单选题The power factor at which a paralleled AC generator operates is usually adjusted by the ().Aconnected loadBprime mover speedCfield excitationDgenerators rated voltage

单选题
The power factor at which a paralleled AC generator operates is usually adjusted by the ().
A

connected load

B

prime mover speed

C

field excitation

D

generators rated voltage


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When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is _____.A.laggingB.leadingC.maximumD.minimum

The power factor of an AC generator operating singularly is determined by the_______ .A.connected loadB.prime mover speedC.field excitationD.generator's rated voltage

A technician suspects the AC voltage into a PC power supply is bad. Which of the following toolswould MOST likely be used to confirm the diagnosis?() A. MultimeterB. OscilloscopeC. Cable testerD. Power supply tester

Equal power factors on paralleled AC generators are maintained by an automatic ________.A.governor control switchB.reverse power relayC.reverse current relayD.voltage regulator

材料:The field current supply in older machines comes from a lower voltage direct current generator or exciter on the same shaft as the alternator. Modern machines however are either statically excited or of the high-speed brush-less type. The exciter is required to operate to counter the effects of power factor for a given load. The power factor is a measure of the phase difference between voltage and current and is expressed as the cosine of the phase angle. With a purely resistance load the voltage and the current are in phase, giving a power factor of one. The power consumed is therefore the product of voltage and current. Inductive or capacitive loads, combined with resistance loads, produce lagging or leading power factors which have a value less than one.The power consumed is therefore the product of current, voltage and power factor. The alternating current generator supplying a load has a voltage drop resulting from the load. When the load has a lagging power factor this voltage drop is considerable. Therefore the exciter, in maintaining the alternator voltage, must vary with load current and also the power factor. The speed change of the prime mover must also be taken into account.问题: The word “machines” in the passage refers to _____.A.the direct current generatorB.the alternating current generatorC.the exciterD.the prime moverWhich of the following statements is true according to the passage ?A.With a purely resistance load, the power factor is zeroB.Inductive loads combined with resistance loads produces leading power factorsC.Capacitive loads combined with resistance loads produces lagging power factorsD.With a purely resistance load, the phase angle is zeroWhen the load has a lagging power factor this voltage drop is considerable. This sentence means that _____.A.with a purely resistance load, the voltage drops too muchB.there is a considerable voltage drop in the capacitive load combined with resistance loadC.when the load is the capacitive load combined with resistance load, the voltage drops to zeroD.when the load is the inductive load combined with resistance load, the voltage drop is fairly largeThe exciter must vary with: ① load current ② the power factor, ③ speed change of the prime mover.A.①B.②C.①②D.①②③请帮忙给出每个问题的正确答案和分析,谢谢!

英译汉:power factor

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