单项选择题
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
单项选择题 The voltage developed by an AC generator is controlled by varying the （）
单项选择题 Moisture absorbed in the windings or condensed on the surface of electrical machinery insulation （）
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 （）