Transformers

The size of a transformer core will depend on__________?

A. frequency
B. area of the core
C. flux density of the core material
D. A. and B. both

The secondary winding of which of the following transformers is always kept closed?

A. Step-up transformer
B. Step-down transformer
C. Potential transformer
D. Current transformer

The function of breather in a transformer is___________?

A. to provide oxygen inside the tank
B. to cool the coils during reduced load
C. to cool the transformer oil
D. to arrest flow of moisture when outside air enters the transformer

The efficiencies of transformers compared with that of electric motors of the same power are____________?

A. about the same
B. much smaller
C. much higher
D. somewhat smaller
E. none of the above

The transformer oil should have _______ volatility and _______ viscosity?

A. low,low
B. high,high
C. low,high
D. high,low

In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of_________________?

A. less than 15 A
B. more than 15 A
C. 15 A
D. none of the above

For the parallel operation of single phase transformers it is necessary that they should have___________?

A. same efficiency
B. same polarity
C. same kVA rating
D. same number of turns on the secondary side.

Minimum voltage regulation occurs when the power factor of the load is_____________?

A. unity
B. lagging
C. leading
D. zero

Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is_________________?

A. approximately equal to one
B. less than one
C. great than one
D. none of the above

Short circuit test on transformers is conducted to determine____________?

A. hysteresis losses
B. copper losses
C. core losses
D. eddy current losses