單項(xiàng)選擇題

A.When it is a DC machine
B.When it is an AC machine
C.Any machine that operates on over 100 volts
D.Only when working on wet steel plates

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A.the speed of the alternators
B.the field strength of the machines
C.the power factor of the alternators
D.steam supply to the prime movers

A.change AC to DCcurrent
B.change DC to AC current
C.neutralize a armature reaction
D.carry current to the outside circuit