Description : A 220/440 V, 50 Hz, 5 KVA, single phase transformer operates on 220V, 40Hz supply with secondary winding open circuited. Then (A) Both eddy current and hysteresis losses decreases. (B) Both ... same but hysteresis loss increases. (D) Eddy current loss increases but hysteresis loss remains the same.
Last Answer : (A) Both eddy current and hysteresis losses decreases.
Description : A CT has 2 – secondary windings. If we use only one secondary winding can we keep the unused secondary winding short circuited?
Last Answer : No. If it is short-circuited then the ratio will not get correctly. The turns of primary winding will be shared between 2 secondary windings. So the unused secondary winding should kept open.
Last Answer : If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.
Description : Why SC test is generally performed on HV side of a transformer?
Last Answer : The rated current is less on HV side. This will also permit to use ammeter and wattmeter of lower current range.
Description : Why the tap changers are always connected to HV side of the transformer?
Last Answer : During tap changing action the load current has to be shifted from one tap to another tap. In case HV wining the load current will be less. Hence lesser arcing will take place.
Description : Why in transformer the LV CB also be tripped along with HV CB for a primary side fault?
Last Answer : Auxiliary transformer 415v delta star transformer, if HV CB alone tripped then back feeding from LV side (say DG runs parallel with transformer)—arcing voltage at the fault on primary—fault fed for more time – more damage.
Description : If fuse 'F-1' in the illustrated schematic diagram opens, ____________. EL-0017 A. the motor will run slowly B. 'A-1' and 'A-2' will open C. the motor will not start D. the start button will jam in the closed position
Last Answer : Answer: C
Description : In the lighting distribution circuit shown in the illustration, if all switches are closed and fuse 'F2' were to open, all lights on branches ____________. EL-0013 A. '1', '2', and '3' would go out B. '1' ... and '3' would burn dimly D. '1' and '3' would go out, while branch '2' would remain lit
Last Answer : Answer: D
Description : If a single-phase induction motor fails to start, the problem may be _____________. A. an open in the main winding B. a shorted shunt field C. a closed centrifugal switch D. low circuit frequency
Last Answer : Answer: A
Description : If a single-phase induction motor fails to start, the problem may be _____________. A. an open in the run winding B. a shorted shunt field C. a closed centrifugal switch D. low circuit frequency
Description : When secondary of a current transformer is open-circuited its iron core will be?
Last Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.
Last Answer : High Voltage side is open circuited.
Description : When troubleshooting motor controllers, a shorted relay or contactor coil is often indicated by _______________. A. a resistance reading of 'infinity' on an ohmmeter B. charred insulation and/or a blown ... of the coil's leads to ground D. a higher-than-normal voltage reading across the winding
Last Answer : Answer: B
Description : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: (1) Slip frequency (2) Supply frequency (3) Frequency corresponding to rotor speed (4) Zero
Last Answer : A three phase slip ring induction motor is fed from the rotor side with stator winding short circuited stator is: Slip frequency
Description : Why CT should not be open circuited?
Last Answer : Very high voltage will be induced in secondary due to less back emf resulting in the failure of the insulation.
Description : If the field circuits of an unloaded salient pole synchronous motor gets suddenly open circuited, then (A) The motor stops. (B) It continues to run at the same speed. (C) Its runs at the slower speed. (D) It runs at a very high speed.
Last Answer : Ans: B The motor continues to run at the same speed because synchronous motor speed does not depend upon load, Nα f.
Description : A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is
Last Answer : A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is 20 V
Description : In order to take a current reading with a 'clamp-on' ammeter, the instrument's jaws _________________. A. should remain open B. cannot touch the adjacent conductor C. must be fully closed D. will act as a transformer primary
Description : A single-phase induction motor will only start if you spin the rotor rapidly with the line switch closed. After starting, its speed fluctuates between very slow and half-speed. The problem ... in the ________. A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : A single-phase induction motor fails to start. The rotor is spun rapidly with the line switch closed. Having started by this method it is noted that the motor fluctuates between a very slow ... lies in the ______ A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : In the system shown in the illustration, the station at section I is unable to signal any other station nor is any other station able to signal the station in section I. The station can, however, ring ... only a single station to respond to itself. D. The switch at component 'C' is stuck open.
Description : 32 With S2 closed and S1 open, the current waveform in the delta winding will be [GATE 2009] A. a sinusoidal at fundamental frequency B. flat-topped with third harmonic C. only third-harmonic D. none of these
Last Answer : C. Only third harmonic
Description : Why the tapings are placed on HV side?
Last Answer : 1.A fine voltage regulation is possible with hV side as it has large number of turns. 2.LV side carries large current 3. HV side is placed outside so its feasible 4. In case of step ... large no. of turns the flux and flux density decreases. Hence core losses decreases results in higher efficiency.
Description : Mention the various tests carried out in a circuit breaker at HV labs.
Last Answer : Short circuit tests, Synthetic tests& direct tests.
Description : Why REF is now is used for HV side also in GT/SUT?
Last Answer : The E/F setting of differential is poor.
Description : What is the purpose of HV / leakage current test on stator?
Last Answer : This is to find out weakness in the stator winding. If the ambient conditions are right, and the insulation is weak, the leakage current will increase non-linearly. The record of voltage ... current. In HV test starting leakage current should be more than switching off current in μ Amps.
Description : What is the DC HV test voltage range?
Last Answer : 1.7* 1.5* rated voltage.
Description : An auto transformer is preferred over an ordinary two winding transformer due to: a) Safety of operation b) Availability of taps on secondary c) Copper savings d) All the above
Last Answer : Ans: C
Description : The hook-on AC volt-ammeter consists essentially of a split-core and a rectifiertype instrument connected to the secondary winding of a _____________. A. potential transformer B. control transformer C. current transformer D. reactance transformer
Description : Which of the listed transformer uses a single winding to produce voltage transformation? A. Stepup transformers B. Stepdown transformers C. Autotransformers D. Isolation transformers
Description : Relative to the secondary winding of a step-up transformer, the primary winding will have _____________. A. more turns B. fewer turns C. half as many turns D. twice as many turns
Description : When a transformer is used to step down voltage, the low voltage winding is _____________. A. part of the core B. the primary coil C. not insulated D. the secondary coil
Description : What is tertiary winding? What is Three Winding Transformer? What are its advantages?
Last Answer : A. In some high rating transformers, one winding, in addition to the primary and secondary winding, is used. This is known as Tertiary Winding of Transformer. Because of this third winding, the ... it assists in limitation of fault current in the event of a short circuit from line to neutral.
Description : What are the necessary tests to determine the efficiency, voltage regulation, and temperature rise of winding & insulation of transformer?
Last Answer : 1.Direct loading test 2.Open circuit test 3. Short circuit test 4. Sumpner's or back to back test
Description : What is Six winding transformer?
Last Answer : Three windings in primary and three windings in secondary are used, They are three phase transformers.They are connected in either star-star, delta-delta, star delta or delta star.
Description : What is Three winding transformer?
Last Answer : Three windings are used each work as primary and secondary. Also primary and secondary windings are conductively couple. They are three phase auto transformer
Description : What is Two winding transformer?
Last Answer : Two separate windings one as primary and other as secondary are used. Both windings are magnetically coupled.
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 : The primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz supply. The secondary output voltage will be (A) 3.6 V. (B) 2.5 V. (C) 3.0 V. (D) 6.0 V.
Last Answer : (C) 3.0 V.
Description : 66 While conducting short-circuit test on a transformer the following side is short circuited A. High voltage side B. low voltage side C. primary side D. secondary side
Last Answer : B. Low voltage side
Description : 30 In performing the short circuit test of a transformer A. high voltage is usually short circuited B. low voltage side is usually short circuited C. any side is short circuited with preference D. none of the above
Last Answer : B. Low voltage side is usually short circuited
Description : The secondary of a current transformer is always short-circuited under operating conditions because it?
Last Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.
Last Answer : Low voltage side is short circuited.
Description : Which of the following equipment, for regulating the voltage in distribution feeder, will be most economical ? (a) Static condenser (b) Synchronous condenser (c) Tap changing transformer (d) Booster transformer
Last Answer : (d) Booster transformer
Description : If your multimeter gives a reading in ohms when testing each end of each conductor of a three-conductor cable, this indicates ______________. A. continuity of the conductor B. an infinite resistance C. the presence of a partial ground D. that the conductor is not short circuited
Description : If the illustrated device is fully discharged, what will be the result? EL-0061 A. The battery will be short circuited because the mud space will be filled with lead sulfate B. The electrolyte ... minimum sulfuric acid. D. The plates will be maximum lead oxide and sponge lead minimum lead sulfate.
Description : In the illustration, the chemical reaction depicted indicates that the _________. EL-0061 A. battery is being charged at a high rate B. cell is short circuited C. cell is discharging D. battery is attached to a trickle charger
Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. will continue to operate B. will probably burn out immediately C. will operate on reduced current D. temperature will drop
Description : Before servicing the device indicated as 'A' in panels #1 and #3 of the illustration, the device labeled 'CT' must __________. EL-0003 A. have the disconnected leads taped to prevent ... D. have one lead grounded to discharge static electricity for the prevention of damage to electronic components
Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. temperature will drop B. will probably burn out immediately C. will continue to operate D. will operate on reduced current