單項(xiàng)選擇題（） is provided to alternators, in the event of prime mover failure to ensure that the alternator does not act as a motor.

A.Reverse current protection
B.Reverse power protection
C.Synchronising device
D.Frequency meter


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1.單項(xiàng)選擇題To parallel an incoming machine to a running machine therefore it is necessary to ensure firstly that （）.

A.two frequencies must be brought into phase
B.the incoming machine accepts a small amount of load
C.the running machine must be unload
D.both voltages are equal

2.單項(xiàng)選擇題The magnetic field is provided by electromagnets so arranged that adjacent poles have （）.

A.opposite polarity
B.the same polarity
C.negative polarity
D.positive polarity

3.單項(xiàng)選擇題An a-cswitchboard is usually（） the corresponding d-cboard because of the higher voltage and lower currents and smaller bus-bars.

A.larger and heavier than
B.as much as
C.smaller and lighter than
D.more dangerous than

4.單項(xiàng)選擇題The star formation is most commonly used and requires（） on the alternator.

A.one slip-ring
B.two sliprings
C.three sliprings
D.four sliprings

5.單項(xiàng)選擇題The field coils（） and the armature is（）This is in fact the arrangement adopted for large, heavy duty alternators.

A.stationary；rotate
B.stationary；stationary
C.rotate；stationary
D.rotate；rotate