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
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to any other source that will help you master the subject of this chapter. No one source meets the
complete needs of everyone.