501 MCQ Questions on Transformer

351. For an ideal transformer, the incorrect statement is:

(a) transformer core has infinity permeability.
(b) primary winding has zero resistance.
(c) infinite resistive voltage drop.
(d) zero magnetic leakage flux.

352. Auto transformer has:

1. higher efficiency
2. lower p.u. impedance
3. high voltage regulation

as compared to 2-winding transformer.
Which of these is/are INCORRECT?
(a) Only 1
(b) Only 3
(c) 1, 2 and 3
(d) None of these

353. Open circuit test and short circuit test does not determines

1. Parameters of equivalent circuit
2. Constant losses
3. Voltage regulation
4. Efficiency

INCORRECT amongst the given is/are:
(a) 1, 2, 3 and 4
(b) Only 1
(c) Only 3
(d) None of these

354. An additional condition for parallel operation of three-phase transformers over single-phase transformers is that

(a) the transformers should belong to the same vector group.
(b) ratios of the winding resistance to resistances for the transformers should be equal.
(c) the transformes should have the same kVA ratings.
(d) the transformers should not belong to the same vector group.

355. The inrush current of a transformer at no load is maximum if the supply voltage is switched on

(a) at peak voltage value.
(b) at zero voltage value.
(c) at half voltage value.
(d) at 0.866 time voltage value.

356. Two transformers, each having iron loss of P_i watts and full-load copper loss of P_c, are put to back to back test and full-load current is allowed to flow through the secondaries, the total input power will be

(a) 2P_i
(b) P_c
(c) P_i + P_c
(d) 2(P_i + P_c)

357. The phase difference between any two successive third harmonic voltages in 3-φ transformers is

(a) zero radians
(b) π/2 radians
(c) π/3 radians
(d) 2π/3 radians

358. A transformer has maximum efficiency at ¾ of full load. The ratio of its iron loss (P_i) and full load copper loss (P_c), is

(a) 3/4
(b) 16/9
(c) 9/16
(d) 4/3

359. An Isolation transformer has primary to secondary turn’s ratio of

(a) 1 : 1
(b) 1 : 2
(c) 2 : 1
(d) 1 : 3

360. The saving in copper achieved by converting a 2 winding transformer into and auto-transformer is determined by

(a) voltage transformation ratio.
(b) load on the secondary.
(c) iron losses in the transformer.
(d) permeability of core material.

361. Which one of the following connection of 3 phase transformers will give highest secondary voltage?

(a) Delta primary, Delta secondary
(b) Delta primary, Star secondary
(c) Star primary, Star secondary
(d) Star primary, Delta secondary [UPRVUNL AE – 2016]

362. Transformers are connected in parallel for supplying:

(a) load in excess of rating of an existing transformer.
(b) load less than the rating of an existing transformer.
(c) load equal to the rating of an existing transformer.
(d) load less or equal to the rating of an existing transformer.

363. Distribution Transformers

1. Have good voltage regulation
2. Are designed for small value of current.

Which of these is/are correct?
(a) 1
(b) 2
(c) Both 1 and 2
(d) Neither 1 nor 2

364. Which of the following statements regarding a shell type transformer is INCORRECT?

(a) It provides shorter magnetic path.
(b) Magnetizing current is lesser as compared to core type.
(c) Natural cooling is quite good.
(d) It gives better support against electromagnetic forces between current carrying transformer.

365. Core of transformer has:

1. High reluctance
2. High permeability
3. Silicon steel lamination

Correct amongst the given is/are
(a) Only 1
(b) 2 and 3
(c) Only 3
(d) 1 and 3

366. In a step up transformer:

(a) N_p > N_s
(b) N_s > N_p
(c) N_s + N_p
(d) Varies accordingly

367. The best material for the core of transformer is:

(a) mild steel.
(b) stainless steel.
(c) aluminium.
(d) soft iron. [UPPCL (JE) 2016]

369. If the output power of a transformer is 600 W whereas the losses are 200 W, the efficiency of the transformer will be:

(a) 66.6%
(b) 75%
(c) 50%
(d) 41.4% [UPPCL JE – 2016]

370. Due to magnetostriction, which one of the following problem occurs in the transformer?

(a) Oil leakage
(b) Humming sound
(c) Speed destruction
(d) No problem occurs [UPPCL JE 2016]

371. In an ideal transformer

(a) The flux is 180° out of phase with induced emf.
(b) The applied voltage is in phase with the induced emf.
(c) The phase angle between applied voltage and emf is 90°.
(d) The magnetizing current is in phase with the flux. [UPPCL AE – 2015]

372. The source of harmonics in a transformer supplied by a voltage source of fundamental frequency is:

(a) overloading.
(b) poor insulation.
(c) saturation of core.
(d) loose laminations.

373. The winding used in 3-phase shell type transformer is

(a) circular.
(b) cylindrical.
(c) sandwich type.
(d) rectangular. [RRB SSE – 2015]