# Transformer MCQ Questions and Answers

1. Which of the following would refer to an ideal transformer?

1. Winding resistances are negligible.
2. Leakage-fluxes are included.
3. Core losses are negligible.
4. Magnetization characteristic is linear.
1. i, ii and iii only
2. i, iii and iv only
3. i, ii and iv only
4. ii, iii and iv only

2. An ideal transformer is having 150 turns primary and 750 turns secondary. The primary coil is connected to a 240 V, 50 Hz source. The secondary winding supplies a load of 4 A at lagging power factor of 0.8. What is the power supplied by the transformer to the load?

1. 4200 W
2. 3840 W
3. 2100 W
4. 1920 W

3. A 1000V/400V power transtormer has a nominal short-circuit voltage VSC = 40%. Which one of the following statements is correct?

1. A voltage of 400 V appears across the short-circuited secondary terminals.
2. A voltage of 16V appears across the short-circuited secondary terminals.
3. When the secondary terminals are short-circuited, the rated current flows at the primary side at a primary voltage of 400V.
4. The primary voltage drops to 400 V, when the secondary terminals are short-circuited.

4. Eddy current losses in transformer cores and be reduced by the use of

1. Solid cores
2. Laminated cores
3. Ferrites

Select the correct answer using the codes given below

1. ii and iii only
2. i and ii only
3. i, ii and iii
4. i and iii only

5. A transformer may have negative voltage regulation if the load power factor (p.f.) is

1. Leading for some values of p.f.
2. Unity p.f.
3. Lagging but not zero p.f.
4. Only zero p.f. lag

6. A 2400/240 V, 200 kVA, single-phase transformer has a core loss of 1.8 kW at rated voltage. Its equivalent resistance is 1.1%. Then the transfer efficiency at 0.9 power factor and on full load is

1. 96.71%
2. 95.60%
3. 98.93%
4. 97.82%

7. In a power transformer, the core loss is 50 W at 40 Hz, and 100 W at 60 Hz, under the condition of same maximum flux density in both cases. The core loss at 50 Hz will be

1. 73 W
2. 64 W
3. 91 W
4. 82 W

8. The regulation of a transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage, when operating at 0.8 power factor lagging is

1. 4.8%
2. 3.8%
3. 5.8%
4. 5.2%

9. Consider the following losses for short circuit test on a transformer:

1. Copper loss
2. Copper and iron losses
3. Eddy current and hysteresis losses
4. Friction and windage losses
1. ii only
2. i only
3. ii, iii and iv
4. iii only

10. A 4kVA transformer has iron-loss of 200 W and full load copper loss of 200 W. The maximum efficiency at unity power factor will be

1. 90.9%
2. 85.6%
3. 70.9%
4. 80.6%

11. The percentage resistance and reactance of a transformer are 2% and 4% respectively. The approximate regulation on full load at 0.8 pf lag is

1. 8%
2. 12%
3. 4%
4. 6%

12. In a normal operation of 400 V, 50 Hz transformer, the total iron loss is 2500 W. When the supply voltage and frequency are reduced to 200 V and 25 Hz respectively, the corresponding loss is 850 W. The eddy-current loss at normal voltage

1. 800 W
2. 400 W
3. 1600 W
4. 200 W

13. A 250 kVA, 11000 V/400 V and 50 Hz single-phase transformer has 80 turns on the secondary, what is the maximum value of flux?

1. 2475 mWb
2. 0.2 mWVb
3. 22.5 mWb
4. 55.2 mWb

14. A 2000/200 V, 50 Hz single-phase transformer has an exciting current of 0.5 A and a core-loss of 600 W. When H.V. side is energized by the rated voltage and frequency, the magnetizing current is

1. 0.1 A
2. 0.2 A
3. 0.3 A
4. 0.4 A

15. In the core-type two winding transformer, the low voltage winding is placed adjacent to the steel core, in order to

1. facilitate dissipation of heat during the operation of the transformer
2. minimize the amount of insulation required.
3. reduce the chances of axial displacement with respect to the high voltage winding placed outside.
4. reduce the mutual radial stress between the two windings.

16. If the percentage impedance of the two transformers working in parallel are different then

1. transformers will be overheated
2. power factors of both the transformers will be same
3. parallel operation will not be possible
4. parallel operation will still be possible

17. The voltage regulation of a transformer having 2% resistance and 5% reactance, at full load, 0.8 pf lagging is

1. -4.6%
2. 4.6%
3. 6.4%
4. -1.4%

18. In a transformer the core loss is 100 Watt at 40 Hz and 72 Watt at 37 Hz, then eddy current and hysteresis losses at 50 Hz respectively are

1. 25 Watt and 105 Watt
2. 20 Watt and 100 Watt
3. 100 Watt and 32 Watt
4. 32 Watt and 100 Watt

19. In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will be efficiency be maximum?

1. 0.57
2. 0.80
3. 0.90
4. 0.70