Principles of Electric Machines with Power Electronic Applications

by Mohamed E. El-Hawary

Overview

A thoroughly updated introduction to electric machines and adjustable speed drives

All machines have power requirements, and finding the right balance of economy and performance can be a challenge to engineers. Principles of Electric Machines with Power Electronic Applications provides a thorough grounding in the principles of electric machines and the closely related area of power electronics and adjustable speed drives. Designed for both students and professionals seeking a foundation in the fundamental structure of modern-day electric power systems from a technical perspective, this lucid, succinct guide has been completely revised and updated to cover:
* The fundamental underpinnings of electromechanical energy conversion devices
* Transformers
* Induction machines
* Synchronous machines
* DC machines
* Power electronic components, systems, and their applications to adjustable speed drives


Enhanced by numerous solved problems, sample examinations and test sets, and computer-based solutions assisted by MATLAB scripts, this new edition of Principles of Electric Machines with Power Electronic Applications serves equally well as a practical reference and a handy self-study guide to help engineers maintain their professional edge in this essential field.

Product Details

ISBN-13:	9780471208129
Publisher:	Wiley
Publication date:	06/25/2002
Series:	IEEE Press Series on Power and Energy Systems , #51
Edition description:	2nd ed.
Pages:	496
Product dimensions:	6.34(w) x 9.15(h) x 1.59(d)

About the Author

MOHAMED E. EL-HAWARY received a bachelor of engineering degree in electrical engineering from the University of Alexandria in Egypt and a PhD in electrical engineering from the University of Alberta, Canada. He is currently Associate Dean of Engineering at DalTech of Dalhousie University. Dr. El-Hawary is a Fellow of both the IEEE and the Engineering Institute of Canada.

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Principles of Electric Machines with Power Electronic Applications

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By Mohamed E. El-Hawary

John Wiley & Sons

ISBN: 0-471-20812-4

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Chapter One

INTRODUCTION

Electrical engineering is a wide and diversified area of human activity that plays a very important role in today's civilization. If one were to attempt to single out a field of electrical engineering that heralded the dawn of the Electrical Age, the field of electromechanical energy conversion would emerge as a strong contender. It is the main purpose of this chapter to discuss the origins and historical developments that led to present-day electromechanical energy conversion engineering and related areas. The treatment is brief but is intended to provide a historical perspective that highlights advances gained over the years. The brief history is followed by an outline of the text.

1.1 ELECTRIC MACHINES

An electric machine is an electric apparatus with one or more components capable of rotary or linear motion. The operation of the machine depends on electromagnetic induction, which is defined as the production of an electromotive force in an electric circuit by a change in the magnetic flux linking with the circuit.

Electric machines are encountered in almost all areas of activity and, it is worth noting that present high-tech applications such as robotics and computers depend, in no small measure, on advanced, precise, and energy-efficient electric machines operating as motors. Disk and tape drives,printer mechanisms, and manipulator arms rely on the electric motor in their performance.

1.2 ROOTS IN OBSERVATION

For many centuries, human beings have observed natural electric and magnetic effects. Atmospheric electrical phenomena such as lightning have been known to the human race since antiquity. Italian sailors navigating the Mediterranean discovered emissions of light from the mastheads of their ships on nights of dry stormy weather. This light is known as the St. Elmo's fire mentioned in the records of the second voyage of Columbus in 1493. Polar lights in the north (aurora borealis) and in the south (aurora australis) have been observed for many centuries.

Biological electric-field effects displayed by certain creatures of the sea have been observed and reported over 2000 years ago in the writings of Greek philosophers, including Aristotle. A human being could receive a shock by touching the marine creature known as an electric torpedo with a spear. The connection between the torpedo's electric property and that of atmospheric electric effects is recognized in the Arabic name for the torpedo, ráad, which is also the word for thunder. The electric torpedo was used for medical treatment of headaches at the time of Anthony and Cleopatra.

Lightning, St. Elmo's fire, polar lights, and animal electricity are phenomena that people observe, but in whose generation they do not take an active part. Two other phenomena, however, were observed that do require human action. The property of amber to acquire the power of attracting light objects through friction has been known for at least 2500 years, as evidenced by the writings of Thales, one of the seven wise men of Greece. An ancient reference to the electric property of amber is found in the Middle Eastern romance The Loves of Majnoon and Leila. In the text, Majnoon says of his beloved, "She was an amber, and I but a straw; she touched me and I shall ever be attracted to her." The second phenomenon involves the emission of sparks from the human body due to friction. It was known, for example, that Servius Tullius, the sixth King of Rome, gave off sparks as his locks were combed. These are manifestations of static electricity.

The observations of the ancients led to the 1660 invention by Otto Von Guericke of Magdeburg of the first frictional machine. The machine consisted of a sulfur globe mounted on an axis that when rotated against a cloth pressed to its surface emitted sparks and attracted light pieces of straw.

Protection of buildings against damage due to lightning strikes is believed to date back several thousand years. The nature of construction of famous buildings such as the Temple of Juno and Solomon's Temple was such that their roofs were covered by metallic points. The concept of deliberate protection of buildings using lightning conductors was introduced by Benjamin Franklin following the famous (but extremely dangerous) kite experiments in 1750.

Magnetic-field effects appearing in nature have been observed since antiquity. Ancient civilizations made use of magnetism in direction finding as early as 2637 B.C., one of the earlier gadgets being attributed to the time of the Chinese emperor Hoang-Ti. In that invention, a prominent female figure that contained magnetic material was mounted on a chariot and always pointed to the south regardless of the chariot's direction of motion. Chinese south-seeking instruments were again reported 16 centuries later for use as navigational aids on land and sea. By the twelfth century, knowledge of the magnetic compass and its application had spread to many countries. It is well known that Christopher Columbus employed the magnetic compass on his voyages in 1492.

The attraction of iron to lodestone has been known for countless years. Attempts to explain this phenomenon date back to the poetic work of Lucretius in 55 B.C. The early Christian writer Saint Augustine described in his De Civitate Dei (A.D. 428) magnetic experiments involving the attraction of a piece of iron lying on a silver dish by a lodestone underneath. The phenomenon of magnetic attraction led to the story of sympathetic needles that prevailed in the sixteenth to eighteenth centuries. William Gilbert of Colchester, physician to Queen Elizabeth I, published a book entitled De Magnete dealing with observed phenomena of magnetism and electricity. The publication of the book helped to focus the attention of investigators on new directions that resulted in significant discoveries.

1.3 BEGINNINGS

Further discoveries and applications of electricity resulted from the availability of the frictional machine in the eighteenth century. A notable discovery occurred in 1720, with Stephen Grey announcing the principle of insulation and conduction of electricity. Electric charges were transmitted for hundreds of feet through a hempen cord suspended by silk threads. Transmission of an electric charge for several miles was made possible using metallic wire instead of the hempen cord. Grey's discoveries were a prelude to the discovery of charge storage in a Leyden jar that took place a quarter of a century later.

It has been observed that electrified bodies lost their charge quickly, and it was believed that air abstracted the charge from the conductor. It thus seemed that if an electrified body were surrounded by an insulating material, contact with air, and hence loss of charge, would be reduced. Water appeared to be a convenient recipient of the electric charge and glass seemed to be the most effective insulator. This provided the basis for experiments carried out by many investigators. It is believed that Cunaeus working with Musschenbröek of Leyden on this concept discovered in January 1746 what is now known as the Leyden jar for storing electric charge. Cunaeus held the glass bottle in his right hand; the prime conductor of a powerful frictional machine was connected by a wire to the water inside the bottle. Using his left hand, Cunaeus attempted to disengage the wire from the conductor, believing that enough charge had been accumulated in the water. Needless to say, our friend received quite a convulsive shock, which made him drop the bottle. Musschenbröek repeated the experiment and felt struck in the arms and shoulders and lost his breath. It took him two days to recover, and he stated later that he would not repeat the experiment for the entire kingdom of France.

Improvements on the Leyden experiments followed in many parts of Europe. The object of the experiments was to transmit shock for long distances using chains of Leyden jars. William Watson, a London physician, originated the idea of using two coatings separated by a dielectric to improve the Leyden jar. He also established the idea of positive and negative electrical charges.

The discovery of steady electric current is due to the observation of muscle contractions in the legs of dead frogs when in contact with two different metals. In 1678, the Dutch scientist Swammerdam produced convulsions in the muscle of a frog by holding it against a brass ring from which it hung by a silver wire. This experiment clearly resembles that by which Luigi Galvani became famous over 100 years later. The Swiss philosopher Sulzer described an experiment carried out in 1762, in which he placed two pieces of different metals (silver and zinc) above and below his tongue. When the metals were brought in contact, Sulzer reported an itching sensation and a taste of sulfate of iron. Obviously, both Swammerdam and Sulzer had the opportunity to discover galvanism but did not have the good fortune to do so.

Luigi Galvani, born in Bologna in September 1737, was destined to discover the significance of the Swammerdam and Sulzer experiments following his own famous experiments. On November 6, 1780, Galvani was preparing a frog for dissection in the vicinity of an electrical machine and observed that the animal's body suddenly convulsed. After a number of similar experiments, he resolved in 1781 to try the effect of atmospheric electricity. Galvani erected a lightning conductor on the roof of his house and connected it to his laboratory. Nerves of frogs and other animals were connected to the lightning conductor and their muscles were observed to convulse whenever lightning appeared. In 1786, Galvani resumed the experiments with the help of his nephew Camillo Galvani. On September 20, 1786, Camillo had some frogs prepared for the experiments and hung them by an iron hook from the top of an iron rail of the balcony. Soon, he noted convulsions when a frog was pressed against a rail. Luigi Galvani experimented at length and concluded that the convulsions were the result of the simultaneous contact of iron with nerves and muscles. It is interesting to note that Galvani attributed the convulsions to animal electricity, that is, electricity excited by the animal organs themselves.

Alessandro Volta, then a professor of physics at Pavia, was interested in the results of Galvani's experiments. He concluded that the exciting cause of convulsions was nothing but ordinary electricity produced by the contact of two metals. His theory of contact was derived from the Sulzer experiments. In August 1796, Volta took disks, one of copper and the other of zinc, brought them into contact, and suddenly separated them without friction. The usual indications of electricity were found. On June 26, 1800, he made his formal announcement to the Royal Society describing the now-famous voltaic pile. In his setup, Volta placed a disk of silver on a table; on top of it, he placed a disk of zinc, followed by a disk of spongy matter (cardboard) impregnated with a saline solution. The arrangements were repeated thirty to forty times. Shocks and sparks were found to occur, but it was remarkable that the pile recharged itself after a shock has been given. Thus was "born" one of humanity's greatest boons, the electric current.

The thermal effects of electricity were known as early as 1772, when the lightning conductors of St. Paul's Cathedral were observed to become red hot during thunderstorms. The idea of electric conduction through a liquid was established, and decomposition of water into its constituent gases by the use of electricity from a Leyden jar was accomplished by the English physician George Pearson in 1797. Following the invention of the voltaic pile, Nicholson and Carlisle established that water can be decomposed using voltaic current. The similarity between the chemical effects of static and voltaic electricity was thus established.

At the forefront of contributors to the electrochemistry in the nineteenth century is Humphry Davy, who was born in Penzance on December 17, 1778, and became professor of chemistry at the Royal Institution in 1801. His discoveries advanced the understanding and appreciation of the newly found steady electric current. In 1808, Davy made the first public display of the electric arc between two carbon electrodes connected to a voltaic pile. His most brilliant success was the decomposition of fixed alkalies by electricity in 1807.

1.4 FOUNDATIONS OF ELECTROMAGNETISM

The strong resemblance between electricity and magnetism had been observed for many years. These observations were supported by many facts, discovered as early as 1630, when Gassendi observed that lightning imparted magnetism to iron. In 1675, English navigators reported that the compass needles of their ships had their poles weakened and even reversed by lightning strokes. By the middle of the eighteenth century, speculation about the nature of the link between electricity and magnetism was a favorite pursuit.

Franklin noted that electricity is capable of reversing the polarity of magnetic needles. He also showed that the discharge of Leyden jars through a common sewing needle resulted in its magnetization. Many other investigators attempted at the turn of the nineteenth century to establish the connection between electricity and magnetism using the then available voltaic pile. It appears, however, that many of these attempts to demonstrate the effect of the voltaic pile on a magnetic needle were made with the pile open-circuited.

The main breakthrough is credited to a discovery by Hans Christian Oersted (1777-1851), born in Rudköbing on the island of Langeland in the Baltic, and was destined to discover the answer to the mystery of electromagnetism. He was appointed in 1806 to the Chair of Physics at the University of Copenhagen, where it is reported that in a private lecture to advanced students in the winter of 1819-1820, Oersted was demonstrating the then familiar experiment with a magnetic needle in the vicinity of a voltaic pile. Previously, the battery circuit had always been left open, as mentioned earlier. Is it not clear whether in making the demonstration Oersted closed the circuit by a lucky chance or on purpose. In any event, to his delight, he saw the needle move from its position of rest. Oersted pointed to the apparatus with trembling hands and invited his students to repeat the experiment. An account of this significant discovery was published in July 1820.

The enormous effect of Oersted's discovery on the direction of investigations in electricity and magnetism is evidenced by the quantum leap in related reports during that period. Sir Humphry Davy repeated Oersted's experiment and noted that iron filings on a paper near the wire were immediately attracted.

Continues...

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Table of Contents

PREFACE ix

Chapter 1 INTRODUCTION 1

1.1 Electric Machines 1

1.2 Roots in Observation 2

1.3 Beginnings 3

1.4 Foundations of Electromagnetism 5

1.5 The Dawn of Electrodynamics 7

1.6 Early Electric Generators 9

1.7 Early Electric Motors 10

1.8 Alternating Current 11

1.9 Power Electronics: Scope and A Brief History 13

1.10 Structure of the Power System 18

1.11 Outline of the Text 21

Chapter 2 PRINCIPLES OF ELECTROMAGNETISM AND ELECTROMECHANICAL ENERGY CONVERSION 23

2.1 Introduction 23

2.2 Magnetic-Field Laws 24

2.3 Permeability and Magnetic-Field Intensity 31

2.4 Magnetic Circuits 35

2.5 Flux Linkages, Induced Voltages, Inductance, and Energy 50

2.6 Hysteresis Loop 54

2.7 Eddy-Current and Core Losses 59

2.8 Energy Flow Approach 60

2.9 Field Energy 64

2.10 Multiply Excited Systems 69

2.11 Reluctance Motors 72

2.12 Doubly Excited Systems 75

2.13 Salient-Pole Machines 77

2.14 Round or Smooth Air-Gap Machines 80

2.15 Machine-Type Classification 84

2.16 P-Pole Machines 85

Problems 89

Chapter 3 POWER ELECTRONIC DEVICES AND SYSTEMS 103

3.1 Introduction 103

3.2 Power Semiconductor Devices 103

3.3 Control Characteristics of Power Devices 106

3.4 Power Semiconductor Diodes 108

3.5 Power Transistors 115

3.6 The Thyristors 138

3.7 Power Electronic Systems 175

3.8 Power Integrated Circuits and Smart Power 178

Problems 179

Chapter 4 DIRECT-CURRENT MOTORS 183

4.1 Introduction 183

4.2 Construction Features 184

4.3 Circuit Model of dc Generator 185

4.4 Circuit Model of dc Motors 187

4.5 dc Series Motors 190

4.6 dc Shunt Motors 203

4.7 Compound Motors 212

4.8 Motor and Load Matching 224

4.9 Conventional Speed Control of dc Motors 224

4.10 Reversal of Direction of Rotation 241

4.11 Starting dc Motors 241

4.12 Adjustable Speed dc Motor Drives 251

4.13 ac-dc Drives for dc Motors 255

4.14 dc-dc Drives for dc Motors 261

Problems 265

Chapter 5 TRANSFORMERS 273

5.1 Introduction 273

5.2 Ideal Transformers 274

5.3 Transformer Models 278

5.4 Transformer Performance Measures 286

5.5 Single-Phase Connections 292

5.6 Three-Winding Transformers 296

5.7 Three-Phase Systems and Transformer Connections 300

5.8 Autotransformers 313

Problems 316

Chapter 6 INDUCTION MOTORS AND THEIR CONTROL 323

6.1 Introduction 323

6.2 MMF Waves and the Rotating Magnetic Field 324

6.3 Slip 329

6.4 Equivalent Circuits 331

6.5 Simplified Equivalent Circuits 334

6.6 Torque Characteristics 338

6.7 Some Useful Relations 341

6.8 Internal Mechanical Power 344

6.9 Effects of Rotor Impedance 348

6.10 Classification of Induction Motors 351

6.11 Starting Induction Motors 354

6.12 Conventional Speed Control of Induction Motors 362

6.13 Adjustable Speed Drives: General Considerations 370

6.14 Variable-Voltage-Constant-Frequency Drives 372

6.15 Variable-Voltage-Variable-Frequency Drives 376

6.16 dc-Link-Converter Drives 381

6.17 Voltage-Fed Inverter Drives 383

6.18 Current-Fed Inverter Drives 385

6.19 Cycloconverter Drives 386

6.20 Regulation of Slip Power 387

Problems 389

Chapter 7 SYNCHRONOUS MACHINES 397

7.1 Introduction 397

7.2 Round-Rotor Machines: Equivalent Circuit 401

7.3 Armature Reaction 406

7.4 Principal Steady-State Characteristics 410

7.5 Power Angle Characteristics and the Infinite-Bus Concept 415

7.6 Synchronous-Motor Operation 423

7.7 Salient-Pole Machines 430

Problems 437

Chapter 8 FRACTIONAL-HORSEPOWER ALTERNATING CURRENT MOTORS 443

8.1 Introduction 443

8.2 Rotating Magnetic Fields in Single-Phase Induction Motors 443

8.3 Equivalent Circuits for Single-Phase Induction Motors 448

8.4 Power and Torque Relations 454

8.5 Starting Single-Phase Induction Motors 459

Problems 473

BIBLIOGRAPHY 475

INDEX 477

Editorial Reviews

Intended for both students and professionals, this book covers the fundamental principles of electric machines, power electronics, and adjustable speed drives. Focusing on the basic structure of modern electric power systems, the guide brings a technical perspective to the description of electromechanical energy conversion devices, transformers, induction machines, synchronous machines, DC machines, and power electronic components. Solved problems, sample exams, and MATLAB scripts enhance the discussion. El-Hawary teaches engineering at Dalhousie University. Annotation c. Book News, Inc., Portland, OR (booknews.com)