Transformer MCQ Questions and Answers

361. The ordinary efficiency of a given transformer is maximum when ________

  1. It runs at half full-load
  2. It runs at full-load
  3. Its copper loss equals iron loss
  4. It runs overload
Answer. c

362. When a 400-Hz transformer is operated at 50 Hz, its kVA rating is _________

  1. Reduced to 1/8
  2. Increased 8 times
  3. Unaffected
  4. Determined by the load on secondary
Answer. a

363. During the short-circuit test, the iron loss of a transformer is negligible because ________

  1. The entire input is just sufficient to meet copper losses only
  2. Voltage applied across the HV (High voltage) side is a small fraction of the rated voltage and so its flux
  3. Iron core becomes fully saturated
  4. Supply frequency is held constant
Answer. b

364. Under the operating condition, the secondary of a current transformer is always short circuit because ______

  1. It protects the primary circuits
  2. It is safe for human beings
  3. It avoids core saturation and high voltage induction
  4. None of these
Answer. c

365. Compared to the secondary of a loaded step-up transformer, the primary has ________

  1. Lower voltage and higher current
  2. Higher voltage and lower current
  3. Lower voltage and lower current
  4. Higher voltage and higher current
Answer. a

366. Centrifugal method of reconditioning transformer oil is effective for the removal of

  1. Water
  2. Dissolved gases
  3. Solid impurities
  4. All options are correct
Answer. c

367. The main purpose of using core in a transformer is to

  1. Decrease iron losses
  2. Prevent eddy current loss
  3. Eliminate magnetic hysteresis
  4. Decrease reluctance of the common magnetic
Answer. d

368. In relation to a transformer, the ratio 20 : 1 indicates that

  1. There are 20 turns on primary and one turn on secondary
  2. Secondary voltage is 1/20th of primary voltage
  3. Primary current is 20 times greater than secondary current
  4. For every 20 turns on primary, there is one turn on secondary
Answer. d

369. Under heavy loads, transformer efficiency is comparatively low because

  1. Voltage drops both in primary and secondary becomes large
  2. Secondary output is much less as compared to the primary input
  3. Copper loss becomes high in proportion to the output
  4. Iron loss is increased considerably
Answer. c

370. The short-circuit test in a transformer is used to determine

  1. Iron loss at any load
  2. Copper loss at any load
  3. Hysteresis loss
  4. Eddy-current loss
Answer. b

371. Which of the following transformers is the smallest?

  1. 1 kVA, 50 Hz
  2. 1 kVA, 200 Hz
  3. 1 kVA, 400 Hz
  4. 1 kVA, 600 Hz
Answer. d

372. Two transformers operating in parallel will share the load depending upon their

  1. Efficiency also
  2. Ratings also
  3. Leakage resistance
  4. None of these
Answer. b

373. A transformer has a core loss of 64 W and copper loss of 144W, when it is carrying 20% overload current. The load at which this transformer will operate at the maximum efficiency

  1. 80%
  2. 66%
  3. 120%
  4. 44%
Answer. a

374. What is the efficiency of the transformer compared with that of electrical motors of the same power?

  1. Much smaller
  2. Somewhat smaller
  3. About same
  4. Much higher
Answer. d

375. For a 100% efficient transformer, the primary winding has 1000 turns and the secondary 100 turns. If the power input to the above transformer is 1000 watts, the power output is

  1. 1000 W
  2. 100 W
  3. 10 W
  4. 10 kW
Answer. b

376. If the AC supply to transformer is replaced by DC _________

  1. The primary winding will burn
  2. The secondary winding will burn
  3. The transformer has no effect
  4. All options are correct
Answer. a

377. The voltage regulation of a transformer having a copper loss 1% of output and percentage reactance drop of 5% and power factor 0.9 lagging is _________

  1. 3.08%
  2. 3%
  3. -3.08%
  4. 3.8%
Answer. a

378. Distribution transformers must be designed to have maximum efficiency at

  1. Full load
  2. No-load
  3. About 90%of the full load
  4. About 50% of the load
Answer. d

379. Which of the following part of a transformer consists of a small vessel which contains a drying agent?

  1. Conservator
  2. Breather
  3. Oil tank
  4. Windings
Answer. b

380. In a transformer, the occurrence of dimensional changes both perpendicular and parallel to the directional of magnetization is referred to as

  1. Damping
  2. Magnetostriction
  3. Coupling
  4. Oscillation
Answer. b
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