transformers MCQs – Page 4

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

transformers Mcqs
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