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Electrical Machines, Drives and Power Systems / Edition 6

Electrical Machines, Drives and Power Systems / Edition 6

by Theodore Wildi
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This best-selling book employs a theoretical, practical, multidisciplinary approach to provide introductory users with a broad understanding of modern electric power. The scope of the book reflects the rapid changes that have occurred in power technology over the past few years–allowing the entrance of power electronics into every facet of industrial drives, and expanding the field to open more career opportunities. The author covers thefundamentals of electricity, magnetism and circuits, mechanics and heat, electrical machines and transformers, electrical and electronic drives, and electric utility power systems. For managers of electrical utilities, electricians, electrical contractors and electrical maintenance personnel.

Product Details

ISBN-13: 9780131776913
Publisher: Pearson
Publication date: 02/09/2005
Edition description: 6TH
Pages: 960
Product dimensions: 7.80(w) x 9.40(h) x 2.10(d)

Table of Contents


1. Units.
2. Fundamentals of Electricity, Magnetism and Circuits.
3. Fundamentals of Mechanics and Heat.

4. Direct-Current Generators.
5. Direct-Current Motors.
6. Efficiency and Heating of Electrical Machines.
7. Active, Reactive, and Apparent Power.
8. Three-Phase Circuits.
9. The Ideal Transformer.

10. Practical Transformers.

11. Special Transformers.

12. Three-Phase Transformers.

13. Three-Phase Induction Motors.

14. Selection and Application of Three-Phase Induction Machines.

15. Equivalent Circuit of the Induction Motor.

16. Synchronous Generators.

17. Synchronous Motors.

18. Single-Phase Motors.

19. Stepper Motors.


20. Basics of Industrial Motor Control.

21. Fundamental Elements of Power Electronics.

22. Electronic Control of Direct-Current Motors.

23. Electronic Control of Alternating Current Motors.


24. Generation of Electrical Energy.

25. Transmission of Electrical Energy.

26. Distribution of Electrical Energy.

27. The Cost of Electricity.

28. Direct-Current Transmission.

29. Transmission and Distribution Solid-State Controllers.

30. Harmonics.

31: Programmable Logic Controllers


Appendix A: Conversion Charts.

Appendix B: Properties of Insulating Materials.

Appendix C: Properties of Conductors and Insulators.

Appendix D: Properties of Round Copper Conductors.

Answers to Problems.

Answers to Industrial Application Problems.




This fifth edition was prompted in part by the great increase of computers in industrial controls and automation, which has produced computer programs that can simulate relays and relay contacts. These on/off discrete controls have eliminated the wiring and installation of hardware components in favor of virtual relays and contacts that can be programmed on a keyboard. The devices that perform these operations are called Programmable Logic Controllers (PLCs), or simply programmable controllers. These devices were initially stand-alone computers that controlled a specific robot or manufacturing operation. However, with the advent of the Internet, they have now been integrated with the overall manufacturing process, leading seamlessly to integration with management, sales, procurement, and consumer satisfaction.

The relay control of machines covered in Chapter 20 is now supplemented by coverage of PLC controls in Chapter 31. Chapter 31 covers the basic principles of PLCs and shows, by way of example, how they are used in running the activities of a large service enterprise. This new chapter illustrates how these trend-setting computer-based activities involving controls and automation are being integrated with other business activities, including e-commerce.

As I mentioned in the last edition, similar upheavals have occurred in power technology. It is simply amazing to witness the entrance of power electronics into every facet of industrial drives. Thus, it is no longer pertinent to discuss do and ac machines in isolation because wherever they are being installed, an electronic control forms part of the package. Consequently, the term drive now involves not the motor alonebut the entire unit that directs the torque and speed of the machine. This is having a direct influence on the way electrical machinery courses are being taught.

How has this dramatic change come about? It is mainly due to the high-power solid state switching devices, such as insulated gate bipolar transistors (IGBTs), which can operate at frequencies of up to 20 kHz. The change has also been driven by thyristors and gate turn-off thyristors (GTOs) that can handle currents of several thousand amperes at voltages of up to 5 kV Another key element is the computing power of microprocessors that can process signal data in real time with incredible speed.

The high switching frequencies of IGBTs permit the use of pulse-width-modulation techniques in power converters. This, in turn, enables torque and speed control of induction motors down to zero speed. This was not feasible in rectangular-wave converters that were employed only a few years ago.

Most industrial drives are in the fractional horsepower to the 500 hp range. That is precisely the range now available for control by IGBTs. The result has been an explosion in the retrofitting of existing drives. Lower maintenance costs, higher efficiency, and greater productivity have made such changeovers economically attractive. Thus, do drives are being replaced by induction motor drives, which require less maintenance while offering equal and often superior dynamic performance.

Every sector of industrial and commercial activity is therefore being affected by this revolutionary converter technology. Electric elevators, electric locomotives, electric transit vehicles, servomechanisms, heating, ventilating and air conditioning systems, fans, compressors, and innumerable industrial production lines are being modified to utilize this new technology.

The change is also affecting the transmission and distribution of electric power—an industry that has been relatively stable for over 50 years. Here, we are seeing large rotating machines, such as synchronous condensers and frequency changers, being replaced by solid-state converters that have no moving parts at all.

Important development work, carried out by the Electric Power Research Institute (EPRI) in Palo Alto, California, in collaboration with several electrical manufacturers, has also resulted in the creation of high-power static switches, thyristor-controlled series capacitors, and converters that can fill the role of phase-shift transformers.

These new methods of power flow control, known by the acronym FACTS (Flexible AC Transmission Systems) will permit existing transmission and distribution lines to carry more power to meet the ever-increasing demand for electricity. On account of their extremely fast response, the converters can also stabilize a network that may suddenly be menaced by an unexpected disturbance.

It is remarkable that these innovations all rest on a common base. In other words, the converter technology used in electric motor drives is similar to that employed to control the flow of power in electric utilities. As a result, everything falls neatly and coherently into place. The teaching and learning of electric machines, drives, and power systems are thereby made much easier.

The following changes have been made in the fourth and fifth editions:

  • Every page of the original work was examined for clarity of expression and reviewed as to its pedagogical quality. As a result, more than 20 percent of the pages were altered.
  • The end-of-chapter problems and their solutions were revised and double-checked.
  • Chapter 7 on Active, Reactive, and Apparent Power was completely revised to make this important topic easier to understand.
  • Most importantly, I have added a new chapter on harmonics. Chapter 30 reveals how harmonics are generated and how they affect the behavior of capacitors, inductors, cables, transformers, and the quality of electric power.

I also devised a simple method that enables students to calculate the harmonic content in a distorted wave. Once they know how to unravel a wave into its harmonic components, their interest in harmonics quickly rises.

All the important changes first introduced in previous editions have been kept in this fifth edition. Thus, the writing of circuit equations, the discussion of higher frequency transformers, and the equivalent circuit diagram of the single-phase induction motor have all been retained.

  • A new section covering the writing of circuit equations was added to Chapter 2. Most students know how to solve such equations, but many experience difficulty in formulating them. I disclose an ac/dc circuit-solving methodology that is particularly easy to follow. Readers will be glad to refer to this section as a convenient reminder of the circuit-solving procedure.
  • Chapter 11 on Special Transformers was expanded to include higher frequency transformers. The reader is guided through the reasoning behind the design of such transformers, and why they become smaller as the frequency increases. High-frequency transformers are directly related to the higher frequencies encountered in switching converters.
  • Chapter 16 on Synchronous Generators has been expanded to show why an increase in size inevitably leads to higher efficiencies and greater outputs per kilogram. This fundamental aspect of machine design will interest many readers.
  • A new section was added to Chapter 18 to develop the equivalent circuit diagram of a single-phase induction motor. It presents a rigorous, yet simple approach, based on the 3-phase induction motor. Hand-held computers can be programmed to solve the circuit, which permits a better understanding of this ubiquitous single-phase machine.
  • Chapter 21, Fundamental Elements of Power Electronics, was revised and expanded to include switching converters and pulse width modulation (PWM) techniques. It illustrates the extraordinary versatility of IGBT converters and how they can be made to generate almost any waveshape and frequency.
  • Chapter 23, Electronic Control of Alternating Current Motors, was greatly expanded to cover the properties of induction motors operating at variable speeds. A special section explains the basics of PWM drives and flux vector control.
  • Chapter 29, Transmission and Distribution, represents a major addition to Part IV dealing with Electric Utility Power Systems. It explains the technologies that are being developed to control the flow of electric power electronically. It also discusses the quality of electric power as regards sags, swells, harmonics, and brownouts. As deregulation of electric power becomes a reality, these electronic methods of controlling the quality of electricity will become increasingly important.

The subject matter covered in this book requires only a background in basic circuit theory, algebra, and some trigonometry.

Owing to its user-friendly treatment of even complex topics, this book will meet the needs of a broad range of readers. First, it is appropriate for students following a two-year electrical program in community colleges, technical institutes, and universities. Owing to its very broad coverage, the text can also be incorporated in a 4-year technology program. Many universities have adopted the book for their electric power service courses.

Instructors responsible for industrial training will find a wealth of practical information that can be directly applied to that greatest laboratory of all—the electrical industry itself.

Finally, at a time when much effort is being devoted to continuing education, this book, with its many worked-out problems, is particularly suitable for self-study.

The exercises at the end of each chapter are divided into three levels of learning—practical, intermediate, and advanced. Furthermore, to encourage the reader to solve the problems, answers are given at the end of the book. A Solutions Manual is also available for instructors. The Industrial Application problems that appear at the end of most chapters will also appeal to hands-on users. The reader is invited to consult the list of books, technical articles, and Websites in the Reference section toward the end of the book.

A quick glance through the book shows the importance given to photographs. All equipment and systems are illustrated by diagrams and pictures, showing them in various stages of construction or in actual use. Some students may not have had the opportunity to visit an industrial plant or to see at close hand the equipment used in the transmission and distribution of electrical energy. The photographs help convey the magnificent size of these devices and machines.

Throughout the 31 chapters, a conscious effort was made to establish coherence, so that the reader can see how the various concepts fit together. For example, the terminology and power equations for synchronous machines are similar to those found in transmission lines. Transmission lines, in turn, bring up the question of reactive power. And reactive power is an important aspect in electronic converters. Therefore, knowledge gained in one sector is strengthened and broadened when it is applied in another. As a result, the learning of electrical machines, drives, and power systems becomes a challenging, thought-provoking experience.

In order to convey the real-world aspects of machinery and power systems, particular attention has been paid to the inertia of revolving masses, the physical limitations of materials, and the problems created by heat. This approach falls in line with the multidisciplinary programs of many colleges and technical institutes.

In summary, I employ a theoretical, practical, multidisciplinary approach to give a broad understanding of modern electric power. Clearly, it is no longer the staid subject it was considered to be some years ago. There is good reason to believe that this dynamic, expanding field will open career opportunities for everyone.

I would like to make a final remark concerning the use of this book. As mentioned previously, power technology has made a quantum jump in the past eight years, mainly on account of the availability of fast-acting semiconductors. In the field of electrical machines, drives, and power systems, there will now be a long period of consolidation during which existing machines and devices will be replaced by newer models. But the basic technology covered herein will not change significantly in the foreseeable future. Consequently, the reader will find that this book can also be used as a valuable long-term reference.

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