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單項(xiàng)選擇題

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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單項(xiàng)選擇題

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

單項(xiàng)選擇題

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

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