单项选择题

The （） is a measure of the phase difference between voltage and current and is expected as the cosine of phase angle.

A.power
B.efficiency
C.effective power
D.power factor

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单项选择题

The overcurrent relay （） the motor contactor when the motor exceeds its rated current.

A.connects
B.trips
C.fouls
D.destructs

单项选择题

In a modern three-phase A-Csynchronous brushless generator, the excitation winding is on the rotorThat means （）.

A.The generator needs not excitation
B.The winding on the rotor is for inputting excitation current
C.There are three phase windings on the rotor
D.The generator has brushes

单项选择题

Ammeter is to measure the （）.

A.current
B.voltage
C.power
D.frequency