Page 601 - Basic Electrical Engineering

a. Magnetization
b. Demagnetization
c. Polarization
d. No effect.

18. On which of the following does the voltage regulation of a transformer depend?

a. Load power factor
b. Magnitude of load
c. Winding resistance and reactance
d. all factor as in (a), (b), and (c).

19. The no-load current of a transformer is

a. The algebraic sum of I and I c
m
b. Phasor sum of I and I c
m
1
c. Algebraic sum of I and I 1
o
1
d. Phasor sum of I and I .
o
1
20. The no-load current of a transformer as compared to its full-load current can be expressed as

a. 0 to 2 per cent
b. 2 to 5 per cent
c. 10 to 20 per cent
d. 20 to 30 per cent.

21. Power factor of a transformer of no load is low due to

a. Large component of magnitizing current, which lags the voltage by 90°
b. Large component of loss component of current
c. Secondary ampere-turns interfering with the primary ampere-turns
d. The fact that the primary and secondary windings are not firmly coupled.

22. The core loss and copper loss of a transformer on full load are 400 W and 600 W,
respectively. Their values at one-third full load will be

a. 133.3 W and 200 W
b. 400 W and 66.66 W
c. 133.3 W and 600 W
d. 400 W and 200 W.

23. The full-load core loss and copper loss of a transformer are 400 W and 600 W, respectively.
At approximately what percentage of full-load will the efficiency be maximum?

a. 81 per cent
b. 91 per cent