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


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1.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

2.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

3.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

4.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