单项选择题
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
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相关考题
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单项选择题
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 -
单项选择题
When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is （）
A.lagging
B.leading
C.maximum
D.minimum -
单项选择题
While paralleling two AC generators using synchronizing lamps only, both lamps will go dark when the generators are （）.
A.running at the same speed
B.grounded
C.of the same polarity
D.in phase
