單項(xiàng)選擇題When paralleling two AC generators, the frequency of the machine coming on-line, immediately prior to closing its breaker, should be （）

A.slightly less than the oncoming generator frequency
B.the same as the bus frequency
C.slightly greater than the bus frequency
D.the same as the bus voltage


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1.單項(xiàng)選擇題When two AC generators are being paralleled, the breaker should be closed with the synchroscope pointer mating in the （）

A."slow" direction, just before the 12 o'clock position
B."fast" direction, just after the 12 o'clock position
C."fast" direction, just before the 12 o'clock position
D."slow" direction, just after the 12 o'clock position

2.單項(xiàng)選擇題AC voltmeters are generally calibrated to read the （）

A.instantaneous voltage
B.average voltage
C.RMS voltage
D.peak voltage

3.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

4.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

5.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