Large transformers, when used for some time, become very hot and are cooled by circulating oil. The heating of the transformer is due to:

For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used?

A

1.0 to 1.2 A/mm²

B

1.5 to 2.0 A/mm²

C

2.2 to 3.2 A/mm²

D

3.2 to 4.2 A/mm²

After the increase of price of oil by 40%, a family decided to reduce its oil consumption so that the expenditure for oil goes up by 26% only. If the total consumption of oil before the price rise was 10 kg per month, then what is the current consumption of oil per month (in kg)?

A

8

B

8.50

C

9

D

None of these

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

A

Conservator

B

Breather

C

Bushings

D

Buchholz relay

In self cooled motors the cooling time constant is about ______ than the heating time constant because cooling conditions are worse at standstill.

A

2 to 3 times greater

B

3 to 4 times greater

C

4 to 5 times greater

D

none of the above

Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds

A

50°C

B

80°C

C

100°C

D

150°C

Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

A

short-circuiting of the secondaries

B

power factor of one of the transformers is leading while that of the other lagging

C

transformers having higher copper losses will have negligible core losses

D

loading of the transformers not in proportion to their kVA ratings

Mineral oils (e.g. petroleum oils) are preferred over fatty oils (e.g. mustard oil, ghee, tallow, palm oil, olive oil etc.) as a lubricant due to its

A

Poor oxidation stability and high gum forming tendency

B

Greater tendency of decomposition at elevated temperature

C

Hydrolysis tendency in presence of water

D

All of the above

RBC remain separate from each other in the circulating blood due to the repulsive force caused by

A

Constant movement of RBCs

B

Negative electrostatic charge imparted by sialic acid of RBC membrane

C

Attraction of vascular endothelium

D

Distraction of band 3 protein

E

Biconcave shape of RBC

RBCs remain separate from each other in the circulating blood due to the repulsive force caused by

A

Constant movement of RBCs

B

Negative electrostatic charge imparted by sialic acid of RBC membrane

C

Attraction of vascular endothelium

D

Distraction of band 3 protein

E

Biconcave-shape

In heating the ferromagnetic material by induction heating, heat is produced due to

A

Induced current flow through the charge

B

Hysteresis loss taking place below Curie temperature

C

Due to hysteresis loss as well as eddy current loss taking place in the charge

D

None of the above factors

Large transformers, when used for some time, become very hot and are cooled by circulating oil. The heating of the transformer is due to:

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