Electrical Machines and Drives

John Hindmarsh, Alasdair Renfrew

• Publisher: Butterworth-Heinemann
• Year: 1996
• ISBN:
  9780080505190
• Edition: 3
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Recent years have brought substantial developments in electrical drive technology, with the appearance of highly rated, very-high-speed power-electronic switches, combined with microcomputer control systems.This popular textbook has been thoroughly revised and updated in the light of these changes. It retains its successful formula of teaching through worked examples, which are put in context with concise explanations of theory, revision of equations and discussion of the engineering implications. Numerous problems are also provided, with answers supplied.The third edition includes enhanced coverage of power-electronic systems and new material on closed-loop control, in addition to thorough treatment of electrical machines.

Chapter 1

Introduction and review of basic theory

1.1 Aim of the book

On entering the world of electrical machines, the student meets many conceptual difficulties not experienced for example in the early studies of digital systems, with their simple and precise 2-state operation. More assistance is required to permit the new-comer to gain confidence in dealing with non-linear, 3-dimensional, rotating electromagnetic devices. The purpose of this book is to provide this aid to understanding by showing how, with a limited number of equations derived from basic considerations of power flow and elementary circuit and electromagnetic theory, the electromechanical performance can be explained and predicted with reasonable accuracy.

Such an aim, which will permit the calculation of power-input/output characteristics almost close enough in engineering terms to those of the device itself, can be achieved by representing the machine as a simple electrical circuit – the equivalent-circuit model. This concept is explained in many books, for example in the author’s companion volume Electrical Machines and Their Applications. Though more detailed theoretical treatment is given there, substantial portions of the present text may be regarded as suitable revision material. This expanded 3rd edition can, as a whole, be considered as a textbook with particular, but not exclusive, emphasis on Electrical Drives, taught through worked examples, for a reader having some familiarity with basic machine theory.

Perhaps it is appropriate to point out that complete and exact analysis of machine performance is so complex as to be virtually impossible. The additional accuracy achieved by attempts to approach such methods is primarily of interest to the specialist designer who must ensure that his product will meet the user’s needs without breakdown and he must judge when the analytical complication is justified. For the user, and for the engineering student who is not yet a specialist, the simpler methods are adequate for general understanding and provide a lead-in if necessary for later specialisation.

There are many features of all machine types which are common, the obvious example being the mechanical shaft equations. But apart from these and the fundamental electromagnetic laws, the input/output relationships and modes of operation have many similarities. These are brought together where possible and also in this first chapter, some elementary mechanical, magnetic and circuit theory is discussed briefly, as a reminder of the basic knowledge required. Students should beware of underestimating the vital importance of this material, since experience shows that it is these very points, improperly understood, which hold back progress in coming to feel at ease with machines problems.

However familiar one may become with theory, as a student, the true test of an engineer is his ability to make things work. First steps to this goal of confidence are reached when a student is prepared to commit himself to selecting equations and inserting values in the algebraic expressions, producing answers to a specific problem. Hence the importance of practice with numerical examples. Understanding grows in proportion to one’s ability to realise that the equations developed really can be used in a systematic fashion to solve such problems, since they describe the physical behaviour in mathematical terms. Appreciation of this last statement is the key to successful problem-solving.

The chapters are planned to sequence the examples at increasing levels of difficulty. Much theoretical support is given, in that the equations are discussed either at the beginning of each chapter, or as the need arises. Solution programmes indicate the kind of problems which can be formulated for the three basic types of rotating machine: d.c., induction, and synchronous. Readers are encouraged to adopt an ordered approach to the solution; for example it is a good idea to incorporate the question data on a diagram. One of the difficulties of machines problems often lies in the amount of data given. By putting the values on a simple diagram, assimilation is easier and it helps to avoid mistakes of interpretation, especially when working with 3-phase circuits. In following this recommended pattern, it is hoped that the text will help to remove the mystery with which some students feel the machines area is shrouded.

The emphasis is on machine terminal-characteristics, rather than on the internal electromagnetic design. In other words, the electrical-drives aspect is uppermost since this is the area in which most engineering students need to have some good knowledge. It is worm noting that about 60–70% of all electrical power is consumed by motors driving mechanical shafts and virtually all tins po...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Authors’ preface to the Third Edition
• Author’s preface to the Second Edition
• Author’s preface to the First Edition
• Symbols
• Chapter 1: Introduction and review of basic theory
• Chapter 2: Transformers
• Chapter 3: D.C. machines
• Chapter 4: Induction machines
• Chapter 5: Synchronous machines
• Chapter 6: Transient behaviour; closed-loop control
• Chapter 7: Power-electronic/electrical machine drives
• Chapter 8: Mathematical and computer simulation of machine drives
• Appendix A: Table of Laplace transforms
• Appendix B: Voltage/current/power relationships for bridge-rectifier circuits
• Appendix C: Summary of equations for d-q simulations
• Appendix D: Tutorial examples with answers
• Answers to tutorial examples
• References