Page 602 - Basic Electrical Engineering

c. 95 per cent
d. 99 per cent.

24. The full load output of a transformer at unity power factor is 800 W. Its output at half load 0.8
power factor will be

a. 400 W
b. 320 W
c. 160 W
d. 640 W.

25. Large capacity transformers are placed in tanks filled with transformer oil. Which of the
following are not valid for the above?

a. Oil provides insulation between the two windings.
b. Oil cools the transformer.
c. Oil prevents magnetizing flux from getting reduced with time.
d. Temperature rise of the winding is kept under control.

26. The full-load copper loss of a transformer is 1200 W. At half load the copper loss will be

a. 600 W
b. 1200 W
c. 300 W
d. 900 W.

27. The full-load core loss of a transformer is 1200 W. At half load the core loss will be

a. 600 W
b. 1200 W
c. 300 W
d. 900 W.

28. The no-load current of a certain transformer is 2 A. Its magnetizing component may be

a. 1.8 A
b. 0.2 A
c. 0.4 A
d. 0.02 A.

29. When the primary and secondary windings of a transformer are perfectly magnetically
coupled

a. The leakage reactance will be high and voltage regulation will be high (i.e., poor)
b. The leakage reactance will be low and voltage regulation will be low (i.e., good)
c. The leakage reactance will be low and voltage regulation will be high (i.e., poor)
d. The leakage reactance will be high and voltage regulation will be low (i.e., good).