Transformer MCQ Questions and Answers

81. The permissible flux density in the case of cold-rolled grain-oriented steel is around

1. 3.2 Wb/m²
   
2. 1.7 Wb/m²
   
3. 3.7 Wb/m²
   
4. 5.7 Wb/m²

82. Sumpner’s test is conducted on transformers to determine

1. temperature
2. stray losses
3. all-day efficiency
4. none of the above

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

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

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

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

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

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

86. The no-load current drawn by the transformer is usually what per cent of the full-load current?

1. 2 to 5 %
2. 0.2 to 0.5 %
3. 20 to 30 %
4. 12 to 15 %

87. The degree of mechanical vibrations produced by the laminations of a transformer depends on

1. tightness of clamping
2. gauge of laminations
3. size of laminations
4. all of the above

88. A transformer core is laminated to

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

89. 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

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

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

91. The no-load primary input is approximately equal to the

1. Iron loss of a transformer
2. Sum of Iron loss and copper loss of a transformer
3. Neither Iron loss of transformer nor copper loss
4. Copper loss of a transformer

92. While conducting short-circuit test on a transformer the following side is short-circuited

1. Primary side
   
2. HV side
3. LV side
4. None of these

93. The ordinary efficiency of a transformer is maximum when

1. it runs at full-load
2. it runs at half full-load
3. its copper loss equals iron loss
4. it runs overload

94. When a 400-Hz transformer is operated at 50 Hz, its kVA rating is

1. reduced to 1/8
2. increased 8 times
3. unaffected
4. determined by load on secondary

95. During the short-circuit test, the iron loss of a transformer is negligible because

1. the entire input is just sufficient to meet copper losses only
2. voltage applied across the HV (High Voltage) side is a small fraction of the rated voltage and so its flux
3. iron core becomes fully saturated
4. supply frequency is held constant

96. Compared to the secondary of a loaded step-up transformer, the primary has

1. lower voltage and higher current
2. higher voltage and lower current
3. lower voltage and lower current
4. higher voltage and higher current

97. Centrifugal method of reconditioning transformer oil is effective for the removal of

1. water
2. dissolved gases
3. solid impurities
4. All options are correct

98. The current transformer that is used to measure a 100A current by 5 A ammeter is

1. step-up transformer
2. step down transformer
3. power transformer
4. distribution transformer

99. The main purpose of using core in the transformer is to

1. Decrease iron losses
2. Prevent eddy current loss
3. Eliminate magnetic hysteresis
4. Decrease reluctance of the common magnetic

100. The iron losses are neglected during the short circuit test of a transformer because

1. The flux produced is very small as compared to the normal flux
2. Copper losses include iron losses
3. The iron core is fully saturated
4. The supply frequency influences copper losses