Transformers

1. No-load current in a transformer

lags behind the voltage by about 75°
leads the voltage by about 75°
lags behind the voltage by about 15°
leads the voltage by about 15°

Detailed SolutionNo-load current in a transformer

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

Detailed SolutionThe efficiency of two identical transformers under load conditions can be determined by

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
none of the above

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

Detailed SolutionThe highest voltage for transmitting electrical power in India is

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

Detailed SolutionIn an actual transformer the iron loss remains practically constant from noload to fullload because

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

Detailed SolutionThe hum in a transformer is mainly attributed to

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

Detailed SolutionThe thickness of laminations used in a transformer is usually

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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