501 MCQ Questions on Transformer

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

(a) increases.
(b) decreases.
(c) remains constant.
(d) changes erratically.

282. A transformer steps up or down:

(a) a.c. only.
(b) d.c. only.
(c) either a.c. or d.c.
(d) a.c. mixed with d.c.

283. The equivalent resistance of the primary of a transformer whose transformation ratio is 5 and resistance is 0.1 ohms, when referred to the secondary will be:

(a) 0.5 ohms
(b) 2.5 ohms
(c) 0.02 ohms
(d) 0.004 ohms

284. Buchholz relay is used on:

(a) welding transformers.
(b) air cooled transformers.
(c) furnace transformers.
(d) oil cooled transformers.

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

(a) 50 Hz
(b) 50/2 Hz
(c) 2 x 50 Hz
(d) 3 × 50 Hz

286. 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:

(a) full brightness.
(b) poor brightness.
(c) a little less than full brightness.
(d) more than full brightness.

287. In a Y-Y system, a line voltage of 220 V produces a phase voltage of

(a) 381 V
(b) 311 V
(c) 220 V
(d) 127 V

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

(a) reduce to 1/8.
(b) increased 8 times.
(c) unaffected.
(d) increased 64 times.

289. What is the use of higher flux density in the transformer design?

(a) For increasing the weight/kVA.
(b) For decreasing the weight/kVA.
(c) For reducing iron losses.
(d) For improving insulation.

290. When a sinusoidal exciting current is applied to a transformer, what is the mutual flux produced?

(a) Flat top
(c) Zero
(b) Sinusoidal
(d) Second harmonic only

291. The efficiency of a transformer at full load, 0.8 p.f. lagging is 95%. What will its efficiency at full load, 0.8 p.f. leading be?

(a) 85%
(c) 95%
(b) 90%
(d) 100%

292. A transformer is connected to a constant voltage supply. As the supply frequency increases, what happens to the magnetic flux in the core?

(a) Decreases
(b) Increases towards saturation
(c) Becomes zero
(d) Become constant

293. The degree of mechanical vibrations produced by the laminations of a transformer depends on

(a) tightness of clamping.
(b) gauge of laminations.
(c) size of laminations.
(d) all of the above.

294. Which of the following is the main advantage of an auto-transformer over a two winding transformer?

(a) Hysteresis losses are reduced.
(b) Saving in winding material.
(c) Copper losses are negligible.
(d) Eddy losses are totally eliminated.

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

(a) flux density remains unaffected.
(b) iron losses are reduced.
(c) core flux density is reduced.
(d) core flux density is increased.

296. If the supply frequency to the transformer is increased, the iron loss will

(a) no change.
(b) decrease.
(c) increase.
(d) any of the above.

297. In an actual transformer the iron loss remains practically constant from no load to full load because

(a) value of transformation ratio remains constant.
(b) permeability of transformer core remains constant.
(c) core flux remains practically constant.
(d) primary voltage remains constant.

298. The transformer equation V₁I₁ = V₂I₂, is the manifestation of

(a) Ampere’s law.
(b) Coloumb’s law.
(c) Law of energy conservation.
(d) Biot Savart’s law.

299. Which three-phase connection can be used in a transformer to introduce a phase difference of 30° between its output and corresponding input line voltages? [RRB SSE – 2014]

(a) Star-Delta
(b) Star-Star
(c) Delta-Delta
(d) Delta-Zigzag

300. With core type transformers, the limbs are stepped to

(a) reduce the zinc material and, therefore, zinc loss.
(b) reduce the conductor material and, therefore I²R loss.
(c) provide better cooling.
(d) supply more mechanical strength to the core. [MP JE – 2016]

301. Which one of the following relay has the capability of anticipating the possible major fault in a transformer? [MP JE – 2015]

(a) Buchholz relay
(b) Over current relay
(c) Differential relay
(d) Over flux relay

302. In Merz Price percentage differential protection of Δ-Y transformer, the CT secondary connection in the primary and secondary windings of the transformer would be in the form of

(a) Δ-Y
(b) Y-Δ
(c) Δ-Δ
(d) Y-Y

303. Under heavy loads, transformer efficiency is comparatively low because

(a) voltage drop both in primary and secondary becomes large.
(b) secondary output is much less as compared to primary input.
(c) copper loss becomes high in proportional to the output.
(d) iron loss is increase considerably.

304. Transformer oil is used as

(a) insulant only.
(b) coolant only.
(c) inert medium.
(d) both insulant and coolant.

305. Out of following choices for poly-phase transformer connections which one will you select for three-to-two phase?

(a) Scott
(b) Star/Star
(c) Double Scott
(d) Star/double

306. Before disconnecting an ammeter from an energized current transformer circuit, the current transformer

(a) primary should be opened.
(b) secondary should be opened.
(c) primary should be shorted.
(d) secondary should be shorted.

307. The essential feature of an auto-transformer is that it

(a) is more suited for single-phase supply.
(b) is completely automatic in its operation.
(c) uses only one winding.
(d) is particularly suited for situations where voltage transformation ratio exceeds unity.

308. When a given transformer is operating at its rated voltage with reduced frequency, its

(a) iron losses are reduced.
(b) flux density remains unaffected.
(c) core flux density is increased.
(d) core flux density is reduced.

309. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

(a) short-circuiting of the secondaries.
(b) power factor of one of the transformers is leading while that of the other is lagging.
(c) loading of the transformers not in proportion to their kVA ratings.
(d) transformers having higher copper losses will have negligible core losses.

310. The cold rolled grain oriented steel has ……… permeability in the direction of the grain orientation.

(a) minimum
(b) maximum
(c) nil
(d) none of these

311. The machine in which energy transfer happens both through induction and conduction, in called

(a) two winding transformer.
(b) auto transformer.
(c) three phase induction motor.
(d) single phase induction motor.

312. Transformer oil should have

(a) high flash point.
(b) high viscosity.
(c) high sludging tendencies.
(d) none of the above.

313. In star-star connected transformer

(a) line voltage is equal to phase voltage.
(b) line voltage is equal to √3 phase voltage.
(c) there is no line current.
(d) there flows no phase current. [UPSSSC – 2015]

314. 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.

315. A CT is connected in ……… with the line. [UPSSSC – 2015]

(a) series
(b) across
(c) both a and b
(d) not connected