单项选择题

The part of a fuse that melts and opens the circuit is made of （）.

A.copper and antimony
B.steel and babbitt
C.aluminum or beryllium alloy
D.zinc or an alloy of tin and lead

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单项选择题

Time delayed or delayed action-type fuses are designed to （）.

A.prevent grounds in branch circuits
B.prevent opens in motor circuits
C.permit momentary overloads without melting
D.guard lighting and electronic circuits

单项选择题

Which of the following statements is true concerning all three-phase alternators?（）

A.Each has three separate but identical armature windings acted on by one system of rotating magnets
B.Each has one armature winding acted on by three identical but separate systems of rotating magnets
C.All three-phase alternators are designed to operate with a O8 leading power factor
D.The three phases always provide power to the load through three sets of slip rings and brushes

单项选择题

The function of damper windings in a synchronous motor is to （）.

A.eliminate slippage
B.provide excitation
C.provide starting torque
D.increase efficiency