Transformer MCQ Questions

1. In a power transformer

(a) primary winding is closer to core
(b) secondary winding is closer to core
(c) low voltage winding is closer to core
(d) high voltage winding is closer to core

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

(a) increasing the number of turns
(b) using soft material for windings
(c) using the magnetic core of low reluctance
(d)using transformer oil of batter quality.

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

(a) frequency of secondary winding will change
(b) wave shape on secondary side will be distorted
(c) size of transformer can be reduced
(d) eddy current loss will reduce.

4. If the supply frequency is increased keeping voltage constant

(a) eddy current losses will decrease
(b) hysteresis losses will decrease
(c) eddy current losses will remain unchanged
(d) hysteresis losses will remain unchanged.

5. At no load, the current taken by a transformer

(a) lags behind the applied voltage by 80 degree
(b) lags behind the applied voltage by 50 degree
(c) leads the applied voltage by 80 degree
(d) leads the applied voltage by 50 degree.

6. If the secondary of a 1:10 step up transformer is connected to the primary of a 1:5 step up transformer, the total transformation ratio will be

(a) 15
(b) 30
(c) 50
(d) 2500

7. A 1600 kVA, 200 Hz transformer is operated at 50 Hz. Its kVA rating should be restricted to

(a) 800 kVA
(b) 400 kVA
(c) 200 kVA
(d )100 kVA

8. Leakage flux of a transformer may be minimized by

(a) sectionalizing and interleaving the primary and the secondary windings
(b) constantly cooling the core
(c) under rating the transformer
(d) reducing the reluctance of the iron core to the minimum.

9. Power transformers are usually designed to have maximum efficiency

(a) near full load
(b) at 75% of full load
(c) at 50% of full load
(d) between 50% and 75% of full load.

10. Distribution transformers are usually designed to have maximum efficiency

(a) near full load
(b) at 75% of full load
(c) near 50% of full load
(d) between 50% and 75% of full load.

11. In a transformer it is difficult to measure the efficiency by output-input measurement method because

(a) the output is sinusoidal and hence cannot be measure
(b) losses are abnormally high
(c) efficiency of transformer is usually high and hence extremely accurate measurements will be necessary
(d) output is out of phase with respect to input.

12. The leakage flux in a transformer depends upon

(a) load current
(b) load current and voltage
(c) load current, voltage and frequency
(d) load current, voltage, frequency and power factor.

13. What is maximum order of flux density used in cores using CRGO sheets

(a) 0.04 webers/m²
(b) 0.4 webers/m²
(c) 1.04 webers/m²
(d) webers/m²

14. The phase difference between the primary and the secondary voltage of a transformer is

(a) 0 degree
(b) 180 degree
(c) 90 degree
(d) between 30 degree and 60 degree

15. The desirable properties of transformer core material is

(a) low permeability and low hysteresis loss
(b) high permeability and high hysteresis loss
(c) low permeability and high hysteresis loss
(d) high permeability and low hysteresis loss

16. Full load copper loss in a transformer is 1600 watts. At half load the losses will be

(a) 6400 W
(b) 1600 W
(c) 800 W
(d) 400 W

17. Buchholz relay is generally not provided on transformer below

(a) 1 kVA
(b) 5 kVA
(c) 50 kVA
(d) 500 kVA

18. Operating time of Buchholz relay is in the order of

(a) 0.1 micro second
(b) 0.1 milli second
(c) 0.1 second
(d) 1 second

19. For a transformer, operating at a constant load current, maximum efficiency will occur at

(a) Zero power factor
(b) unity power factor
(c) 0.8 leading power factor
(d) 0.8 lagging power factor.

20. “A” class insulation can withstand

(a) temperature rise of 105 degree Celsius
(b) maximum temperature rise of 105 degree Celsius
(c) temperature gradient of 105 degree Celsius
(d) heating rate of 105 Celsius in 24 hours.

21. In which of the following the highest rating transformer is likely to find application ?

(a) Transmission
(b) Substation
(c) Generator
(d) Distribution

22. In a transformer maximum voltage regulation occurs when the power factor of the load is

(a) 0.4
(b) lagging
(c) leading
(d) unity

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

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

24. When a delta connected primary of a 3-phase transformer is connected to 3-phase supply

(a) magnetizing current in phase winding will carry third harmonics but line current will be free from it.
(b) magnetizing current in phase winding will contain third harmonica and line current will also contain third harmonics.
(c) magnetizing current will not contain third harmonics but line current will contain third harmonics.
(d) none of the above.

25. Scott connections are used to convert

(a) three-phase supply to D.C. supply
(b) three-phase supply to three-phase supply
(c) three-phase supply to two-phase supply
(d) three-phase supply to single-phase supply

26. Which of the following 3-phase connections of transformer create disturbances in communication systems

(a) star/delta
(b) delta/star
(c) star/star
(d) delta/delta.

27. Delta-delta power transformer is protected by current transformer having

(a) star/star connections
(b) delta/delta connections
(c) star/delta connections
(d) delta/star connections

28. Star-star power transformer is protected by current transformer having

(a) star/star connections
(b) delta/delta connections
(c) star/delta connections
(d) delta/star connections

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