Transformers

91. The noise resulting from vibrations of laminations set by magnetic forces, is termed as

1. magnetostrication
2. boo
3. hum
4. zoom

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

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

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

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

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94. The path of the magnetic flux in transformer should have

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

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95. The permissible flux density in case of cold rolled grain oriented steel is around

1. 1.7 Wb/m2
2. 2.7 Wb/m2
3. 3.7 Wb/m2
4. 4.7 Wb/m2

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96. The power transformer is a constant

1. voltage device
2. current device
3. power device
4. main flux device

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97. 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

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98. The purpose of providing iron core in a step-up transformer is

1. to provide coupling between primary and secondary
2. to increase the magnitude of mutual flux
3. to decrease the magnitude of magnetizing current
4. to provide all above features

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99. The secondary of a current transformer is always short-circuited under operating conditions because it

1. avoids core saturation and high voltage induction
2. is safe to human beings
3. protects the primary circuit
4. none of the above

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100. 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

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