网友您好， 请在下方输入框内输入要搜索的题目：
题目内容
（请给出正确答案）
单选题
With a （） load the voltage and current are in phase.
A
pure resistance
B
capacitive
C
inductive
D
None of the above
参考答案
参考解析
解析：
暂无解析
更多 “单选题With a （） load the voltage and current are in phase.A pure resistanceB capacitiveC inductiveD None of the above” 相关考题
考题
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
考题
The Buck(降压式变换器) is a ( ) converter.
A.voltage step-upB.current step-downC.current step-upD.resistance
考题
下列哪些测试不须考虑输入电压的偏差()
A．Input TestB．Touch current TestC．Working Voltage MeasurementD．Discharge Test
考题
any pointer positionDue to failure of one of the carbon brushes the excitation voltage is lost on one alternator that operating in parallel.Then that alternator will()
A.completely loose its share of the load causing the auxiliary engine to speed up.B.overload due to reduced voltage output and increased currentC.continue to share the active load(kw)but have high very reactive loadD.try to take all the load and so trip the main circuit breaker
考题
The output voltage of a 440 volt, 60 hertz, AC generator is controlled by theA.prime mover speedB.exciter output voltageC.load on the alternatorD.number of poles
考题
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！
考题
A switchboard for an AC electrical system requires the use of which of the following devices?A.Frequency meter.B.Ohmmeter.C.Induction voltage regulator.D.Current transformer governor.
考题
单选题The instantaneous reduction in voltage of an AC generator, resulting from an increase in load, and prior to the automatic voltage regulator correcting the situation, is called voltage （）.A
droopB
dropC
dipD
regulation
考题
单选题Voltage will always lead current in a/an （）A
capacitive circuitB
inductive circuitC
magnetic circuitD
resistive circuit
考题
单选题Which is a function of the voltage regulators used with AC generators?（）A
To cut out generators when they are no longer requiredB
To cut in additional generators automatically as requiredC
To divide the KW load equally between generators operating in parallelD
To divide reactive current between generators operating in parallel
考题
单选题The （） is a measure of the phase difference between voltage and current and is expected as the cosine of phase angle.A
powerB
efficiencyC
effective powerD
power factor
考题
单选题If the resistance of a circuit is cut in half and the applied voltage is kept constant, the current flow will be （）.A
doubledB
quadrupledC
unchangedD
cut in half
考题
单选题Generators should have an excitation/voltage regulation system which will enable them to share the steady state reactive load （） no machine exceeds its proportional share of reactive load by more than 10% of the rated reactive load of the largest generator.A
whenB
so asC
such thatD
though
考题
单选题With a （） load the voltage and current are in phase.A
pure resistanceB
capacitiveC
inductiveD
None of the above
考题
单选题With a purely resistance load the voltage and current are in phase, giving a power factor of （）.A
oneB
less than oneC
more than oneD
negative one
考题
单选题With a purely （） load the voltage and current are in phase, giving a power factor of one.A
inductiveB
resistanceC
combinedD
capacitate
考题
单选题When current and voltage reach maximum values at the same time, the power factor is（）A
minimumB
maximumC
leadingD
lagging
考题
单选题Self-excited a-cgenerator with "error operated" voltage control systems draw the full excitation power for the machine terminalsThis dispenses with the current transformers, reactors and capacitors necessary for accurate compounding, but renders the excitation system vulnerable to variations in its output voltageWhich of the following is correct about the generator mentioned according to the sentences above （）.A
It consumes no excitation powerB
It has current transformersC
Components are needed for accurate compoundingD
Its excitation system is vulnerable to voltage variations
考题
单选题The power factor is a measure of the phase difference between voltage and current and is expressed as the（） of the phase angle.A
sineB
cosineC
tangentD
cotangent
考题
单选题Reduced voltage applied to a motor during the starting period will （）.A
result in decreased acceleration time onlyB
lower the starting current and increase accelerating timeC
cause a greater starting torqueD
increase the starting current and pump capacity
考题
单选题Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions?（）A
Current and voltage may be in phaseB
Current may lead the voltageC
Current may lag the voltageD
All of the above
考题
单选题The alternating current generator supplying a load has a voltage drop resulted from the loadWhen the load has a lagging power factor this voltage drop （）.A
is smallB
may be neglectedC
is usefulD
is considerable
考题
单选题The most inefficient method of voltage reduction from the stand point of power loss, is a/an （）A
capacitor in series with the loadB
inductor in series with the loadC
capacitor and inductor in series with the loadD
resistor in series with the load
考题
单选题The initial voltage of self-excitation generator set up by（）A
residual magnetismB
voltage regulatorC
electrical current for excitationD
the other running generator
考题
单选题A fuse that blows often should be replaced only with a fuse of （）.A
the recommended current and voltage ratingB
higher current and voltage ratingC
higher current and lower voltage ratingD
lower current and higher voltage rating
考题
单选题When two DC generators operate in parallel, they are protected against motorizing by（）A
blow out coilsB
governor relayC
under voltage tripsD
reverse current trips
考题
单选题Which of the following statements concerning a simple parallel resistance circuit is correct?（）A
The voltage drop across each resistor is the sameB
The total current flow equals the reciprocal of the sum of the individual currentsC
The total resistance equals the sum of the individual resistancesD
The total voltage equals the sum of the individual voltages across each resistance
考题
单选题A transformer in an electric circuit serves to （）A
generate its own electrical powerB
transform electrical energy into mechanical energyC
increase or decrease circuit voltage as requiredD
convert AC current to DC current
热门标签
最新试卷
