ELECTRIC MOTOR DRIVES

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2 ELECTRIC MOTOR DRIVES Prof. M.S. BERDE Retd. Prof. Department of Electrical Engineering N.I.T. (formerly, MACT) Bhopal (MP) KP KHANNA PUBLISHERS 4575/15, ONKAR HOUSE, OPP. HAPPY SCHOOL DARYAGANJ, NEW DELHI Phone : ; Fax : khannapublishers@yahoo.in Website :

3 Published by : Romesh Chander Khanna for KHANNA PUBLISHERS Nai Sarak, Delhi (India). This book or part thereof cannot be translated or reproduced in any form (except for review or criticism) without the written permission of the Authors and the Publishers.] ISBN NO. : Third Edition : 2012 Price : ` Text Composition by : Excellent Graphics, Delhi. Printed at : Bright Printers, Turkman Gate, Delhi

4 Preface Electric motor drive is an evergreen subject and the variables are the type of motor, use of control method and the type of supply. Particularly, due to the use of power electronics and microelectronics, each application is unique in itself and challenging in nature. The objective of this book is to explain the various types of motors alongwith their characteristics and use of control circuits that may be applicable and methods of starting, stopping and calculating their power ratings. Chapters on preventive maintenance of motors & allied equipment and industrial applications are also given in the book. To illustrate the use of concept, formulae ; solved problems and university questions are also included with text. The recent advances in technical education require additionally special knowledge to educate the student to become a specialist. From this point of view, two more chapters have been added one on Methods of Protection of Motors and the other on Energy Saving as applied to motor loads. Chapter 4 is revised to explain in detail the starting methods of Induction Motors with special reference to control circuits. In fact mostly all the chapters have been revised and as per comments received many new concepts and refinements have been made throughout the book. Chapters on applications of electric motors and a separate chapter on worked examples, objective type of questions will benefit the students at large. It is hoped that the book will be useful for a course on Electric Motor Drives. ( iii )

5 ( iv ) I am thankful to M/s Telemecanique for the information on starters. Special efforts have been made to use relevant standards ISS, BSS, ISO, IEC etc. My thanks are mainly due to our U.G. and P.G. students as this book has mainly evolved in the teaching of the subject and also due to my colleagues whom I involved in discussions from time to time. Prof. M.S. Berde A-1/30, Girijashankar, Karvenagar, Pune

6 Contents Chap. Pages 1. Introduction to Electric Drives Prologue Historical Background Drive Systems Choice of Drive System Selection of Drive for Individual Application Control Panel Requirements Motor Construction and Trends Questions Dynanics of Electrical Drives Torque Production in Electrical Machines Mechanical System Choice of Gear Ratio Torque-Speed Characteristics of Industrial Loads Torque-Speed Characteristics of Electric Motors Traction or Transportation Drive Mechanics of Drives Questions D.C. Motor Characteristics, Control and Drives Introduction Separately Excited D.C. Motor Armature Resistance Control Field Control of Separately Excited D.C. Motor Dual Control of Separately Excited D.C. Motor Series Wound D.C. Motor Transfer Function of a Separately Excited D.C. Motor D.C. Motor Feedback Control System Braking Methods for D.C. Motors SCR Converters ( v )

7 Chap. ( v ) Pages 3.11 D.C. Motors for Operation on Converters Questions Three Phase Induction Motors Characteristics, Control and Drives Introduction Induction Motor Characteristics at Constant Frequency Supply Starting Methods for 3-Phase Induction Motors Variable Frequency Static Converters for Induction Motor Control Induction Motor Control at Power Frequency Variable Frequency Operation of Induction Motors Testing Methods for Induction Motors No Load and Blocked Rotor Tests Bee Test Method-2: Estimation of Motor Efficiency at Operating Load Method-2: Estimation of Motor Efficiency at Operating Load Questions Synchronous Motor Characteristics, Control and Drives Introduction Excitation Methods for Synchronous Motors Speed Control of Synchronous Motors Reluctance Motor Permanent Magnet Synchronous Motors Stepper Motors Drive Circuits for Stepper Motors Servomotors and their Control Motor Power Ratings Introduction Motor Loading and Standard Duty Classes Motor Heating and Cooling Under Continuous Duty Determination of Motor Ratings

8 Chap. ( vii ) Pages 6.5 Short Time Rating of Motor Load Equalisation Selection of Motors Introduction Squirrel-Cage Motors Wound Rotor Motors Applications of Induction Motors Fractional Horsepower Motors Single Phase Squirrel-Cage Motors Single-phase Wound-Rotor Motors Schrage Motor or Brush-Shifting Polyphase Shunt Motor Use of Standards in Choice of Drives Motor Terminology Preventive Maintenance of Electric Motors and Allied Equipment Introduction Insulation Care Evaluation of Insulation Maintenance of Electrical Insulation Maintenance of Commutators, Slip Rings and Brushes Bearing Maintenance Maintenance of Transformers Maintenance of Contactors Questions Industrial Applications of Electric Motors Introduction Steel Industry Textile Industry Control Systems for Elevators Mining Paper Industry Cement Mills Machine Tools Marine Applications Oil and Gas Applications

9 Chap. ( viii ) Pages 9.11 Chemical, Petrochemical, Rubber Industries Applications Material Handling Food and Agricultural Applications Protection of A.C. Motors Introduction Modes of Failures Protection Against Mechanical Faults Overload Protection Heating of Motor Windings Undervoltage Protection Unbalance Protection Overvoltage Protection Ground Fault Protection Differential Protection Stator RTD Protection Loss of Load Protection Negative Phase Sequence Protection Energy Conservation in Motor Drives Introduction Running Costs Load Matching with the Motor Idle Running Drive Transmission Driven Equipment High Efficiency Motors Guidelines for Identifying Energy Saving Opportunities Reduced Voltage Operation Energy Saving with Fans Flow Control in Pumps Worked Problems on Electric Drives Index

10 CHAPTER 1 Introduction to Electric Drives 1.1 PROLOGUE Every machine that is used in a modern factory, manufacturing unit or transportation unit consists of three parts: (a) Prime mover i.e., motor or engine, (b) transmission system such as belt, gears etc., and (c) proper machine. The prime mover with its system of control and transmission system is called as drive. Since the most convenient form of power that is available for use in home or industry or farm is electrical, in most places we have electric drive only and is used for converting electric power into mechanical power. Electric drive is therefore defined as: a form of machine equipment designed to convert electric energy into mechanical energy and provide electric control of this process. In view of this, fundamental elements of an electric drive are the electric motor, transmission system and electrical control. Since there is a variety of motors, a converting equipment that changes the characteristics of the electric supply, such as form (a.c., d.c. or chopped a.c. or d.c. and frequency and voltage) are changed to match the motor performance to the required load and is also a part of the drive. The main function of the electric drive is to impart motion to the working machine but a modern electric drive with complexity of feedback control can perform several other functions so that the production process is performed in the most efficient manner with high productivity and high quality of the drive. Historically, the development of different kinds of electric drives used in industry may be divided into three stages: (a) Group Drives, (b) Individual Drives, and (c) Multimotor Drives. 1

Electric Motor Drives 25% OFF Publisher : KHANNA PUBLISHERS ISBN : 9788174093127

11 Electric Motor Drives 25% OFF Publisher : KHANNA PUBLISHERS ISBN : Author : M. S. Berde Type the URL : Get this ebook

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