451. 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
452. 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
453. 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
454. N atural air coo ling is generally restricted for transformers up to__________?
A. 1.5 MVA
B. 5 MVA
C. 15 MVA
D. 50 MVA
455. A shell-type transformer has_________?
A. high eddy current losses
B. reduced magnetic leakage
C. negligibly hysteresis losses
D. none of the above
456. The secondary of a current transformer is always short-circuited under operating conditions because it____________________?
A. avoids core saturation and high voltage induction
B. is safe to human beings
C. protects the primary circuit
D. none of the above
457. In a transformer the resistance between its primary and secondary should be_____________?
A. zero
B. 10 Q
C. 1000 Q
D. infinity
458. A transformer can have regulation closer to zero___________?
A. on full-load
B. on overload
C. on leading power factor
D. on zero power factor
459. A Transformer transforms____________?
A. voltage
B. current
C. current and voltage
D. power
460. For a transformer, operating at constant load current, maximum efficiency will occur at______________?
A. 0.8 leading power factor
B. 0.8 lagging power factor
C. zero power factor
D. unity power factor
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