are known to reach very high levels of variation. This, barrage will trap tidal water behind it creating a difference, in water level, which will in turn create potential energy., 188, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished

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Physical concepts of the tidal phenomena, , 1 Ebb method, , Tidal movements in seas are due to the increase of water, levels at certain areas in the globe and the decrease of, water levels at other areas. This is basically due to two, factors., , 1st - Water starts to ebb or go toward the sea, , 1 The gravitational forces between the Sun, Moon and, Earth., 2 The rotation of the moon and earth., As there are gravitational forces between the moon and the, earth, seas or oceans water is pulled away from earth, toward the moon at the area where the moon and the earth, are in front of each other. At the opposite side of the earth, the water is being pushed away from the earth due to, centrifugal forces. Thus there are two areas where the, water levels are high and other areas where the water level, is low. Thus, the tidal motion of water is created. This is, called the lunar tide., Working of tidal power generation system, In very simple terms a barrage is built at the entrance of a, gulf and the water levels vary on both sides of the small, dam. Passages are made inside the dam and water flows, through these passage and turbines rotate due to this flow, of water under head of water. Thus, electricity is created, using the turbines. A general diagram of the system is in, Fig.2., , 2nd - The gates are left closed keeping the water trapped, in basin to increase its level., 3rd - Then water is released out toward the sea rotating, turbines creating electrical energy., 2 Flood method, 1st - Water is let into the basin when it is empty, 2nd - As the turbines are rotated and the electrical energy, is created., 3 Ebb plus pumping method, 1st- The turbines are operated as pumps and pumping the, water into the basin at the flood period., 2nd - The water level in the basin is increased and creating, greater head., 3rd - At the ebb phase the water is let out of the basin,, creating energy for longer time than usual due to be, increased head., 4 Two way power generation, 1st - Starting with the basin full, the gates are opened,, letting water flow out and generating energy., 2nd - The turbines are reversed as the flow will be reversed, 3rd - The gates are closed when the flood period or cycle, starts., 4th - Water starts to build up behind the dam., , The components of a tidal power station are :, 1 A barrage : a barrage is a small wall built at the, entrance of a gulf in order to trap water behind it. It will, either trap it by keeping it from going into the gulf when, water levels at the sea are high or it will keep water from, going into the sea when water level at the sea is low., 2 Turbines : They are the components responsible for, converting potential energy into kinetic energy. They, are located in the passage ways that the water flows, through when gates of barrage are opened., 3 Sluices : Sluice gates are the ones responsible for the, flow of water through the barrage they could be seen, Fig 2., 4 Embankments : They are caissons made out of, concrete to prevent water from flowing at certain parts, of the dam and to help maintenance work and electrical, wiring to be connected or used to move equipment or, cars over it., The following is a list of different methods of obtaining, power from tidal power stations., , 5th - When a sufficient head is achieved, the gates are, opened to start the flood generation cycle as the water, flows into the basin., 5 Two basin generation method, 1st - Two basins are built one called a high - level basin, and the other is the low - level basin ., 2nd - The turbines are placed in the wall dividing the two, basins., 3rd - The high level basin is filled at high tide or flood period., 4th - Then the low - level basin is filled through the turbines, from the high level basin., 5th - The low level basin is emptied at low tide ebb period., Advantages of tidal power generation, There are many advantages of generating power from the, tide; some of them are listed below., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished, , 189

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•, , Tidal power is a renewable and sustainable energy, resource., , •, , It reduces dependence upon fossil fuels., , •, , It produces no liquid or solid pollution., , •, , It has little visual impact., , •, , Tidal power exists on a world wide scale from deep, ocean waters., , •, , It offers short time scale between investing in the, modular construction and benefiting from the revenue., , •, , Tidally driven coastal currents provide an energy density, four times greater than air, meaning that a 15-m, diameter turbine will generate as much energy as a, 60m - diameter windmill., , •, , Tidal currents are both predictable and reliable, a, feature which gives them an advantage over both wind, and solar systems. Power outputs can be accurately, calculated far in advance, allowing for easy integration, with existing electricity grids., , •, , The tidal turbine offers significant environment, advantages over wind and solar systems; the majority, of the assembly is hidden below the water line and all, cabling is along the sea bed., , •, , Sea water is 832 times as dense as air; therefore the, kinetic energy available from a 5-knot ocean current is, equivalent to a wind velocity of 270 km/h., , Disadvantages and constraint to tidal power, generation, Unfortunately, there are also disadvantages and limitations, to generating tidal power. Some of these are;, •, , At the present time both tide and wave energy are, suffering from orientation problems, in the sense that, neither method is strictly economical (except in few, locations throughout the world) on a large scale in, comparison with conventional power sources., , •, , Tidal power systems do not generate electricity at a, steady rate and thus not necessarily at times of peak, demand, so unless a way can be found of storing, energy efficiently - and any storage devices currently, available incur a considerable loss - they would not, help in reducing the overall need for fossil power, stations, but only allow them to run at a lower rating for, a certain amount of the time., , •, , Tidal fences could present some difficulty to migrating, fish., , Magneto hydro dynamic (MHD) power generation, Objectives: At the end of this lesson you shall be able to, • explain the features of magneto hydro dynamic power generation (MHD), • state and explain the system components of MHD power generation, • state the advantages of MHD power generation., Magneto hydro dynamic power generation, The way of generating electricity directly from a fast, moving stream of ionised gases without the need for any, moving mechanical parts - no rotating turbines and, generators is termed as magneto hydrodynamic power, generation., MHD power generation has also been studied as a method, for extracting electrical power from nuclear reactors and, also from more conventional fuel combustion systems., Working principle, Fig 1 explains the principle of operations of MHD. The, MHD generator can be considered to be a fluid dynamo., This is similar to a mechanical dynamo in which the, motion of a metal conductor through a magnetic field, creates a current in the conductor where as in the MHD, generator the metal conductor is replaced by a conducting, gas plasma., , The MHD system, The MHD generator needs a high temperature gas source,, which could be the coolant from a nuclear reactor or more, likely high temperature combustion gases generated by, burning fossil fuels, including coal, in a combustion, chamber. The Fig 2 shows the components of this system., , The flow (motion) of the conducting plasma through a, magnetic field causes a voltage to be generated (and an, associated current to flow) across the plasma, perpendicular, to both the plasma flow and the magnetic field according, to Fleming’s Right Hand Rule., 190, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished

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Expansion nozzle, , The faraday current, , It reduces the gas pressure and consequently increases, the plasma speed (Bernoulli’s Law) through the generator, duct to increase the power output. At the same time, the, pressure drop causes the plasma temperature to fall (GayLussac’s Law) which also increases the plasma resistance,, so a compromise between Bernoulli and Gay-Lussac, must be found. The exhaust heat from the working fluid is, used to drive a compressor to increase the fuel combustion, rate but much of the heat will be wasted unless it can be, used in another process., , A powerful electromagnet provides the magnetic field, through which the plasma flows and perpendicular to this, field, two electrodes are installed on opposite sides of the, plasma across which the electrical output voltage is, generated. The current flowing across the plasma between, these electrodes is called the Faraday’s current. This, provides the main electrical output of the MHD generator., , The plasma, The prime MHD system requirement is creating and, managing the conducting gas plasma since the system, depends on the plasma having a high electrical, conductivity. The plasma can be the fourth state of matter, after the solid, liquid and gaseous states, in which the, atoms or molecules are stripped of their electrons leaving, positively charged ions. Suitable working fluids are gases, which derived from combustion, noble gases and alkali, metal vapours., The gas plasma, To achieve high conductivity, the gas must be ionised by, detaching the electrons from the atoms or molecules, leaving the positively charged plasma. The plasma flows, through the magnetic field at high speed, in some designs,, more than the speed of sound, the flow of the positively, charged particles providing the moving electrical conductor, necessary for inducing a current in the external electrical, circuit., Methods of lonising the gas, Various methods for ionising the gas are available, all of, which depend on imparting sufficient energy to the gas., It may be accomplished by heating or radiating the gas, with X rays or Gamma rays. It has also been proposed to, use the coolant gases such as helium and carbon dioxide, employed is some nuclear reactors as the plasma fuel for, direct MHD electricity generation rather than extracting, the heat energy of the gas through heat exchangers to, raise steam to drive turbine generators., Seed materials such as Potassium carbonate or Cesium, are often added in small amounts, typically about 1% of, the total mass flow, to increase the ionisation and improve, the conductivity, particularly of combustion gas plasmas., , Power output, The output power is proportional to the cross sectional, area and the flow rate of the ionised plasma. The, conductive substance is also cooled and slowed in this, process. MHD generators typically reduce the temperature, of the conductive substance from plasma temperatures to, just over 1000°C., An MHD generator produces a direct current output which, needs an expensive high power inverter to convert the, output into alternating current for connection to the grid., Efficiency, Typical efficiencies of MHD generators are around 10 to, 20 percent mainly due to the heat lost through the high, temperature exhaust., This limits the MHD’s potential applications as a stand, alone device but they were originally designed to be used, in combination with other energy converters in hybrid, applications where the output gases (flames) are used as, the energy source to raise steam in a steam turbine plant., Total plant efficiencies of 65% could be possible in such, arrangements., Experience, Demonstration plants with capacities of 50 MW or more, have been built in several countries but MHD generators, are expensive. Typical use could be in peak shaving, applications but they are less efficient than combined cycle gas turbines which means there are very few, installations and MHD is currently not considered for, mainstream commercial power generation., Advantages of MHD generation, 1 Here only working fluid is circulated, and there are no, moving mechanical parts. This reduces the mechanical, losses to nil and makes the operation more efficiency., , Containment, , 2 The temperature of working fluid is maintained the, walls of MHD., , Since the plasma temperature is typically over 1000°C,, the duct containing the plasma must be constructed from, non conducting materials capable of withstanding these, high temperatures. The electrodes must be conducting as, well as heat resistant., , 3 It has the ability to reach full power level almost, directly., 4 MHD has very high efficiency, 5 The price of MHD is very low., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.193, , Copyright @ NIMI Not to be Republished, , 191

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Electrical, Related Theory for Exercise 4.5.194 & 4.5.195, Electrician - Power Generation and Substation, Power generation by solar and wind energy, Objectives: At the end of this lesson you shall be able to, • state the necessity of tapping natural resources for energy, • explain the basic principle and construction of the solar cell, • explain the characteristic and general specification of a solar cell, • explain the features of solar power generation system, • explain the features of wind power generation system, • calculate the required series parallel group of solar cells for a given power requirement., Solar cells: Heat energy is the most sought energy for, human being to cook the food as well as to keep warm in, cold climate. However the use of wood as the fuel for fire,, has ended up in deforestation and resulted in drought., Search of fuel lead the man to use coal and then oil., However these commodities are fast dwindling and after, few hundred years both may completely vanish from earth., As such it is essential that human race should find, alternative source of energy from nature., Hence the use of natural resources like heat from sun, thought by several scientists and one of the solutions to, the energy crisis is the invention of solar cells., The solar cells is essentially a large photo diode designed, to operate solely as photo voltaic device and to give as, much output power as possible. When these cells are, under the influence of light rays from sun, they give out, about 100 mw/cm2 power., The construction and cross section of a typical power, solar cell is in Fig 1. The top surface consist of a extremely, thin layer of P-type material through which light can, penetrate to the junction., , negative output terminal. commercially produced solar, cells will be available in flat strip form for efficient coverage, of available surface areas. The circuit symbol of solar cell, is shown in Fig 1., According to different manufacturing standards, the output, power varies from 50mw/cm2 to 125mw/cm2 as shown in, Fig 2. The graph (Fig 2) shows the characteristic of a solar, cell which gives 100mw/cm2. Considering the characteristic, curve it is apparent that the cell will deliver an output, current of 50mA when the output terminals are short, circuited the output voltage will be zero. On the other hand, open circuited voltage of the cell will be 0.55mv but the, output current is zero. Therefore again the output power, is zero. For maximum output power the device must be, operated at the knee of the characteristic. In solar cells, the output power decreases at high temperature., Typical output characteristics of power photocell for use, as a solar energy converter. (Fig 2), , Array of solar cells connected as a battery charger., (Fig 3), The nickel plated ring around the P-type material is the, positive output terminal, and the button plating is the, 192, , Fig 3 shows a group of series-parallel connected solar, cells operating as a battery charger. Several cells must, , Copyright @ NIMI Not to be Republished

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be series connected to produce the required output, voltage, and number of parallel groups to be provided as, per the required output current., , = 59 x 21, = 1239 cells., Solar energy generation, Solar energy is very large, inexhaustible source of energy., The power from the sun intercepted by the earth is, approximately 1.8 x 1011 MW, which is many thousands, of time large than the present consumption rate on the, earth of all commercial energy sources. Thus, in principle,, solar energy could supply all the present and future energy, needs of the world on a continuous basis. This makes it, one of the most promising of the non conventional energy, sources., , Example, A village welfare club is having a black and white TV which, operates at 24V taking a current of 3amp for four hours., Normally an array of solar cells are used for charging the, 24V batteries and the light source from sun available to, energise the cells for about 10hours a day. Calculate the, total number of solar cells of 125mw/cm2 required and the, series parallel grouping of cells., Solution, Refer Fig 2. As per the graph the solar cells (energy, converters) should be operated at approximately 0.45V, and 57mA. Assuming the charging voltage should be, higher than the battery voltage of 24V the solar cells, should supply 26.4volt for charging the battery circuit., Number of series connected cells, Output voltage 26.4V, = Cell voltage = 0.45V, , = 58.5 = say 59 cells, The charge taken by the batteries after every day of TV, programme will be 3amp x 4hours = 12 ampere hours., This should be supplied by the solar cells in 10 hours., Hence the ampere (current) requirement, Current =, , Ampere hours 12, =, hours, 10, , = 1.2 amp, Total number of groups of cells in parallel, =, , Output current 1.2amp, =, cell current, 57mA, , = say 21 cells, The total number of cells required, , In addition to its size the solar energy has two other, factors in its favour. Firstly, unlike fossil fuels and nuclear, power, it is an environmentally clean source of energy., Secondly, it is free and available in adequate quantities in, almost all parts of the world where the people live., However, there are many problems associated with it use., The main problem is that it is a dilute source of energy., Even in the hottest regions of earth, the solar radiation flux, available rarely exceeds. 1 KW/m2, which is a low value for, technological utilization. Consequently, large collecting, areas are required in many applications and these result, in excessive costs., Solar electricity, When sunlight strikes on photovoltaic (PV) solar panel,, the electricity is produced. The method of generating the, electrical energy from the solar panel (cells) is termed as, solar energy generation., Generation of electricity by using solar energy depends, up on the photovoltaic effect in some specific materials., There are certain materials that produce electric current, when these are exposed to direct sun light. This effect is, seen in combination of two thin layers of semiconductor, materials. One layer of this combination will have a, depleted number of electrons., When sunlight strikes on this layer, it absorbs the photons, of sun light ray and consequently the electrons are excited, and jump to the other layer. This phenomenon creates a, charge difference between the layer and resulting to a tiny, potential difference between them., The unit of such combination of two layers of semi, conductor materials, for producing electric potential, difference in sunlight is called solar cell. Silicon is normally, used as solar cell. For building cell, silicon material is cut, into very thin wafers. Some of these wafers are doped with, impurities. Then both doped and undoped wafers are, sandwiched together to build solar cell. A metallic strip is, attached to two extreme layers to collect current., , = Number of cells in series x number of groups in parallel, Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished, , 193

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A desired number of solar cell are connected together in, both parallel and series to form a solar module for producing, desired electricity., , Fig 4 describes the typical system of solar panels,, controller, energy storage, inverter for converting DC into, AC and how the system is connected to power grid., , The solar cell can also work in cloudy weather as well as, is moon light but the rate of production of electricity low as, and it depends up on intensity of incident light ray., , Solar panel installation norms, , •, , Solar modules must have some industry standards known, as the standard test condition (STC)., , For efficient cell, if must have the following key, factors., , •, , It must have a high short circuit current., , •, , The open circuit voltage is also must be high for, obtaining the above possible character with possible, condition must be fulfilled., , Irradiance (sunlight intensity), , •, , It is the amount of sunlight falling on a plain surface. Its unit, is watt per square metre. The measurement standard is, unit 1000Kw/m2., , By choosing low band gap materials to get high value, of short circuit current and high open circuit voltage., , Assembling and installation of solar panels, , It is a set of conditions to test a module, mainly includes, these factors., , Air mass, It is the thickness and clarity of air through which the, sunlight passes to reach the modules its standard is 1.5., Cell temperature : It is the testing temperature as 250°C., Module efficiency : It is the ratio of output power to the, input power is called module efficiency. Module uses the, photons in the sunlight to produce DC electricity., •, , Normally 1000W/M2 of sunlight strikes 1 square metre, area of a module. If 100W of power is produced from, that square metre, then the module efficiency is 10%, If it is 50W power is produced from that square metre, it a has an efficiency of 5%., , 194, , A solar panel is a able to function using the solar energy, which is derived from the sun. The solar panel installed, on the roof top absorb sun's light (photons) from the sun., Silicon and the conductors in use for solar panel converts, the sunlight into direct current (DC) electricity flows into, the inverter. It is an renewable energy. The process of, converting sunlight to electrical energy and more efficient, than other process., Solar panel contains many different silicon cells (or) solar, cells. The energy derived from the sun is connected into, electricity with help of solar panels., 1 The solar panels installed on the roof top absorb sun's, light from the sun., 2 The silicon and the conductor in the panel convert the, sunlight into DC flows into inverter., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished

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3 The inverter then converts DC to AC which can be used, at home., 4 Excess electricity that is not used, can be feedback, to the grid., 5 When the solar panels produce less power than, required at home., , A module cannot be connected directly to a battery, so, a, charge controller ON charge regulator is used in between, module and battery and inverter are required to operate, AC appliances. So, the whole system excepts the module, is known as balance of system (BOS). (Fig 6), , Process of connecting solar panel to electricity, Solar panels is used a special process of connecting, photons to electrons to generate a current by making, use of a special type of cell known as photovoltaic cell., These cells are commonly found on the front of calculation, and small gadgets are connected together, called as solar, panels (photovoltaic cells) are made up of semiconductor, materials such as silicon, which absorb the light from the, sun. The photons in the sunlight current the electron within, the sunlight., Basic idea of a solar module, array and balance of, system (BOS), The main components is BOS assembly are:, , Module, Solar cells are made in various shapes and sizes. The, smallest of the cells can be seen in devices like an ordinary, calculator, these type of devices are very little amount of, power used in home lighting system needs more power, to run on. The number of cells are put together to produce, more power. The group of cells is packaged together in, an enclosed space is called as a module., It helps to give higher voltage, high power and protects, the panel from rain, snow and wind etc. voltage and power, output of module depend on the size and number of cells, used. So, more number of modules are to be connected, in a simple assembly of modules is known as array., (Fig 5), , •, , Storage battery, , •, , Charge controller, , •, , Inverter, , •, , Support structure, , •, , Junction boxes, , •, , Wire, cables and fuses, , •, , Connections and switches, , The functions of the above components are explained, briefly below:, Storage battery, The most small systems used for lightening needs only, 12V battery for longer system like refrigerator, 24V is used., If helps to keep the wire size small and system losses to, a minimum. It needs to be handled carefully. If must not, be over charged or fully discharged to prevent from, damage., Charge controller, If the battery is not able to control charge on its own. This, work is done by a simple automatic device known as a, charge controller in the following way., , Balance of system (BOS), The cells modules and arrays are the power producing, part, a small devices like radio, needs a small amount of, power, can be directly connected to a small module. But, most of the devices appliances need more power at night., The assembly of module, battery and an appliance is, simple form a P.V system., , •, , It senses the battery charge and switches ‘OFF’ the, charging current and avoid from damage., , •, , It disconnects the appliances when the battery charge, goes below a set limit., , •, , Prevents reverse current and protects from short circuit., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished, , 195

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Inverter, A solar system produces only DC power. But home, appliances need AC power. The device (example CFL) is, required for this purpose to convert DC into AC is called, as inverter., Support structure, The solar module cannot be simply placed either on ground, or roof. It needs to collect the sunshine at an angle. To, keep the module safe from any strong winds support, structure is used for solar PV system., Junction boxes, It is meeting point for many wires. These may be from a, raw of modules are from modules to a battery bank. A, junction box is made of an unbreakable material (ie), polycarbonate. It makes use of copper connectors for a, high current flow. It protects the system from moisture., Wires and fuses, This solar systems carry a low voltage but high current., So, the large diameter wire is needed. Fuses keep the, solar equipment safe against the short circuit., CFL( Compact Fluorescent Lamp), It is not only energy saving lamp but also having long life, (8000hrs) and less heat output common available CFL, are:, •, , 5W - 235 Lumens, , •, , 7W - 370 Lumens, , •, , 9W - 600 Lumens, , •, , 11W - 900 Lumens, , Check for the any damage from outride on the different, parts of system., , -, , Connect the load to junction box controller, , -, , Connect all lighting loads charge controller to load, junction box with interconnecting cables., , -, , Place the charge controller on batter box, keep the, battery inside., , -, , Fire module on the support structure., , -, , Wore the system appear box layout., , Mounting of charge controller, -, , Mount the controller to the wall into screws that fit to, the wall material., , -, , Connect the battery cable assembly with fuse supplied, along with the controller., , -, , Connect first controller and then battery and two, modules, , -, , Connect the wires to the load and only then to, controller., , Electrical connection, , The solar panels are installed for some applications like:, -, , Solar power plant, , -, , Solar lantern, , -, , Solar lighting system, , -, , Solar water pumping system, , -, , Solar battery charging system, , -, , Solar Hybrid system, , -, , Solar grid connected power plants, , -, , • Connect the battery to the system only after getting, fully charged., • Do not switch ‘ON’ charged the loads for 2 - 3 days, (when battery is ‘ON’ a full charged), • Connect the array cable to charge controller with correct, polarity., •, , Keep the switch in ‘OFF’ position and connect the, load cables and battery cables to charge controller., , •, , Switch ‘ON’ the load (ie) lamps for the normal, operation., , Solar home system, , •, , Test the solar panel installation for it's functioning., , Solar water heater etc.,, , (Fig 8a & b) shows the installed solar panel with mid, clamp and with frame mounted installation are illustrated., , For example the procedure for installing of a solar home, system is explained below:, Fig 7 shows the block diagram of solar panel installation., -, , -, , Collect the system from the packing, , 196, , Functionality of solar panel, Sunlight is the basic fuel for a solar panel. Sunshine is, the cause to keep the panel for normal functioning. But, the environment around the modules will affect it's working., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished

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not be present on it. In such a place only it must be put, up. But due to extended free transformer, T.V antennas, etc, may cause to present shades., A solar modules are made of a string of individual solar, cells and connected in series with one another. Suppose, as an example one cell from 36 cells in a module is fully, shaded, the power output from the module will become, zero due to high resistance. But if one cell is 50% shaded, then the power output is reduced to 50% only offers high, resistance., Light intensity, More power is produced from the panel in bright sunlight., For 1000W/M2 of sunlight, the rated output power will be, full. But, if it is 500W/M2 only the rated power output will, be half. The output power is directly proportional with the, increasing of solar in isolation., The following few factors will affect it's normal working, cause for power loss., , Temperature, The higher the temperature the output power is reduced, from a module, due to power loss. It is tested at standard, temperature at 25°C. During the bright sunlight, cell may, reach 70°C also. If crystalline silicon decrease from, 0.4 to 0.5% per°C temperature increases above 25°C., Amorphous silicon module temperature coefficient is 0.2, to 0.25 % per°C of temperature increase., , -, , Tilt angle, , -, , Dust, , -, , Shading, , -, , Light intensity, , -, , Temperature, , -, , Charge controller, , -, , Semiconductor energy loss, , -, , Cabling losses, , -, , Improper connections, , Tilt angle, , Charge controller, If the charger controller is in continuous operation and, draws a small current of about 5mA to 25mA, then the, power loss is around 1%., Semiconductor energy loss, , The solar module must be installed in the proper path of, sun and it is tilted properly at an angle, equal to the latitude, of the place. If any error in the tilt angle will lead to same, amount of power loss., , The charge controller is having the components as, MOSFET and blocking diodes, which is cause for heat, energy loss., Cabling loss, , Dust, If the modules is not cleaned properly, dust will form on, the modules surface in the dry season, and it may cause, for high energy loss 5-10%., Shading, Solar module faces the sun all day. Their shade should, , The cables are also cause for power loss, It can be, minimized by choosing a large diameter of wire size., Improper connection, If the electrical connections are not made properly, it, results in less power is fed to the battery. It can be reduced, by keeping clean, and tight connections., , Wind power generation, Objectives: At the end of this lesson you shall be able to, • explain the features of wind power generation, • state the advantages and disadvantages of wind power generation., The method of generating the electrical energy by using, the wind is termed as wind power generation. Since the, wind has velocity and kinetic energy, it can be used to, , produce electricity. For that, we can use windmills. The, important part of a windmill is a structure with large leaves,, fixed at the top of a high tower. The speed of leaves, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished, , 197

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changes with the speed of the wind. If the rotation of the, windmill is given to the rotor of a generator, then the, electricity will be obtained from the generator. If the, windmill is connected to a water pump, the leaves of the, windmill rotate the pump and pumping out the water., Wind power can be usefully exploited for the generation of, electricity as there are large, coastal, hill and desert, areas. Wind turbines comprising of machines with blade, diameter of 17 m, which can generate about 100 kilowatts., A strike of blowing wind on specially designed blades of a, windmill’s rotor causes both to rotate. This rotation, which, is the mechanical energy, when coupled to a turbine, drive, the power generator., Operation, The schematic arrangement of wind power station is given, in Fig 1., , 3 There is a strong reason why wind power should be, welcome by grids which have some hydroelectricity, inputs in India. The water level in the hydel reservoir is, at its lowest before the onset of the South West, monsoon. If less water is drawn during the monsoon,, a high level could be maintained for longer period., During the monsoon period wind energy can be used, to feed the grid., 4 It is non polluting, 5 It does not require high technology., 6 Electricity can be produced at a lower cost after, installation., Disadvantages, 1 The major disadvantage associated in the wind power, is that it is not constant and steady, which make the, complications in designing the whole plant., 2 The rotor blades of wind turbine generators must sweep, out large areas to produce worthwhile amount of power., 3 The wind is a very dangerous such storms can cause, tremendous shear stresses which may spoil the whole, plant within no time. To avoid this, special and costly, designs and controls are always required., , When the wind strikes the rotor blades, blades start, rotating. Rotor is directly connected to high speed gear, box. Gear box converts the rotor rotation into high speed, which rotates the electrical generator. An exciter is, needed to give the required excitation to the coil so that it, can generate required voltage. The exciter current is, controlled by a turbine controller which senses the wind, speed based on that it calculate the power what we can, achieve at that particular wind speed., The output voltage of electrical generator is given to a, rectifier and rectifier output is given to line converter unit to, stabilise the output AC that is fed to the grid by a high, voltage transformer. An extra units is used to give the, power to internal auxiliaries of wind turbine (like motor,, battery etc), this is called internal supply unit. ISU can, take the power from grid as well as from wind. Chopper is, used to dissipate extra energy from the Rectifier Unit (RU), for safety purpose., Advantages, 1 The wind energy is free, inexhaustible and does not, need transportation., 2 Wind power plant on the other hand does not take long, time to construct. Such wind mills will be highly, desirable & economical to the rural areas which are far, away from the existing grids., 198, , 4 Among all the disadvantages mentioned above, the, cost factor is the major which has restricted the, development of wind power on large scale for feeding to, the existing grid. The estimated cost of wind electricity, generation, storage & distribution system is over 1 lakh, rupees which may be considered beyond the means of, most Indian villages., Modern wind machines are still wrestling with the problem, of what to do when the wind is not blowing. Large turbines, are connected to the utility power network some other type, of generator picks up the load when there is no wind. Small, turbines are often connected to diesel/electric generators, or sometimes have a battery to store the extra energy they, collect when the wind is blowing hard., The wind energy is utilized by means of a wind mill or a, series of wind mills. A wind mill consists of few vanes, (normally 3 to 6) which rotate about their axis, when the, wind blows against them. The rotational motion (i.e., mechanical energy) thus created is utilized for various, applications, such as,, 1 Lifting water from the well, 2 Battery charging, 3 Water pumping, 4 Operating a simple machine, 5 Wind energy is used for agricultural& rural applications, such as grinding flour mills, wood cutting saw, stone, crushers, mixers, water pumps and irrigation facility, etc., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.5.194 & 4.5.195, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.6.196 to 4.6.198, Electrician - Transmission & Distribution, Electrical supply system - transmission - line insulators, Objectives: At the end of this lesson you shall be able to, • explain the electrical supply system and layout of AC power supply scheme, • list out the various power transmission, • compare AC and DC transmission, • state the advantages of high voltage transmission, • state single phase and 3 phase - 3 wire system in transmission., Electrical supply system, The electrical energy generated from the power plants, has to be supplied to the consumers. This is large network,, which can be broadly divided into two stages, (ie.), Transmission and distribution., The conveyance of electric power from a power station to, the consumers / premises is called is Electrical supply, system., The Electrical power supply system consists of 3 main, components viz (i) The power station / plant (ii) The, transmission lines and (iii) The distribution systems. The, power is produced at power plant which is away from the, consumers, It has to be transmitted over long distances, to load centres by transmission and to consumers through, distribution network., This supply system can be classified into, -, , DC or AC system, , -, , Over head lines (or) underground system, , Now a days, 3 phase, 3 -wire AC system is universally, adopted as an economical proposition. In some places 3, phase - 4 wire AC system is adopted., The underground system is more expensive than the overhead system, therefore in our country O.H system is, almost adopted., , ii Single - phase two wire with mid point earthed, iii Single phase three wire, 3 AC Two - phase system, i, , Two- phase three wire, , ii Two - phase - four wire, 4 AC three phase system, i, , Three - phase - three wire, , ii Three - phase - four wire, The line network between generating station (Power, station) and consumer of electric power can be divided, into two parts., -, , Transmission system, , -, , Distribution system, , This system can be categorized as primary transmission, and secondary transmission. Similarly primary distribution, and secondary distribution. This is in Fig 1., It is not necessary that the entire steps which are shown, in the diagram must be included in the other power, schemes. There may be difference, there is no secondary, transmission in many, schemes, in some (small) schemes, there is no transmission, but only distribution., Various stages of a typical electrical power supply, system, are as follows, , Types of power transmission system, , 1 Generating station, , Universally, 3 - phase - 3 wire AC system is adopted in, most of the places. However other systems can also be, used for transmission under special circumstances., , 2 Primary transmission, , Possible systems are :-, , 4 Primary distribution, , 1 DC system, i, , 3 Secondary transmission, , 5 Secondary distribution, , DC two wire, , ii DC two - wire with mid point earthed, , Generating station, , iii DC three wire, , The place where electric power produced by the parallel, connected three phase alternators / generators is called, generating station (i.e power plant)., , 2 AC single phase system, i, , Single-phase two wire, , Copyright @ NIMI Not to be Republished, , 199

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Generally, electric supply is given to heavy consumer, whose demands is 11KV, from these lines which carries, 11KV (in three phase three wire overhead system) and, they make a separate sub station to control and utilize, this power., In other cases, for heavier consumer (at large scale) their, demand is about 132 KV or 33KV they take electric supply, from secondary transmission or primary distribution (in, 132KV, 66KV or 33KV) and then step down to the level of, voltage by step -down transformers in their own sub station, for utilization (i.e for electric traction etc)., Secondary distribution, Electric power is given to (from primary distribution line, (i.e.) 11KV) distribution sub station. This sub station is, located near by consumers area where the level of voltage, reduced by step down transformers is 415V. These, transformers are called distribution transformers, in, 3 phase four wire system ( 3 phase - 4 wires), there is, 415 volts (Three phase supply system) between any two, phases and 240 volts (single phase supply) between, neutral and any one of the phase (lives) wire., Residential load (i.e. Fans, light, and TV etc) may be, connected between any one phase and neutral wires, while, three phase load may be connected directly to the three, phase lines., Elements of distribution system, Secondary distribution may be divided into three parts., The ordinary power plant capacity and generating voltage, may be 11KV, 11.5 KV, 12KV or 13KV. But economically., It is good to step up the produced voltage from (11KV,, 11.5KV or 12KV) to 132KV, 220KV, 400KV or 500KV or, greater (in some countries, up to 1500KV) by step up, transformer (power transformer)., Primary transmission, The electric supply (132KV, 220 KV, 500KV or greater), is transmitted to load center by three phase three wire, (3 phase - 3 wires) overhead transmission system., Secondary transmission, , 1 Feeders, 2 Distributors, 3 Service lines or service mains, Those electric lines which connect generating station, (power station) or sub station to distributors are called, feeders. Remember that current in feeders (in each point), is constant while the level of voltage may be different, the, current flowing in the feeders depends on the size of, conductor., Distributors, , Area far from city (outskirt) which have connected with, receiving station by line is called secondary transmission., At receiving station, the level of voltage reduced by stepdown transformers up to 132KV, 66 or 33KV and electric, power is transmitted by three phase three wire (3 phase 3 wires) overhead system to different sub stations. So, this is a secondary transmission., Primary distribution, , Those tapings which extracted for supply of electric power, to the consumers or those lines, from where consumers, get electric supply is called distributors, (Fig 2). Current is different in each section of the, distributors while voltage may be same. The selection of, distributors depends on voltage drop and may be designed, according to voltage drop. It is because consumers get, the rated voltage according to the rules., , At a sub station, the level of secondary transmission, voltage (132KV, 66 or 33KV) is reduced to 11KV by step, down transformers., 200, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished

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Advantages of DC electric power transmission, 1 It requires only two conductors, 2 There is no problem of inductance, capacitance and, phase displacement which is common in AC, transmission., 3 For the same load and sending end voltage, the voltage, drop in DC transmission lines is less than that in AC, transmission., 4 As there is no skin effect on conductors, therefore, entire cross - section of conductor is usefully utilized, thereby affecting saving in material., 5 For the same value of voltage insulating material on, DC lines experience less stress as compared to those, on AC transmission lines., Service lines or service mains, The normal cable which is connected between distributors, and consumer load terminal are called service line or, service mains. A complete typical AC power supply, system scheme is in Fig 3., , 6 A DC line has less corona loss and reduced, interference with communication circuits., 7 There is no problem of system instability which is so, common in AC transmission., Disadvantages of DC transmission, 1 Generation of power at high DC voltages is difficult, due to commutation problems and cannot be usefully, utilized at consumer ends., 2 Step up or step -down transformation of DC voltages, is not possible in equipment like transformer., Advantages of AC electric power transmission, 1 Power can be generated at high voltages as there is, no commutation problems., 2 AC voltages can be conveniently stepped up or stepped, down by using transformers., 3 High voltage transmission of AC power reduces losses., Disadvantages of AC electric power transmission, 1 Problems of inductances and capacitances exist in, transmission lines., 2 Due to skin effect, more copper is required., 3 Construction of AC transmission lines is more, complicated as well as costly., , Comparison of DC and AC transmission, The electric power can be transmitted either by means, of DC (or) AC. Each system has it’s own merits and, demerits. Some technical advantages and disadvantages, of two systems are stated below., AC transmission, Some years ago, the transmission of electric power by, DC has been receiving of the active consideration of, engineers due to it’s appreciable advantages., , 4 Effective resistance of AC transmission lines is, increased due to skin effect., From the above comparison, it is clear that high voltage, DC transmission is superior to high voltage AC, transmission. At present, transmission of electric power, is carried by AC and effort is making towards DC, transmission also. The convertor and inverter have made, it possible to convert AC into DC and vice versa easily., Such devices can operate upto 30MW at 400KV in single, units. The present day trend is towards AC for generation, and distribution at high voltage DC for transmission., The single line diagram of high voltage DC transmission, is in Fig 4. The power is generated as AC and stepped up, to high voltage by the transformer at sending end (Ts) ., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished, , 201

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The AC power at high voltage is fed to the convertor which, convert AC to DC. The transmission of electric power is, carried at high DC voltage. At the receiving emf DC is, converted into AC with the help of invertors. The AC supply, is stepped down to low voltage by receiving end transformer, (TR) for distribution., , Distribution system at 11KV may be radial system offers, continuous supply., Advantages of high voltage transmission, Very high voltages are used for transmission systems, because, as a general principle, the bigger the voltage, the cheaper is the supply., Since power in an AC system is expressed as, θ , that means increase in voltage will reduce, P=VI cosθ, the current for a given amount of power. A lower current, will result in reduced cable switch gear size and the line, power losses, given by the equation P = I2R will also be, reduced., The 132KV grid and 400KV supergrid transmission lines, are for the most part, steel - cored aluminimum conductors, suspended on steel lattice towers, since this is about 16, times cheaper than the equivalent underground cable., , The maintenance of a secured supply is an important, consideration for any electrical engineer or supply, authority because in industrial society, a loss of supply, may cause inconvenience, financial loss and danger to, the consumer or the public., The principle employed with a ring system is that any, consumer’s substation is fed from two directions, and by, carefully grading the overload and cable protection, equipment a fault can be disconnected without loss of, supply to the consumers., Fig 7 is a simplified diagram of distribution of electricity, from power station to consumer., , The conductors are attached to porcelain insulator strings, which are fixed to the cross - members of the tower is in, Fig 5. Three conductors comprise a single circuit of a, three phase system so that towers with six arms carry, two separate circuits., , High voltage distribution, High voltage distribution to primary substation is used by, the electricity boards to supply small industrial,, commercial and domestic consumers., Primary distribution to consumers is from 11KV, substations, which for the most part are fed from 33 KV, substations, but direct transformation between 132 and, 11KV is becoming common policy in city areas where, over 100 MW can be economically distributed at 11KV, from one site., Fig 6 shows a block diagram indicating the voltage at the, various stages of the transmission and distribution, system., 202, , This distribution method is also suitable for large industrial, consumers where 11KV substations as in Fig 8 may be, strategically placed at load centres around the factory, site., The final connections to plant, distribution boards,, commercial or domestic loads are usually by simple, underground radial feeders 415V/240V., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished

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These outgoing circuits are usually protected by circuit, breakers in a distribution board., The 415 V/240V is derived from the 11KV/415V sub-station, transformer by connecting the secondary winding in star, is in Fig 9., , The star point is earthed to an earth electrode sunk into, the ground below the substation, and from this point is, taken the fourth conductor, the neutral. Loads connected, between phases are fed at 415V, and those fed between, one phase and neutral at 240V., A three - phase 415V, supply is used for supplying small, industrial and commercial loads such as garages, schools, and blocks of flats. A single - phase 240V supply is usually, provided for individual domestic consumers., , Line insulators, Objectives: At the end of this lesson you shall be able to, • explain the types of insulators and their uses, • explain the method of binding of the insulators., Line insulators, , The following are the common types of insulators in use., , The aim of using a line insulator in an overhead line is to, hold the live conductor to prevent leakage of current from, the conductor to the pole. These are made of porcelain, clay and are thoroughly glazed to avoid the absorption, of moisture from the atmosphere., , •, , Pin type insulator, , •, , Shackle insulator, , •, , Suspension insulator, , •, , Strain insulator, , Properties of insulators, , •, , Post insulator, , •, , Stay insulator, , •, , Disc insulator, , i, , High mechanical strength in order to withstand, conductor load, wind load etc., , ii High electrical resistance of insulator material in order, to avoid leakage currents to earth., iii High relative permittivity of insulator material in order, that dielectric strength is high., iv The insulator material should be non - porous, free, from impurities and cracks otherwise the permittivity, will be lowered., v High ratio of puncture strength to flash over., The most commonly used material for insulators of, overhead line is porcelain but glass, steatite and special, composition materials are also used to a limited extent., , Pin Insulators : Pin insulators are used for holding the, line conductors on straight running of poles. Pin insulators, are three types. i.e single shed (Fig 1) double shed, (Fig 2) and triple shed (Fig 3) The single -shed pin, insulators are used for low and medium voltage lines. The, double and triple shed pin insulators are used for over, 3000V. These sheds are used to drip off the rain water., The part section of a pin type insulator is in Fig 4a & 4b, As the name suggest, the pin type insulator is secured, to the cross - arm on the pole. There is a groove on the, top of the insulator for housing the conductor. The, conductor passes through this groove and is bound by, the annealed wire of the same material as the conductor., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished, , 203

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Suspension type insulators, The cost of pin type insulator increases rapidly as the, working voltage is increased. Therefore, this type of, insulator is not economical beyond 33 KV. For high voltage, (>33KV), it is a usual practice to use suspension type, insulators as in Fig 7. They consist of a number of porcelain, discs connected in series by metal links in the form of a, string. The conductor is suspended at the bottom end of, this string while the other end of the string is secured to, the cross- arm of the tower. Each unit or disc is designed, for low voltage, say 11KV. The number of discs in series, would obviously depend upon the working voltage. For, instance, if the working voltage is 66KV, then six discs, in series will be provided on the string., , Shackle insulators : Shackle insulators are generally, used for terminating on corner poles. These insulators, are used for medium voltage line only. (Fig 5a & 5b), , Advantages, 1 Suspension type insulators are cheaper than pin type, insulators for voltage beyond 33 KV., , But now a days, they are frequency used for low voltage, distribution lines. Such insulators can be used either in, horizontal position or in a vertical position. They can be, directly fix to the pole with a bolt or to the cross arm., Fig 6 shows a shackle insulator fixed to the pole. The, conductor in the groove is fixed with a soft binding wire., , 204, , 2 Each unit or disc of suspension type insulator is, designed for low voltage, usually 11KV. Depending upon, the working voltage, the desired number of discs can, be connected in series., 3 If any one disc is damaged, the whole string does not, become useless because the damaged disc can be, replaced by the sound one., 4 The suspension arrangement provides greater flexibility, to the line. The connection at the cross arm is such, that insulator string is free to swing in any direction, and can take up the position where mechanical, stresses are minimum., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished

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5 In case of increased demand on the transmission line, it is found more satisfactory to supply the greater, demand by raising the line voltage than to provide, another set of conductors. The additional insulation, required for the raised voltage can be easily obtained, in the suspension arrangement by adding the desired, number of discs., 6 The suspension type insulators are generally used with, steel towers. As the conductors run below the earthed, cross arm of the tower, therefore, this arrangement, provides partial protection from lighting., Strain insulators, When there is a dead end of the line or there is corner or, sharp curve, the line is subjected to greater tension. In, order to relieve the line of excessive tension, the strain, insulators are used. For low voltage lines (<11KV) shackle, insulators are used as strain insulators. However for high, voltage transmission lines, strain insulator consists of an, assembly of suspension insulators. The discs of strain, insulators are used in the vertical plane. When the tension, in the lines is excessively high, as at long river spans,, two or more strings are used in parallel., , due to tension of the conductor. These stay wires consist, of 4 to 7 strands of GI wire is in Fig 10. The correct size to, be used depends upon the tension on the pole., , Stays and struts: Stays and struts are the different types, of supporting wires for the pole. Stays are generally used, for angle and terminating poles to prevent the bending of, the pole whereas struts are used where space for stay is, very limited. Fig 11 shows both the stay and the strut., , Post insulators, Cap and pin type (Fig 8a & 8b) : Such insulators can be, used for mounting of buses, dropout fuses, line, conductors, G.O.A.B (Gang Operated Air Break) switches., These are of outdoor type and are available in 11, 22 and, 33KV ranges., , One end of the stay is fixed at the top of the pole and its, other end is grouted in the concrete foundation., Disc insulators : Disc insulators are made of glazed, porcelain or tough glass and are used as insulators at, dead ends, or on straight lines as suspension type for, voltages 3.3 kV and above. (Figs 12, 13 and 14), These are available in four designs:, Tongue and clevis type (Fig 12): A round pin with a, cotter pin is used to hold the tongue of one unit in the clevis, of the other., , Stay insulators (Fig 9) : Stay insulators are also known, as strain insulators and are generally used up to 33 KV, line. These insulators should not be fixed below three, metres from the ground level. These insulators are also, used where the lines are strained., , Ball and socket type (Fig 13): In this case insulators are, assembled by sliding the ball of one insulator from the, side. A cotter pin is slipped in from the back of the socket, so that the ball cannot slide out. These are used at dead, ends., , The supporting wire which is used in the opposite direction, of tension on the pole due to overhead conductors is, known as ‘stay wire’. It prevents the bending of the pole, Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished, , 205

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Insulators for cold climate (Fig 14): For cold climate the, depth of the lower cap is increased to get creepage, distance which becomes necessary in cold climates. Two, designs known as fog type and anti-fog types are available., , aluminium steel reinforced conductors (ACSR). The size, of the binding wire should not be less than 2 sq mm., After binding of the aluminium cored conductors, the, binding joint is provided with protective grease. The binding, turns must be very close (without any gap) and must be, very tight enough so that more sparking is avoided., While binding, only a mallet has to be used for making the, conductor straight and hammer should never be used., Current carrying capacity of a conductor, , Guard wires, , Introduction, , These are a set of wires erected as a preventive guard to, falling conductors so that the live conductor after breaking, does not come in touch with the public or moving vehicles., These are erected in places where the line crosses a, street, road or railway line, OH power or communication, lines and others., Minimum clearance required between conductors, on the same support :a) L.T. lines, i) Vertical configuration of conductors :Minimum clearance between earth and live conductors is, 30 cm., Minimum clearance between live conductors is 20 cm., ii) Horizontal configuration of conductors :Minimum clearance between live wires on either side of a, support is 45 cm., Minimum clearance between live wires on the same side, of support is 30 cm., Minimum distance between the centre of insulator pin hole, and end of cross-arm is 8cm., b) H.T. lines, , The current carrying capacity of a insulated conductor or, cable is the maximum current that it can continuously, carry without exceeding its temperature rating it is also, known as ampacity., While the cables are in operation they suffer electrical, losses which is manifest on heat in the conductor,, insulation and any others metallic components in the, construction., The current rating will depend on hand this heat in dissipated, through the cable surface and into the surrounding areas., The temperature rating of the cable is a determining factor, in the current carrying capacity of the cable. The maximum, temperature rating for the cable is essentially determined, by the insulation material., By choosing an ambient temperature as a base for the, surroundings, a permissible temperature rise is available, from which a maximum cable rating can be calculated for, a particular environment. If the thermal resistivity values, are known for the layers of materials in the cable, construction then the current rating scan be calculated., The formula for calculating current carrying capacity in, given an, , Triangular configuration :-, , 1, , Minimum distance between the centre of insulator pin hole, and end of cross arm is 10 cm., The conductors are erected in such a way that they form, an equilateral pattern of side of 1 metre minimum., Necessity of binding: In overhead transmission lines, the, line conductors have to be tied to the post type and, shackle type insulators to hold the wire in the correct, position, without allowing for any further change in position, after stretching the wires by wire stretchers with allowable, ‘sag’ as required., Method of binding insulator in overhead lines: The, insulators should be bound with the line conductor with the, help of copper binding wire in case of copper conductors,, galvanised iron binding wire for galvanised iron conductors, and aluminium binding wire tape for aluminium and, 206, , ⎛, ⎞2, ⎡1, ⎤, ⎜, ⎟, Δθ − W d ⎢ T1 + η(T2 + T3 + T4 )⎥, 2, ⎜, ⎟, ⎣, ⎦, +, I =⎜, RT1 + ηR(1 + λ 1 ) + T2 + ηR (1 + λ 1 + λ 2 )(T3 + T4 ) ⎟, ⎜⎜, ⎟⎟, ⎝, ⎠, , where, I = Permissible current rating, Δθ = Conductor temperature rise in (K), R = AC resistance per unit length of the conductor at, maximum operating temperature (Ω/m), , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished

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T1 = Dielectric loss per unit length between one conductor, and the sheath (Km/W), , η=Number load carrying conductors in the cable, (conductors of equal size and carrying the same load), , T2 = Thermal resistance per unit length of the bedding, between sheath and the armour (Km/W), , λ1 = Ratio of loses in the metal sheath to total losses in, all conductors in that cable., , T3 = Thermal resistance per unit length of the external, sheath of the cable (Km/W), , λ2 = Ratio of losses in the armouring to total losses in all, conductors in that cable., , T4 = Thermal resistance per unit length between the cable, surface and the surrounding medium (Km/W), , NEC (National Electrical Code), , Wd = Dielectric loss per unit length for the insulation, surrounding the conductor. (W/m), , When selecting a cable it must know its wire ampacity, rating. This rating has been determined by the NEC, (National Electrical Code), , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.196 to 4.6.198, , Copyright @ NIMI Not to be Republished, , 207

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Electrical, Related Theory for Exercise 4.6.199 & 4.6.200, Electrician - Transmission & Distribution, Overhead lines /poles erection-fastening of insulator, Objectives: At the end of this lesson you shall be able to, • state the power transmission and distribution by O.H lines, • list out the main components and explain each of them, • explain the line supports used in transmission lines, • state the types of power lines with respect to the classification of voltage, • state about corona effect, sag and skin effect in O.H lines., Overhead lines, Electric power, which is generated from generating plant, / station to the consumer end is transmitted and, distributed either by means of overhead lines (O.H) or by, under ground cables (U.G. cables)., Electrical power transmission is the bulk movement of, electrical energy from generated power plant to electrical, substation. This inter connected lines are known as, transmission network. The electrical link from, substations to customer is typically referred as electrical, power distribution. The combined transmission and, distribution network is known as the ‘Power Grid’., Electricity is transmitted at high voltages (11, 33, 66, 230,, 400, and 500 Kv) to reduce the energy loss which occurs, in long distance transmission. The power is actually, transmitted through O.H lines (or) underground cables., The O.H lines are high voltage three phase alternating, current, and also single phase A.C sometimes used in, Railway Electrification system. High voltage DirectCurrent (HVDC) is used for greater efficiency even for very, long distances, used in submarine power cables and to, stabilize large power distribution network., Main components used in O.H lines, An overhead line may be used to transmit or distribute, electric power. The successful operation of an overhead, line depends to a great extent upon the mechanical design, of the line. While constructing an overhead line, it should, be ensured that mechanical strength of the line is such, so as to provide against the most probable weather, conditions. In general, the main components of an, overhead line are,, i, , Conductors which carry electric power from the, sending end station to the receiving end station., , ii Supports which may be poles or towers and keep the, conductors at a suitable level above the ground., iii Insulators which are attached to supports and insulate, the conductors from the ground., iv Cross arms which provide support to the insulators., , 208, , v Miscellaneous items such as phase plates, danger, plates, lightning arrestors, anti-climbing wires etc., Conductor materials, The conductor is one of the important items as most of, the capital outlay is invested for it. Therefore, proper choice, of material and size of the conductor is of considerable, importance. The conductor material used for transmission, and distribution of electrical power should have the following, properties., i, , High electrical conductivity, , ii High tensile strength in order to withstand mechanical, stresses., iii Low cost so that it can be used for long distances., iv Low specific gravity so that weight per unit volume is, small., Commonly used conductor materials, The most commonly used conductor material for overhead, lines are copper, aluminium, steel reinforced aluminium,, galvanized steel and cadmium copper. The choice of a, particular material will depend upon the cost and the, required electrical and mechanical properties and the local, conditions., All conductors used for overhead lines are preferably, stranded in order to increase the flexibility. In stranded, conductors, there is generally one central wire and round, this, successive layers of wires containing 6, 12, 18, 24..., wires., Copper, Copper is an ideal material for overhead lines owing it its, high electrical conductivity and greater tensile strength., It is always used in the hard drawn form as stranded, conductor. Although hard drawing decreases the electrical, conductivity slightly yet it increases the tensile strength, considerably., Aluminium, Aluminium is cheap and light as compared to copper but, it has much smaller conductivity and tensile strength., The relative comparison of the two materials is briefed, below., , Copyright @ NIMI Not to be Republished

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The conductivity of aluminium is 60% that of copper. The, smaller conductivity of aluminium means that for any, particular transmission efficiency, the cross sectional area, of conductor must be larger in aluminium than in copper., For the same resistance, the diameter of aluminium, conductor is about 1.26 times the diameter of copper, conductor., Steel cored aluminium, In order to increase the tensile strength, the aluminium, conductor is reinforced with a core of galvanized steel, wires. The composite conductor thus obtained is known, as steel cored aluminium and is abbreviated as ACSR, (Aluminium Conductor Steel Reinforced)., Steel-cored aluminium conductor consists of central core, of galvanized steel wires surrounded by a number of, aluminium strands (Fig 1). Usually, diameter of both steel, and aluminium wires is the same., , The line supports used for transmission and distribution, of electric power are of various types including wooden,, poles, steel poles, R.C.C poles and lattice steel towers., The choice of supporting structures for a particular case, depends upon the line span, cross sectional area, line, voltage, cost and local conditions., Wooden poles, These are made of seasoned wood (sal or ehir) and are, suitable for lines of moderate cross sectional area and of,, relatively shorter spans, say up to 50 metres. Such, supports are cheap, easily available, provide insulating, properties and, therefore are widely used for distribution, purposes in rural areas as an economical proposition. ., Double pole structures of the ‘A’ or ‘H’ type are often, used (see Fig 2) to obtain a higher transverse strength, than could be economically provided by means of single, poles., The main objections to wooden supports are: (i) tendency, to rot below the ground level (ii) comparatively smaller life, (20 – 25 years) (iii) cannot be used for voltage higher than, 20 kV (iv) less mechanical strength and (v) require, periodical inspection., Steel poles, , Galvanised steel, Steel has a very high tensile strength. Therefore,, galvanized steel conductors can be used for extremely, long-spans, or for short line sections exposed to, abnormally high stresses due to climatic conditions. They, have been found very suitable in rural areas where, cheapness is the main consideration. Due to poor, conductivity and high resistance of steel, such conductors, are not suitable for transmitting large power over a long, distance., Line Supports, The supporting structures for overhead line conductors, are various types of poles and towers called line supports., In general, the line supports should have the following, properties:, i, , High mechanical strength to withstand the weight of, conductors and wind loads etc., , ii Light in weight without the loss of mechanical strength, iii Cheap in cost and economical to maintain., iv Longer life, v Easy accessibility of conductors for maintenance, , The steel poles are often used as a substitute for wooden, poles. They possess greater mechanical strength, longer, life and permit longer spans to be used. Such poles are, generally used for distribution purposes in the cities. This, type of supports need to be galvanized or painted in order, to prolong its life. The steel poles are of three types viz (i), rail poles (ii) tubular poles and (iii) rolled steel joints., RCC Poles, The reinforced cement concrete (RCC) poles have become, very popular as line supports in recent years. They have, greater mechanical strength, longer life and permit longer, spans than steel poles. Moreover, they give good outlook,, require little maintenance and have good insulating, properties. Fig 3 shows R.C.C poles for single and double, circuit. The holes in the poles facilitate the climbing of, poles and at the same time reduce the weight of line, supports., The main difficulty with the use of these poles is the high, cost of transport owing to their heavy weight. Therefore,, such poles are often manufactured at the site in order to, avoid heavy cost of transportation., Steel towers, In practice, wooden, steel and reinforced concrete poles, are used for distribution purpose at low voltages, say upto, 11 KV. However for long distance transmission at higher, voltage, steel towers are invariably employed. Steel towers, have greater mechanical strength, longer life, can, withstand more severe climatic conditions and permit the, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished, , 209

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use of longer spans. The risk of interrupted service due, to broken or punctured insulation is considerably reduced, owing to longer spans. Tower footings are usually, grounded by driving rods into the earth. This minimizes, the lightning troubles as each tower acts as a lightning, conductor., , Fig 4 (a) shows a single circuit tower. However, at a, moderate additional cost, double circuit tower can be, provided as shown in Fig 4(b). The double circuit has the, advantage that it ensures continuity of supply. In case, there is breakdown of one circuit, the continuity of supply, can be maintained by the other circuit., , Types of power line, , The electric supply is transmitted at different voltages, through over head lines and the types of power lines are, furnished below:, , Electrical energy is generated, transmitted and distributed, in the form of alternating current as an economical, proposition. The electrical energy produced at the power, station is transmitted at very high voltages by 3-phase, 3wire system to step-down sub stations for distribution., The distribution system consists of two parts viz. primary, distribution and secondary distribution. The primary, distribution circuit is 3-phase, 3-wire and operates at, voltages 3.3 or 6.6. or 11 KV which is somewhat higher, than general utilisation levels. It delivers power to the, secondary distribution circuit through distribution, transformers situated near consumers’ localities. Each, distribution transformer steps down the voltage to 415 V, and power is distributed to ultimate consumers by 415/, 240 V, 3-phase, 4-wire system., , 210, , a. Low voltage line ( should not exceed 250V), b. Medium voltage line ( should not exceed 650V), c. High voltage line (should not exceed 33000V (33 KV), d. Extra high voltage line (above 33KV), Voltage standard, The voltage standard of above types have been defined in, I E Rules 2, “Voltage” means the difference of electric potential, measured in volts between any two conductors or between, any part of either conductor and the earth as measured, by a suitable voltmeter and is said to be;, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished

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Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished, , 211

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Low where the voltage does not exceed 250 volts, Medium where the voltage does not exceed 650 volts, High where the voltage does not exceed 33,000 volts, “Extra high” where the voltage exceeds 33,000 volts, The nominal system voltage generally used is given below:, a) 240 V, b) 415 V, , (ii) Corona reduces the effects of transients produced, by surges., Disadvantages, (i) Corona is accompanied by a loss of energy. This, affects the transmission efficiency of the line., (ii) Ozone is produced by corona and may cause, corrosion of the conductor due to chemical action., (iii) The current drawn by the line due to corona is nonsinusoidal. This may cause inductive interference, with neighbouring communication lines., , c) 650 V, d) 11 kV, e) 33 kV, , (e.g. bigger cross arms and supports) may increase to, a considerable extent., , f) 66 kV, , Sag in Overhead Lines, , g) 110 kV, , The difference in level between points of supports and, the lowers point on the conductor is called ‘Sag’., , h) 132 kV, i) 220 kV, , Fig 5 (a) shows a conductor suspended between two, equal level supports A and B. The conductor is not fully, stretched but is allowed to have a dip. The lowest point, of the conductor is O and the sag is S. Fig 5(b) shows, unequal level supports., , j) 400 kV, k) 800 kV, Corona, The phenomenon of violet glow, hissing noise and, production of ozone gas around an overhead transmission, line is known as corona., When an alternating potential difference is applied across, two conductors whose spacing is large as compared to, their diameters, there is no apparent change in the, condition of atmospheric air surrounding the wires if the, applied voltage is low. However, when the applied voltage, exceeds a certain value, called critical disruptive voltage,, the conductors are surrounded by a faint violet glow called, corona., Factors affecting Corona, The phenomenon of corona is affected by the physical, state of the atmosphere as well as by the conditions of, the line. The following are the factors upon which corona, depends:, 1 Atmosphere, 2 Conductor size, 3 Spacing between conductors, 4 Line voltage, Advantages and Disadvantages of Corona, Corona has many advantages and disadvantages., Advantages, (i) Due to corona formation, the air surrounding the, conductor becomes conducting and hence virtual, diameter of the conductor is increased. The increased, diameter reduces the electrostatic stresses between, the conductors., 212, , Conductor sag and tension, This is an important consideration in the mechanical, design of overhead lines. The conductor sag should be, kept to a minimum in order to reduce the conductor, material required and to avoid extra pole height for sufficient, clearance above ground level., Classification of Overhead Transmission Lines, The capacitance effect introduces complications in, transmission line calculations. Depending upon the, manner in which capacitance is taken into account, the, overhead transmission lines are classified as:., (i) Short transmission lines: When the length of an, overhead transmission line is up to about 50 km and, the line voltage is comparatively low (<20 KV), it is, usually considered as a short transmission line. Due, to smaller length and lower voltage, capacitance, effects are small and hence can be neglected., (ii) Medium transmission lines : When the length of an, over-head transmission line is about 50 – 150 km and, the line voltage is moderately high (20 KV - 100 KV),, it is considered as a medium transmission line. Due, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished

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to sufficient length and voltage of the line, the, capacitance effects are taken into account., (iii) Long transmission lines: When the length of an, over-head transmission line is more than 150 km and, line voltage is very high (>100 KV), it is considered as, a long transmission line. For the treatment of such a, line, the line constants are considered uniformly, distributed over the whole length of the line., The two important terms for performance of transmission, lines are, (i) Voltage Regulation, The difference in voltage at the receiving end and sending, end of a transmission line is called Voltage regulation, and is expressed as a percentage of the receiving end, voltage., Mathematically, %age Voltage regulation =, VS − VR, ×100, VR, , (i) Resistance: It is the opposition of line conductors to, the current flow. The resistance is distributed uniformly, along the whole length of the line as shown in Fig 6, (ii) Inductance: When an alternating current flows, through a conductor, a changing flux is set up which, links the conductor. Due to these flux linkages, the, conductor possesses inductance. Mathematically,, inductance is defined as the flux linkage per ampere, i.e., , ϕ, Inductance, L = henry, I, Where, , φ = flux linkages in weber-turns, I = current in amperes., , The inductance is also uniformly distributed along the, length of the line is in Fig 6 (a). Again for the convenience, of analysis, it can be taken to be lumped as in, Fig 6 (b)., , V = Sending end voltage, s, , V = Receiving end voltage, R, , Obviously, it is desirable that the voltage regulation of a, transmission line should be low i.e. the increase in load, current should make very little difference in the receiving, end voltage., (ii) Transmission efficiency: The power obtained at the, receiving end of a transmission line is generally less, than the sending end power due to losses in the line, resistance., The ratio of receiving end power to the sending end power, of a transmission line is known as the transmission, efficiency of the line.i.e., Percentage of Transmission efficiency =, Receiving end power, ×100, Sending end power, , VR IR Cosφ R, = V I Cosφ ×100, S S, S, , Where, VRIR and cosφR are the receiving end voltage,, current and power factor while VSIS and cosφS are the, corresponding values at the sending end., , (iii) Capacitance. If any two conductors of an overhead, transmission line are separated by air which acts as, an insulation. The capacitance exists between any, two overhead line conductors. The capacitance, between the conductors is the charge per unit potential, difference i.e., , Capacitance, C =, , q, farad, v, , Where q = charge on the line in coulomb, , Constants of a Transmission Line, , v = p.d. between the conductors in volts., , A transmission line has resistance, inductance and, capacitance uniformly distributed along the whole length, of the line., , The capacitance is uniformly distributed along the whole, length of the line and may be regarded as a number of, capacitors connected between the conductors as in, Fig 7 (a). When an alternating voltage is impressed on a, transmission line, the charge on the conductors at any, point increases and decreases with the increase and, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished, , 213

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decrease of the instantaneous value of the voltage between, conductors at the point., , (i) Nature of material, (ii) Diameter of wire – skin effect increases with the, diameter of wire, (iii) Frequency – increases with the increase in frequency, (iv) Shape of wire – less for stranded conductor than for, solid conductor., It may be noted that skin effect is negligible when the, supply frequency is low (< 50 Hz) and conductor diameter, is small (<1 cm)., Erection of overhead line poles, , The result is that a current (known as charging current), flows between the conductors [see Fig 7 (b)]. This, charging current flows in the line even when it is opencircuited i.e. supplying no load. It affects the voltage, drop along the line as well as the efficiency and power, factor of the line., Resistive Line, The resistance of transmission line conductors is the most, important cause of power loss in a transmission line. The, resistance R of a line conductor having resistivity ρ length, l, and area of cross section a is given by, R= ρ, , I, a, , (i) In a single phase or 2-wire d.c. line, the total resistance, (known as loop resistance is equal to double the, resistance) of either conductor., (ii) In case of a 3-phase transmission line, resistance per, phase is the resistance of one conductor., Skin Effect, The tendency of an alternating current to concentrate only, near the surface of a conductor is known as Skin effect., Due to skin effect, the effective area of cross-section of, the conductor through which current flows is reduced., Consequently, the resistance of the conductor is slightly, increased when carrying an alternating current., The skin effect depends upon (Fig 8), , Length of span, The length of span of line supports will depend upon, various factors like the type of pole and conductors, used, voltage of transmission, environment, ground, clearances for safety etc., However, following data given in Table 1 may be taken, as a rough guide., Table 1, Type of poles and permissible span, Sl.No, , Span length in m., , 1, , Wooden poles, , 40 - 50, , 2, , Steel tubular poles, , 50 - 80, , 3, , RCC poles, , 60 - 100, , 4, , Steel tower, , 100 - 300, , 5, , G.I pipe (Medium), , 30 - 50, , When distribution lines and street lighting fixtures are, erected on the same support, the span should not, exceed 45 metres., The recommended span for power lines over 11KV is, given in Table 2., Table 2, Relation between voltage, circuits and span, Nominal system, voltage KV (rms), , No. of, circuits, , Span range in m, , 33 (over poles), , 1, , 90 - 135, , 2, , 180 - 305, , 1, , 240 - 305, , 2, , 240 - 320, , 1, , 305 - 335, , 2, , 305 - 365, , 1, , 305 - 365, , 2, , 305 - 380, , 1, , 320 - 380, , 2, , 320 - 380, , 66, 110, 132, 220, , 214, , Type of pole, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished

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Choice of spans : The following factors influence the, choice of spans, i, , Ease of construction and the cost of the line, , ii Ease of maintenance and cost of line maintenance, iii Terrain conditions, The depth of the pit depends upon the soil and height, of the pole: The depth of pit below the ground level should, be about 1/6 of the length of the pole. (ie) a 9 metres long, pole should go down atleast 1.5 metres below the ground, level leaving 7.5 metres above the surface., The depth of foundation setting is dependent upon the, density of the soil and depth of frost penetration. In addition, to the above we should take into account disturbances to, the structure of the earth as the soil filled up is always, less strong than the natural earth., , Method of erection of poles : The poles to be erected, may be brought to the pit location by manual labour or by, improvised carts. Then the pole may be erected in the, pit. Wooden support poles may be utilized to facilitate, lifting of the pole at the pit locations as in Fig 12., , Wooden and reinforced concrete : Supports for the, 33 KV overhead lines with pin insulators are placed directly, in the earth with no special foundations. Holes for these, supports having a diameter 5 -10 cm greater than that of, the pole to be erected as in Fig 9., , The poles are also reinforced by log heels placed at the, pole inside the area of excavation bottom as in, Fig 10., , If water is found at a depth of 1.5 to 2 metres, the poles, are generally placed above the underground water level, and reinforced by embankment or special measures are, taken as in Fig 11., In such locations mass concrete foundations are to be, adopted to avoid collapse of foundation in the black cotton, soil., , Before the pole is placed into the pit, RCC padding or, alternatively a suitable base plate maybe given below the, pole to increase the surface contact between the pole, and the soil. The padding will distribute the density of the, pressure due to the weight of the pole on the soil., Having lifted the pole, the same should be kept in a vertical, position with the help of Manila /sisal ropes of 20/25 mm, dia. using the rope as a temporary anchor. As the poles, are being erected, say, from an anchor point to the next, angle point, the alignment of the poles are to be checked, and set right by visual check. The verticality's of the poles, are to be checked with a spirit level on both transverse, and longitudinal directions., Having satisfied that the vertical and longitudinal alignment, are all right, earth filling is to be done. In some soils the, poles are to be concreted up to ground level of the pit., After the poles have been set, the temporary anchors, are to be removed., Use of cross - arms : These are also known as insulator, supports and are made of either wood or angle iron. Crossarms are installed at the top of the pole for holding the, insulators on which conductors are fastened. They are, also known according to their relative position on the poles., If the cross - arm is fixed in the centre of the poles then it, is called a cross - arm (Fig 13a) and if installed on one, side of the pole, then it is termed as side cross -arm, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished, , 215

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(Fig 13b) U-shaped cross - arms are specially used for, three phase lines., Channel iron cross-arms fabricated from channels of size, 75 mm x 40 mm x 5.7 kg/m or size 100mm x 50 mm x, 7.9 kg/m are used for H.T. lines, and those made from, angle irons of size 50 mm x 50 mm x 6 mm are used for, L.T lines., , Joining of aluminium conductors, Objectives: At the end of this lesson you shall be able to, • state the type of joints, • explain the type and use of connectors used to joining conductors, • explain the steps to testing of O.H lines, • state the preliminary safety procedure for OH line erection., Joining accessories in O.H lines: Normally connectors, are used for joining the O.H. aluminium conductors., Connectors maybe of several types of which few are, described below., , are to be adopted to avoid collapse of foundation in the, black cotton soil., , 1 Sleeved joints, 2 Straight through connectors / taps, 3 Vice - clamp connectors /taps with parallel grooves, 4 Nut and bolt connector, Sleeved joints, Twisted joints: Oval shaped aluminium sleeves are, inserted over the conductors to be joined and then twisted, as in Fig 1. Only one sleeve is sufficient for all aluminium, conductors whereas two concentric sleeves are used for, ACSR conductors. One each for the aluminium and steel, portions. Twisting joints are recommended for conductors, up to 15 mm diameter. Only special wrenches should, be used for twisting the sleeves., , Compression joints : ACSR conductors are joined by, compression joints having two sleeves as in Fig 2. The, larger sleeve is of aluminium , fitting over the entire, conductor, and the smaller one is of steel fitted on the, steel portion of the wire eccentrically. Conductors to be, joined are inserted into the sleeves one after the other, and compressed either by hand or by hydraulic, compressors. Compression joints for all aluminium, conductors consist of aluminium sleeve only ., Straight through connectors / taps : Two types of, connectors are used to join two straight through run of, wires in such locations where mass concrete foundations, 216, , Straight sleeve and nut connector: This is in, Fig 3. It has a sleeve (round or oval in section) made of, cadmium plated brass or aluminium. The conductors are, inserted into the sleeve and tightened by the nuts., , Compression connector: In this, the conductors are, wrapped at both ends and then compressed with nuts as, in Fig 4., , Vice-clamp connectors/taps with parallel grooves, (PG):There are several types as explained below., Standard P.G. clamps: This clamp as in Fig 5 consists, of, two, aluminium, halves,, having, two, semi-circular parallel grooves in each half. After inserting, the conductors to be joined, the galvanized steel nuts are, , Copyright @ NIMI Not to be Republished

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tightened. As the grooves are of the same size, it is useful, only when the joining conductors are also of the same, size., , Nut and bolt connectors are of two types, Nut connector, This is in Fig 9. It has a transverse hole through which the, conductors to be joined are inserted and then tightened by, the bolt., , Universal P.G. clamp: This is in Fig 6. It has grooves of, slightly different shape to accommodate different sizes of, conductors, and has only one bolt. This clamp is not for, heavy duty service but can be used for tapping connections, from the distribution line to individual consumers through, aluminium conductors., Split bolt connector: This is in Fig 10. It is split at the, stem. The conductors to be joined are to be inserted into, the split and then tightened by the external nut., , Bimetallic universal parallel groove clamps (B.M.P.G., clamps), This clamp is in Fig 7. It has a brass body with cadmium, plating. The two halves are tightened by a galvanised bolt., This is used for connecting copper wire to aluminium, conductors in the case of consumer service connections., , Precautions to be followed while using aluminium, conductors: Technical problems involved in electric, connections in connectors for aluminium wire, are quite, different from those encountered, with copper conductors., There are several ways to approach these problems, but, it is essential that connectors for aluminium must be, specially designed for aluminium., Several problems arise which must be taken into account, when aluminium is to be connected to copper. All these, technical problems are related to the oxide film on the, surface of aluminium, the contact pressures exerted by, the connector, and the possibility of galvanic corrosion, between dissimilar metals., , U bolt clamps: This is in Fig 8. It uses ‘U’ bolts as these, bolts exert 4 times more pressure than the conventional, straight bolts. Such clamps are suitable for heavy duty, conductors., , Basically, the efficiency of any electrical contact depends, on the cleanliness of the contacting surfaces, the area of, the contacting surfaces, and the pressure applied. A, joining compound applied just after abrading will protect, the surface from further oxidation and prevent the formation, of an oxide film thick enough to interfere seriously with, most connections., To ensure complete elimination of the oxide film under the, most extreme service conditions, apply the joining, compound prior to abrading so that the oxide film underneath, the compound will be removed. The joining compound, prevents or retards re-formation of the oxide film and so it, should not be removed before the connection is made., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished, , 217

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A satisfactory connector for aluminium will exert about the, same overall pressure as on satisfactory for copper, but, will provide considerably more contact area and thus hold, unit stresses to values the aluminium is capable of, withstanding., If a connector is made of a metal different from that of the, conductors, the difference in the rates of expansion and, contraction of the two metals, with changes in temperature,, will cause contact pressure to vary with the temperature., Very often, aluminium conductors must be connected to, copper conductors and the possibility of galvanic corrosion, must be forestalled. When two different metals are in, contact with each other in the presence of moisture,, (thereinafter called the electrolyte) a small voltage is, developed between them which causes a flow of electric, current., This electric current ultimately tends to corrode the, conductor. The possibility of galvanic corrosion is, completely eliminated if connectors used to connect the, aluminium conductors to other aluminium or copper, conductors are made of aluminium., It is recommended that a good joining compound must, always be used on electrical connections to aluminium, regardless of the metals involved. The joining compound,, when liberally applied, will fill all voids in the contacting, surface and all voids in the vicinity of the contacting, surfaces. By doing so, it excludes the entry of air and, moisture and makes oxidation or corrosion impossible., There are several good joining compounds in the market,, all of which are grease-type materials. However, the period, of time a joining compound will provide protection cannot, be established except by experience, but when liberally, applied, they will last for many years under any service, condition., , 218, , Testing of overhead line: Before connecting the services, to the transformer, equipments etc., a pressure voltage, test of appropriate standard shall be carried out on the line,, as desired by the Engineer in-Charge., Before charging the M.V. lines, the same shall be tested, with a 500V Megger for insulation., Where pressure test is not done on H.V. lines, it shall be, tested with a 2500V/5000V Megger for insulation, before, charging., The distribution lines shall be charged only if the pressure/, Megger test is satisfactory., The lines shall be commissioned in the presence of the, Engineer in-Charge., Preliminary safety procedures: Before starting any, major work on a pole, carry out the following drill., – Before working on an overhead line which already, exists, shut down permission should be taken from, competent authorities., – Before working on overhead lines which are already, supplying power, the line should be made dead by, opening the concerned switches and the line should be, earthed through earth rods., – Use a safety belt while working on poles., – Inspect the structure, Eg. pole etc., – Decide the best way to approach the job., – Select the best ladder position., – Erect the ladder. The ladder must be ‘footed’, that is,, the ladder feet should be prevented from slipping and, the ladder should be held by other workmates until the, ladder head has been secured., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.199 & 4.6.200, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.6.201, Electrician - Transmission & Distribution, Domestic service line - IE rules, Objectives: At the end of this lesson you shall be able to, • explain the domestic service connection with bare and insulated conductors, • state the method of laying the service cable from the pole to the consumer premises, • state the safety precautions to be followed in domestic service connections, • list out the IE rules pertaining to domestic service connections, • explain the methods of taping service connections., Service connections, The distribution networks ends at consumer premises, either single phase or three phase connections. The, category of connections either single phase or three, phase depends as the maximum load demand by the, consumer and the wiring of the house or the premises. The, decision of power allocation by the electricity officials after, surveying the wiring and load demand by the consumer., Once the power requirement finalised and arrived the, connection to the consumer the point from where the, service line to be connected. It is also decided the drawing, of line from the pole cross arm structure to the consumer, mains panel either in over head or through UG cable. If the, distance from over head pole terminal to consumer panel, board is more than 50 Mtrs separate pole should be, erected and OH line to be drawn from the distribution pole, cross arm structure., Service connection with bare conductor: Any of the, following methods shall be adopted as specified., The bare conductors shall be strung with shackle insulators, fixed to the cross arms on both ends. The feeding end, cross-arms shall be fixed to the support and the one at the, receiving end shall be mounted on a G.I. pipe of a, maximum diameter of 5 cm. The bare conductors shall be, kept at a height of atleast 2.5 m from the top of the, structure in accordance with Rule 79 of I.E. rules., The G.I. pipe shall be provided with double bends at the, top. The pipe shall be secured by alteast 2 clamps made, of 50 mm X 6 mm. with M.S. flats fixed firmly to the wall, in the vertical position. It shall in addition be provided with, a G.I. stay wire of 7/3.15 mm size anchored to the building, with one eye bolt. Service connection shall be given with, weather proof/PVC insulated cable through this G.I. pipe., Wooden/PVC pushings shall be provided at both ends of, this G.I. pipe., The bare conductors shall be strung with shackle insulators, as above except at the receiving end where the insulators, shall be fixed to a bracket made of an angle iron, of a size, not less than 50 mm x 50 mm x 6 mm. The ends of the, bracket shall be cut and split and embedded in the wall, with cement mortar. The bare conductor shall be kept, , atleast 1.2 m away from the edge of the structure, in, accordance with Rule 79 of I.E. Rules., The service connection shall be given with weather proof/, PVC insulated cable through GI pipe of a minimum, diameter of 4 cm. fixed to the wall. The GI pipe shall be bent, downwards near the service entry. Wall fitting wooden/, PVC bushes shall be provided at both ends of the G.I. pipe., Service connection with insulated conductors: Service, connection may be given by weather-proof/PVC insulated, cable on a GI bearer wire. The cables shall be supported, by the bearer wire by means of suitable link clips spaced, 30 cm apart or by wooden/porcelain cleats 50 cm. apart., The GI bearer wire shall be of a minimum 10 SWG size., One end of the GI bearer wire shall be attached to a clamp, which is fastened to the nearest pole carrying distribution, lines from where the service connection is intended to be, given. The other end of the GI bearer wire shall be fastened, to a 5 cm. dia. GI pipe for a span up to 4.5m which is fixed, to the wall with guy etc., The GI pipe shall be fixed to an angle iron of size 40 mm, x 40 mm x 6 mm with a suitable guy for high supports and, for a span exceeding 4.5 m. Alternatively when the height, of the structure permits minimum ground clearance, the, other end of this GI bearer wire may be fixed to a hook, eye, bolt or bracket embedded with cement mortar in the wall., The weather proof/PVC insulated cable shall pass through, a GI pipe of minimum diameter 5 cm, which is bent, downwards. Wall fittings wooden/PVC bushes shall be, provided at both ends of the GI pipe., Method of laying the service cable from the pole to, the consumer main: In practice either a glass or porcelain, ring insulator or wooden fibre cleats are used to lay the, overhead service line from the pole to the consumer mains, as in Fig 1., Safety Precautions to follow while connecting pole, to consumer premises, 1 The cable conductor size must be as per the IE rule, standard either single phase or three phase., 2 If the service line crosses public road the clearance, must be as per IE rule., , Copyright @ NIMI Not to be Republished, , 219

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2 The consumer shall also ensure that the installation, under his control is maintained in a safe condition., Rule 31. Cut-out on consumer’s premises., The supplier shall provide a suitable cut-out in each, conductor of every line other than an earthed or earthed, neutral conductor, or the earthed external conductor of, concentric cables within a consumer’s premises, in an, accessible position. Such cut-out shall be contained, within adequately enclosed fire-proof receptacle., , 3 The conductor slag should not exceed as per the IE, rules., 4 If UG cables are providing the depth of cable in ground, should be as per IE rules., 5 Do not keep much more cable unused and buried in soil, in the coil form in case of UG cable laying., 6 The excess cable should not be kept by making coil, and kept on the pole cross arm. Use only required, cable for connection., 7 If the cable passing through excess heat producing, areas in near to chimney, kitchen etc; adequate, protection from heat to be provided., 8 Service cable run along with stay wire tightly tied with, stay wire to avoid tension on service cable., , Where more than one consumer is supplied through a, common service line, each such consumer shall be, provided with an independent cut-out at the point of, junction to the common service., Rule 33. Earthed terminal on consumer’s premises., The supplier shall provide and maintain on the consumer’s, premises, for the consumer’s use, a suitable earthed, terminal in an accessible position at or near the point of, commencement of supply as defined under Rule 58., Provided that in the case of medium, high or extra high, voltage installation the consumer shall, in addition to the, afore-mentioned arrangement provide his own earthing, system with an independent electrode., Rule 48. Precautions against leakage before, connecting., , 10 The connection to main line is to be made so tight and, clean surface, so that loose contact, sparking and, formation of oxide coating can be avoided., , 1 The supplier shall not connect with his works the, installation or apparatus on the premises of any, applicant for supply unless he is reasonably satisfied, that the connection will not at the time cause a leakage, from the installation or the apparatus exceeding five, thousandth part of the maximum current supplied to, the premises., , I.E. Rules pertaining to domestic service connection, , 2, , 9 No rain water flows along with service cable and reach, to consumer main panel. Necessary looping of cable to, be provided either side., , Rule 10. Construction, installation, protection,, operation and maintenance of electric supply lines, and apparatus, All electric supply lines and apparatus shall be sufficient, in power and size and of sufficient mechanical strength for, the work they may be required to do, and so far as, practicable, shall be constructed, installed, protected,, worked and maintained in accordance with standards of, the Indian Standards Institution so as to prevent danger., Rule 30. Service lines and apparatus on consumer’s, premises., 1 The supplier shall ensure that all electric supply lines,, wires, fittings and apparatus belonging to him or under, his control which are on a consumer’s premises are in, a safe condition and in all respects fit for supplying, energy, and the supplier shall take due precautions to, avoid danger arising in the premises from such supply, lines, wires, fittings and apparatus., 220, , If the supplier declines to make connection under the, provisions of sub-rule(1) he shall serve upon the, applicant a notice in writing stating his reason for so, declining., , Rule 54. Declared voltage of supply to consumer., Except with the written consent of the consumer or the, previous sanction of the State Government, a supplier, shall not permit the voltage at the point of commencement, of supply as defined under Rule 58, to vary from the, declared voltage by more than 5 percent in the case of low, or medium voltage or by more than 12½ percent in the, case of high or extra high voltage., Rule 77. Clearances above ground of the lowest, conductor., 1 No conductor of an overhead line, including service, lines erected across a street shall at any part thereof, be at a height less than :-, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.201, , Copyright @ NIMI Not to be Republished

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a) for low and medium voltage lines 5.791 m, b) for high voltage lines 6.096 m., 2 No conductor of an overhead line including service lines, erected along any street shall at any part thereof be at, a height less than:, a) for low and medium voltage lines 5.486 m, b) for high voltage lines 5.791 m., 3 No conductor of an overhead line including service, lines, erected elsewhere than along or across any, street shall be at a height less than:, a) for low, medium and high voltage lines upto and, including 11,000 V if bare 4.572 m, b) for low, medium and high voltage lines upto and, including 11,000 V if insulated 3.963 m., Rule 79. Clearances from building of low and medium, voltage lines and service lines., 1 Where a low or medium voltage overhead line passes, above or adjacent to or terminates on any building,, the following minimum clearances from any accessible, point, on the basis of maximum sag, shall be observed., a) for any flat roof, open balcony, verandah, roof and leanto-roof., , i) when the line passes above the building, a vertical, clearance of 2.439 m from the highest point., ii) when the line passes adjacent to the building, a, horizontal clearance of 1.219 m from the nearest point., b) For pitched roof, i) when the line passes above the building, a vertical, clearance of 1.219 m immediately under these lines., ii) when the line passes adjacent to the building, a, horizontal clearance of 1.219 m., 2 Any conductor so situated as to have a clearance less, than that specified in sub-rule (i) shall be adequately, insulated and shall be attached by means of metal, clips at suitable intervals to a bare earthed bearer wire, having a breaking strength of not less than 517.51 kg., 3 The horizontal clearance shall be measured when the, line is at maximum deflection from the vertical due to, wind pressure., Tapping service connections: No service connection, line should be tapped from an OH line from any point mid, span, except at the point of support. When a service, connection is taken overhead with a bare conductor, it, should be provided with guard wires., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.201, , Copyright @ NIMI Not to be Republished, , 221

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Electrical, Related Theory for Exercise 4.6.202, Electrician - Transmission & Distribution, Bus-bar system - power tariff terms and definitions, Objectives: At the end of this lesson you shall be able to, • explain the bus-bar system and the method of installation, • state the advantages of the bus-bar system, • determine the rating of the bus-bar, • state the use of plug-in boxes and their construction, • state the method of cable or conduit termination in plug-in boxes., In industrial workshops and factories, a number of machines, are installed in the shop floor closely but apart from each, other. connecting these machines to electrical supply, through underground cables or overhead wires or cables, may involve cumbersome methods resulting in shock, hazards. For such places, an overhead enclosed bus-bar, system as in Fig 1a and 1b is recommended., , thus forming a continuous bus-bar along the entire length, of the workshop. Method of coupling two bus-bars is in, Fig 3., , This bus-bar system is sometimes referred to as bus way, or bus duct., Bus-bar assembly should be installed at a height of, 2.75metre from ground, suspended by M.S. angles or flats, from ceiling/roof or supported by framed structure from, ground as in Fig 2., Bus coupler, The bus-bars are either of high conductivity, high purity, copper or alloy aluminium having rectangular sections, mounted on insulating supports enclosed in standard, length of metal trunking. The bus-bar sections are, available in standard lengths (3.65metre for 200 ampere, and 2.44metre for 400 ampere) which can be connected to, another bus-bar by blowing the respective bus-bar ends, 222, , The standard rating of bus-bar are 100, 200, 400, 600, 800,, 1200, 1600, 2000, 2400 and 3600 ampere with rated, voltage of 500V. These bus-bars also available for indoor, or outdoor use as point to point feeders or as plug-in take, off points for power. These bus-bars are used in generating, stations, sub stations, in metal industry and textile industry., These bus-bars are also used in multi storied flats to, facilitate connection to various stories from the mains by, , Copyright @ NIMI Not to be Republished

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using vertically mounted bus-bars as in Fig 4. These, vertical bus-bars are provided with a fine barrier made up, of high grade fire-resisting material positioned at the top, of each fixed section of the trucking passing through the, floors. This barrier is the collecting points for dirt, dust and, moisture which could be removed at intervals., , Recommended current density for a copper bus-bar which, is not enclosed should not exceed 165A/sqcm and for, aluminium 118A/sqcm., Recommended section of aluminium and copper bus-bars, and their respective ratings are in Table., Earthing continuity is provided by two strips of aluminium, or copper running throughout the bus-bar assembly., When extending the bus-bar lengths, these earthing strips, also to be connected to have earth continuity., Note:, 1 Above rating is for rectangular cross-section, of E-91 E-WP grade as per IS : 5082-1969 in, still unconfined air without enclosure,, presuming longer section vertical., 2 Denting factor of 0.88 may be applied for, ambient of 30°C and temperature rise of, 35°C. Similarly in outdoor application, denting may be done for 0.85 to 0.9. Indoor, well ventilated 0.6 to 0.8 and partly, ventilated areas 0.5 to 0.6., , Bus-bar size, in mm, , Rating at 50Hz AC current at average ambient of 35°C and 40°C maximum and, temperature rise of 50°C., Aluminium, Single bar, , Two bars, , Copper, Three bars, , Four bars, , Single bar, , 12.5 x 3, , —, , —, , —, , —, , 160, , 25 x 3, , —, , —, , —, , —, , 290, , 50 x 3, , 335, , 650, , 850, , 950, , 525, , 75 x 3, , 475, , 875, , 1150, , 1300, , 750, , 100 x 3, , 600, , 1075, , 1400, , 1600, , 970, , 12.5 x 4.5, , 125, , 260, , 315, , 370, , 205, , 25 x 4.5, , 225, , 525, , 635, , 750, , 365, , 32 x 4.5, , 320, , 660, , 800, , 940, , 510, , 50 x 4.5, , 500, , 970, , 1270, , 1425, , 650, , 25 x 6, , 350, , 700, , 950, , 1000, , 430, , 50 x 6, , 675, , 1300, , 1700, , 1925, , 760, , 75 x 6, , 950, , 1750, , 2300, , 2600, , 1080, , 100 x 6, , 1225, , 2150, , 2800, , 3200, , 1380, , 125 x 6, , 1500, , 2500, , 3200, , 3700, , 1680, , 25 x 10, , —, , —, , —, , —, , 540, , 50 x 10, , 85, , 1500, , 1950, , 2250, , 960, , 75 x 10, , 1180, , 2050, , 2650, , 3000, , 1350, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.202, , Copyright @ NIMI Not to be Republished, , 223

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Bus-bar size, in mm, , Rating at 50Hz AC current at average ambient of 35°C and 40°C maximum and, temperature rise of 50°C., Aluminium, Single bar, , Copper, , Two bars, , Three bars, , Four bars, , Single bar, , 100 x 10, , 1500, , 2475, , 3150, , 3550, , 1710, , 125 x 10, , 1850, , 2925, , 3600, , 4200, , 2070, , 150 x 10, , 2100, , 3325, , 4000, , 4606, , 2430, , 250 x 10, , 2750, , 4100, , 4900, , 5700, , —, , 25 x 12.5, , —, , —, , —, , —, , 650, , 50 x 12.5, , —, , —, , —, , —, , 1120, , 75 x 12.5, , 1350, , 2250, , 800, , 3200, , 1570, , 100 x 12.5, , 1750, , 2700, , 3350, , 3900, , 2050, , 125 x 12.5, , 2100, , 3100, , 390, , 4500, , 2420, , 150 x 12.5, , 2400, , 3500, , 4450, , 5100, , 2820, , 200 x 12.5, , 3050, , 4500, , 5300, , 6100, , —, , Advantages of Bus-bar system, Following are the advantages of bus-bar system, 1 Reduced cost: Simple rapid installation with complete, elimination of expensive floor chasing (cutting) reduces, cost at the initial period of installation and needs no, expenditure for maintaining the bus-bar system while, in regular use., 2 Maximum flexibility: As plug-in-points are provided, at intervals of 60.96cm (2 feet) along every length of, bus-bar the connections can be taken for machines, installed on either side. Refer Fig 5., , 6 Easily extended for layout modification in the, factory: As the bus-bars can be extended in straight, lengths or at an angle to suit the layout with the help, of standard accessories, the bus-bars can be remounted, or rearranged within a short time., 7 Saving of time while initial erection: The advantages, of this system are that the trucking and bus-bars can, be erected before the installation of the machinery, and, the latter can be connected up and set to work as soon, as they are installed., 8 Reduction of voltage drop in feeders: By bringing, the heavy main feeders near to the actual loads, the, circuit wiring is reduced to a minimum and voltage drop, is lower than would otherwise be the case., 9 Addition and alterations: Subsequent additions and, alterations to plant layout can be easily accomplished,, and where bus-bar sections have to be removed they, can be used again in other positions., , 3 Complete safety: As the plug-in-point are completely, insulated, safety is ensured for operating and, maintenance personnel., 4 ‘Live’ connection: As the plug-in-boxes could be, connected to ‘live’ bus-bars quickly and safely without, shut down and the time is saved without disturbing the, normal work of the factory., 5 Guaranteed protection: As the fuse in the plug-in, boxes of HRC type the circuit is protected positively, and reliably against short circuit., 224, , 10 Internal grid for welders: The overhead bus-bar, system is especially advantageous where a large, number of electric welders have to be fed with heavy, currents from a step down transformer., 11 Branching from plug-in-boxes for small loads: If a, large number of small machines are to be fed it is usual, to fix a distribution box near the trucking system and, to protect this with a tap-off fitted with HRC fuses of, suitable capacity., 12 Durable and trouble free service: Normally busbars give much durable service than U.G. Cables and, give many years of trouble free service., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.202, , Copyright @ NIMI Not to be Republished

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Method of determining the ratings of the bus-bars, In a small factory, ten motors having each of 5 HP ratings, to be installed. The total load is approximately 10 x 5 i.e., 50 HP Assuming 5 HP motor takes approximately full load, current at 7.5A. The total current in the factory load will be, 75A and has to be supplied through a single bus-bar., Normally the ratings of bus-bar is 200A or 400A. Hence, a 200A rating bus-bar is selected for this case as the same, bus-bar also could be used when there is expansion of, load in the factory in future. Considering the overload, busbars are manufactured in standard sections of 3.65m, (200A) and 2.44m (400A). We can decide the number of, bus-bars to meet the entire length of machine layout., , Two earth pins are located at the two ends of these boxes, which also serves to mount the plug-in-boxes on bus-bars., , Technical Data, Rating, , Overall dimensions, in mm, , No.of plug, , 200A, , 3658 x 248 x 76, , 6, , 400A, , 2440 x 248 x 108, , 4, , Bus-bar length can be increased by providing mechanical, coupling and any length at run in multiples of the standard, length may be thus achieved., Plug-in-Boxes, Plug-in-boxes (Fig 6) are compact sheet steel boxes with, hinged doors housing the HRC fuse holders, which are, solidly connected to high conductivity copper clip on, contacts reinforced by spring steel strips. These clip on, contacts plug directly to the bus-bars at the plug-in-points., , Rating of plug in boxes, Plug in Boxes must be able to withstand faults current, capability of bus-bars. There are rated in 16, 32, 63 and, 100Amp at 415/500V (TPN)., Cables (or) conductors with termination connection to, plug-in-boxes for outgoing supply by using conduit pipe to, conduit glands supplied with plug in boxes either vertically, down or on to either side., However remember to use oxide inhibiting grease at all, aluminium joint to maintain conductivity., , Power tariff - terms and definitions, Objectives: At the end of this lesson you shall be able to, • state the term maximum demand, • explain the concept of average demand, • explain load factor, • state the term of diversity factor and its application, • explain the importance of plant utility factor., Introduction, The alternators in the power station should run at their, rated capacity for maximum efficiency and on the other, hand, the demands of the consumers have wide variations, from time to time due to uncertain demands of the, consumers. This makes the design of a power station, highly complex. We shall focus our attention on the, problems of variable load on power stations., Maximum Demand, It is the highest level or greatest electrical demand, monitored in a particular period or a month., , The maximum demand is in between 18 hours and 24, hours in the night during summer as well as in winter, seasons as in Fig 1. All other times the maximum demand, falls very low to the connected load. However the maximum, load demand less than the connected load because all the, consumers do not switch ‘ON’ their connected load of the, system at a time., The importance of the maximum demand knowledge is, very important as it helps in determining the installed, capacity of the stations, and the station must be capable, of meeting the maximum demand., The ratio of maximum demand as the power station to its, connected load is known as demand factor; Mathematically, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.202, , Copyright @ NIMI Not to be Republished, , 225

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f Load =, , Total load, Maximum load in given time period, , or, , Total load, Peak load., , An example, using a large commercial electrical bill:, •, , peak demand = 436 KW, , •, , use = 57 200 kWh, , •, , number of days in billing cycle = 30, , Hence:, •, , Demand factor =, , Max. Demand, Connected load, , Usually it always less than one. The knowledge of demand, factor is vital in determining the capacity of the plant, equipment., Average demand, It is the total demand in a month divided by number of days, in that time period., The average demand in a month taken to find the load, requirement for a certain period is in Fig 2. It is evident that, average load requirement is not uniform among all the, months consumption as it depend on the environmental, conditions; such as Winter, Summer, Monsoon seasons., , load factor = { 57 200 kWh/ (30 d x 24 hours per day, x 436 kW) } x 100% = 18.22%, , It can be derived from the load profile of the specific device, or system. Its value is always less than one because, maximum demand is always higher than average demand,, since facilities likely never operate at full capacity for the, duration of an entire 24 hours day. A high load factor, means power usage is relatively constant. Low load factor, shows that occasionally a high demand is set. To service, that peak, capacity while remaining idle for long periods,, thereby imposing higher costs on the system. Electrical, rates are designed so that customers with high load factor, are charged less over all per kWh., The load factor is closely related to and often confused, with demand factor., , f Demand =, , Maximum load in given time period, Maximum possibe load, , The major difference to note is that the denominator in the, demand factor is fixed depending on the system. Because, of thiss the demand factor cannot be derived from the load, profile but needs the addition of the full load of the system, in question., Diversity factor, Diversity factor (Or simultaneity factor KS) is a measure of, the probability that a particular piece of equipment will turn, on coincidentally to another piece of equipment. For, aggregate system it is defined as the ratio of the sum of, the individual non - coincident maximum loads of various, sub divisions of the system to the maximum demand of the, complete system., , Load factor, In electrical engineering the load factor is defined as the, total load divided by the peak load in specified time period., It is a measure of the utilization rate, or efficiency of, electrical energy usage; a low load factor indicates that, load is not putting a strain on the electric system, whereas, consumers or generators that put more of a strain on the, electric distribution will have a high load factor., , 226, , Diversity factor =, , Sum of individual max Demands, Maximum Demand, , The diversity factor is almost always larger than 1 since all, components would have be on simultaneously at full load, for it to be one. The aggregate load is time dependent as, well being dependent upon equipment characteristics., The diversity factor recognizes that the whole loads does, not equal the sum of its parts due to this time, interdependence (i.e. diverseness). For example, we might, have ten air conditioning units that are 20 tons each at a, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.202, , Copyright @ NIMI Not to be Republished

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facility. We typically assume that the average full load, equivalent operating hours for the units are 2000 hours per, year. However, since tha units are each thermostatically, controlled, we do not known exactly when each unit turns, on. If the ten units are substantially bigger than the, facility’s actual peak A/C load, then fewer than all ten units, will likely come on at once. Thus, even though each unit, run a total of 2000 hours a year, they do not all come on, at the same time to affect the facility’s peak load. The, diversity factor gives us a correction factor to use, which, results in a lower total kW load for the ten A/C units. If, energy balance we do for this facility comes out within, reasons, but the demand balance shows far to many kW, for the peak load, then we can use the diversity factor to, bring the kW into line with facility’s true peak load. The, diversity factor does not affect the kWh; it only affects the, kW., Plant utility factor, The utility factor or use factor is the ratio of the time that, a piece of equipment is in use to total time that it could, be in use. If is often averaged over time in the definition, such that the ratio becomes the amount of energy used, divided by the maximum possible to be used. These, definitions are equivalent., , The utility factor, Ku, is the ratio of the maximum load, which could be drawn to rated capacity of the system. This, is closely related to the concept of load factor. The factor, is the ratio of the load that piece of equipment actually, draws (time averaged) when it is in operation to the load it, could draw (which we call full load., Utility Factor =, , Ratio of maximum power, ×100, Plant capacity, , For example, an oversized motor - 15 kW - drives a, constant 12 kW load whenever it is on. The motor load, factor is then 12/15 = 80%. The motor above may only be, used for eight hours a day, 50 weeks a year, The hours of, operation would then be 2800 hours, and the motor use, factor for a base of 8760 hours per year would be 2800/, 8760 = 31.96%. With a base of 2800 hours per year, the, motor use factor would be 100%., In power plant utility factor various according to the, demand on the plant from the electricity market., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.6.202, , Copyright @ NIMI Not to be Republished, , 227

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Electrical, Related Theory for Exercise 4.7.203 & 4.7.204, Electrician - Circuit Breakers and Relays, Line protective relays - types - operation, Objectives: At the end of this lesson you shall be able to, • state the classification of relays, • list the types of relays and their uses, • explain the principle of operation of over current, differential, earth fault, distance and non directional relays, • state the characteristics of relays, • explain the principle of operation of a over voltage end under voltage relay, • state the necessity of time multiplier setting of relay., Introduction, , 3 Under voltage relay, , The relays is the element that senses as abnormal, condition in the circuit and commands the operation of the, breaker. It interpret the fault quantities ie, CT output, current and PT output voltage and sending the command, to the tripping circuits of breaker for operation in accordance, with the characteristic set in the relay and the value of the, time multiplier setting., , 4 Differential relay, 5 Earth fault relay, 6 Distance relay, 7 Impedance relay, 8 Admittance relay, 9 Reactance relay, , Classification of Relays, Relays are classified mainly in three categories; they, are according to:, 1 Quantity sensed : Current, Voltage, active power,, reactive power & impedance, 2 Tripping : Instantaneous trip, delayed trip inverse time, response and definite time, 3 Operating principle: Electro magnetic relays,, Induction relays, Thermal relays and static or digital, relays, Types or relays : Various types of relays are used as per, the requirement; they are:, , Relay is one of the main device used for switch gear, protection networks to protect the transmission lines,, transmission equipments and sub station equipments., The equipments used for transmission and in substation, for distribution such as transformers, lightening, arrestors,earth switches, isolators, CTs & PTs etc; are, very costly and needs continuous protection from damage., Replacement or repairs are not easy and to provide an, uninterrupted supply to consumers. So, protection of, these devices/equipments are very essential, Reasons for over current, Over voltage and under voltage, fault:, Many reasons constituted for over current, over and under, voltage or earth faults; type of fault and the cause effect is, listed in Table 1., , 1 Over current relay, 2 Over voltage relay, , Table 1, Sl No, , 228, , Type of Fault, , Cause, , Effect, , 1, , Phase to neutral, short, , - Insulation failure, - Components failure, - Human error, , - High current flow, in line., - Fire, , 2, , Phase to phase short, in transmission lines, , - Tree branches falls on line, - Snakes crossing on, tower lines and, - Birds falls, - Strong winds, - Natural calamities, - Riots, and human made faults, , - Very high, current flows, - Fire, - Extensive, damage of, equipments, , 3, , Phase to ground, fault, , - Insulation failure, - Component failure, , - High current, flow in line, - Fire, - Low voltage, , Copyright @ NIMI Not to be Republished

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Sl No, , Type of Fault, , Cause, , Effect, , 4, , Lightening, storm etc;, , - Natural calamities, , - Very high, current flows, - Fire, - High voltage spikes, , 5, , Sudden removel, of heavy load, , - Fuse failure, , - High voltage, , 6, , Increasing, Load beyond, the rated level, , - Human Error, , - Low voltage, in line, - Over loading, the line, , Sensors used for Relays, The relay cannot accept the total line voltage or load, current. A small part of the electrical quantity is supplied, to the relay through sensors. A current transformer, popularly known as CT and a potential transformer PT, is, serves the purpose of sensors in current relay and voltage, relay. Various input and output ratios are in practice to, supply the sensing quantity to the relays according to the, load conditions., Working principle of current relay, The electro magnetic relay widely using in the substation, and transmission lines are serves the protection from the, disaster conditions. The latest version of modern static or, digital relays are now a days out dated the conventional, electro magnetic relays, because of their many of, advancements compare to electro magnetic relay. (Fig 1), , 1, 2, 3, 6, , 4, 5, 7, , 5 Tap setting plug, 6 Input fault quantity (VONI), 7 Contact plug terminals, An induction type over current relay giving inverse time, operation with a definite minimum time characteristic is in, Fig 1. It consists essentially of an ac energy meter, mechanism with slight modification to give required, characteristics. The relay has two electromagnets. The, upper electromagnet has two windings, one of these is, primary and is connected to the secondary of a CT in the, line to be protected and is tapped at intervals., , Fig 2 shows the front panel setting of a electric magnetic, relay., 1 Time multiplier setting (TMS), 2 Trip flag, 3 Aluminium rotating disc, 4 Percentage fault quantity time reference dial, , The tappings are connected to a plug setting bridge by, which the number of turns in use can be adjusted, thereby, giving the desired current setting. The plug bridge is, usually arranged to give seven sections of tappings to give, over current range from 50% to 200% in steps of 25%. If, the relay is required to response for earth fault the steps, are arranged to give a range from 10% to 70% or 20 to 80%, in steps of 10%. The values assigned to each tap are, expressed in terms of percentage of full-load rating of CT, with which the relay is associated and represents the, value above which the disc commences to rotate and, finally closes the trip circuit., Thus pick-up current equals the rated secondary current, of CT multiplied by current setting. For example suppose, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.203 & 4.7.204, , Copyright @ NIMI Not to be Republished, , 229

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that an over current relay having a current setting of 150%, is connected to a supply circuit through a CT of 500/5A., The rated secondary current of CT is 5 A and, therefore, the, pick-up value will be 1.5 x 5i.e., 7.5 A. It means that with, above current setting, the relay will actually operate for a, relay current equal to or greater than 7.5 A., , •, , Operates in a definite time when fault quantity exceeds, its pick-up valve., , •, , Its operation criteria is only fault quantity magnitude, , •, , Operating time is constant, , •, , No intentional time delay, , Similarly for current settings of 50, 100 and 200% the relay, will operate for relay currents of 2.5A, 5 A and 10 A, respectively. Adjustment of current setting is made by, inserting a pin between the spring loaded jaws of the bridge, socket at the tap value required. When the pin is, withdrawn for the purpose of changing the setting value, while the relay in service, the relay automatically adopts, higher setting, thus the CT’s secondary is not opencircuited., , •, , These are varies with position of the fault occurred, because of the difference in impedance between the, fault and the source, , •, , It can operates in 0.1s or less., , The disc spindle carries a moving contact which bridges, two fixed contacts ( trip circuit contacts) when the disc has, rotated through a preset angle. The angle can be set to any, value between 0° and 360° and there by giving desired time, setting. This adjustment is known as time-setting multiplier., Time multiplier setting is generally in the form of an, adjustable back-stop which decides the arc length through, which the disc travels, by reducing the length of travel, the, operating time is reduced., The time setting multiplier is calibrated from 0 to 1 in steps, of 0.05. These figures do not represent the actual operating, times but are multipliers to be used to convert the time, known from the relay name plate curve (time-PSM curve), into the actual operating time. Thus if time setting is 0.2, and the operating time obtained from the time-PSM curve, of the relay is 5 seconds, then actual operating time of the, relay will be equal to 0.2 x 5 i.e., 1 second., Since the time required to rotate the disc through a preset, angle depends upon the torque which varies as the current, in the primary circuit, therefore, more the torque lesser will, be the time required. So the relay has inverse-time, characteristic., Relay Time setting characteristics, 1 Instantaneous over current/voltage relay, , 2 Definite time, Two conditions must be satisfied on the fault quantity, continued to be present up to the time setting of the relay., (Fig 4), , •, , Its operating time is constant, , •, , Its operation is independent of the magnitude of the, fault quantity, , •, , It has time dial settings; Time delay can be varied, , •, , Tripping time independent on fault location., , 3 Inverse time, Operating time is inversely changed fault quantity. So,, high the fault quantity will operate relay faster than lower, ones (Fig 5). There are few more settings also in practice,, They are;, , Definite current/voltage (over or under) relay operate, instantaneously when the fault quantity reaches a, predetermined value. (Fig 3), , 230, , •, , Standard inverse, , •, , Very inverse, , •, , Extremely inverse, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.203 & 4.7.204, , Copyright @ NIMI Not to be Republished

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Discrimination by both time and fault quantity, the relay, operation time is inversely proportional to the fault quantity., , Normal inverse time over current relay is relatively small, change in time/unit of change of current, , Inverse time relays also referred as Inverse Definite Minimum, Time (IDMT) relays., , Very inverse time characteristics, •, , Gives more inverse characteristics than that of IDMT, , The operating time of relay can be moved up (made slower), by adjusting the time dial setting. The lowest time dial, setting (fastest operating time) is generally 0.5 seconds, and the slowest is 10s., , •, , Used when there is a reduction in fault quantity, as the, distance from source increases, , •, , Effective with ground faults because of their steep, characteristics, , Silent features of inverse time settings, , •, , Suitable where the fault distance from the power, source increase, , •, , Operates when fault quantity exceeds its pick-up, value., , •, , •, , Operating time depends on the magnitude of the fault, quantity, , Particularly suitable if the short circuit fault current, drops rapidly with the distance from the substation, , •, , •, , It gives inverse time current characteristics at lower, values of fault quantity and definite time characteristics, at higher values., , The grading margin may be reduced to very low time, (0.1 second) in this characteristics, , •, , Used when fault quantity is dependent on fault location, , •, , An inverse characteristics is obtained if the value of, plug setting multiplier is below 10, for values between, 10 and 20 characteristics tends towards definite time, characteristics. Fig 6 shows the different inverse types., Based on the inversness it has three different types of, curves shown in Fig 6., , Extremely inverse time characteristics, •, , It has more inverse characteristics than that of IDMT, and very inverse characteristics, , •, , Suitable for protection against over heating, , •, , Operative time approximately inversely proportional to, the square of the fault quantity, , •, , It makes possible to use short time delay in spite of, high switching in current, , •, , Used when fault quantity is dependent on fault location, , •, , Suitable for protection of feeders, with peak current on, switching (refrigerators, pumps water heaters etc) and, also for alternator transformers and expensive cables., , Long time inverse characteristics, This characteristics is used as back up earth fault protection, as the time inversely proportional to the intensity of fault, quantity., Over voltage and under voltage relays, This electromagnetic relays are working on the same, principle of induction type disc type relays. The sensor, used in this relay input is from PT (potential transformer), where output generally kept on 110v AC., , Normal Inverse Characteristics, The accuracy of the operating time may range from few, percentage of the nominal operating time. The uncertainty, of the operating time and the receiving operating time may, require a grading margin of less than one seconds., , When the fault occurs the PT output produces a voltage, which in turn energise the disc mechanism to rotate. As, the fault continue to represent; and the trip time settled,, the relay disc rotates and make the trip coil to activate in, the trip mechanism in the breakers. The tripping time, settled as per the characteristics selected. The pick up, voltage has to be verified with the plug setting value of fault, voltage which can be selected in different fault voltages in, both over/ under voltage relay. Time Multiplier Setting, (TMS) shorten the trip time if necessary on the fault, quantity is more as the case may be., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.203 & 4.7.204, , Copyright @ NIMI Not to be Republished, , 231

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Time multiplier setting, This setting is helps the relay to shorten the time selected, without change of any other settings made in the relay., Time multiplier helps the relay to activate fast the breaker, in case the fault quantity is more than 50% of the fault, quantity selected by the tap setting., , to a predetermined point (the reach point) Such a relay is, described as a distance relay and is designed to operate, only for faults occurring between the relay location and the, selected reach point thus giving discrimination for faults, that may occur in different line sections, , Differential protection relay, Differential protection is a very reliable method of protecting, generators, transformers, busbar and transmission lines, from the effects of internal faults. In normal operating, conditions the current through the CTs is the same. So the, relay sense no differential current. This is also the case for, external faults. Differential protection can be used for, protecting generators from faults to ground. Differential, protection of busbars in substations uses one CT for each, incoming line. All incoming currents are added up and, compared to the sum of all out going currents., General schematic diagram of differential protection relay, is in Fig 7., , Reactance relays (or) Shaded pole type non, directional relay, The reactance relay is a straight line characteristic that, responds only to the reactance (XL) of the protected line ., It is non directional and is used to supplement the, admittance relay as a tripping relay to make the overall, protection independent of resistance. It is particularly, useful on short lines where the fault arc resistance is the, same order of magnitude as the line length., , The installation of differential relay for protection of power, transformers used in transmission line is in Fig 8., Distance relays / Admittance relay, , The relay serves an important part in switchgear protection., The electromagnetic relay is the first generation of protective, relays and it has many moving parts and working in the, principles of induction. Electromagnetic relay can carry, one function ie., over current, over voltage or under voltage, at a time. This draw back is overcome by the use of static, or digital relay which can use for multi function, as well as, more accurate than electromagnetic relays., , The impedance of a transmission line is proportional to its, length, for distance measurement it is appropriate to use, a relay capable of measuring the impedance of a line up, , 232, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.203 & 4.7.204, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.7.205 & 4.7.206, Electrician - Circuit Breakers and Relays, Circuit breakers - parts - functions- tripping mechanism, Objectives: At the end of this lesson you shall be able to, • state about circuit breaker, • list the various types of circuit breakers, • explain the parts of each circuit breakers, • explain the principle of operation of circuit breaker, • explain the application and uses of circuit breaker., Circuit breaker, , Fig 1, , Circuit breakers are the electrical device (or) equipment,, which makes or breaks the electrical circuit. In a 240 volt, single phase system a low rated single pole switch can, use the circuit to break or make. But in this case the, resultant spark at the contacts are negligible and this will, not make any fire, in the circuit or contacts since the, current is very low., But in the case of heavy loads; say some hundreds, of, ampere are flowing in a circuit the resultant spark at, contact are heavy and this leads to electrical fire. To, overcome this problem the sparks at the contacts are to, be controlled or quenched, when any load makes or, breaks. The equipment or device used to make or break, a circuit under control at the same time it prevents or, quenching the resultant fire is called as a circuit breaker., The breakers are named after the quenching medium used, to control the fire such (1) air circuit breaker, (2) oil circuit, breaker, (3) vaccum circuit breaker and (4) Sulphur, hexafluoride (SF6) circuit breaker., , 5 Reset button, , Air circuit breaker (ACB), , 6 LED indicators, , A circuit breaker which uses the either natural air or blast, air as an Arc quenching medium is termed as Air-circuit, breakers., ACB is widely used upto 15KV in place of oil circuit, breaker because there is no chance of the fire due to the, quenching oil as in case of OCB., Air- Circuit breakers are widely used in industries as well, as power system for controlling and protection of different, section of the circuit like, Transformers, Motors, Generators, / Alternator etc and leads the system stable and reliable., Other components are also associated with circuit, breakers like fuses, relays, switches etc., Construction of air - circuit breaker, External lables / parts of ACB in Fig.1, 1 OFF button (O), , EXTERNAL VIEW OF ACB, , 7 Controller, 8 "Connection" "Test" and "isolated" position latching /, locking mechanism, 9 User padlock, 10 Connection, "Test", and isolated position indication, 11 Connection, contacts, , test and isolated position indication, , 12 Name plate, 13 Digital displays, 14 Energy storage handle, 15 Draw out /in hole, 16 Rocker repository, 17 Trip reset button, Internal construction of air circuit breaker, The internal parts of an ACB in Fig.2, , 2 ON button (I), 3 Main contact position indicator, 4 Energy storage mechanism status indicator, , 1 Sheet steel supporting structure, 2 Current transformer for protection trip unit, , Copyright @ NIMI Not to be Republished, , 233

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•, , By splitting the arc into a number of series in Arc chute, will increases the arc voltage., , •, , Arc voltage can be increased by lengthening the arc, path. As length of arc path is increased its resistance, of the arc path will increase hence the arc voltage is, increased., , Some ACB contains two pairs of contact . The main pair, carries the current and the made of copper. An additional, pair of contact (Arc contact) is made of carbon. When the, breaker is opened, the main contact opens first. and the, arc contact remains in touch. The arcing gets initiated, when arc contacts are separated., Hence transition voltage will be reduced., Application and uses of air circuit breaker, 3 Pole group insulating box, 4 Horizontal rare terminals, 5 Plate for fixed main contacts, 6 Plates for fixed arcing contacts, 7 Plate for main moving contacts, 8 Plates for moving arcing contacts, 9 Arcing chamber, , •, , It is used for protection of plants, , •, , It is used for common protection of electrical machines, , •, , Air circuit breaker is also used in electricity sharing, system upto 15KV, , •, , Also used in low as well as high voltage and current, applications., , •, , It is used for protection of transformers, capacitors and, generators., , 10 Terminal box for fixed version - sliding contacts for, withdrawable version, , Types of air circuit breaker, •, , Plain air circuit breaker, , 11 Protection trip unit, , •, , Air blast circuit breaker, , 12 Circuit breaker closing and opening control, , Plain air circuit breaker, , 13 Closing springs, 14 Spring loading arrangement, 15 Manual releasing lever, Principle of operation of air circuit breaker, •, , When the circuit breaker opens the circuit either under, the normal condition or in the fault condition, some Arc, is produced between the main contacts and some, current flows to the load, called transition current, through the arc., , •, , This Arc and the current should be suppressed /, eliminated especially during the fault condition otherwise, the severity of the fault level will be more and damages, the circuit which leads to the electric fire., , •, , During the period of Arc some voltage appears across, the main contacts called transition voltage, which, will be more than the rated system / supply voltage., , •, , To quench the Arc, this transition voltage should be, reduced or the Arc voltage to be increased. The, minimum voltage required to maintain the arc is called, as Arc voltage. In ACB, the Arc voltage is increased, in the following three ways., , •, , Arc voltage can be increased by cooling arc plasma by, air. The temperature of arc plasma is reduced, more, voltage will be required to maintain the arc., , 234, , In this circuit breaker a chamber is fitted surrounding the, contact. The chamber is known as "arc chute". The arc, chute will help in achieving cooling. Arc chute is made from, some refractory material., The arc chute is divided into a number of small, compartments by using metallic separation plates called, arc splitters and behave as a mini arc chute as in Fig.3., Initial arc will split into a series of arcs and make the arc, voltages higher than system voltage. They are preferable, choice in low voltage application., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished

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Air blast circuit breaker, ACB which uses the high pressure (blast) air as an Arc, quenching medium is known as Air-Blast- CircuitBreaker(ABCB)., , Secondly, the gas sets up turbulence in the oil and forces, it into the space between contacts, thus eliminating the, arc as in Fig 4. The result is that arc is extinguished and, circuit current is interrupted., , This type of circuit breaker is used for high voltage, application and can be further divided into three categories., •, , Axial blast air circuit breaker, , •, , Cross blast air circuit breaker, , •, , Radial blast air circuit breaker, , Advantages of air - blast circuit breaker, •, , Air blast circuit breaker is used where the frequent, operation is required because of lesser arc energy., , •, , The risk of fire due to oil is eliminated in the air blast, circuit breaker, , •, , Arc quenching is much faster, , •, , Air blast circuit breaker is small in size, because of the, fast Arc quenching., , •, , The duration of the arc is same for all the values of, current., , •, , Operating speed of circuit breaker is much higher., , •, , Stability of operation is high because of speed of, operation., , •, , It requires less maintenance, , The advantages of oil as an arc quenching medium, i, , It absorbs the arc energy to decompose the oil into, gases which have excellent cooling properties., , ii It acts as an insulator and permits smaller clearance, between main contacts., iii The surrounding oil presents the cooling surface in, close proximity to the arc., The disadvantages of oil as an arc quenching, medium., i, , It is inflammable and there is a risk of a fire., , ii It may form an explosive mixture with air., iii The arcing products (e.g. carbon) remain in the oil and, it deteriorates the quality of insulating oil., , Disadvantages of air -blast circuit breaker, , iv Periodic checking and replacement of the insulating oil, is required., , •, , Additional air supply plant requires hence require, additional maintenance., , Types of oil circuit breakers, , •, , It require high capacity air compressor., , •, , There is a chance of air pressure leakage., , •, , There is chance of a high rate of re - striking voltage and, current chopping., , •, , The air has relatively lower arc extinguishing properties, than oil., , Oil circuit breakers (OCB), Circuit breakers which uses the insulating oil (e.g, transformer oil ) as an arc quenching medium is called as, oil circuit breaker. The main contacts of the OCB are, opened under the oil and an arc is struck between them., The heat of the arc evaporates the surrounding oil and, dissociates it into gaseous of hydrogen at high pressure., The hydrogen gas occupies a volume about one thousand, times that of the oil decomposed. The oil is, therefore,, pushed away from the arc and an expanding hydrogen gas, bubble surrounds the arc region of the contacts. The arc, extinction is completed by two processes. Firstly, the, hydrogen gas has high heat conductivity and cools the, arc, thus aiding the de-ionization of the medium between, the contacts., , a) Plain break oil circuit breakers, b) Arc control oil circuit breakers., ii Low oil circuit breakers, Plain break oil circuit breakers, In plain- break oil circuit breaker the main contacts are, placed under the whole oil in the tank. There is no special, system for arc control other than the increase in length of, separation of the contacts. The arc extinction occurs, when a critical gas is reached between the contacts., The plain - break oil circuit breaker is the oldest type and, has a very simple construction. It consists of fixed and, moving contacts enclosed in a strong weather- tight, earthed tank containing transformer oil upto a certain level, and an air cushion above the oil level., The air cushion provides sufficient room to arc gases, without the generation of unsafe pressure in the circuit, breaker. It also absorbs the upward oil movement. Fig 5, shows a double break plain oil circuit breaker. It is called, a double break because it provides two breaks in series., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished, , 235

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Low oil circuit breakers, In the bulk oil circuit breaker, only a small percentage of, oil (about 10% of total) is actually used for arc extinction., But the huge volume of oil used in bulk oil circuit breaker, increases the expenses, tank size, weight of the breaker,, increases the fire risk and maintenance problems., To over come the above disadvantages the low oil circuit, breaker is developed which employs solid materials for, insulation purposes and uses a small quantity of oil which, is just sufficient for quenching the arc. By using suitable, arc control devices, the arc extinction can be further, simplified in a low oil circuit breaker., Principle of working, Under normal operating conditions, the fixed and moving, contacts remain closed and carries the normal circuit, current. When a fault occurs, the moving contacts are, pulled down by the tripping mechanism and an arc is, produced which vaporizes the oil into hydrogen gas. The, arc extinction is completed by the following processes., i, , Construction : Fig 6 shows the single phase low oil, circuit breaker. There are two compartments separated, from each other and filled with oil. The upper chamber is, the circuit breaking chamber whereas the lower one is, thesupporting chamber. The two chambers are separated, and the oil from one chamber is prevented from mixing with, the other chamber., , The hydrogen gas bubble generated around the arc,, cools the arc., , ii The gas sets up turbulence in the oil and helps in, eliminating the arc., iii As the arc lengthens due to the separation of contacts,, the Arc voltage is increased., The result is at some critical gap, the arc is extinguished, and the circuit current is interrupted., Disadvantages, i, , There is no special control over the arc other than the, increase in gap length., , ii These breakers have long and inconsistent arcing, times., iii The speed of interruption is less., Due to these disadvantages, plain - break oil circuit, breakers are used only for low - voltage not exceeding, 11 KV applications where high breaking- capacities are, not important., Arc control oil circuit breakers, In plain -break oil circuit breaker there is very little artificial, control over the arc. Therefore long arc length is essential, in order to quench the Arc. If some arc control is, incorporated at still short contact gap than the breakers, are called arc control oil circuit breakers., They are two types, a Self - blast OCB, b Forced - blast OCB, , 236, , This arrangement has three advantages., 1 The circuit breaking chamber requires a small volume, of oil which is enough for arc extinction., 2 The amount of oil to be replaced is considerably, reduced, 3 The oil in the supporting chamber does not get, contaminated by the arc., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished

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i, , Supporting chamber : It is a porcelain chamber filled, with oil which is physically separated from the oil in, the circuit breaking compartment. The oil inside the, supporting chamber and porcelain insulation is, employed for insualtion purposes only., , ii Circuit breaking chamber : It is a porcelain enclosure, mounted on the top of the supporting chamber and, filled with oil and has the following parts., a), , Fixed contacts, , b), , Moving contacts, , c), , Turbulator, , The moving contact enters top chamber through a fixed, piston. The turbulator is an arc control device and has both, axial and radial vents. The axial vent for low currents, whereas radial vent for heavy currents rating breakers., iii Top chamber : It is a metal chamber mounted on top, of the circuit - breaking chamber. It provides space for, the oil expansion in the circuit breaking chamber. The, top chamber also has a gas vent pipe and breather, through which the escaping gas and entering air may, pass through to the circuit breaking chamber during, the breaking of fault current., Operation : Under normal operating conditions, the, moving contact engages with the fixed contact. When a, fault occurs, the moving contact is pulled down by the, tripping mechanism and an arc is produced. The arc, vaporizes the oil and produces gas to escape through the, gas vent., , Vacuum circuit breaker (VCB), Circuit breaker which uses vacuum as an arc quenching, medium is called as vacuum circuit breaker., Vacuum offers the highest insulating strength and have, the superior arc quenching properties than any other, medium. When the contacts of a breaker are opened in, vacuum, the interruption occurs instantly as the dielectric, strength between the contacts are many times higher, than the other circuit breakers., The technology is only suitable for medium voltage, application. For higher voltage application, the vacuum, technology has been developed., Principle of vacuum circuit breaker, •, , When the contacts of the breaker are opened in, vacuum (107 to 105 torr), an arc is produced between the, contacts by the ionisation of metal vapours i.e,, combination of electrons and ions of contacts. However,, the arc is quickly extinguished because the metallic, vapours, rapidly cools resulting quick recovery of, dielectric strength., , •, , The salient feature of vacuum is, as soon as the arc is, produced in vacuum, it is quickly extinguished due to, the rapid recovery of dielectric strength of vacuum., , Construction of vacuum circuit breaker, Fig 7 shows the typical parts of vacuum circuit breaker, , This action results the oil to pass through a central hole, of the moving contact and forcing the oil through the, respective vents of the turbulator. The arc are successively, quenched by the effect of streams of oil passes through, the vent while gas passes., Advantages : A low oil circuit breaker has the following, advantages over a bulk oil circuit breaker., i, , It requires lesser quantity of oil, , ii Cost of the breaker is less, iii It requires smaller space, iv The weight of the breaker in less, iv There is reduced risk of fire, , •, , It consists of the fixed contact, moving contact and arc, shield mounted inside a vacuum chamber., , •, , The movable member is sealed by a stainless steel, bellows, is connected to the control mechanism . This, enables the permanent sealing of the vacuum chamber,, to eliminate the possibility of leak., , •, , A glass vessel or ceramic vessel is used as the outer, insulating body., , •, , The arc shield prevents the metallic vapours falling on, the inside surface of the outer insulating cover., , vi Maintenance problems and cost are reduced, Disadvantages : A low oil circuit breaker has the following, disadvantages as compared to a bulk oil circuit breaker, i, , There is a difficulty of removing the gases from the, contact space., , ii Due to smaller quantity of oil, the effect of carbonization, is increased., iii The dielectric strength of the oil deteriorates fastly due, to high degree of carbonization., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished, , 237

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Working of vacuum circuit breaker, •, , When the breaker opens, the moving contact is, separated from the fixed contact and an arc is produced, between the contacts. The production of arc is due to, the ionisation of metal ions and depends upon the, material of contacts., , •, , The arc is quickly extinguished because the metallic, vapours , are diffused in a short time and condensed on, the surfaces of moving and fixed members and arc, shields., , •, , Since vacuum has rapid Arc recovery rate of dielectric, strength, the arc extinction in a vacuum breaker occurs, with a short separation (say 0.625 cm) of contacts., , Application of VCB, •, , Vacuum circuit breakers are employed for outdoor, applications ranging from 22KV to 66KV., , •, , They are suitable for majority of applications in rural, areas., , The tips of fixed contact, moving contact and arcing horn, are coated with copper - tungsten arc resistant material., Since sulphur hexafluoride gas is costly, it is reconditioned, and reclaimed using suitable auxiliary system after each, operation of breaker., , Sulphur hexafluoride (SF6) circuit breaker, , Working of SF6 circuit breaker, , Circuit breakers which uses the sulphur hexafluoride gas, (SF6) as an arc quenching medium is called as SF 6 circuit, breaker., , In the closed position of the breaker, the contacts remain, surrounded by SF6 gas at a pressure of about 2.8 kg/cm2., When the breaker opens, the moving contact is pulled, apart and an arc is struck between the contacts. The, movement of the moving contact is synchronized with the, opening of a valve which permits SF6 gas at 14kg /cm2, pressure from the reservoir to the arc interruption chamber., , The sulphur hexafluoride gas (SF6) is an electronegative, gas and has a strong tendency to absorb the free electrons., When the contacts of the breaker are opened in a high, pressure sulphur hexafluoride (SF6) gas medium and an, arc is struck between them., The SF6 gas capture the conducting free electrons in the, arc and form immovable negative ions. This loss of, conducting electrons in the arc quickly improve the, insulation strength to extinguish the arc., The sulphur hexafluoride (SF6) circuit breakers are very, effective for high power and high voltage applications., Construction of SF6 circuit breaker, A sulphur hexafluoride (SF6) circuit breaker consists of, fixed and moving contacts enclosed in a chamber as in, Fig 8. The chamber is called arc interruption chamber, which contains the sulphur hexafluoride (SF6) gas and it is, connected to sulphur hexafluoride (SF6) gas reservoir., When the contacts of breaker are opened, the valve, mechanism permits a high pressure sulphur hexafluoride, (SF6) gas from the reservoir to flow towards the arc, interruption chamber., The fixed contact is a hollow cylindrical contact fitted with, an arc horn. The moving contact is also a hollow cylinder, with rectangular holes in the sides. The holes permit the, sulphur hexafluoride gas (SF6) to let out through them after, flowing along and across the arc., , 238, , The high pressure flow of SF6 gas rapidly absorbs the free, electrons in the arc path to form immovable negative ions, which are ineffective as charge carriers. The result is that, the medium between the contacts rapidly improve the, dielectric strength and causes the extinction of the arc., After the breaker operation (i.e. after arc extinction), the, valve mechanism is closed by a set of springs., Advantage of SF6 circuit breaker, Due to the superior arc quenching properties of SF6 gas,, the sulphur hexafluoride gas circuit breakers have many, advantages over oil or air circuit breakers. Some of them, are listed below., 1 Such circuit breakers have very short arcing time., 2 Since the dielectric strength of SF6 gas is 2 to 3 times, more than the air, such breakers can interrupt much, larger currents., 3 SF6 circuit breaker gives noiseless operation due to, its closed gas circuit and no exhaust to the atmosphere, unlike the air blast circuit breaker., , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished

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Tripping mechanism of circuit breakers, Objectives: At the end of this lesson you shall be able to, • State the necessity of tripping mechanism, • state the types of tripping mechanism., Tripping mechanism of circuit breakers, Trip mechanism : Trip mechanism is incorporated in the, circuit breaker to switch off the circuit breaker at faulty, condition either automatically or manually at the desired, time., , Shunt trip coils : The shunt trip coil requires an auxiliary, supply, a C.T and a relay. The relay can be set to give timegraded protection. The relay closes the trip coil circuit, when the load current exceeds the stipulated value. This, relay is in Fig 3., , Fig 1 shows the arrangement. When the circuit breaker is, closed, the mechanism is locked in position by a system, of linkages. This lock can be released by lifting the trip bar., , Series trip coil: The series trip coil mechanism is in, Fig 4 consists of a series solenoid with a plunger controlled, by a spring. When current in the load become excessive, the plunger rises and trips the mechanism., Trip bar is attached to the tripping lever which in turn can, be operated manually. The tripping lever is generally kept, locked. When the trip bar is lifted the mechanism opens, the breaker contacts., Trip coils: When remote operation is desired, trip coils, are used. The trip coils are small solenoids either operated, by AC or DC supplies. Fig 2 shows the general arrangement, of the trip coil mechanism. A plunger moves freely inside, the solenoid. When the solenoid is energised by the trip, switch the plunger moves up and release the lock which, holds the trip bar. Further the trip coils are also actuated, by short circuit /overload and under -voltage relays as, described in the following paragraphs., , The current necessary to trip the circuit breaker is regulated, by a screw which adjusts the tension of the spring, controlling the plunger. Time-lag can be adjusted by the, position of the dash pot which holds the piston of the, plunger in the oil bath., In three-phase circuit breakers, there are three series trip, coils, three dash pots, three plungers. They can operate, the trip mechanism together or independently., Under voltage release coils : The under-voltage release, coil is used in installations where detection and isolation, of abnormally low voltage is required. The construction of, the under-voltage trip coil is in Fig 5 is similar to the trip, coils discussed above except that the plunger is held, away from the pole piece by a coiled spring. Under normal, operating conditions, the solenoid is energised and the, plunger is held down against the force of the spring. When, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished, , 239

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the supply voltage falls, the under - voltage release coil will, not be in a position to hold the plunger down against the, spring tension. Thus the plunger moves up and pushes the, trip bar to trip the circuit breaker., , 240, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.205 & 4.7.206, , Copyright @ NIMI Not to be Republished

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Electrical, Related Theory for Exercise 4.7.207, Electrician - Circuit Breakers and Relays, Repair and maintenance of CBs, Objectives: At the end of this lesson you shall be able to, • explain the procedure to carry out maintenance and repair of a OCB, • state the method to adopt checking and maintenance/repair of ACB & VCB, • explain the procedure of the condition of SF6 circuit breakers and their repair and maintenance., Any circuit breaker has the fundamental operation is to, make and break the circuit. The design and operating, procedure depends on the breaking/making load current, in the circuit. Selection of quenching medium (oil, air,, vacuum or gas) and the volume is involved main factors, and proper maintenance is very important to keep the, breaker accurate performance and long life., Maintenance & repair of oil breaker, It is the first generation of circuit breaker used in the, electrical protection circuit and it is still in use. High, insulated oil is the main quenching medium and the oil, storage maintenance is quite difficult. Frequent, purification, reconditioning, refilling and leak proof storage, etc. keeps the breaker always healthy. Due to this oil, storage, recondition and refilling problem, oil circuit, breakers are replaced by modern vacuum circuit breaker., Troubleshooting chart at this end will help to carryout, smooth maintenance and repair of OCB., Maintenance & repair of ACB, & VCB, Air circuit breaker are found in variety of applications such, as very low, low, medium and high current applications., Natural air with arc chutes in chamber found useful in, very low and low to medium circuit breaker. Very high, voltage to EHT lines the VCB are used very extensively., Natural air or forced air used for ACBs arc chutes are, common in both ACB chamber, but in high voltage ACB, forced or compressed air blow is used. To produce, compressed air, air chamber, air compressor is necessary, inorder to operate ACB., , Maintenance is also required at fixed and moving contacts, of OCB. Alloy metals are used to make the tips of contacts, part in conductors. But in usage these contacts are, partially melted or damaged or repaired frequently, otherwise quenching time will increase rapidly., The tension of loading springs and manual operating levers, are to be checked and rectified if any mechanical part is, found defective. The coils, electromagnets and other, electrical parts are to be checked for its effectiveness. A, comprehensive service flow chart is attached for detailed, repair and maintenance., Maintenance & repair of SF6 circuit breaker, It is a advanced version and compact to use mainly for, indoor substation. Since the SF6 gas is poisonous proper, protective gadgets are to be used while handling SF6 circuit, breaker., The loading, tripping mechanism almost same as that of, VCB and air blast ACB. The maintenance and repair, mentioned may have to follow in this case also., The main maintenance requirement in SF6 circuit breaker, are handling gas or charging gas. No recondition is possible, the SF6 total replacement is required in case of any gas, failure. More cycle of operation will cause the reduction, of gas strength and reducing gas pressure also will be, the reason of SF6 circuit breaker failure., The SF6 chart illustrate the relevant failure/repair of the, circuit breaker., , Troubleshooting chart - 1, S.No, , Type of fault, , Cause, , Effects/remedy, , 1, , Excesive heat in oil, , - Poor dielectric strength, , - Heavy spark inside the tank in, long duration, - Change the oil, , 2, , Oil level diminishing fast, , - Leak in tank, , - Arrest the leak, , 3, , Sledge deposit in bottom of tank - Adultered oil, very old oil filled, , - No proper contacts in the, bottom of tank, - Filter the oil, , Copyright @ NIMI Not to be Republished, , 241

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S.No, , Type of fault, , Cause, , 4, , Spark continuing in the, electrode contact after making, circuit, , 5, , Manual breaking not functioning - Loading spring defect, - Loading mechanism defective, , - No breaking is possible, - Rectify, , 6, , No tripping in fault condition, , - Defective tripping mechanism, - Defective tripping coil, , - Fault condition will continue, - Damage the machine, connected in line, , 7, , Very loud noise in ACB, while operation, , - Insufficient air flow air pressure, in chamber, , - Continuous vibration once it is, operated., - Maintain air pressure, , 8, , Moving contact broken, , - Excessive heat, - Excess spring tension, - Miss alignment, , - Moving contact, fail to make contact with fixed, contact, - Change the contact, , 9, , Melting of electrode tip, , - Excessive current produces, heavy spark, - Substandard alloymetal, - Arc quenching is extended, beyond the set values, , - Check the source of excessive, current, - Use standard alloymetal, - Maintain arc quenching, medium in good condition, , 10, , Intermittent tripping of breaker, , - Wrong setting in relay, - Deflective or faulty loading, spring, - Faulty moving mechanism, , - Correct the setting, - Repair spring and loading, mechanism, , 11, , Shock in the breaker, , - Earth fault, , - Do proper earth connection, , 242, , - Conductor tip damaged, - No proper contact, - Pressure spring defect, , Effects/remedy, - Increased oil temperature, - Leads to breakage of the tank, - Rectify spring (or) contact tip, , Electrical : Electrician (NSQF LEVEL - 5) - Related Theory for Exercise 4.7.207, , Copyright @ NIMI Not to be Republished

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Project work, Objectives: At the end of this project, you shall be able to, • plan to prepare the project report for selected project, • draw circuit diagram/layout diagram, • list the specification of the material/component to be procured, • list the plan of action to be executed, • develop the project report complete and submit it., Selection of project and its execution, , •, , Project should have the flexibility for further expansion, to an advanced version without major changes., , •, , Discuss in details of the project - necessity, marketing, facility, cost involvement, availability of material and, hope of future development and expansion., , •, , Report should be listed with reference books and, website details., , •, , Collect all materials and tools required to start the, work., , •, , Complete the report and submit, , •, , The project has to be agreed by all the members, involved and get the approval of the concerned, authority., , •, , List of project works, 1 Battery charger/Emergency light, 2 Control of motor pump with tank level, , Prepare an action oriented plan to execute the work, within a stipulated time table which is to be accepted, by all the members and also the approval of instructor, concerned., , 3 DC voltage converter using SCRs, , •, , Complete the project as per the plan., , Note :, , •, , Test, calibrate and finish the project as per the plan, and execution., , 1 Some of the sample project works (indicative only), are given against each semester., , •, , Keep the project with optimum finish and good, workmanship., , 2 Instructor may design their own project and also inputs, from local industry may be taken for designing such, new project., , Preparation of project report, •, , Report should start with an introductory information, connected with a known subject and highlight its, importance in present conditions., , •, , A survey to be conducted regarding the marketing and, its commercial applications., , •, , A brief working principle and its operation has to be, illustarted in the report., , •, , Highlight the maintenance, repair and periodic servicing, etc in the report., , •, , Costing should be competitive and affordable to the, concerned without any reservations., , 4 Logic control circuits using relays, 5 Alarm/indicator circuits using sensors, , 3 The project should proudly cover maximum skills in, the particular trade and must involve some problem, solving skill. Emphasis should be on Teamwork:, Knowing the power of synergy/collaboration, work to, be assigned in a group (Group of at least 4 trainees)., The group should demonstrate Planning, Execution,, Contribution and Application of Learning. They need, to submit Project report., 4 If the instructor feels that for execution of specific, project more time is required than he may plan, accordingly to produce components /sub-assemblies, in appropriate time i.e., may be in the previous, semester or during execution of normal trade practical., , Copyright @ NIMI Not to be Republished, , 243

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