AC MACHINES 6

1. A transformer is working at its maximum efficiency. Its iron-loss is 500 W. Its copper-loss will be
a) 250 W
b) 300 W
c) 400 W
d) 500 W
ans. d

2. Distribution transformers are designed to have maximum efficiency nearly
a) at full load
b) at 50% of FL
c) at no load
d) none of these
ans. b

3. Distribution transformers have good all day efficiency due to
a) low copper-loss
b) low iron loss
c) low copper as well as iron losses
d) none of these
ans. b

4. The special silicon steel is used for lamination's because
a) eddy current losses are induced
b) hysteresis losses are reduced
c) both losses are reduced
d) none of these
ans. b

5. The yoke sections of transformers using hot-rolled lamination's is made 15% greater than that of the core so as to
a) to reduce the copper-loss
b) to increase the size of transformers
c) to reduce the iron loss in yoke and magnetizing current
d) to provide better cooling
ans. c

6. The concentric windings are used in core-type transformers with
a) HT winding placed next to core
b) LT winding placed next to core
c) LT winding on the outer side
d) HT winding on the outer side
ans. b

7. In power transformers the tapping's are provided on
a) high voltage side
b) low voltage side
c) in the middle of both windings
d) LV as well as on HV side
ans. a

8. The advantage of putting tappings at the phase ends of transformer is
a) to obtain fine variation of voltage
b) to operate with ease
c) to obtain better regulation
d) reduce the number of bushings
ans. d

9. Transformer transforms
a) frequency
b) voltage
c) current
d) power
ans. b

10. A step-up transformer increases
a) voltage
b) current
c) power
d) frequency
ans. a