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MCQ of Transformer page-18


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71. The short circuit test on a transformer gives its

A) Magnetizing current and core loss
B) Magnetizing impedance
C) Equivalent resistance and reactance
D) Equivalent resistance and core loss.

Ans : (C)

72. Magnetizing impedance of a transformer is determined by

A) Open circuit test
B) Short circuit test
C) Both open and short circuit test
D) Other then above test.

Ans : (A)

73. The open circuit test on a transformer gives

A) Equivalent resistance and leakage reactance
B) Magnetizing current and core loss rated voltage
C) Copper loss
D) Both (B) and (C).

Ans : (B)

74. There are two …… 800 kW transformers each having a maximum efficiency of 98% but in out the maximum efficiency occurs at full load which in the other it occurs at half load. Each transformer is on full load for 4 hours; one-half load for 6 hours and one-tenth load for 14 hours per day. Which transformer former will have better all day efficiency ?

A) Transformer with maximum efficiency at full load
B) Transformer with maximum efficiency at half load
C) Both will have same efficiency.

Ans : (B)

75. The regulation of a good transformer should be near

A) 100 %
B) 50 %
C) 10 %
D) 1 %.

Ans : (C)

76. A 20 kVA, 44/220 V. 1 - ф, 50 Hz transformer has iron loss of 100 W. The copper loss is found to be 100 W when delivering half full-load current. The percentage, of full load when the efficiency will be maximum, is

A) 55.56 %
B) 72 %
C) 81 %
D) 90 %

Ans : (A)

77. Buchholz relay is used in

A) Motor protection
B) Transformer protection
C) Greater protection
D) Lime protection.

Ans : (B)

78. No load current in a transformer as a percentage of full load current is approximately

A) 1 % to 3 %
B) 5 % to 10 %
C) 15 % to 20 %
D) 25 %.

Ans : (A)

79. If the frequency of supply voltage is doubled, which loss will increase

A) Hysteresis loss
B) Eddy current loss
C) Both (A) and (B)
D) None of the above.

Ans : (C)

80. 1 kVA, 230 V, 50 Hz single phase transformer has an eddy current loss of 30 watts. The eddy current loss when the transformer is excited by the dc source of same voltage will be.

A) Zero watts
B) Less than 30 watts
C) More than 30 watts
D) 30 watts.

Ans : (A)


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