Transformers

 Transgormers

1. The BDV of transformer oil should be

1. 20 kV
2. 30 kV
3. 40 kV
4. 50 kV

b. 30 kV

2. The colour of moisten silica gel is

1. Pink
2. Blue
3. Yellow
4. Green

b. Blue

3. The material filled in breather of transformer is

1. Silica gel
2. Sulphuric acid
3. SF6
4. Mineral oil

a. Silica gel

4. The protective device to indicate the internal fault in a transformer is

1. Thermal relay
2. Bucholz relay
3. OVR
4. EFR

b. Bucholz relay

5. The minimum allowable BDV for transformer oil should stand for

1. 15 sec
2. 30 sec
3. 45 sec
4. 60 sec

d. 60 sec

6. While testing transformer oil the gap between electrodes is kept at a distance of

1. 1 mm
2. 2 mm
3. 3 mm
4. 4 mm

d. 4 mm

7. Core of a transformer is made up of

1. Aluminium
2. Carbon
3. Lead
4. Silicon steel

d. Silicon steel

8. Which of the following is not the function of a transformer oil

1. Cooling of primary coils
2. Cooling of secondary coils
3. Providing additional insulation
4. Providing inductive coupling

d. Providing inductive coupling

9. For a transformer, the condition for maximum efficiency is

1. Hysteresis loss = eddy current loss
2. Core loss = hysteresis loss
3. Copper loss = Iron loss
4. Total loss = 2/3 copper loss

c. Copper loss = Iron loss

10. Transformer oil shall be free from

1. Odour
2. Gases
3. Temperature
4. Moisture

d. Moisture

11. The power factor in a transformer

1. Is always unity
2. Is always leading
3. Is always lagging
4. Depends on power factor of load.

d. Depends on power factor of load.

12. The short circuit test of a transformer gives

1. Copper loss at full load
2. Copper loss at half load
3. Iron loss at any load
4. Sum of iron loss and copper load.

a. Copper loss at full load

13. The open circuit test of transformer determines

1. Iron loss
2. Copper loss at full load
3. Copper loss at half load
4. Total losses.

a. Iron loss

14. The type of oil, which is suitable as transformer oil is

1. Crude oil
2. Organic oil
3. Mineral oil
4. Animal oil.

c. Mineral oil

15. A step up transformer increases

1. Power
2. Current
3. Voltage
4. Frequency.

c. Voltage

16. Which test is conducted on all transformers in a manufacturing concern

1. Routine test
2. Type test
3. Special test
4. All above

a. Routine test

17. The colour of fresh dielectric oil for a transformer

1. Pale yellow
2. Dark brown
3. White to grey
4. Colourless

d. Colourless

18. The ratio of kW to kVA is known as

1. Voltage regulation
2. power factor
3. Transformation ratio
4. None above

b. power factor

19. Core lifting of a transformer is done after a period of

1. 3 yrs.
2. 4 yrs.
3. 5 yrs.
4. 6 yrs.

c. 5 yrs.

20. The purpose of conservator tank in a transformer is to

1. Monitor the oil level
2. Top up the oil level
3. Both a & b above
4. None of the above.

c. Both a & b above

21. Transformers placed in a room enclosed from all the four sides, the minimum spacing between the walls and the transformer should be

1. 0.5 m
2. 0.75 m
3. 1 m
4. 1.25 m

d. 1.25 m

22. For indoor installation the minimum clearance between the highest point of the conservator tank to the ceiling of the transformer room should be

1. 0.25 m
2. 0.5 m
3. 0.75 m
4. 1 m

b. 0.5 m

23. At an atmospheric temperature of 45 deg C and keeping in view the working condition, the winding temperature of the transformer should not exceed

1. 80 deg C
2. 95 deg C
3. 110 deg C
4. 130 deg C

b. 95 deg C

24. Which of the following does not change in a transformer?

1. Current
2. Voltage
3. Frequency
4. All of the above

c. Frequency

25. In a transformer the energy is conveyed from primary to secondary

1. through cooling coil
2. through air
3. by the flux
4. none of the above

c. by the flux

26. A transformer core is laminated to

1. reduce hysteresis loss
2. reduce eddy current losses
3. reduce copper losses
4. reduce all above losses

b. reduce eddy current losses

27. The path of a magnetic flux in a transformer should have

1. high resistance
2. high reluctance
3. low resistance
4. low reluctance

d. low reluctance

28. No-load test on a transformer is carried out to determine

1. copper loss
2. magnetizing current
3. magnetizing current and loss
4. efficiency of the transformer

c. magnetizing current and loss

29. The dielectric strength of transformer oil is expected to be

1. 1 kV
2. 33 kV
3. 100 kV
4. 330 kV

b. 33 kV

30. The efficiency of a transformer will be maximum when

1. copper losses = hysteresis losses
2. hysteresis losses = eddy current losses
3. eddy current losses = copper losses
4. copper losses = iron losses

d. copper losses = iron losses

31. No-load current in a transformer

1. lags behind the voltage by about 75°
2. leads the voltage by about 75°
3. lags behind the voltage by about 15°
4. leads the voltage by about 15°

a. lags behind the voltage by about 75°

32. The purpose of providing an iron core in a transformer is to

1. provide support to windings
2. reduce hysteresis loss
3. decrease the reluctance of the magnetic path
4. reduce eddy current losses

c. decrease the reluctance of the magnetic path

33. Which of the following is not a part of transformer installation?

1. Conservator
2. Breather
3. Buchholz relay
4. Exciter

d. Exciter

34. While conducting short – circuit test on a transformer the following side is shortcircuited

1. High voltage side
2. Low voltage side
3. Primary side
4. Secondary side

b. Low voltage side

35. In the transformer following winding has got more cross-section area

1. low voltage winding
2. High voltage winding
3. primary winding
4. secondary winding

a. low voltage winding

36. A transformer transforms

1. voltage
2. current
3. power
4. frequency

c. power

37. A transformer cannot raise or lower the voltage of a D.C. supply because

1. there is no need to change the D.C. voltage
2. a D.C. circuit has more losses
3. Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero
4. none of the above

c. Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero

38. Primary winding of a transformer

1. is always a low voltage winding
2. is always a high voltage winding
3. could either be a low or high voltage winding
4. none of the above

c. could either be a low or high voltage winding

39. Which winding in a transformer has more number of turns?

1. Low voltage winding
2. High voltage winding
3. Primary winding
4. Secondary winding

b. High voltage winding

40. Efficiency of a power transformer is of the order of

1. 100 percent
2. 98 percent
3. 50 percent
4. 25 percent

b. 98 percent

41. A common method of cooling a power transformer is

1. natural air cooling
2. air blast cooling
3. oil cooling
4. any of the above

c. oil cooling

42. In a transformer routine efficiency depends upon

1. supply frequency
2. load current
3. power factor of load
4. both (b) and (c)

d. both (b) and (c)

43. The maximum efficiency of a distribution transformer is

1. at no load
2. at 50% full load
3. at 80% full load
4. at full load

b. at 50% full load

44. Transformer breaths in when

1. load on it increases
2. load on it decreases
3. load remains constant
4. none of the above

b. load on it decreases

45. No-load current of a transformer has

1. has high magnitude and low power factor
2. has high magnitude and high power factor
3. has small magnitude and high power factor
4. has small magnitude and low power factor

d. has small magnitude and low power factor

46. Spacers are provided between adjacent coils

1. to provide free passage to the cooling oil
2. to insulate the coils from each other
3. both (a) and (b)
4. none of the above

a. to provide free passage to the cooling oil

47. In a transformer the tappings are generally provided on

1. primary side
2. secondary side
3. low voltage side
4. high voltage side

c. low voltage side

48. The chemical used in breather for transformer should have the quality of

1. ionizing air
2. absorbing moisture
3. cleaning the transformer oil
4. cooling the transformer oil

b. absorbing moisture

49. The chemical used in breather is

1. asbestos fibre
2. silica sand
3. sodium chloride
4. silica gel

d. silica gel

50. The transformer ratings are usually expressed in terms of

1. Volts
2. amperes
3. kW
4. kVA

b. amperes

51. Material used for construction of transformer core is usually

1. Wood
2. copper
3. Aluminium
4. silicon steel

d. silicon steel

52. The thickness of lamination used in a transformer is usually

1. 0.4mm to 0.5 mm
2. 4 mm to 5 mm
3. 14mm to 15mm
4. 25mm to 40 mm

a. 0.4mm to 0.5 mm

53. The function of conservator in a transformer is

1. to protect against internal fault
2. to reduce copper as well as core losses
3. to cool the transformer oil
4. to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings

d. to take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings

54. A Buchholz relay can be installed on

1. auto-transformers
2. air-cooled transformers
3. welding transformers
4. oil cooled transformers

d. oil cooled transformers

55. Buchholz’s relay gives warning and protection against

1. electrical fault inside the transformer itself
2. electrical fault outside the transformer in outgoing feeder
3. for both outside and inside faults
4. none of the above

a. electrical fault inside the transformer itself

56. The transformer laminations are insulated from each other by

1. mica strip
2. thin coat of varnish
3. paper
4. any of the above

b. thin coat of varnish

57. During open circuit test of a transformer

1. primary is supplied rated voltage
2. primary is supplied full-load current
3. primary is supplied current at reduced voltage
4. primary is supplied rated kVA

a. primary is supplied rated voltage

58. Open circuit test on transformers is conducted to determine

1. hysteresis losses
2. copper losses
3. core losses
4. eddy current losses

c. core losses

59. Short circuit test on transformers is conducted to determine

1. hysteresis losses
2. copper losses
3. core losses
4. eddy current losses

d. eddy current losses

60. The function of breather in a transformer is

1. to provide oxygen inside reduced load
2. to cool the coils during reduced load
3. to cool the transformer oil
4. to arrest flow of moisture when outside air enters the transformer

d. to arrest flow of moisture when outside air enters the transformer

61. The secondary winding of which of the following transformers is always kept closed?

1. Step-up transformer
2. Step-down transformer
3. Potential transformer
4. Current transformer

d. Current transformer

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

1. 0.8 leading power factor
2. 0.8 lagging power factor
3. zero power factor
4. unity power factor

d. unity power factor

63. Which of the following protection is normally not provided on small distribution transformers?

1. Over-fluxing protection
2. Buchholz relay
3. Over-current protection
4. All of the above

b. Buchholz relay

64. Which of the following acts as a protection against high voltage surges due to lightning and switching?

1. Horn gaps
2. Thermal overload relays
3. Breather
4. Conservator

a. Horn gaps

65. Which of the following parts of a transformer is visible from outside?

1. Bushings
2. Core
3. Primary winding
4. Secondary winding

a. Bushings

66. The noise produced by a transformer is termed as

1. zoom
2. hum
3. Ringing
4. buzz

b. hum

67. Which of the following loss in a transformer is zero even at full load?

1. core loss
2. friction loss
3. eddy current loss
4. hysteresis loss

b. friction loss

68. If a transformer is continuously operated the maximum temperature rise will occur in

1. Core
2. windings
3. Tank
4. any of the above

b. windings

69. An open-circuit test on a transformer is conducted primarily to measure

1. Insulation Resistance
2. Copper loss
3. Core loss
4. Total loss

c. Core loss

70. A no-load test is performed on a transformer to determine

1. Core loss
2. Copper loss
3. Efficiency
4. Magnetising current and loss

d. Magnetising current and loss

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