Transformer MCQ Questions and Answers

221. The iron loss in a 100 KVA transformer is 1 KW and full load copper losses are 2 KW. The maximum efficiency occurs at a load of

  1. 100 KVA
  2. 70.7 KVA
  3. 141.4 KVA
  4. 50 KVA
Answer. b

222. In a 1-phase transformer, the copper loss at full load is 600 Watts. At half of the full load, the copper loss will be

  1. 150Watts
  2. 75 Watts
  3. 600 Watts
  4. 300 Watts
Answer. a

223. The high-voltage and low-voltage winding resistances of a distribution transformer of 100 KVA, 1100/220 volts. 50Hz are 0.1 Ω and 0.004 Ω respectively. The equivalent resistances referred to high-voltage side and low-voltage side are respectively.

  1. 2.504 Ω and 0.2 Ω
  2. 0.2 Ω and 0.008 Ω
  3. 0.10016 Ω and 2.504 Ω
  4. 0.008 Ω and 0.10016 Ω
Answer. b

224. If the frequency of input voltage of a transformer is increased keeping the magnitude of the voltage unchanged, then

  1. Both hysteresis loss and eddy current loss in the core will increase.
  2. Hysteresis loss will increase but eddy current loss will decrease.
  3. Hysteresis loss will increase but eddy current loss will remain unchanged
  4. Hysteresis loss will decrease but eddy current loss will increase
Answer. c

225. A 10 ohm resistive load is to be impedance matched by a transformer to a source with 6250 Ω of internal resistance. The ratio of primary to secondary turns of the transformer should be

  1. 15
  2. 20
  3. 25
  4. 10
Answer. c

226. Low voltage windings are placed near to the core in the case of concentric windings because

  1. It reduces hysteresis loss
  2. It reduces eddy current loss
  3. It reduces insulation requirement
  4. It reduces leakage fluxes
Answer. c

227. A stepped core is used in transformers in order to reduce

  1. Volume of iron
  2. Volume of copper
  3. Iron loss
  4. Reluctance of core
Answer. b

228. When a 400-Hz transformer is operated at 50Hz, its rating is

  1. Reduced to 1/8
  2. Increased 8 times
  3. Unaffected
  4. Increased 64 times
Answer. a

229. The rating of a transformer is expressed in

  1. KVA
  2. KW
  3. HP
  4. W
Answer. a

230. Short circuit test on transformer is conducted to obtain

  1. Core losses at any load
  2. Hysteresis loss only
  3. Ohmic loss
  4. Eddy current loss only
Answer. c

231. Total losses occurring in a transformer when it is operating at its maximum efficiency are 2000 W. The total copper losses at this load are

  1. 2000 W
  2. 1000 W
  3. 1500 W
  4. 800 W
Answer. b

232. One 200 V, 100 W bulb is connected in series with primary of a 200 V, 10 KVA transformer. If its secondary is left open-circuited then the bulb would have

  1. Full brightness
  2. Poor brightness
  3. A little less than full brightness
  4. More than full brightness
Answer. b

233. The primary to secondary turns ratio of a transformer is 1 : 2. If the primary is connected to 50 Hz supply, then the frequency of secondary supply in Hz is

  1. 50 Hz
  2. 25 Hz
  3. 100 Hz
  4. 150 Hz
Answer. a

234. Buchholz relay is used on

  1. Welding transformers
  2. Air-cooled transformers
  3. Furnace transformers
  4. Oil cooled transformers
Answer. d

235. The power transformer is a constant

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

236. No-load test on a transformer is carried out to determine

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

237. The equivalent resistance of the primary of a transformer whose transformation ratio is 5 and resistance is 0.1 Ω. When referred to the secondary will be

  1. 0.5 Ω
  2. 2.5 Ω
  3. 0.02 Ω
  4. 0.004 Ω
Answer. b

238. A transformer steps up or down

  1. a.c. only
  2. d.c. only
  3. either a.c. or d.c.
  4. a.c. mixed with d.c.
Answer. a

239. When power is drawn from a secondary coil of the transformer, the dynamic resistance

  1. Increases
  2. Decreases
  3. Remains constant
  4. Changes erratically
Answer. a

240. Distribution transformers have core losses

  1. More than full load copper losses
  2. Equal to full load copper losses
  3. Less than full load copper losses
  4. Negligible compared to full load copper losses
Answer. c
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