multiple choice questions on transformer # 6

                                Hi friends, this post is about transformer objectives. These are some of the questions asked in previous question papers of Gate, IES and other competitive exams. check out and comment if you have any doubts.....

1) The main purpose of performing open current on a transformer is to measure its
A) copper loss
B) core loss
C) total loss
D) insulation resistance

Ans:B

2) The open-circuit test on a transformer gives
A) equivalent resistance and leakage reactance
B) magnetizing current and core loss at rated voltage
C) copper losses
D) both (B) and (C)

Ans:B

3) Transformer will operate at maximum efficiency when
A) hysteresis loss = eddy current loss
B) eddy current loss = copper loss
C) copper loss = iron loss
D) hysteresis loss = copper loss

Ans:C

4) Open circuit test in a transformer is performed with
A) rated transformer voltage
B) rated transformer current
C) direct current
D) high frequency supply

Ans:A

5) The efficiency of two identical transformers under load conditions can  be determined by
A) back to back test
B) open circuit test
C) short circuit test
D) any of the above

Ans:A

6) The efficiency of a power transformer can be determined indirectly by
A) open circuit test alone
B) short circuit test alone
C) open circuit and short circuit tests
D) back to back test

Ans:C

7) The transformer efficiency will be maximum at a power factor of
A) 0.8 lead
B) unity
C) 0.8 lag
D) 0.5 lag or lead

Ans:B

8) During short circuit test, the core losses are negligible. This is because
A) the voltage applied across the high voltage side is a fraction of its rated voltage and so is the mutual flux
B) the current on the lv side is very small
C) the power factor is high
D) iron becomes fully saturated

Ans:A

9) A transformer has a percentage resistance of 2% and percentage reactance of 4%. what are its regulation at power factor 0.8 lagging and 0.8 leading respectively?
A) 4% and -0.8%
B) 3.2% and -1.6%
C) 1.6% and -3.2%
D) 4.8% and -0.6%

Ans:A

10) A 4 KVA, 400/200 V single phase transformer has resistance of 0.02 pu and reactance of 0.06pu. Its actual resistance and reactance referred to hv side, are , respectively
A) 0.2 ohm and 0.6 ohm
B) 0.8 ohm and 2.4 ohm
C) 0.08 ohm and 0.24 ohm
D) 2 ohm and 6 ohm

Ans:B

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