Transformer MCQ Questions and Answers

261. A tap changer is used on a transformer for adjustments in

  1. Primary voltage
  2. Secondary voltage
  3. Both primary and secondary voltages
  4. Neither primary nor secondary voltages
Answer. b

262. In a transformer, the magnitude of mutual flux is

  1. Varies at low loads and constant at high loads
  2. Low at low loads and high at high loads
  3. High at low loads and low at high loads
  4. Same at all loads
Answer. d

263. A part of primary winding also serves as secondary winding in

  1. Potential transformers
  2. Auto transformer
  3. Current transformer
  4. All types of transformers
Answer. b

264. The value of useful flux least depends on

  1. Voltage
  2. Current
  3. Load
  4. Magnetomotive force
Answer. c

265. Oil is invariably used in large transformers to

  1. Lubricate the core
  2. Insulate the core
  3. Lubricate the coil
  4. Provide fuel for operation
Answer. b

266. Voltage regulation of a transformer is negative for

  1. Inductive load
  2. Capacitive load
  3. Resistive load
  4. No-load
Answer. b

267. Consider the following statements regarding the parallel operation of the transformers.

  1. Transformers must be operated at the same frequency.
  2. Transformers must have equal voltage ratings.
  1. Only 1
  2. Only 2
  3. Both 1 and 2
  4. Neither 1 nor 2
Answer. c

268. The highest rating transformer is likely to found application in

  1. Distribution
  2. Transmission
  3. Generator
  4. Substation
Answer. c

269. In a transformer, minimum voltage regulation occurs when the power factor of the load is

  1. Leading
  2. Lagging
  3. Unity
  4. 0.8
Answer. a

270. Why is the core of the transformer built up of the laminations?

  1. To reduce eddy current loss
  2. For the convenience of fabrication
  3. No specific advantage
  4. For increasing the permeability
Answer. a

271. The maximum flux density in the core of a 250/3000 volts, 50Hz single phase transformer is 1.2 Wb/m2. If the e.m.f. per turn is 8 volt. Then what is the value of primary and secondary turns?

  1. 208 & 32
  2. 375 & 32
  3. 208 & 375
  4. 32 & 375
Answer. d

272. The efficiency of a transformer is

  1. Independent of load
  2. Maximum at no load
  3. Maximum at a given load such that variable losses equal constant losses
  4. Maximum when copper losses are zero
Answer. c

273. Transformers are rated in kVA instead of kW because

  1. Load power factor is often not known
  2. kVA is fixed whereas kW depends on load pf
  3. Total transformer loss depends on load pf
  4. It has become customary
Answer. c

274. The magnitude of magnetic flux in a transformer

  1. Decreased with an increase in load
  2. Increases with increase in load
  3. Is same at all loads
  4. Increases as load increases from zero and remain nearly constant at high loads
Answer. c

275. At low frequencies, the material used for transformer cores is

  1. Copper
  2. Silicon iron
  3. Soft iron
  4. None of these
Answer. b

276. At relatively light loads, transformer efficiency is low because

  1. Secondary output is low
  2. Transformer losses are high
  3. Fixed loss is high in proportion to the output
  4. Copper loss is small
Answer. c

277. In a transformer, the ratio of primary to secondary is 9 : 4. If power input is P, what will be the ratio of power output to the power input

  1. 4:9
  2. 9:4
  3. 5:4
  4. 1:1
Answer. d

278. In an ideal transformer the no-load primary current I0

  1. is in phase with V1
  2. Leads V1 by 90°
  3. Lags V1 by 90°
  4. Lags V1 behind 90°
Answer. d

279. Calculate the regulation of the transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage when the power factor is 0.8 lagging

  1. 3.8 %
  2. 3.5 %
  3. 1 %
  4. 5 %
Answer. b

280. A good transformer must have voltage regulation as high as possible.

  1. True
  2. False
  3. Can’t be said
  4. None of these
Answer. b

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