單項(xiàng)選擇題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


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1.單項(xiàng)選擇題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

2.單項(xiàng)選擇題Electric circuits are protected against overloads and short circuits by means of a/an （）.

A.circuit breaker
B.amplifier
C.diode
D.capacitor

3.單項(xiàng)選擇題Ambient temperature is the （）.

A.amount of temperature rise with no load
B.temperature of the compartment where the motor is located
C.normal operating temperature, less the room temperature
D.amount of temperature developed by an operating motor

4.單項(xiàng)選擇題You are attempting to parallel two AC generators and the synchroscope pointer is revolving in the slow directionThis indicates that the frequency of the incoming machine is （）.

A.higher than the bus frequency
B.lower than the bus freouencv
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

5.單項(xiàng)選擇題The need for insulation cleaning may be determined by （）

A.visual inspection for dirt accumulation
B.high megger readings
C.low operating temperature
D.the time period since the last cleaning