單項(xiàng)選擇題

You are attempting to parallel two AC generators, and the syncope pointer is revolving in the fast directionThis indicates that the frequency of the incoming machine is （）.

A.higher than the bus frequency
B.lower than the bus frequency
C.the same as the bus frequency but out of phase with it
D.the same as the bus frequency and the circuit breaker may be closed at any pointer position

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單項(xiàng)選擇題

The voltage developed by an AC generator is controlled by varying the （）

A.speed of the prime mover
B.AC excitation to the field
C.DC excitation to the field
D.DC excitation of the voltage regulator

單項(xiàng)選擇題

Moisture absorbed in the windings or condensed on the surface of electrical machinery insulation （）

A.is good for long term preserving since most insulation is organic and contains some amount
B.lowers the insulation value and is a common cause of fault grounds in idle machines
C.will enhance insulation resistance only if it is fresh water and contains no salt
D.reduces the amount of current supplied or drawn by the machine so horsepower is limited