Electrical Machines (Generator Characteristics)
1. The external characteristic of a shunt generator can be obtained directly from its —— characteristic.
(d ) performance
2. Load saturation characteristic of a d.c. generator gives relation between
(a) V and Ia
(b) E and Ia
(c) E0 and If
(d ) V and If
3. The slight curvature at the lower end of the O.C.C. of a self-excited d.c. generator is due to
(a) residual pole flux
(b) high armature speed
(c) magnetic inertia
(d) high field circuit resistance.
4. For the voltage built-up of a self-excited d.c. generator, which of the following is not an essential condition?
(a) There must be some residual flux
(b) Field winding mmf must aid the residual flux
(c) Total field circuit resistance must be less than the critical value
(d) Armature speed must be very high.
5. The voltage build-up process of a d.c. generator is
6. Which of the following d.c. generator cannot build up on open-circuit ?
(c) short shunt
(d) long shunt
7. If a self-excited d.c. generator after being installed, fails to build up on its first trial run, the first thing to do is to
(a) increase the field resistance
(b) check armature insulation
(c) reverse field connections
(d) increase the speed of prime mover.
8. If residual magnetism of a shunt generator is destroyed accidentally, it may be restored by
connecting its shunt field
(a) to earth
(b) to an a.c. source
(b) in reverse
(d) to a d.c. source.
9. The three factors which cause decrease in the terminal voltage of a shunt generator are
(a) armature reactances
(b) armature resistance
(c) armature leakages
(d) armature reaction
(e) reduction in field current
10. If field resistance of a d.c. shunt generator is increased beyond its critical value, the generator
(a) output voltage will exceed its name-plate rating
(b) will not build up
(c) may burn out if loaded to its name-plate rating
(d ) power output may exceed its name-plate rating
11. An ideal d.c. generator is one that has ......... voltage regulation.
12. The ......... generator has poorest voltage regulation.
13. The voltage regulation of an over compound d.c. generator is always ..........
14. Most commercial compound d.c. generator are normally supplied by the manufacturers as over compound machines because
(a) they are ideally suited for transmission of d.c. energy to remotely-located loads
(b) degree of compounding can be adjusted by using a divertor across series field
(c) they are more cost effective than shunt generators
(d) they have zero percent regulation.
1. (b) 2. (d ) 3. (c) 4. (d ) 5. (c) 6. (b) 7. (c) 8. (d) 9. (b,d,e) 10. (b) 11. (b) 12. (a) 13. (b) 14. (b).