单项选择题
The purpose of DC generator brushes is to （）.
A.neutralize armature reaction
B.conduct electric current to an outside circuit
C.convert DC current to AC current
D.provide excitation to a DC generator
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相关考题
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单项选择题
Which of the listed precautions should be taken when cleaning the internals of a motor with compressed air?（）
A.Open the machine on both ends so as to allow the air and dust to escape
B.Be certain that the circuit breaker is opened and tagged on the feeder panel
C.Be certain that the air is clean and as dry as possible
D.All of the above -
单项选择题
Since fuse elements are made of zinc or any alloy of tin and lead, the melting point of the fuse element must be （）.
A.higher than that of copper
B.lower than that of copper
C.equal to that of copper
D.reached when the conductor it is protecting becomes "white hot" -
单项选择题
The most common source of excitation for synchronous motors is a/an （）.
A.low voltage battery
B.motor attenuator set
C.DC exciter generator
D.AC supply
