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CHAPTER 3
ALTERNATING CURRENT GENERATORS
LEARNING OBJECTIVES
Upon completion of this chapter, you will be able to:
1. Describe the principle of magnetic induction as it applies to ac generators.
2. Describe the differences between the two basic types of ac generators.
3. List the advantages and disadvantages of the two types of ac generators.
4. Describe exciter generators within alternators; discuss construction and purpose.
5. Compare the types of rotors used in ac generators, and the applications of each type to different
prime movers.
6. Explain the factors that determine the maximum power output of an ac generator, and the effect
of these factors in rating generators.
7. Explain the operation of multiphase ac generators and compare with single-phase.
8. Describe the relationships between the individual output and resultant vectorial sum voltages in
multiphase generators.
9. Explain, using diagrams, the different methods of connecting three-phase alternators and
transformers.
10. List the factors that determine the frequency and voltage of the alternator output.
11. Explain the terms voltage control and voltage regulation in ac generators, and list the factors that
affect each quantity.
12. Describe the purpose and procedure of parallel generator operation.
INTRODUCTION
Most of the electrical power used aboard Navy ships and aircraft as well as in civilian applications is
ac. As a result, the ac generator is the most important means of producing electrical power. Ac generators,
generally called alternators, vary greatly in size depending upon the load to which they supply power. For
example, the alternators in use at hydroelectric plants, such as Hoover Dam, are tremendous in size,
generating thousands of kilowatts at very high voltage levels. Another example is the alternator in a
typical automobile, which is very small by comparison. It weighs only a few pounds and produces
between 100 and 200 watts of power, usually at a potential of 12 volts.
Many of the terms and principles covered in this chapter will be familiar to you. They are the same
as those covered in the chapter on dc generators. You are encouraged to refer back, as needed, and to refer
