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Transformers

Study 132 Electrical Engineering MCQs with correct answers and explanations.

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71Electrical EngineeringMedium

Buchholz’s relay gives warning and protection against________?

Aelectrical fault outside the transformer in outgoing feeder

Bnone of the above

Celectrical fault inside the transformer itself

Dfor both outside and inside faults

Correct answer

C. electrical fault inside the transformer itself

Explanation

The correct answer is electrical fault inside the transformer itself.

72Electrical EngineeringMedium

If a transformer is continuously operated the maximum temperature rise will occur in________?

Atank

Bwindings

Ccore

Dany of the above

Correct answer

B. windings

Explanation

The correct answer is windings.

73Electrical EngineeringMedium

Delta/star transformer works satisfactorily when________?

Aon balanced as well as unbalanced loads

Bload is balanced only

Cload is unbalanced only

Dnone of the above

Correct answer

A. on balanced as well as unbalanced loads

Explanation

The correct answer is on balanced as well as unbalanced loads.

74Electrical EngineeringMedium

A transformer cannot raise or lower the voltage of a D.C. supply because________?

Anone of the above

BFaraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero

Ca D.C. circuit has more losses

Dthere is no need to change the D.C. voltage

Correct answer

B. Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero

Explanation

The correct answer is Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero.

75Electrical EngineeringMedium

No-load current of a transformer has________?

Ahas high magnitude and low power factor

Bhas small magnitude and low power factor

Chas high magnitude and high power factor

Dhas small magnitude and high power factor

Correct answer

B. has small magnitude and low power factor

Explanation

The correct answer is has small magnitude and low power factor.

76Electrical EngineeringMedium

In a power or distribution transformer about 10 per cent end turns are heavily insulated________?

Ato reflect the line surge and save the winding of a transformer from damage

Bto absorb the line surge voltage and save the winding of transformer from damage

Cnone of the above

Dto withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

Correct answer

D. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

Explanation

The correct answer is to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns.

77Electrical EngineeringMedium

During open circuit test of a transformer:

Aprimary is supplied rated kVA

Bprimary is supplied current at reduced voltage

Cprimary is supplied rated voltage

Dprimary is supplied full-load current

Correct answer

C. primary is supplied rated voltage

Explanation

The correct answer is primary is supplied rated voltage.

78Electrical EngineeringMedium

Part of the transformer which is most subject to damage from overheating is________?

Aframe or case

Btransformer tank

Ccopper winding

Dwinding insulation

Eiron core

Correct answer

D. winding insulation

Explanation

The correct answer is winding insulation.

79Electrical EngineeringMedium

Greater the secondary leakage flux________?

Aless will be the primary terminal voltage

Bnone of the above

Cless will be the primary induced e.m.f.

Dless will be the secondary induced e.m.f.

Correct answer

D. less will be the secondary induced e.m.f.

Explanation

The correct answer is less will be the secondary induced e.m.f..

80Electrical EngineeringMedium

The permissible flux density in case of cold rolled grain oriented steel is around________?

A4.7 Wb/m2

B1.7 Wb/m2

C3.7 Wb/m2

D2.7 Wb/m2

Correct answer

B. 1.7 Wb/m2

Explanation

The correct answer is 1.7 Wb/m2.

Buchholz’s relay gives warning and protection against________?

Aelectrical fault outside the transformer in outgoing feeder

Bnone of the above

Celectrical fault inside the transformer itself

Dfor both outside and inside faults

Correct answer

C. electrical fault inside the transformer itself

Explanation

The correct answer is electrical fault inside the transformer itself.

A transformer cannot raise or lower the voltage of a D.C. supply because________?

Anone of the above

BFaraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero

Ca D.C. circuit has more losses

Dthere is no need to change the D.C. voltage

Correct answer

B. Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero

Explanation

The correct answer is Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero.

In a power or distribution transformer about 10 per cent end turns are heavily insulated________?

Ato reflect the line surge and save the winding of a transformer from damage

Bto absorb the line surge voltage and save the winding of transformer from damage

Cnone of the above

Dto withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

Correct answer

D. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

Explanation

The correct answer is to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns.