Transformer MCQ Questions and Answers

281. In a transformer, the resistance between the primary and secondary must be

  1. Zero
  2. 1 kΩ
  3. 100 kΩ
  4. Infinite
Answer
Answer. d

282. Current drawn by the primary of a transformer which steps down from 220 V to 22 V to operate a device having an impedance of 220 Ω will be

  1. 1 A
  2. 0.1 A
  3. 0.01 A
  4. 10 A
Answer
Answer. c

283. In a step-up transformer, turn’s ratio is 1 : 2. A Leakage cell (emf 1.5V) is connected across the primary. The voltage across the secondary is

  1. 3.0 V
  2. 0.75 V
  3. 0 V
  4. 1.5 V
Answer
Answer. c

284. In order to achieve all-day efficiency in a transformer

  1. The copper losses should be less
  2. The operating temperature should be low
  3. The shell-type construction should be used
  4. The iron losses should be less
Answer
Answer. a

285. For higher voltage ranges __________ transformers are used.

  1. Core type
  2. Shell type
  3. Both core type & Shell type
  4. None of these
Answer
Answer. a

286. A 200 KVA transformer has an iron loss of 1 kW and full load copper loss of 2 kW. Its load kVA corresponds to maximum efficiency is

  1. 100 kVA
  2. 70.7 kVA
  3. 200 kVA
  4. 141.4 kVA
Answer
Answer. d

287. A T-T transformer can not be paralleled with __________ transformer.

  1. V-V
  2. Y-Δ
  3. Y-Y
  4. Δ-Δ
Answer
Answer. b

288. An ideal transformer does not change

  1. Voltage
  2. Power
  3. Current
  4. None of the above
Answer
Answer. b

289. In a single-phase transformer the magnitude of leakage reactance is twice that of resistance of both primary and secondary. With secondary short-circuited, the input power factor is

  1. \frac{1}{\sqrt{3}}
  2. \frac{1}{\sqrt{5}}
  3. \frac{2}{\sqrt{5}}
  4. \frac{1}{3}
Answer
Answer. c

290. The emf per turn for a single phase 2200/220V, 50Hz transformer is approximately 12V. The number of primary and secondary turns are

  1. 18,183
  2. 183,18
  3. 155,26
  4. 172,21
Answer
Answer. b

291. The maximum efficiency of a 200 kVA transformer having an iron loss of 1800 W and full load copper loss of 3200 W occurs at

  1. 100 kVA
  2. 150 kVA
  3. 200 kVA
  4. 125 kVA
Answer
Answer. b

292. Which test is performed to determine core loss at full load of a transformer?

  1. Short circuit test
  2. Sumpner test
  3. Open circuit test
  4. None of these
Answer
Answer. c

293. If the transformer frequency is changed from 50 Hz to 60 Hz, the ratio of eddy current loss at 60Hz to 50Hz at constant voltage will be

  1. 5/6
  2. 6/5
  3. 25/36
  4. 36/25
Answer
Answer. d

294. A pulse transformer is used in a driver circuit

  1. To prevent dc triggering
  2. To shape the trigger signal
  3. To generate high-frequency pulses
  4. To provide high-frequency pulses
Answer
Answer. d

295. Biased differential protection for transformers are used for

  1. Low fault settings and high operating speeds
  2. High fault settings and high operating speeds
  3. Low fault setting and low operating speeds
  4. High fault setting and low operating speeds
Answer
Answer. a

296. Single-phase transformer voltage is maximum when the primary and secondary coils are

  1. Aligned along the same axis
  2. Have a phase shift of 120° from each other
  3. Normal to each other
  4. Have a phase shift of 90° to each other
Answer
Answer. a

297. When moist air passes through a bed of silica gel, the

  1. Dry bulb temperature of air decreases
  2. Dry bulb temperature of air increases
  3. Specific humidity of air increases
  4. It undergoes adiabatic saturation
Answer
Answer. b

298. The full-load copper loss (Pcu) and iron loss (Pi) of the transformer are 6400 Watts and 5000 Watts, respectively. The copper loss (Pc) and iron loss at the half-load will be, respectively

  1. 1600 Watts and 5000 Watts
  2. 3200 Watts and 5500 Watts
  3. 3200 Watts and 2500 Watts
  4. None of these
Answer
Answer. a

299. The iron losses in a 100 kVA transformer are 1 kW and the full load copper losses are 2 kW, then maximum efficiency occurs at a load of

  1. 100\sqrt{2}
  2. \frac{100}{\sqrt{2}}
  3. 50 kVA
  4. None of these
Answer
Answer. b

300. What is the cause of occurrence of stray load losses in the transformer?

  1. under frequency operation
  2. overloading
  3. poor cooling
  4. leakage flux
Answer
Answer. d
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