Transformers

101. The size of a transformer core will depend on

1. frequency
2. area of the core
3. flux density of the core material
4. (a) and (b) both

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102. The thickness of laminations used in a transformer is usually

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

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103. The transformer laminations are insulated from each other by

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

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104. The transformer oil should have _________ volatility and _________ viscosity.

1. low,low
2. high,high
3. low,high
4. high,low

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105. The transformer ratings are usually expressed in terms of

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

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106. The use of higher flux density in the transformer design

1. reduces weight per kVA
2. reduces iron losses
3. reduces copper losses
4. increases part load efficiency

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107. The value of flux involved m the e.m.f. equation of a transformer is

1. average value
2. r.m.s. value
3. maximum value
4. instantaneous value

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108. The voltage transformation ratio of a transformer is equal to the ratio of

1. primary turns to secondary turns
2. secondary current to primary current
3. secondary induced e.m.f. to primary induced e.m.f.
4. secondary terminal voltage to primary applied voltage

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109. Transformer breaths in when

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

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110. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

1. short-circuiting of the secondaries
2. power factor of one of the transformers is leading while that of the other lagging
3. transformers having higher copper losses will have negligible core losses
4. loading of the transformers not in proportion to their kVA ratings

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