501 MCQ Questions on Transformer

247. The efficiency of a transformer is

(a) independent of load.
(b) maximum at no load.
(c) maximum at a given load such that variable losses equals constant losses.
(d) maximum when copper losses are zero. [BSNL TTA 2016]

248. The maximum flux density in the core of a 250/ 3000-volts, 50 Hz 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? [BSNL TTA – 2016]

(a) 208 & 32
(b) 375 & 32
(c) 208 & 375
(d) 32 & 375

249. Why is the core of the transformer built up of the laminations? [UPSSC JE – 2016]

(a) To reduce eddy current loss.
(b) For convenience of fabrication.
(c) No specific advantage.
(d) For increasing the permeability.

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

(a) leading
(c) unity
(b) lagging
(d) 0.8

251. The highest rating transformer is likely to found application in:

(a) distribution.
(b) transmission.
(c) generator.
(d) substation.

252. Current transformers for meters and relays usually have:

(a) 1 : 2 ratio
(b) 5 : 1 ratio
(c) 5-A secondary’s
(d) 5-A primary’s

253. Consider the following statements regarding parallel operation of transformer’s

1. Transformers must be operated at same frequency.
2. Transformers must have equal voltage ratings.

(a) Only 1
(b) Only 2
(c) Both 1 and 2
(d) Neither 1 nor 2

254. Voltage regulation of a transformer is negative for

(a) inductive load.
(c) resistive load.
(b) capacitive load.
(d) no load.

255. Oil is invariably used in large transformers to

(a) lubricate the core.
(b) insulate the core.
(c) lubricate the coil.
(d) provide fuel for operation.

256. The value of useful flux least depends on:

(a) voltage.
(c) load.
(b) current.
(d) magneto motive force.

257. A part of primary winding also serves as secondary winding in:

(a) potential transformers.
(b) auto transformer.
(c) current transformer.
(d) all types of transformers.

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

(a) varies at low loads and constant at high loads.
(b) low at low loads and high at high loads.
(c) high at low loads and low at high loads.
(d) same at all loads.

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

(a) primary voltage.
(b) secondary voltage.
(c) both primary and secondary voltages.
(d) neither primary nor secondary voltages.

260. Ferrite cores are used in high frequency transformer because it has:

(a) low resistance.
(b) high resistance.
(c) high hysteresis.
(d) low permeability.

261. A transformer having a turn ratio 1 : 5 and a resistance of 1000 ohms is connected across the secondary terminals, the resistance to the current flowing in the primary will be:

(a) 10 ohm
(b) 20 ohm
(c) 40 ohm
(d) 60 ohm

262. In a power transformer, at full load, the efficiency is:

(a) minimum.
(b) maximum.
(c) half the normal efficiency.
(d) 20% of the maximum efficiency.

263. Which of the following losses in transformer is zero even at full load?

(a) Core loss
(b) Friction loss
(c) Eddy current loss
(d) Hysteresis loss

264. Basically, a booster is a :

(a) synchronous motor.
(b) capacitor.
(c) inductor.
(d) transformer.

265. Which of the following statement is true about the windings of a transformer?

(a) Windings are conductively linked.
(b) Windings are inductively linked.
(c) Windings are not linked at all.
(d) Windings are electrically linked.

266. No winding resistance means

(a) primary windings have constant resistance.
(b) secondary windings have infinite resistance.
(c) no ohmic power loss.
(d) infinite resistive voltage drop.

267. Which of the following is not a type of construction used for single phase transformer?

(a) Core type
(b) Shell type
(c) Berry type
(d) Roof type

268. An ideal transformer has

(a) very high losses
(b) very low losses
(c) moderate losses
(d) no losses

269. Which of the following statement/s is/are true?

1. DC supply cannot be used for transformers.
2. The transformer works on the principle of mutual induction.

Choose the correct answer from the options given below.
(a) Only 1
(b) Both 1 and 2
(c) Only 2
(d) Neither 1 nor 2

270. Short circuit test on transformer is also known as:

(a) capacitance test.
(b) impedance test.
(c) inductance test.
(d) current test. [RRB JE – 2015]

271. No load loss of a transformer has two components. They are eddy current and hysteresis loss. In which part of a transformer hysteresis will occur? [DMRC – 2015]

(a) Core
(b) Breather
(c) Transformer oil
(d) Conservator

272. What principle makes the instrument transformer working?

(a) Self induction
(b) Lenz law
(c) Mutual induction
(d) Fleming’s right hand rule

273. Step up transformer increase

(a) power.
(b) power factor.
(c) frequency.
(d) voltage.

274. Which of the following prevents the damage to a transformer due to lightening? [DMRC – 2015]

(a) Buchholz relay
(b) Conservator
(c) Breather
(d) Horn gap

275. The frequency of ac supply is increased keeping impressed voltage of a transformer constant. Its core loss will:

(a) increase.
(b) decrease.
(c) not change.
(d) depends upon the design of transformer.

276. Power transformers are designed with:

(a) low leakage reactances.
(b) high leakage reactances.
(c) high all day efficiency.
(d) low full load voltage regulation.

277. A delta/delta connected three-phase transformer can be connected in parallel with:

(a) star/delta.
(b) delta/star.
(c) star/star.
(d) star/zigzag. [DMRC – 2015]

278. To conduct Sumpners test on a transformer

(a) only one transformer is sufficient.
(b) two identical transformers are needed.
(c) two un-identical transformers are needed.
(d) at least three transformers are necessary.

279. Distribution transformers have core losses:

(a) more than full load copper losses.
(b) equal to full load copper losses.
(c) less than full load copper losses.
(d) negligible compared to full load copper losses.

280. Distribution transformers have the rating of

(a) up to 50 kVA
(b) up to 100 kVA
(c) up to 150 kVA
(d) up to 200 kVA [RRB JE – 2015]