ELECTRIC DRIVES N.K. DE P.K. SEN

ELECTRIC DRIVES N.K. DE P.K. SEN

Electric Drives NISIT K. DE Associate Professor Department of Electrical Engineering Indian Institute of Technology Kharagpur and PRASANTA K. SEN Assistant Professor Department of Electrical Engineering Regional Engineering College Durgapur Delhi-110092 2014

ELECTRIC DRIVES by Nisit K. De and Prasanta K. Sen 1999 by PHI Learning Private Limited, New 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-978-81-203-1492-4 The export rights of this book are vested solely with the publisher. Sixteenth Printing January, 2014 Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Meenakshi Printers, Delhi-110006.

CONTENTS Preface ix 1. INTRODUCTION 1 7 1.1 Concept of Electric Drives 1 1.2 Classification of Electric Drives 2 1.2.1 Group Electric Drive 2 1.2.2 Individual Electric Drive 3 1.2.3 Multi-motor Electric Drive 3 1.3 Classification of Control Schemes 3 1.3.1 Manual Control 3 1.3.2 Semiautomatic Control 4 1.3.3 Automatic Control 4 1.4 Classification of Methods of Speed Control 4 1.4.1 The First Group 4 1.4.2 The Second Group 4 1.4.3 The Third Group 4 1.4.4 The Fourth Group 5 1.4.5 The Fifth Group 5 1.5 Components of Electric Drives 5 1.5.1 Motors 6 1.5.2 Power Electronic Controllers 6 2. SPEED-TORQUE CHARACTERISTICS OF MOTORS 8 59 2.1 Basic Parameters 8 2.2 Types of Loads 8 2.2.1 Quadrantal Diagram 10 2.3 Speed-Torque Characteristics of DC Shunt Motors 10 2.3.1 Construction of Speed-Torque Characteristics 12 2.4 Types of Braking 17 2.4.1 Dynamic or Rheostatic Braking 17 2.4.2 Counter Current Braking (Plugging) 19 2.4.3 Regenerative Braking 22 2.4.4 Determination of Starting, Dynamic Braking and Plugging Resistance for DC Shunt Motors 23 2.5 Speed-Torque Characteristics of DC Series Motors 27 2.5.1 Construction of Speed-Torque Characteristics 29 2.5.2 Determination of Starting Resistance for DC Series Motors 29 2.5.3 Types of Braking (Applications in DC Cranes) 32 iii

iv Contents 2.6 Speed-Torque Characteristics of DC Compound Motors 35 2.6.1 Cumulative Compound Motor 35 2.6.2 Types of Braking 37 2.6.3 Differential Compound Motor 38 2.7 Torque-Speed Characteristics of Induction Motors 38 2.7.1 Torque Equation, Typical Starting Performance 38 2.7.2 Starters for Slip-ring Induction Motors 42 2.7.3 Types of Braking 45 2.8 Synchronous Motor 54 2.8.1 Excitation Control 54 2.8.2 Braking of Synchronous Motors 56 Problems 58 3. SPEED CONTROL OF DC MOTORS 60 118 3.1 Basic Parameters 60 3.2 Speed Control of DC Shunt Motors 61 3.2.1 Ward-Leonard Method 62 3.2.2 Buck-boost Control 64 3.3 Speed Control of DC Series Motors 65 3.3.1 Series-Parallel Control 65 3.3.2 Speed Control (during Lowering) of a DC Series Motor in a Crane using Dynamic Braking 65 3.4 Solid State DC Drives 74 3.4.1 Thyristor Bridge Rectifier Circuits 75 3.4.2 Chopper Circuits 79 3.4.3 Bridge Rectifier-fed Drive 82 3.5 DC Motor Controllers 90 3.5.1 Controllers for DC Shunt Motors 90 3.5.2 Microprocessor-based Controller for DC Motor Drives 90 3.6 State Feedback Controller for DC Motor Drives 101 3.6.1 Combined Observation and Control 104 3.6.2 Feedforward Control 105 3.6.3 Software for the Controller 106 3.6.4 DC Motor Speed Control System 107 3.7 Stepper Motors 109 3.7.1 VR Stepper Motor 109 3.7.2 Permanent Magnet (PM) Stepper Motor 113 3.7.3 Hybrid Stepper Motor 114 3.7.4 Stepper Motor Control 114 Problems 116 4. SPEED CONTROL OF AC MOTORS 119 165 4.1 Introduction 119 4.2 Speed Control of Induction Motors 120 4.2.1 Pole Changing Induction Motor 120 4.2.2 Stator Frequency Variation 123

Contents v 4.3 Speed Control of Slip-Ring Induction Motors 129 4.3.1 Stator Voltage Variation 129 4.3.2 Rotor Resistance Variation 130 4.3.3 Slip Power Recovery 131 4.4 Basic Inverter Circuits 135 4.4.1 Variable Voltage Variable Frequency (VVVF) Control 140 4.4.2 Current Source Inverter 142 4.5 AC Regulator 144 4.6 Cycloconverter 144 4.7 Speed Control of Synchronous Motors 146 4.7.1 Input Frequency Variation 146 4.7.2 Self-controlled Synchronous Motor Drive using Load Commutated Thyristor Inverter 147 Problems 164 5. HEATING AND POWER RATING OF DRIVE MOTORS 166 197 5.1 Load Diagram, Overload Capacity 166 5.2 Insulating Materials 167 5.3 Heating and Cooling of Motors 168 5.4 Service Conditions of Electric Drives: Continuous, Intermittent and Short Time 172 5.5 Selection of Motor Power Capacity 176 5.5.1 Continuous Duty Constant Load Motor Applications 176 5.5.2 Continuous Duty Variable Load Motor Applications 176 5.6 Operation of Electric Drives Incorporating Flywheel under Shock Loading Conditions 193 Problems 195 6. TRANSIENTS AND DYNAMICS 198 249 6.1 Equation of Motion 198 6.2 Equivalent System 199 6.3 Referring Torque to a Single Axis (Motor Shaft) 199 6.4 Referring Moment of Inertia to a Single Axis (Motor Shaft) 200 6.5 Referring Forces and Masses having Translational Motion to Motor Shaft 202 6.6 Moment of Inertia 202 6.6.1 Determination of Moment of Inertia 203 6.7 Optimal Gear Ratio 204 6.8 Referring Torques and Masses having Translational Motion at Variable Speeds 208 6.9 Transients in DC Motors 210 6.10 Transients in DC Motors with Armature Inductance 213 6.11 Dynamic Braking of DC Shunt Motors 220 6.11.1 Time of Braking 222 6.11.2 Current during Dynamic Braking 222 6.12 Counter Current Braking and Speed Reversal of DC Shunt Motors 223

vi Contents 6.13 Energy Associated with Transient Process of DC Shunt Motors 227 6.13.1 Energy Loss during Starting 228 6.13.2 Energy Loss during Dynamic Braking 229 6.13.3 Energy Loss during Speed Reversal 230 6.14 Dynamic (Transient) Response of Induction Motors 231 6.14.1 Starting an Induction Motor with Pure Inertia Load 234 6.14.2 Induction Motor Started on Load 237 6.15 Counter Current Braking of Induction Motors 237 6.15.1 Rotor Heating 238 6.16 Dynamic Braking of Induction Motors 239 6.17 Reduction of Energy Losses during Starting 242 Problems 248 7. MOTOR STARTERS AND CONTROLLERS 250 266 7.1 DC Motor Starters 250 7.1.1 Starters Using Voltage Sensing Relays 250 7.1.2 Starters Using Current Sensing Relays 250 7.1.3 Starters Using Time Delay Relays 252 7.2 Wound Rotor Induction Motor Starters by Variation of Rotor Resistance (Mine Hoist) 253 7.2.1 Starters Using Time Delay Relays 253 7.2.2 Starters Using Frequency Sensing Relays 254 7.3 Induction Motor Starters 255 7.3.1 DOL Starter with Provision for Speed Reversal 255 7.3.2 Auto-transformer Starter 256 7.4 Master Controller for Wound Rotor Induction Motors 257 7.4.1 Starting 257 7.4.2 Plugging and Speed Reversal 259 7.4.3 Dynamic Braking 259 7.5 Starters for Two-Speed Pole Changing Induction Motors 260 7.5.1 Starter for Two-Winding Two-Speed Pole Changing Induction Motors with Provision for Reversal at Both Speeds 260 7.5.2 Starter for Single-Winding Two-Speed Pole Changing Induction Motors with Provision for Speed Reversal (Constant Torque) 261 7.5.3 Starter for Single-Winding Two-Speed Pole Changing Induction Motors with Provision for Speed Reversal (Constant Horsepower) 261 7.6 Programmable Logic Controller (PLC) 264 8. INDUSTRIAL APPLICATIONS 267 301 8.1 Introduction 267 8.1.1 Synchronous Motor Drives 267 8.1.2 Induction Motor (Cage) Drives 267 8.1.3 Induction Motor (Wound Rotor) Drives 268 8.1.4 DC Motor Drives 270 8.1.5 Control Systems 270

Contents vii 8.2 Rolling Mill Drives 271 8.2.1 Reversing Mill Drives 271 8.2.2 Screw-down Mechanism 272 8.2.3 Continuous Mills 273 8.2.4 Cold Rolling Mills and Automatic Gauge Control 273 8.3 Cement Mill 275 8.3.1 Weighfeeder 275 8.3.2 Mill Drive 275 8.3.3 Separator 277 8.3.4 Blower Drive 277 8.3.5 Cyclone 278 8.4 Electric Traction 278 8.4.1 Tractive Effort 278 8.4.2 Requirements of Electric Traction 279 8.4.3 Suitability of Series Motors 279 8.4.4 Coefficient of Adhesion 280 8.4.5 Supply Systems and Traction Motors 280 8.4.6 Train Movement 281 8.4.7 Layout of Electric Drives 282 8.4.8 Speed Control 282 8.5 Coal Mines 282 8.5.1 Precautions 282 8.5.2 Drum Winder 284 8.5.3 Modern Winder Drives 285 8.5.4 Shearer 288 8.5.5 Conveyors in Long-wall Systems 289 8.5.6 Auxiliary Motors 290 8.6 Paper Mill 290 8.6.1 Pulp Manufacture 290 8.6.2 Paper Manufacture 290 8.6.3 Paper Mill Drives and Control 294 8.7 Machine Tool Drives 294 8.7.1 Lathe 295 8.7.2 Drilling Machine 296 8.7.3 Milling Machine 296 8.7.4 Shaping Machine 297 8.7.5 Planer 297 8.7.6 Grinding Machine 299 8.7.7 Hydraulic Drives 299 8.8 Textile Mill 299 8.8.1 Spinning Mill 299 8.8.2 Weaving 300 8.8.3 Loom Motors 301 Bibliography 303 Answers to Problems 305 309 Index 311 314

PREFACE The purpose of this book is to provide a thorough grounding in fundamental aspects of electric drives and is, therefore, suitable for use as a text by students pursuing undergraduate courses in electrical engineering and those preparing for AMIE examinations. The principal topics covered in sufficient depth are: motor characteristics, speed control of motors, selection of drive motors, transients in drive systems, motor starters and controllers, and application of drives in industries. The introductory discussion of Chapter 1 provides an idea of the coverage of the book and outlines important issues involved in design and application of electric drive systems. Chapter 2 discusses the speed-torque characteristics of both dc and ac motors and the methods of braking applied to electric drives. Chapters 3 and 4 deal with the speed control methods of dc and ac motors, respectively. Both the conventional and state-of-the-art methods of speed control, with an example of a microprocessor-based dc controller, are discussed in detail. Several forms of power electronic controllers are also described. Chapters 5 and 6 cover several other aspects of drive systems such as selection of drive motors for different duty cycles and transient behaviour and dynamics of drive systems during starting/braking, etc. Chapter 7 gives a description of various types of controller circuits used in starting/braking of motors. Lastly, Chapter 8 is devoted to a discussion of drive systems as used in different industries such as steel mills, cement mills, electric traction, coal mines, paper mills, machine tools, and textile mills. Each application is covered in depth and supported by appropriate illustrations. A large number of solved examples and unsolved problems are included in Chapters 2 to 6, necessary to enhance the understanding of the material presented. Answers to all the problems are provided at the end of the book. We wish to express our gratitude to our teachers who initiated us in this area, and several other colleagues in our respective institutes who helped us in improving the quality of the book. We are also grateful to all of those who assisted in preparing the manuscript. Finally, we want to express our love and appreciation to our families for their active support, patience and encouragement throughout the time we were writing this book. Nisit K. De Prasanta K. Sen ix

Electric Drives Publisher : PHI Learning ISBN : 9788120314 924 Author : Nisit K De And Prasanta K Sen Type the URL : http://www.kopykitab.com/product/6179 Get this ebook