Transformer MCQ Questions and Answers

321. A phase shift transformer is designed to control 150 MVA on a phase line. The phase angle is variable between zero and ±15°. The basic power rating of the transformer is

1. 150 MVA
2. 56 MVA
3. 75 MVA
4. 750 MVA

322. A single-phase transformer rated at 3000 kVA, 69 kV/4.16 kV, 60Hz has a total internal impedance Z_p of 127 Ω, referred to the primary side. Find the primary current if the secondary side is accidentally short-circuited.

1. 43.5 A
2. 543 A
3. 9006 A
4. 721 A

323. The efficiency of a power-transformer under no-load condition is approximate

1. 75%
2. 50%
3. 25%
4. None of the above

324. A 600 KVA, single-phase transformer when working at unity power factor has an efficiency of 92% at full load. The total losses at full load are

1. 104.4 kW
2. 48 kW
3. 52.2 kW
4. 26.1 kW

325. A Transformer has full load copper losses of 800 Watts & core loss of 600 Watts. Total losses at no load will be

1. 1400 W
2. 1100 W
3. 100 W
4. 600 W

326. The full-load copper loss in a transformer is 1600 W. At a half-load, the copper losses will be

1. 6400 W
2. 1600 W
3. 800 W
4. 400 W

327. For a transformer of the full-load, copper losses are P and iron losses are Q. Then the load at which these two losses would be equal is given by

1. Full load x $\frac{P}{Q}$
2. Full load x $\frac{Q}{P}$
3. Full load x $\sqrt(\frac{P}{Q})$
4. Full load x $\sqrt(\frac{Q}{P})$

328. In a transformer, the magnetic coupling between the primary and secondary circuit can be increased by

1. Increasing the number of turns
2. Using soft materials for windings
3. Using a magnetic core of low reluctance
4. Using transformer oil of better quality

329. Which of the following transformer will be the largest in size?

1. 1 kVA, 25 Hz
2. 1 kVA, 50 Hz
3. 1 kVA, 60 Hz
4. 1 kVA, 100 Hz

330. If the flux density in the core of a transformer is increased then

1. Frequency on secondary windings will change
2. Wave shape on the secondary side will be distorted
3. Size of the transformer can be reduced
4. Eddy current losses will be reduced

331. Which test on the transformer provides information about regulation efficiency and heating under loaded conditions?

1. Open circuit test
2. Back to back test
3. Hopkinson test
4. Short circuit test

332. A transformer used for A.C. welding set is

1. Booster type
2. Step-up transformer
3. Step-down transformer
4. None of these

333. In a transformer having 1000 primary turns and 400 secondary turns, if the primary voltage is 250 V, the secondary voltage will be

1. 400 V
2. 100 V
3. 625 V
4. 1600 V

334. The percentage resistance of a 100kVA, 5kV, 55ohm reactance is given by

1. 2%
2. 20%
3. 40%
4. 4%

335. A transformer having a turn’s ratio 1:5 and a resistance of 500 Ω is connected across the secondary terminals. What is the equivalent resistance for the current flowing in the primary?

1. 100 Ω
2. 10 Ω
3. 20 Ω
4. 50 Ω

336. CRGO laminations in a transformer are used to minimize

1. Eddy current loss
2. Ohmic loss
3. Hysteresis loss
4. Both eddy current and hysteresis losses

337. Two transformer are to be operated in parallel such that they share load in proportion to their kVA ratings. The rating of the first transformer is 500kVA and its pu leakage is 0.05 pu. If the rating of the second transformer is 250kVA then its pu leakage impedance is:

1. 0.025
2. 0.1
3. 0.05
4. 0.2

338. The transformer core laminations are insulated from each other by

1. Cotton
2. Paper
3. Mica strip
4. Thin coat of varnish

339. The full-load efficiency at unity power factor of a 230/115V, 2 kVA single-phase transformer having a Copper loss of 60W at half load and iron loss of 50W is

1. 92%
2. 87%
3. 90%
4. 98%

340. A transformer has efficiency of 80% and works at 100V and 4 kW. If the secondary voltage is 240V, find the primary current.

1. 16.67 A
2. 40 A
3. 30 A
4. 10 A