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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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
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单项选择题
Ammeter is to measure the （）.
A.current
B.voltage
C.power
D.frequency
