单项选择题
Electrical failures in motors are caused by the breakdown of insulation, which may be caused by （）
A.penetration of moisture
B.accumulation of dirt
C.overheating
D.All of the above
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相关考题
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单项选择题
A three-phase alternator operates at 450 volts with a power factor of 0~8.If the ammeter indicates 250 amperes, what should be the KW meter reading （）.
A.90~0 kw
B.127~27 kw
C.155~70 kw
D.194~85 kw -
单项选择题
Sparking at the brushes of a running motor could be an indication of （）.
A.normal operation
B.a dirty commutator
C.increased brush capacity
D.water vapor absorption -
单项选择题
If a DC motor runs hot, the cause may be （）
A.high mica condition
B.low ambient temperature
C.clogged ventilation ducts
D.an open in the shunt field
