transformers Mcqs
51. Which winding in a transformer has more number of turns ?
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A. High voltage winding

B. Low voltage winding

C. Secondary winding

D. Primary winding

52. If a transformer is continuously operated the maximum temperature rise will occur in_______________?
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A. windings

B. any of the above

C. core

D. tank

53. For given applied voltage, with the increase in frequency of the applied voltage?
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A. eddy current loss will remain unchanged

B. eddy current loss will decrease

C. eddy current loss will increase

D. none of the above

54. The transformer oil should have _______ volatility and _______ viscosity?
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A. low,high

B. high,high

C. low,low

D. high,low

55. In an actual transformer the iron loss remains practically constant from no load to full load because:____________?
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A. secondary voltage remains constant

B. core flux remains practically constant

C. permeability of transformer core remains constant

D. value of transformation ratio remains constant

E. primary voltage remains constant

56. The degree of mechanical vibrations produced by the laminations of a transformer depends on____________?
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A. gauge of laminations

B. all of the above

C. size of laminations

D. tightness of clamping

57. Which of the following insulating materials can withstand the highest temperature safely ?
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A. Glass fibre

B. Asbestos

C. Mica

D. Cellulose

58. The dielectric strength of transformer oil is expected to be______________?
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A. 33 kV

B. lkV

C. 100 kV

D. 330 kV

59. In a transformer routine efficiency depends upon_____________?
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A. supply frequency

B. load current

C. power factor of load

D. both B. and (c)
60. While conducting short-circuit test on a transformer the following side is short circuited?
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A. Primary side

B. Low voltage side

C. Secondary side

D. High voltage side

61. The permissible flux density in case of cold rolled grain oriented steel is around__________?
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A. 1.7 Wb/m2

B. 3.7 Wb/m2

C. 2.7 Wb/m2

D. 4.7 Wb/m2

62. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in____________?
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A. loading of the transformers not in proportion to their kVA ratings

B. power factor of one of the transformers is leading while that of the other lagging

C. transformers having higher copper losses will have negligible core losses

D. short-circuiting of the secondaries

63. Distribution transformers are generally designed for maximum efficiency around________________?
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A. 90% load

B. zero load

C. 50% load

D. 25% load

64. Transformer breaths in when_______________?
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A. load remains constant

B. load on it decreases

C. load on it increases

D. none of the above

65. During short circuit test iron losses are negligible because of _____________?
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A. full-load current is not supplied to the transformer

B. the voltage applied on primary side is low

C. the current on secondary side is negligible

D. the voltage on secondary side does not vary

66. The chemical used in breather for transformer should have the quality of____________?
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A. ionizing air

B. cleansing the transformer oil

C. absorbing moisture

D. cooling the transformer oil

67. Sumpners test is conducted on transformers to determine_____________?
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A. none of the above

B. temperature

C. stray losses

D. all-day efficiency

68. The no-load current drawn by transformer is usually what per cent of the full-load current ?
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A. 20 to 30 per cent

B. 0.2 to 0.5 per cent

C. 2 to 5 per cent

D. 12 to 15 per cent

69. No-load on a transformer is carried out to determine______________?
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A. efficiency of the transformer

B. magnetising current and loss

C. magnetising current

D. copper loss

70. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be___________?
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A. R2IK2

B. R22!K2

C. R22/K

D. R2/VK

71. The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer?
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A. Bushings

B. Conservator

C. Buchholz relay

D. Breather

72. When secondary of a current transformer is open-circuited its iron core will be__________?
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A. none of above will happen

B. hot because of heavy iron losses taking place in it due to high flux density

C. hot because primary will carry heavy current

D. cool as there is no secondary current

73. Which of the following does not change in an ordinary transformer ?
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A. Voltage

B. Frequency

C. Current

D. Any of the above

74. Silicon steel used in laminations mainly reduces___________?
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A. all of the above

B. copper losses

C. hysteresis loss

D. eddy current losses

75. A Buchholz relay can be installed on______________?
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A. air-cooled transformers

B. oil cooled transformers

C. uchholz relay can be installed on

D. auto-transformers

E. welding transformers

76. Which of the following is the most likely source of harmonics in a transformer ?
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A. Overload

B. loose connections

C. poor insulation

D. Core saturation
77. The leakage flux in a transformer depends upon______________?
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A. load current, voltage, frequency and power factor

B. load current

C. load current and voltage

D. load current, voltage and frequency

78. For a transformer, operating at constant load current, maximum efficiency will occur at______________?
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A. 0.8 lagging power factor

B. 0.8 leading power factor

C. unity power factor

D. zero power factor

79. Helical coils can be used on___________________?
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A. low voltage side of high kVA transformers

B. high voltage side of high kVA rating transformers

C. high frequency transformers

D. high voltage side of small capacity transformers

80. In the transformer following winding has got more cross-sectional area______________?
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A. High voltage winding

B. Primary winding

C. Secondary winding

D. Low voltage winding
81. If the percentage impedances of the two transformers working in parallel are different, then______________________?
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A. transformers will be overheated

B. power factors of both the transformers will be same

C. parallel operation will be not possible

D. parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load
82. A transformer transforms__________________?
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A. power

B. current

C. voltage

D. frequency

83. An ideal transformer will have maximum efficiency at a load such that?
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A. copper loss iron loss

B. copper loss = iron loss

C. none of the above

84. In a transformer the resistance between its primary and secondary is____________?
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A. 1 ohm

B. 1000 ohms

C. zero

D. infinite
85. N atural air coo ling is generally restricted for transformers up to__________?
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A. 15 MVA

B. 1.5 MVA

C. 5 MVA

D. 50 MVA

86. An open-circuit test on a transformer is conducted primarily to measure______________?
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A. total loss

B. none of the above

C. core loss

D. copper loss

E. efficiency

F. insulation resistance

87. Efficiency of a power transformer is of the order of________________?
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A. 100 per cent

B. 25 per cent

C. 98 per cent

D. 50 per cent

88. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds?
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A. 80C

B. 50C

C. 150C

D. 100C

89. The noise produced by a transformer is termed as_______________________?
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A. hum

B. zoom

C. ringing

D. buzz

90. Which of the following loss in a transformer is zero even at full load ____________?
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A. Eddy current loss

B. Friction loss

C. Core loss

D. Hysteresis loss

91. An ideal transformer is one which has_____________?
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A. none of the above

B. interleaved primary and secondary windings

C. no losses and magnetic leakage

D. a common core for its primary and secondary windings

E. core of stainless steel and winding of pure copper metal

92. A transformer oil must be free from________________?
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A. gases

B. moisture

C. odour

D. sludge

93. In a transformer the tappings are generally provided on_____________?
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A. secondary side

B. primary side

C. high voltage side

D. low voltage side

94. Material used for construction of transformer core is usually___________________?
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A. copper

B. aluminium

C. silicon steel

D. wood

95. The maximum efficiency of a distribution transformer is____________?
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A. at no load

B. at full load

C. at 80% full load

D. at 50% full load
96. A shell-type transformer has_________?
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A. negligibly hysteresis losses

B. none of the above

C. high eddy current losses

D. reduced magnetic leakage
97. The size of a transformer core will depend on__________?
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A. frequency

B. flux density of the core material

C. A. and B. both

D. area of the core

98. For the parallel operation of single phase transformers it is necessary that they should have___________?
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A. same efficiency

B. same polarity

C. same kVA rating

D. same number of turns on the secondary side.

99. Primary winding of a transformer________________?
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A. is always a low voltage winding

B. could either be a low voltage or high voltage winding

C. is always a high voltage winding

D. none of the above

100. The maximum load that a power transformer can carry is limited by its________________?
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A. voltage ratio

B. dielectric strength of oil

C. copper loss

D. temperature rise