Transformers Archives

1. No-load current in a transformer

lags behind the voltage by about 75Â°

leads the voltage by about 75Â°

lags behind the voltage by about 15Â°

leads the voltage by about 15Â°

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2. The efficiency of two identical transformers under load conditions can be determined by

short-circuit test

back-to-back test

open circuit test

any of the above

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3. Greater the secondary leakage flux

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

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

less will be the primary terminal voltage

Detailed SolutionGreater the secondary leakage flux

4. A transformer oil must be free from

sludge

odour

gases

moisture

Detailed SolutionA transformer

oil must be free from

5. The highest voltage for transmitting electrical power in India is

33 kV

66 kV

132 kV

400 kV E. 765 kV

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6. In an actual transformer the iron loss remains practically constant from noload to fullload because

value of transformation ratio remains constant

permeability of transformer core remains constant

core flux remains practically constant

primary voltage remains constant

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7. The efficiencies of transformers compared with that of electric motors of the same power are

about the same

much smaller

much higher

somewhat smaller

Detailed SolutionThe

efficiencies of transformers compared with that of electric motors of the same power are

8. The hum in a transformer is mainly attributed to

load changes

oil in the transformer

magnetostriction

mechanical vibrations

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

0.4 mm to 0.5 mm

4 mm to 5 mm

14 mm to 15 mm

25 mm to 40 mm

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10. Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V

Its secondary current is 5 A

Its secondary voltage is 400 V

supply is incorrect? A. Its secondary current is 5 A B. Its secondary voltage is 400 V C. Its rating is 2 kVA

Its secondary current is 20 A

Detailed SolutionWhich of the following statements regarding an idel single-phase transformer

having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V

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