單項選擇題

（） is provided to alternators, in the event of prime mover failure to ensure that the alternator does not act as a motor.

A.Reverse current protection
B.Reverse power protection
C.Synchronising device
D.Frequency meter

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To parallel an incoming machine to a running machine therefore it is necessary to ensure firstly that （）.

A.two frequencies must be brought into phase
B.the incoming machine accepts a small amount of load
C.the running machine must be unload
D.both voltages are equal

單項選擇題

The magnetic field is provided by electromagnets so arranged that adjacent poles have （）.

A.opposite polarity
B.the same polarity
C.negative polarity
D.positive polarity