Transformer MCQ Questions and Answers

301. The core of the transformer is made of good quality material like CRGO steel to minimize

  1. Eddy current loss
  2. Full load copper loss
  3. Hysteresis loss
  4. No-load coper loss
Answer. c

302. For a minimum weight of a transformer, the weight of iron should be

  1. Equal to weight of copper
  2. Less than the weight of copper
  3. Greater than the weight of copper
  4. Zero
Answer. a

303. The voltage transformation ratio of a transformer is equal to the ratio of

  1. Primary turns to secondary turns
  2. Secondary current to primary current
  3. Secondary induced e.m.f to primary induced e.m.f.
  4. Secondary terminal voltage to primary applied voltage
Answer. c

304. Which of the following is the most likely source of harmonics in a transformer?

  1. Poor insulation
  2. Overload
  3. Loose connections
  4. Core saturation
Answer. d

305. When a transformer is run at its rated voltage but at a reduced frequency, its

  1. Flux density remains unaffected
  2. Iron losses are reduced
  3. Core flux density is reduced
  4. Core flux density is increased
Answer. d

306. A transformer can have zero voltage regulation at a

  1. Laggingpower factor
  2. Zero power factor
  3. Unity power factor
  4. Leading power factor
Answer. d

307. Which of the following is not a routine test on transformers?

  1. Core insulation voltage test
  2. Impedance voltage test
  3. Polarity test
  4. Radio interference test
Answer. c

308. The power transformer is a constant

  1. Voltage device
  2. Current device
  3. Power device
  4. Main flux device
Answer. d

309. The Power transformers are designed to have maximum efficiency at

  1. No-load
  2. 70% full load
  3. 50% full load
  4. Nearly full load
Answer. d

310. No-load on a transformer is carried out to determine the

  1. Copper loss
  2. Magnetizing current
  3. Magnetizing current and loss
  4. Efficiency of the transformer
Answer. c

311. A 50 Hz transformer having equally hysteresis and eddy current losses at the rated excitation is operated at 45 Hz at 90 % of its rated voltage. Compared to the rated operating point, the core losses under this condition

  1. Reduced by 10 %
  2. Reduced by 19 %
  3. Reduced by 14.5 %
  4. Remain unchanged
Answer. c

312. A 10 KVA, 400 V/200V single-phase transformer with 10% impedance draws a steady short circuit line current of

  1. 50 A
  2. 150 A
  3. 250 A
  4. 350 A
Answer. c

313. A current transformer has double turn primary and a 100 turn secondary winding. The secondary draws current of 6 Amp and magnetizing ampere-turns is 60 Amp. What is the actual transformation ratio?

  1. 100.5
  2. 101
  3. 50.24
  4. 25.12
Answer. c

314. Transformer utilization factor of TUF = K signifies

  1. That transformer for rectifier should be 1/K times larger than that for ac source
  2. That transformer for rectifier should be K-1 times larger than that for ac source
  3. That transformer for rectifier should be 1-K times larger than that for ac source
  4. That transformer for rectifier should be K time larger than that for ac source
Answer. a

315. The parallel operation of 2 transformers with which of the following vector groups is possible?

  1. Yd11 and Yd1
  2. Yd11 and Yd6
  3. Dd1 and Yd1
  4. Dy1 andYy1
Answer. a

316. The exciting current in a single-phase transformer consists of

  1. Fundamental and odd harmonics
  2. Odd harmonics
  3. Even harmonics
  4. Fundamental component current
Answer. a

317. A transformer is operating at the no-load condition and draws an exciting current (I0) of 5 A when the primary side is connected to a 120 V, 60 Hz source. By doing a wattmeter test, the iron losses are equal to 180 Watts. The reactive power absorbed by the core is

  1. 600 VAR
  2. 572 VAR
  3. 180 VAR
  4. 360 VAR
Answer. b

318. A transformer rated 250 kVA, 4.16 kV/480 V, 60 Hz has an impedance of 5.1%. calculate the total impedance of the transformer referred to the primary

  1. 69 Ω
  2. 0.92 Ω
  3. 3.52 Ω
  4. 0.51 Ω
Answer. c

319. Which test is used to determine the magnetizing impedance of a transformer?

  1. Short-circuit test
  2. Impulse test
  3. Load test
  4. Open-circuit test
Answer. d

320. Find the transformer tap ratios when the receiving end voltage (Vr) is equal to the sending end voltage (Vs). The high-voltage line operates at 220 kV and transmits 80 MW at 0.8 power factor and the impedance of the line is (40+j140) Ω. (Assume that tstr = 1)

  1. 0.6
  2. 0.7
  3. 0.9
  4. 0.8
Answer. c
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