Short notes
Objective questions (Answers are given below)
- The external characteristic of a shunt generator
can be obtained directly from its ——
characteristic.
(a) internal (b) open-circuit
(c) load-saturation (d ) performance - 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 - 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. - 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. - The voltage build-up process of a d.c. generator
is
(a) difficult (b) delayed
(c) cumulative (d) infinite - Which of the following d.c. generator cannot
build up on open-circuit ?
(a) shunt (b) series
(c) short shunt (d) long shunt - 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. - 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. - 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 - 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
- An ideal d.c. generator is one that has ………
voltage regulation.
(a) low (b) zero
(c) positive (d) negative - The ……… generator has poorest voltage
regulation.
(a) series (b) shunt
(c) compound (d) high - The voltage regulation of an overcompound
d.c. generator is always ……….
(a) positive
(b) negative
(c) zero
(d) high - 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).