单项选择题

Which of the following devices are protected from being motorized by a reverse-power relay?（）

A.Alternators
B.Wave guides
C.Exciters
D.Amplidynes

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单项选择题

If the length of a wire is halved and the cross-sectional area is doubled, the resistance will be （）

A.quartered
B.unchanged
C.doubled
D.quadrupled

单项选择题

AC and DC generators are similar in that they （）

A.both generate alternating voltages
B.both rectify the voltage before delivery
C.are constructed at the same physical size for the same kilowatt rating
D.both supply three-phase power

单项选择题

To increase the frequency of an operating AC generator, you should （）

A.increase the field excitation
B.decrease the field excitation
C.increase the number of magnetic poles
D.increase the speed of the prime mover