Description : When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is _____________. A. lagging B. leading C. maximum D. minimum
Last Answer : Answer: C
Description : A transformer has negative voltage regulation when its load power factor is- (a) Zero (b) Unity (c) Leading (d) Lagging
Last Answer : Ans: C
Description : A synchronous motor is operating on no-load at unity power factor. If the field current is increased, power factor will become (A) Leading & current will decrease (B) Lagging & current will increase. (C) Lagging & current will decrease. (D) Leading & current will increase.
Last Answer : Ans: A Initially synchronous motor is operating at no load and unity power factor. When field current increases, the excitation will increase. Therefore, p.f will be leading and current will be I CosΦ < I
Description : 51 A transformer has negative voltage regulation when its load power factor is A. Zero B. Unity C. Leading D. Lagging
Last Answer : C. leading
Description : An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging case. If it is required to deliver rated current at rated voltage and 0.8 power-factor leading, the required excitation will be (A) less. (B) more. (C) more or less. (D) the same.
Last Answer : Ans: B Over excitation gives leading power factor and under excitation gives lagging p.f .
Description : In a transformer the voltage regulation will be zero when it operates at (A) unity p.f. (B) leading p.f. (C) lagging p.f. (D) zero p.f. leading.
Last Answer : (B) leading p.f.
Description : If the excitation of an alternator operating in parallel is decreased below normal, its _____________. A. power factor will change in the lagging direction B. power factor will change in the leading direction C. ampere load will be greatly increased D. kilowatt load will be greatly decreased
Last Answer : Answer: B
Description : If the excitation is increased to one of two alternators operating in parallel, the _____________. A. power factor will change in the lagging direction B. power factor will change in the leading direction C. kilowatt load will be greatly increased D. ampere load will be greatly decreased
Last Answer : Answer: A
Description : A two-winding single phase transformer has a voltage regulation of 4.5% at full-load and unity power-factor. At full-load and 0.80 power-factor lagging load the voltage regulation will be (A) 4.5%. (B) less than 4.5%. (C) more than 4.5%. (D) 4.5% or more than 4.5%.
Last Answer : (C) more than 4.5%.
Description : When is the power factor lagging , leading , unity ?
Last Answer : Power factor lagging in inductive load. Power factor leading in capacitive load is power factor unity in resistive load.
Description : The power factor of industrial loads is generally (a) unity (b) lagging (c) leading (d) zero
Last Answer : (b) lagging
Description : In an alternator at lagging power factor the generated voltage per phase as compared to that at unity power factor?
Last Answer : In an alternator, at lagging power factor the generated voltage per phase as compared to that at unity power factor must be more than terminal voltage.
Description : A three-phase synchronous motor has a terminal voltage of 460 V and a terminal current of 120 A at a power factor of 0.95 lagging, synchronous reactance of 1.68 ohm and the field current is 47 A. The field to armature mutual ... _____________. (a). 20mH (b). 16mH (c). 24mH (d). 22mH
Last Answer : 22
Description : In the flow of one cycle of single phase AC current past any given point in a circuit, the maximum current peak occurs _____________. A. one time B. two times C. three times D. four times
Description : The arc voltage produced in A.C. circuit breaker is always (a) in phase with the arc current (b) lagging the arc current by 90" (c) leading the arc current by 90° (d) none of the above
Last Answer : (a) in phase with the arc current
Description : The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation of the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. type of alternator
Description : The division of kilowatt load between two paralleled alternators is determined by the _____________. A. amount of field excitation to the leading machine B. load-speed characteristics of the governors C. amount of field excitation to the lagging machine D. number of field poles per alternator
Description : If an AC generator experiences voltage failure, the cause may be _____________. A. an open in the field circuit B. the brushes shifting out of the neutral plane C. excessive locked-rotor current D. a rotating slip ring
Description : You are attempting to parallel two AC generators and the synchroscope pointer stops at a position other than 0°. If you close the circuit breaker at this moment _____________. A. the incoming ... hazardous condition will be created by the incoming machine being at a higher frequency than the bus
Description : Capacitance in an AC circuit will _____________. A. stop current flow once the capacitor is fully charged B. allow current flow in only one direction C. oppose any change in circuit voltage D. rectify the current
Description : In a simple dc circuit, voltage equals resistance multiplied by current. This is also considered true in an AC circuit if the what values of the current and voltage are used.
Last Answer : ANSWER: ROOT MEAN SQUARE (RMS) VALUES
Description : Explain lagging quantity and leading quantity, explain this concept with voltage and current waveform
Last Answer : When two alternating quantities attain their respective zero or peak values simultaneously, the quantities are said to be in-phase quantities. When the quantities do not attain their respective zero or ... current is leading the voltage or the voltage is said to be lagging behind the current.
Description : [75] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results A. Short-circuiting of the secondaries B. Power factor of one of the ... have negligible core losses D. Loading of the transformers not in proportion to their kVA ratings.
Last Answer : D. Loading of the transformers not in proportion to their kVA ratings
Description : The most practical method of controlling the RPM of a step-speed AC motor is to _____________. A. change input voltage B. vary the number of poles C. vary power factor D. change the number of brushes
Description : The most practical way to control the voltage output of an AC generator is to vary the _____________. A. number of windings B. speed of the rotating field C. strength of the rotating magnetic field D. power factor of the load
Description : 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. generator's rated voltage
Description : A motor which can conveniently be operated at lagging as well as leading power factors is the (A) squirrel cage induction motor. (B) wound rotor induction motor. (C) synchronous motor. (D) DC shunt motor.
Last Answer : (C) synchronous motor.
Description : Ammeters and voltmeters used in sinusoidal AC power systems indicate which of the following values of the waveforms measured? A. Peak value B. Root-mean-square value C. Average value D. Maximum value
Description : At dead short circuit at terminals of Alternator then the current I is a) ZPF Lag b) ZPF lead c) Unity power factor d) 0.8 Power factor lag
Last Answer : Ans: ZPF Lag
Description : 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
Description : An alternator is delivering rated current at rated voltage and 0.8 power-factor lagging. For delivering rated current at rated voltage and 0.8 poWer—factor leading, the required excitation will be: (A) less (B) more (C) more or less (D) the same
Last Answer : An alternator is delivering rated current at rated voltage and 0.8 power -factor lagging. For delivering rated current at rated voltage and 0.8 power -factor leading, the required excitation will be: more
Description : When Alternator excitation increases and machine is operating at lagging power factor then a) I increase b) I decreases c) No effect on current d) None
Last Answer : Ans: I increase
Description : You are attempting to parallel two AC generators and the synchroscope pointer is revolving slowly in the fast direction. You should _____________. A. use the governor control switch to adjust the incoming ... the 0° position D. use the field rheostat to adjust the speed of the incoming machine
Description : An AC circuit has capacitance arranged in series. If the line voltage remains constant, the capacitive reactance value can be varied by changing the _____________. A. line frequency B. resistance C. number of commutating poles D. number of interpoles
Description : After closing the circuit breaker to place two similar alternators in parallel, the NEXT step is to balance the _____________. A. power factor B. voltage load C. kilowatt load D. ampere load
Description : 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
Description : The electrical supply applied to the anodes shown in the illustration is _____________. EL-0090 A. low voltage, high current DC B. low voltage, high current AC C. high voltage, low current DC D. high voltage, low current AC
Description : Shading coils are installed on AC full-voltage starters to _____________. A. eliminate contact chatter B. dissipate opening contact arcs C. delay current build up in the holding coil D. protect the motor windings from momentary starting current overload
Description : In accordance with Coast Guard Regulations (46 CFR), a circuit breaker located in the machinery space and installed in a 440V AC system must _____________. A. be dependent upon mechanical ... the maximum asymmetrical shortcircuit current available at the point of application D. all of the above
Description : An open shunt field in a direct current machine may be located by connecting the field circuit to an external power source, equal to the rated field voltage or less, and tested with a voltmeter from ... C. any suitable ground to any available line lead D. any field pole to each field coil lead
Description : Decreasing the frequency in a capacitive circuit while maintaining a constant circuit voltage, will result in a/an _____________. A. increase in apparent power B. decrease in circuit current C. decrease in capacitive reactance D. decrease in total impedance
Description : When the voltage remains constant, and the resistance increases in a series circuit, current flow _____________. A. decreases B. remains the same C. increases D. increases by the square
Description : When the voltage remains constant and the resistance is increased in a series circuit, the flow of current _____________. A. increases by the square of the original value B. increases C. remains the same D. decreases
Last Answer : Answer: D
Description : The potential difference in an open circuit is a) Zero b) Unity c) Infinity d) Circuit does not exist open
Last Answer : c) Infinity
Description : Basically, a magnetic amplifier is a saturable reactor with the addition of _____________. A. AC to the bias winding B. variable capacitance to all windings C. eddy current protectors D. a rectifier in the load circuit
Description : The purpose of DC generator brushes is to _____________. A. neutralize armature reaction B. conduct electric current to an outside circuit C. convert DC current to AC current D. provide excitation to a DC generator
Description : Which of the following statements is true concerning a stepdown transformer in an operating AC power circuit? A. Voltage and current will both be increased. B. Voltage and current will both be decreased C. Voltage decreases as current increases. D. Voltage increases as current decreases.
Description : A transformer in an electric circuit serves to ____________. A. generate its own electrical power B. transform electrical energy into mechanical energy C. increase or decrease circuit voltage as required D. convert AC current to DC current
Description : Transformers are used onboard ships with AC generators to _____________. A. change frequency B. increase power output to modulating frequency controllers C. decrease power output to modulating frequency ... D. permit higher voltage for electric motor operation and low voltage for lighting circuits
Description : The division of the kilowatt load between two AC generators operating in parallel is controlled by the settings and characteristics of the _____________. A. voltage regulators B. field rheostats C. reverse power relays D. prime mover governors