Transformers

11. In case of 3-phase induction motors, plugging means

pulling the motor directly on line without a starter
locking of rotor due to harmonics
starting the motor on load which is more than the rated load
interchanging two supply phases for quick stopping

Detailed SolutionIn case of 3-phase induction motors, plugging means

12. The purpose of providing iron core in a step-up transformer is

To provide coupling between primary and secondary
To increase the magnitude of mutual flux
To decrease the magnitude of magnetizing current
To provide all above features

Detailed SolutionThe purpose of providing iron core in a step-up transformer is

13. The chemical used in breather is

asbestos fiber
silica sand
sodium chloride
silica gel

Detailed SolutionThe chemical used in breather is

14. The noise produced by a transformer is termed as

zoom
hum
ringing
buzz

Detailed SolutionThe noise produced by a transformer is termed as

15. The no-load current drawn by transformer is usually what per cent of the full-load current?

0.2 to 0.5 per cent
2 to 5 per cent
12 to 15 per cent
20 to 30 per cent

Detailed SolutionThe no-load current drawn by transformer is usually what per cent of the full-load current?

16. The power factor of an induction motor under no-load conditions will be closer to

0.2 lagging
0.2 leading
0.5 leading
unity

Detailed SolutionThe power factor of an induction motor under no-load conditions will be closer to

17. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

Ns
s.Ns
(1 - s)Ns
(Ns - 1)s

Detailed SolutionIn Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

18. If a transformer is continuously operated the maximum temperature rise will occur in

core
windings
tank
any of the above

Detailed SolutionIf a transformer is continuously operated the maximum temperature rise will occur in

19. The chemical used in breather for transformer should have the quality of

ionizing air
absorbing moisture
cleansing the transformer oil
cooling the transformer oil

Detailed SolutionThe chemical used in breather for transformer should have the quality of

20. Buchholz’s relay gives warning and protection against

electrical fault inside the transformer itself
electrical fault outside the transformer in outgoing feeder
for both outside and inside faults
none of the above

Detailed SolutionBuchholz’s relay gives warning and protection against

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