Transformers

21. The changes in volume of transformer cooling oil due to variation of atmospheric tem-perature during day and night is taken care of by which part of transformer

Conservator
Breather
Bushings
Buchholz relay

Detailed SolutionThe changes in volume of transformer cooling oil due to variation of atmospheric tem-perature during day and night is taken care of by which part of transformer

22. The magnetising current of a transformer is usually small because it has

small air gap
large leakage flux
laminated silicon steel core
fewer rotating parts

Detailed SolutionThe magnetising current of a transformer is usually small because it has

23. Power transformers are generally designed to have maximum efficiency around

no-load
half-load
near full-load
10% overload

Detailed SolutionPower transformers are generally designed to have maximum efficiency around

24. Efficiency of a power transformer is of the order of

100 per cent
98 per cent
50 per cent
25 per cent

Detailed SolutionEfficiency of a power transformer is of the order of

25. Which winding in a transformer has more number of turns?

Low voltage winding
High voltage winding
Primary winding
Secondary winding

Detailed SolutionWhich winding in a transformer has more number of turns?

26. Which of the following properties is not necessarily desirable for the material for transformer core?

Low hysteresis loss
High permeability
High thermal conductivity
Adequate mechanical strength

Detailed SolutionWhich of the following properties is not necessarily desirable for the material for transformer core?

27. Noise level test in a transformer is a

special test
routine test
type test
none of the above

Detailed SolutionNoise level test in a transformer is a

28. In a transformer routine efficiency depends upon

supply frequency
load current
power factor of load
both (B) and (C)

Detailed SolutionIn a transformer routine efficiency depends upon

29. Star/star transformers work satisfactorily when

load is unbalanced only
load is balanced only
on balanced as well as unbalanced loads
none of the above

Detailed SolutionStar/star transformers work satisfactorily when

30. When secondary of a current transformer is open-circuited its iron core will be

hot because of heavy iron losses taking place in it due to high flux density
hot because primary will carry heavy current
cool as there is no secondary current
none of above will happen

Detailed SolutionWhen secondary of a current transformer is open-circuited its iron core will be

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