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transformers MCQs

Practise focused transformers questions with marked answers for exam preparation and subject revision.

transformers Mcqs
1. A transformer core is laminated to__________?
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A. reduce copper losses

B. reduce hysteresis loss

C. reduce eddy current losses

D. reduce all above losses

2. The no load current in a transformer lags behind the applied voltage by an angle of about_____________?
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A. 90

B. 120?

C. 75

D. 180

3. Which type of winding is used in 3 phase shell-type transformer?
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A. Circular type

B. Sandwich type

C. Rectangular type

D. Cylindrical type

4. No-load current of a transformer has_____________?
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A. has small magnitude and low power factor

B. has small magnitude and high power factor

C. has high magnitude and high power factor

D. has high magnitude and low power factor

5. Spacers are provided between adjacent coils?
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A. to provide free passage to the cooling oil

B. to insulate the coils from each other

C. both A. and (b)

D. none of the above

6. A common method of cooling a power transformer is_______________?
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A. any of the above

B. natural air cooling

C. oil cooling

D. air blast cooling

7. The noise resulting from vibrations of laminations set by magnetic forces, is termed as_________________?
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A. zoom

B. magnetostrication

C. hum

D. boo

8. Delta/star transformer works satisfactorily when______________?
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A. on balanced as well as unbalanced loads

B. none of the above

C. load is balanced only

D. load is unbalanced only

9. The path of a magnetic flux in a transformer should have______________?
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A. high reluctance

B. low resistance

C. high resistance

D. low reluctance
10. The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be___________?
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A. 1600 W

B. 800 W

C. 6400 W

D. 400 W
11. Iron loss of a transformer can be measured by____________?
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A. any type of wattmeter

B. frequency meter

C. low power factor wattmeter

D. unity power factor wattmeter

12. Which winding of the transformer has less cross-sectional area?
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A. Low voltage winding

B. Primary winding

C. Secondary winding

D. High voltage winding
13. Which of the following property is not necessarily desirable in the material for transformer core ?
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A. Low hysteresis loss

B. Mechanical strength

C. High permeability

D. High thermal conductivity
14. The magnetising current of a transformer is usually small because it has___________?
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A. laminated silicon steel core

B. small air gap

C. large leakage flux

D. fewer rotating parts

15. In a transformer the resistance between its primary and secondary should be_____________?
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A. 1000 Q

B. infinity

C. zero

D. 10 Q

16. Harmonics in transformer result in___________?
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A. increased I2R losses

B. increased core losses

C. all of the above

D. magnetic interference with communication circuits

17. Which of the following parts of a transformer is visible from outside ?
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A. Primary winding

B. Bushings

C. Core

D. Secondary winding

18. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of_________________?
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A. more than 15 A

B. none of the above

C. less than 15 A

D. 15 A

19. Losses which occur in rotating electric machines and do not occur in transformers are___________?
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A. hysteresis and eddy current losses

B. friction and windage losses

C. copper losses

D. magnetic losses

20. The power transformer is a constant______________?
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A. voltage device

B. power device

C. main flux device

D. current device

21. Natural oil cooling is used for transformers up to a rating of____________?
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A. 1000 kVA

B. 250 kVA

C. 3000 kVA

D. 500 kVA

22. A good voltage regulation of a transformer means________________?
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A. output voltage fluctuation from no load to full load is least

B. ood voltage regulation of a transformer means

C. difference between primary and secondary voltage is maximum

D. output voltage fluctuation with power factor is least

E. difference between primary and secondary voltage is least

23. The function of conservator in a transformer is___________________?
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A. to cool the transformer oil

B. to take care of the expansion and contraction of transformer oil due to variation of temperature of sur-roundings

C. to project againstinternal fault

D. to reduce copper as well as core losses

24. Power transformers are generally designed to have maximum efficiency around__________?
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A. half-load

B. 10% overload

C. near full-load

D. no-load

25. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are______________?
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A. none of the above

B. copper losses

C. hysteresis and eddy current losses

D. friction and windage losses

26. In a power or distribution transformer about 10 per cent end turns are heavily insulated__________?
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A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

B. none of the above

C. to reflect the line surge and save the winding of a transformer from damage

D. to absorb the line surge voltage and save the winding of transformer from damage

27. During open circuit test of a transformer:
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A. primary is supplied rated kVA

B. primary is supplied rated voltage

C. primary is supplied current at reduced voltage

D. primary is supplied full-load current

28. The path of the magnetic flux in transformer should have____________?
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A. high reluctance

B. high resistance

C. low reactance

D. low resistance

29. The voltage transformation ratio of a transformer is equal to the ratio of_______________?
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A. secondary terminal voltage to primary applied voltage

B. secondary induced e.m.f. to primary induced e.m.f

C. secondary current to primary current

D. primary turns to secondary turns

30. Reduction in core losses and increase in permeability are obtained with transformer employing__________?
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A. core built-up of laminations of cold rolled grain oriented steel

B. core built-up of laminations of hot rolled sheet

C. none of the above

D. either of the above

31. The main reason for generation of harmonics in a transformer could be_______________?
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A. poor insulation

B. fluctuating load

C. saturation of core

D. mechanical vibrations

32. Which of the following acts as a protection against high voltage surges due to lightning and switching ?
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A. Horn gaps

B. Thermal overload relays

C. Conservator

D. Breather

33. In the transformer the function of a conservator is to_______________?
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A. none of the above

B. provide fresh air for cooling the transformer

C. protect the transformer from damage when oil expends due to heating

D. supply cooling oil to transformer in time of need

34. The efficiency of a transformer, under heavy loads, is comparatively low because_______________?
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A. copper loss becomes high in proportion to the output

B. iron loss is increased considerably

C. voltage drop both in primary and secondary becomes large

D. secondary output is much less as compared to primary input

35. Star/star transformers work satisfactorily when________________?
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A. none of the above

B. load is balanced only

C. on balanced as well as unbalanced loads

D. load is unbalanced only

36. The use of higher flux density in the transformer design____________?
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A. reduces iron losses

B. reduces copper losses

C. reduces weight per kVA

D. increases part load efficiency

37. No-load current in a transformer________________?
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A. leads the voltage by about 75

B. leads the voltage by about 15

C. lags behind the voltage by about 15

D. lags behind the voltage by about 75
38. The purpose of providing iron core in a step-up transformer is?
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A. to provide coupling between primary and secondary

B. to decrease the magnitude of mag-netizing current

C. to increase the magnitude of mutual flux

D. to provide all above features
39. Which of the following is not a routine test on transformers ?
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A. Impedance test

B. Polarity test

C. Core insulation voltage test

D. Radio interference test
40. Hysteresis loss in a transformer varies as CBmax = maximum flux density) ?
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A. Bmax1-6

B. Bmax

C. Bmax1-83

D. B max

41. The transformer laminations are insulated from each other by____________?
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A. mica strip

B. thin coat of varnish

C. paper

D. any of the above

42. Two transformers operating in parallel will share the load depending upon their____________?
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A. per unit impedance

B. efficiencies

C. ratings

D. leakage reactance

43. An ideal transformer has infinite values of primary and secondary inductances. The statement is______________?
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A. false

B. TRUE

44. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are__________?
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A. hysteresis and eddy current losses

B. friction and windage losses

C. copper losses

D. none of the above

45. A no-load test is performed on a transformer to determine_______________?
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A. magnetising current and loss

B. core loss

C. efficiency

D. copper loss

E. magnetising current

46. A transformer can have zero voltage regulation at______________?
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A. leading power factor

B. lagging power factor

C. unity power factor

D. zero power factor

47. Greater the secondary leakage flux____________?
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A. less will be the primary terminal voltage

B. less will be the secondary induced e.m.f.

C. less will be the primary induced e.m.f.

D. none of the above

48. The efficiency of two identical transformers under load conditions can be determined by_______________?
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A. open circuit test

B. any of the above

C. back-to-back test

D. short-circuit test

49. Which of the following is the main advantage of an auto-transformer over a two winding transformer?
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A. Saving in winding material

B. Eddy losses are totally eliminated

C. Copper losses are negligible

D. Hysteresis losses are reduced

50. Which of the following properties is not necessarily desirable for the material for transformer core ?
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A. High thermal conductivity

B. Low hysteresis loss

C. Adequate mechanical strength

D. High permeability