Transformer MCQ Questions and Answers

341. High silicon content steel is used for transformer core construction to

  1. Improve cooling of core and yoke
  2. Reduce hysteresis loss
  3. Reduce eddy current loss
  4. Reduce weight of steel
Answer. b

342. Open circuit test on a transformer gives

  1. Total loss
  2. Insulation resistance
  3. Core loss
  4. Cu loss
Answer. c

343. A 2000/200V, 20KVA transformer has 66 turns in the secondary. The number of primary turns are

  1. 660
  2. 440
  3. 770
  4. 330
Answer. a

344. An electric transformer is

  1. A magnetic device that consists of two or more multi-turn coils would on a common core
  2. A magnetic device that consists of only two coils wound on a common core
  3. An electric device that consists of two or more multi-turn coils wound on a common core
  4. An electric device that consists of only two coils wound on a common core
Answer. c

345. All-day efficiency of a transformer is defined as the ratio of output to input in

  1. kVA at a particular instant
  2. kWh during 24 hours
  3. kVARh at a particular instant
  4. kW during 24 hours
Answer. b

346. If the voltage ratio of the transformer is 1 : 30 then the ratio of primary and secondary turns will be

  1. 2 : 30
  2. 1 : 30
  3. 1 : 3
  4. 2 : 10
Answer. b

347. Which machine is protected by Buchholz’s relay?

  1. Generators
  2. Transformers
  3. Motors
  4. Transmission lines
Answer. b

348. How the leakage flux is minimized in an actual transformer?

  1. Interleaving and sectionalizing both primary and secondary windings
  2. Sectionalizing primary windings only
  3. Interleaving and sectionalizing secondary windings only
  4. Sectionalizing secondary windings only
Answer. a

349. A single-phase, 10KVA, 2400/240V, 60Hz distribution transformer has the following characteristics:

Core loss at full voltage is 100W and copper loss at half is 60W. what is the efficiency of the transformer when it delivers a full load at 0.8 p.f. lagging?

  1. 93.54%
  2. 94.52%
  3. 95.92%
  4. 97.53%
Answer. c

350. A single-phase, 10kVA, 220/110V, 50 Hz transformer is connected to a 220V supply. It draws rated current at 0.8 p.f leading. The transformer may be considered ideal. What is the kVA rating of the load?

  1. 10
  2. 20
  3. 15
  4. 8
Answer. a

351. The steel used in the transformer core is of high silicon content to

  1. Produce low permeability and low hysteresis loss
  2. Produce high permeability and low hysteresis loss
  3. Produce low permeability and low eddy current loss
  4. Produce high permeability and low eddy current loss
Answer. b

352. Dissolve gas analysis of transformer oil is carried out to determine

  1. Condition of transformer oil
  2. Condition of transformer
  3. Condition of bushings
  4. Condition of bushing stud
Answer. b

353. When operating, two or more transformers in parallel, the % impedance of these transformers should be

  1. Inversely proportional to MVA rating of transformers
  2. Proportional to MVA rating of transformers
  3. Same
  4. Such that actual impedance of all transformers would be same
Answer. b

354. The all-day efficiency of a transformer depends primarily on

  1. Its copper losses
  2. The amount of load
  3. The duration of load
  4. Both the amount and duration of load
Answer. d

355. A 500 kVA transformer has a constant loss of 500 W and copper losses at full load are 2000 W. Then at what load, is the efficiency maximum?

  1. 250 kVA
  2. 500 kVA
  3. 1000 kVA
  4. 125 kVA
Answer. a

356. Stray losses are the sum of

  1. Iron and mechanical losses
  2. Copper and iron losses
  3. Copper and mechanical losses
  4. None of these
Answer. a

357. Sludge formation in transformer oil is due to which one of the following?

  1. Ingress of dust particles and moisture in the oil
  2. Appearance of small fragments of paper, varnish, cotton and other organic materials in the oil
  3. Chemical reaction of transformer oil with the insulating materials
  4. Oxidation of transformer oil
Answer. b

358. The all-day efficiency of a distribution transformer will be high with low

  1. Copper losses
  2. Iron losses
  3. Operating temperature
  4. Copper losses as well as iron losses
Answer. d

359. The advantage of putting tappings at the phase ends of a transformer is

  1. To obtain a fine variation of voltage
  2. To operate with ease
  3. To reduce the number of bushings
  4. To obtain better regulation
Answer. c

360. While conducting short-circuit test on a transformer the following side is short-circuited ______

  1. HV side
  2. LV side
  3. Primary side
  4. None of these
Answer. b
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