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Tuesday, 16 February 2016

Transformer - Multiple Choice Questions

Transformer - Multiple Choice Questions Points : transformer, multiple choice questions and answers, electrical objective type question answers, mcqs 1. A transformer is an efficient device as it …………
(i) is a static device
(ii) uses inductive coupling
(iii) uses capacitive coupling
(iv) uses electric coupling

2. A transformer does not possess …………… change property.
(i) impedance
(ii) voltage
(iii) current
(iv) power

3. The voltage per turn of the primary of a transformer is ……… the voltage per turn of secondary.
(i) more than
(ii) less than
(iii) the same as
(iv) none of the above

4. A transformer will work on …………
(i) a.c. only
(ii) d.c. only
(iii) ac. as well as d.c
(iv) none of the above

5. A transformer transfers electrical energy as of primary to secondary frequently by a change in ………..
(i) frequency
(ii) power
(iii) voltage
(iv) time period

6. The winding of transformer by greater number of turns will be …………….
(i) high voltage winding
(ii) low-voltage winding
(iii) either high or low voltage winding
(iv) none of the above

7. If a transformer core has air gaps, then, …………….
(i) reluctance of magnetic path is decrease
(ii) hysteresis loss is decrease
(iii) manetising current is greatly increased
(iv) eddy current is increased

8. A transformer is so designed that primary and secondary have …………..
(i) high leakage reactance
(ii) large resistance
(iii) tight magnetic coupling
(iv) good electric coupling

9. The primary and secondary of a transformer are ………… coupled.
(i) electrically
(ii) magnetically
(iii) electrically and magnetically
(iv) none of the above

10. A 230/2300 V transformer takes no-load current of 6.5 A and absorb 187 W. If resistance of the of primary is 0.06 ?, what is core loss?
(i) 1225 W
(ii) 1845 W
(iii) 2064 W
(iv) 1913 W

11. When primary of a transformer is linked to a d.c. supply ……………
(i) primary draws small current
(ii) primary leakage reactance is increased
(iii) core losses are increased
(iv) primary may burn out

12. A 2000/200 V, 20 kVA ideal transformer has 66 turns in secondary. The number of primary turns is …………..
(i) 440
(ii) 660
(iii) 550
(iv) 330

13. An ideal transformer is one which ……………
(i) has no losses and leakage reactance
(ii) does not work
(iii) has similar number of primary and secondary turns
(iv) none of the above

14. The highest flux created in the core of a transformer is ………………
(i) directly proportional to supply rate
(ii) inversely proportional to supply frequency
(iii) inversely proportional to primary voltage
(iv) none of the above

15. The no-load ratio of a 50 Hz single phase transformer is 6000/250 V. The highest flux in the core is 006 Wb, What is the number of primary turns?
(i) 450
(ii) 900
(iii) 350
(iv) 210

16. Leakage flux in a transformer happen because
(i) iron core has high permeability
(ii) air is not a good magnetic insulator
(iii) applied voltage is sinusoidal
(iv) transformer is not an efficient device

17. A transformer operate weakly at extremely low frequencies as …………
(i) permeability of core is increased
(ii) magnetising current is abnormally high
(iii) primary reactance is too much increased
(iv) none of the above

18. The iron-core is use to ……….. of transformer.
(i) increase the weight
(ii) provide tight magnetic coupling
(iii) reduce core losses
(iv) none of the above

19. The flux in the core of a single-phase transformer is …………….
(i) purely alternating one
(ii) purely rotating one
(iii) partly alternating and partly rotating
(iv) none of the above

20. The primary leak flux links ………….
(i) primary winding only
(ii) secondary winding only
(iii) both primary and secondary windings
(v) none of the above

21. When load on a transformer is decreased, ……………. failure is decreased.
(i) eddy current
(ii) hysteresis
(iii) copper
(iv) friction

22. A transformer has an effectiveness of 80% and works at 100 V, 4 kW. If the secondary voltage is 240 V. find the primary current?
(i) 40A
(ii) 30A
(iii) 20A
(iv) 10A

23. If a power transformer is operate at extremely high frequencies, then ……….
(i) primary reactance is too much increased
(ii) primary ill draw large power
(iii) core losses will be excessive
(iv) none of the above

24. The all-day efficiency of a distribution transformer is ………. commercial competence is ………….
(i) the same as
(ii) more than
(iii) less than
(iv) none of the above

25. The open circuit test on a transformer Is constantly made on
(i) low-voltage winding
(ii) high-voltage winding
(iii) either low or high voltage winding
(iv) none of the above

26. The noload input power to a transformer is practically equivalent to ............. loss in transformer.
(i) iron
(ii) copper
(iii) eddy current
(iv) none of the above

27. The approximate efficiency of a large transformer is …………….
(i) 65
(ii) 50%
(iii) 80 %
(iv) 95 %

28. In a practical transformer, copper losses account for about ……….. of the total losses.
(i) 10%
(ii) 85%
(iii 25
(iv) 50

29. A two-winding transformer operate at utmost efficiency when its
(i) hysteresis loss equals eddy current loss
(ii) cu loss equals iron loss
(iii) primary resistance equal secondary resistance
(iv) voltage regulation is minimum

30. A 2302300 V transformer takes no load current of 15 A at 0.25 power factor lagging. The core loss is
(i) 300.2 W
(ii) 192.5 W
(iii) 287.5
(iv) 212.6 W

31. When secondary of a transformer is short circuited primary inductance …………
(i) is decreased
(ii) is increased
(iii) remains unchanged
(iv) none of the above

32. Two things which are similar for primary and secondary of transformer are …………
(i) ampere-turns and voltage per turn
(ii) resistances and leak reactances
(iii) currents and induced voltages
(iv) none of above

33. In a transformer, leakage flux
(i) helps in transfer of energy
(ii) is negligible at full-load
(iii) is minimised by interleaving the primary and secondary windings
(iv) produces mutually induced e.m.f..

34. The core-type transformer is usually proper for …………….
(i) high voltage and small output
(ii) high voltage and high output
(iii) low voltage and high output
(iv) none of the above

35. The open-circuit test on a transformer give …………
(i) copper losses
(ii) friction losses
(iii) iron losses
(iv) total losses

36. In an auto transformer, primary and secondary are ………. coupled.
(i) only magnetically
(ii) only electrically
(iii) magnetically as well as electrically
(iv) none of the above

37. The core-type transformer give ……………
(i) much longer magnetic path
(ii) shorter magnetic path
(iii) Lesser average length per turn
(iv) none of the above

38. The result of leakage flux in a transformer is to ……………
(i) increase copper losses
(ii) decrease copper losses
(iii) cause voltage drop in the windings
(iv) none of the above

39. The eddy current loss in a transformer is directly proportional to ………….
(i) thickness of core lamination
(ii) square of thickness of core lamination
(iii) the supply frequency
(iv) the flux density In the core

40. Transformers having ratings less than 5 kVA are usually ……………
(i) oil cooled
(ii) natural air cooled
(iii) water cooled
(iv) none of the above

41. Cores of large transformers are build upto nearly circular cross-section in arrange to decrease ………..
(i) leakage reactance
(ii) iron losses
(iii) eddy current loss
(iv) copper loss

42. A transformer has 200 V as iron loss at full-load. The iron failure at half full-load will be …………
(i) 50 W
(ii) 100 W
(iii) 400 W
(iv) 200 W

43. The transformer that should never have the secondary open-circuited while primary is energised is …………
(i) power transformer
(ii) voltage transformer
(iii) auto transformer
(iv) current transformer

44. By laminating the core of a transformer, we reduce ………….
(i) leakage reactance
(ii) hysteresis toss
(iii) eddy current loss
(iv) copper loss

45. The metal flux in a transformer remains steady at every loads as ……………
(i) applied voltage and frequency are constant
(ii) leakage flux is small
(iii) iron core is used
(iv) losses are small

46. The amount of copper in the primary is ………… that of secondary.
(i) about the same as
(ii) greater than
(iii) smaller than
(iv) none of the above

47. A transformer has full load copper loss of 400 W. The copper loss at half full load will be …………
(i) 100W
(ii) 200W
(iii) 400 W
(iv) none of the above

48. In the short circuit test on a transformer we usually shirt circuit test ………..
(i) high-voltage winding
(ii) low-voltage winding
(iii) either low or high voltage winding
(iv) none of the above

49. The primary and secondary windings are wound on the top of each other in order to decrease ………….
(i) iron losses
(ii) copper losses
(iii) leakage reactance
(iv) winding resistance

50. When load ‘n a transformer is increased, eddy current …………
(i) is increased
(ii) remains unchanged
(iii) is decreased
(iv) none of the above

51. A transformer will contain zero efficiency at ……………
(i) lull-load
(ii) no-load
(iii) half full-load
(iv) none of the above

52. The temperature rise of a transformer is straight proportional to …………
(i) apparent power
(ii) reactive power
(iii) leakage reactance
(iv) none of the above

53. The steel use for transformer core has
(i) high silicon content
(ii) high permeability
(iii) low hysteresis loss
(iv) all of the above

53. The all-day efficiency of a transformer is too called its
(i) energy efficiency
(ii) power efficiency
(iii) current efficiency
(iv) none of the above

54. The short-circuit test helps us to find
(i) cu loss at any desired load
(ii) iron loss at no load
(iii) Cu loss at no load
(iv) none of the above

55. The power efficiency of a lighting transformer is always …….. its all day efficiency.
(i) equal to
(ii) higher than
(iii) less than
(iv) none of the above

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