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MCQ of Transformer page-21


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101. In which of the following transformer path of primary winding also serves as the secondary winding ?

A) Autotransformer
B) Potential transformer
C) Current transformer
D) Step up transformer.

Ans : (A)

102. When a star-delta transformer bank of three single phase transformers is to be used for step down transformation with line voltages of 23000 V and 2300 V, the ratio of transformation will be

A) 5.8 : 1
B) 10 : 1
C) 12.1 : 1
D) 17.2 : 1.

Ans : (B)

103. In a transformer, on load current :

A) Lags the applied voltage by 90°
B) Leads the applied voltage by 90°
C) Leads the applied voltage some what less than 90°
D) Lags the applied voltage by some what less than 90°.

Ans : (D)

104. A 2 KVA transformer has iron loss of 150 W and full load copper loss of 250 W. The maximum efficiency of the transformer would when the total loss is

A) 100 W
B) 300 W
C) 400 W
D) 500 W.

Ans : (B)

105. A transformer has negative voltage regulation when its load power factor is

A) lagging
B) unity
C) leading
D) zero.

Ans : (C)

106. The efficiency of a power transformer at relatively light loads is quite low. This is due to

A) poor power factor
B) high fixed loss in comparison to the output
C) small secondary output
D) small copper losses.

Ans : (B)

107. The voltage regulation of a transformer at full load and 0.8 power factor lagging is 2.5 %. The voltage regulation at full load, 0.8 power factor leading will be

A) 2.5 %
B) 1.0 %
C) Zero
D) - 2.5 %.

Ans : (D)

108. During short circuit test core losses are negligible. This is because

A) Iron becomes fully saturated
B) The power factor is high
C) The current on the low voltage side is very small
D) The voltage applied across the high voltage side is a fraction of its rated voltage and so is the mutual flux.

Ans : (D)

109. Power factor of a transformer on no load is poor due to

A) Low no load current
B) Low primary winding resistance
C) Open circuit secondary
D) Magnetizing reactance of the transformer.

Ans : (D)

110. Power input to a transformer at no load and rated voltage consists of

A) Core loss
B) Copper loss
C) Hysteresis loss
D) Eddy current loss.

Ans : (A)


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