D.C. Machines & Motor/Generator Duality

Chapter 7 D.C. Machines

Fundamental Electrical and Electronic Principles Third Edition Book
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Summary of Contents

Fundamental Electrical and Electronic Principles Third Edition Book

  • D.C. Machines Chapter 7 Learning Outcomes This chapter covers the operating principles of d.c. generators and motors, their characteristics and applications. On completion you should be able to: 1 Understand and explain generator/motor duality. 2 Appreciate the need for a commutator. 3 Identify the different types of d.c. generator, and describe their characteristics. Carry out practical tests to compare the practical and theoretical characteristics. 233 7.1 Motor/Generator Duality An electric motor is a rotating machine which converts an electrical input power into a mechanical power output. A generator converts a mechanical power input into an electrical power output. Since one process is the converse of the other, a motor may be made to operate as a generator, and vice versa. This duality of function is not confi ned to d.c. machines. An alternator can be made to operate as a synchronous a.c. motor, and vice versa. To demonstrate the conversion process involved, let us reconsider two simple cases that were met when dealing with electromagnetic induction. Consider a conductor being moved at constant velocity, through a magnetic fi eld of density B tesla, by some externally applied force Fnewton. This situation is illustrated in Fig. 7.1 . Work done in moving the conductor, WFd newton metre