ELECTRICAL MACHINES. Theory and Practice. M.N. Bandyopadhyay

ELECTRICAL MACHINES Theory and Practice M.N. Bandyopadhyay

ELECTRICAL MACHINES Theory and Practice M.N. Bandyopadhyay Director National Institute of Technology Kurukshetra Delhi-110092 2014

ELECTRICAL MACHINES: THEORY AND PRACTICE M.N. Bandyopadhyay 2007 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-2997-3 The export rights of this book are vested solely with the publisher. Fourth Printing November, 2014 Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli-131028, Sonepat, Haryana. Copy R 608

To Professor Nirmal Kanti Chatterjee and Professor Basudev Barman Ex Vice Chancellor

Contents Preface Introduction xiii xv 1. DC Machines 1 107 1.1 Introduction 1 1.2 Principle of Operation of DC Machine 1 1.3 Components of DC Machine 6 1.4 Armature Windings 7 1.4.1 Lap Winding 7 1.4.2 Wave Winding 11 1.4.3 Method of Connection of Windings in the Slot 14 1.5 Voltage Equation of a DC Machine 14 1.6 Armature Reaction in DC Machines 18 1.6.1 Calculation of Demagnetization and Cross Magnetization Ampereturns Per Pole 20 1.6.2 Compensating Winding 21 1.6.3 Commutation 22 1.7 Excitation of DC Machine 32 1.7.1 Build-up of a DC Shunt Generator 34 1.7.2 Critical Resistance and Critical Speed of DC Machine 35 1.8 Characteristics of DC Generator 38 1.8.1 Characteristics of Separately Excited DC Generator 38 1.8.2 Characteristics of DC Shunt Generator 39 1.8.3 Determination of Internal and External Characteristics from Open-Circuit Characteristic for DC Shunt Generator 39 1.8.4 Characteristics of DC Series Generator 42 1.8.5 Characteristics of DC Compound Generator 42 v

vi Contents 1.9 Parallel Operation of DC Generators 46 1.9.1 Conditions Necessary for Parallel Operation of DC Generators 46 1.9.2 Procedure for Connecting DC Shunt Generators in Parallel 46 1.9.3 Parallel Operation of Compound Generators 47 1.10 Principle of Operation of DC Motor 55 1.11 Different Types of DC Motors 56 1.12 Characteristics of DC Motors 56 1.13 Starting of DC Motor 64 1.13.1 Manual Starters 64 1.13.2 Automatic Starters 67 1.14 Speed Control of DC Motors 70 1.14.1 Shunt Motor Speed Control 70 1.14.2 Series Motor Speed Control 74 1.14.3 Speed Control with the Power Electronic Devices 78 1.15 Braking of DC Motors 86 1.15.1 Plugging 86 1.15.2 Dynamic or Rheostatic Braking 87 1.15.3 Regenerative Braking 88 1.15.4 Application of Various Types of Braking on Different Categories of Motors 88 1.16 Testing of DC Machines 93 1.16.1 Swinburne s Test 93 1.16.2 Hopkinson s Test 95 Summary 102 Rreview Questions 105 2. Transformers 108 188 2.1 Introduction 108 2.2 Construction of a Transformer 109 2.2.1 Windings and Their Insulation from the Iron Core 109 2.2.2 Oil of the Transformer 113 2.2.3 Main Tank and Conservator Tank 113 2.2.4 Silicagel Breather 113 2.2.5 Cooling Arrangements 114 2.2.6 Buchholz Relay 116 2.2.7 Bushings 117 2.2.8 Tap-Changing Device 118 2.3 Principle of Transformer Operation 121 2.4 Equivalent Circuit of Single-Phase Transformer 127 2.5 Phasor or Vector Diagram of Single-Phase Transformer 129 2.6 Regulation of Transformer 132

Contents vii 2.7 Tests on Transformer 134 2.7.1 Polarity Test 134 2.7.2 Open-Circuit Test or No-Load Test 135 2.7.3 Short-Circuit Test 136 2.7.4 Determination of Eddy Current Loss and Hysteresis Loss in Transformers 137 2.7.5 Sumpner s Test or Back-to-Back Test 138 2.8 Efficiency Calculation of Transformer 141 2.9 All-Day Efficiency of Transformer 142 2.10 Autotransformer 143 2.11 Three-Phase Transformer 146 2.11.1 Vector Grouping or Phase Group of Three-Phase Transformer 147 2.11.2 Methods of Connections of Three-Phase Transformer 150 2.12 Parallel Operation of Single-Phase Transformers 158 2.12.1 Parallel Operation of Transformers with +30 and 30 Phase Shift 159 2.12.2 Load Sharing by Two Transformers in Parallel with Equal Voltage Ratios 160 2.12.3 Load Sharing by Two Transformers in Parallel with Unequal Voltage Ratios 161 2.12.4 Per Unit and Percentage Impedance of Transformer 163 2.13 Three Winding Transformers 168 2.13.1 Suppression of Triple Frequency Currents by Tertiary Winding 169 2.14 Open-Delta Connection 170 2.15 Three-Phase to Two-Phase Conversion by Scott Connected Transformer 170 2.15.1 Three-Phase to One-Phase System 173 2.16 Induction Regulator 175 2.17 Transformer Diagnostics 177 Summary 185 Review Questions 187 3. Three-Phase Induction Motor 189 304 3.1 Principle of Rotating Field in Three-Phase Induction Motor 189 3.2 Reason for Not Attaining the Rotating Field Speed by the Three-Phase Induction Motor Rotor 190 3.3 Slip of Three-Phase Induction Motor 190 3.4 Main Difference with the Principle of Transformer 192 3.5 Types of Three-Phase Induction Motors 192 3.5.1 Comparison between Squirrel Cage and Wound Rotors 193

viii Contents 3.6 Construction of Three-Phase Induction Motor 193 3.6.1 Stator 194 3.6.2 Stator Winding 194 3.6.3 Voltage Equation of Rotating Machine 202 3.7 Equivalent Circuit of Three-Phase Induction Motor 207 3.8 Vector Diagram or Phasor Diagram of Three-Phase Induction Motor 210 3.9 Approximate Equivalent Circuit of Three-Phase Induction Motor 212 3.10 Torque Equation of Three-Phase Induction Motor 214 3.10.1 Determination of Maximum Torque of Three-Phase Induction Motor 215 3.10.2 Determination of Approximate Value of the Maximum Torque of Three-Phase Induction Motor 218 3.10.3 Determination of Starting Torque of Three-Phase Induction Motor 219 3.10.4 Approximate Value of Starting Torque 221 3.10.5 Maximum Power Output 221 3.10.6 Torque Slip Characteristics of Three-Phase Induction Motor 222 3.11 Tests of Three-Phase Induction Motor 231 3.11.1 Separation of Core Loss from the Windage and Friction Loss 231 3.11.2 No-Load Test 232 3.11.3 Blocked Rotor Test 234 3.12 Circle Diagram 238 3.13 Starting of Three-Phase Induction Motor 244 3.13.1 Direct-on-Line Starting 245 3.13.2 Reduced Voltage Starting 245 3.13.4 Star-Delta Starting 247 3.13.5 Application of External Resistance to the Rotor Circuit During Starting 249 3.14 Deep Bar Squirrel Cage Motor 258 3.15 Double Cage Rotor 260 3.16 Crawling of Three-Phase Squirrel Cage Induction Motor 261 3.17 Cogging of Three-Phase Squirrel Cage Induction Motor 263 3.18 Vibration Torques on Three-Phase Induction Motor 263 3.19 Impact of Higher Harmonics on Three-Phase Induction Motor 264 3.20 Some Generalized Rules for Selecting Rotor Slots 264 3.21 Speed Control of Three-Phase Induction Motor 265 3.21.1 Voltage Control 265 3.21.2 Rotor Resistance Control 265 3.12.3 Pole Changing 265 3.21.4 Frequency Control 270 3.22 Induction Generator 273 3.22.1 Induction Generator without Capacitor Connection Across It 277

Contents ix 3.23 Dynamics of Induction Machine 278 3.23.1 Starting at No-Load 280 3.24 Injection of Voltage at Slip Frequency in the Rotor Circuit of Three-Phase Induction Motor 281 3.25 Cascade Connection of Three-Phase Induction Motors 282 3.26 Braking of Three-Phase Induction Motor 285 3.26.1 Dynamic Braking 286 3.26.2 Regenerative Braking 293 3.27 Linear Induction Motor 293 3.27.1 Introduction 293 3.27.2 Mathematical Analysis of Operation of Linear Induction Motor 294 3.27.3 Principle of Operation 296 3.27.4 Characteristic of Linear Induction Motor 298 Summary 299 Review Questions 302 4. Single-Phase Induction Motor 305 341 4.1 Principle of Operation of Single-Phase InductIon Motor 305 4.1.1 Double-Revolving Field Theory 307 4.1.2 Mathematical Representation of Double-Revolving Field Theory 308 4.1.3 Tests of Single-Phase Induction Motor 309 4.2 Starting of Single-Phase Induction Motor 319 4.2.1 Resistance Split-Phase Motor 322 4.2.2 Capacitor Split-Phase Motor 324 4.2.3 Shaded-Pole Motor 327 4.3 Optimum Starting Characteristic 329 4.3.1 Resistance Split-Phase Motor 329 4.3.2 Capacitor Split-Phase Motor 332 Summary 339 Review Questions 340 5. AC Commutator Motor (and Some Special Motors) 342 388 5.1 Introduction 342 5.2 Single-Phase AC Series Motor 342 5.2.1 Analysis of the Application of AC Single-Phase Supply to a DC Series Motor 342 5.2.2 Modification Required in the AC Series Motor Design and Construction 344 5.2.3 Compensating Winding and Interpole Winding Arrangements in AC Series Motor 344 5.2.4 Concept of Universal Motor 346

Electrical Machines: Theory And Practice 25% OFF Publisher : PHI Learning ISBN : 9788120329973 Author : BANDYOPADHYAY, M. N. Type the URL : http://www.kopykitab.com/product/7405 Get this ebook