單項(xiàng)選擇題Equal power factors on paralleled AC generators are maintained by an automatic ().

A.voltage regulator
B.reverse power relay
C.reverse current relay
D.governor control switch


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1.單項(xiàng)選擇題To equalize the power factor of two alternators operating in parallel, the ()

A.field excitation of both units is adjusted
B.governors of both units are adjusted
C.phase sequence is altered
D.kilowatt load is evenly divided

2.單項(xiàng)選擇題An advantage of DC motors over AC motors is that they ()

A.are less expensive
B.require less maintenance
C.can be started across the line
D.offer a more effective means of controlling speed

3.單項(xiàng)選擇題Which of the following devices are protected from being motorized by a reverse-power relay?()

A.Alternators
B.Wave guides
C.Exciters
D.Amplidynes

4.單項(xiàng)選擇題If the length of a wire is halved and the cross-sectional area is doubled, the resistance will be ()

A.quartered
B.unchanged
C.doubled
D.quadrupled

5.單項(xiàng)選擇題AC and DC generators are similar in that they ()

A.both generate alternating voltages
B.both rectify the voltage before delivery
C.are constructed at the same physical size for the same kilowatt rating
D.both supply three-phase power

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