1. The armature core of a D.C. generator is usually made of
Correct : A. silicon steel
2. Open circuited armature coil of a D.C. machine is
Correct : C. both (a) and (b)
3. For the parallel operation of two or more D.C. compound generators, we should ensure that
Correct : D. series fields of all generators should be either on positive side or negative side of the armature
4. D.C. series generator is used
Correct : C. voltage at the toad end of the feeder
5. Following D.C. generator will be in a position to build up without any
residual magnetism in the poles
Correct : D. self-excited generator
6. Interpole flux should be sufficient to
Correct : C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
7. D.C. generator generally preferred for charging automobile batteries is
Correct : C. long shunt compound generator
8. In a D.C. generator the number of mechanical degrees and electrical degrees
will be the same when
Correct : D. number of poles is 2
9. Permeance is the reciprocal of
Correct : B. reluctance
10. In D.C. generators the polarity of the interpoles
Correct : A. is the same as that of the main pole ahead
11. The e.m.f. generated in a D.C. generator is directly proportional to
Correct : B. speed of armature
12. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except
Correct : B. dummy coils
13. In D.C. generators on no-load, the air gap flux distribution in space is
Correct : D. flat topped
14. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If thespeed increases to 1200 r.p.m., the generated e.m.f. will be nearly
Correct : C. 240 V
15. The purpose of providing dummy coils in a generator is
Correct : D. to provide mechanical balance for the rotor
16. If a D.C. generator fails to build up the probable cause could not be
Correct : B. field resistance less than the critical resistance
17. Flashing the field of D.C. generator means
Correct : B. creating residual magnetism by a D.C. source
18. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
Correct : D. 580V
19. In a D.C. generator the critical resistance refers to the resistance of
Correct : B. field
20. To achieve sparkless commutation brushes of a D.C. generator are rockedm
ahead soas to bring them
Correct : A. just ahead of magnetic neutral axis
21. Armature coil is short circuited by brushes when it lies
Correct : A. along neutral axis
22. A cumulatively compounded long shunt generator when operating as a motor would be
Correct : B. differentially compounded long shunt
23. To avoid formation of grooves in the commutator of a D.C. machine
Correct : A. the brushes of opposite polarity should track each other
24. The following constitute short-circuit in the armature winding.
Correct : D. All of the above
25. The rapid wear of brushes takes place due to
Correct : D. all of the above factors
26. Number of tappings for each equilizer ring is equal to
Correct : A. number of pole pairs
27. A D.C. generator can be considered as
Correct : C. rotating amplifier
28. In any rotating machine that part which houses the conductors and in
which e.m.f. induced is to be utilised is called
Correct : D. armature
29. In a D.C. machine stray loss is the sum of
Correct : D. iron loss and mechanical loss
30. Lap winding is composed of
Correct : A. any even number of conductors
31. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will
Correct : B. decrease
32. An exciter for a turbo generator is a
Correct : B. shunt generator
33. In case of a flat compounded generator
Correct : C. voltage remains constant irrespec¬tive of the load
34. Which of the following generator will have negligible terminal voltage while running on no-load ?
Correct : A. Series generator
35. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ?
Correct : D. None of the above
36. In over compounded generator, full load terminal voltage is
Correct : C. more than noload terminal voltage
37. In a level compounded D.C. generator, full load terminal voltage is
Correct : B. equal to no-load terminal voltage
38. The terminal voltage of a D.C. shunt generator drops on load because of
all of the following reasons except
Correct : D. commut ation
39. In a D.C. generator
Correct : C. external characteristic = magnetisation characteristic - ohmic drop - armature reaction
40. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
Correct : B. will be of 5 Hz
41. A 220 V D.C. generator is run at full speed without any excitation. The
open circuit voltage will be
Correct : B. about 2 V
42. In a separately excited generator supplying rated load the armature reaction ,
Correct : A. is always present
43. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speedwill be
Correct : A. zero
44. Armature reaction in a generator results in
Correct : A. demagnetisation of leading pole tip and magnetisation of trailing pole tip
45. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
Correct : D. Shunt field
46. Wave winding is composed of
Correct : C. that even number which is exact multiple of poles + 2
47. The critical resistance of the D.C. generator is the resistance of
Correct : A. field
48. When two D.C. series generators are running in parallel, an equilizer bar is used
Correct : C. so that two similar machines will pass approximately equal currents to the load
49. Which of the following generating machine will offer constant voltage on all
loads ?
Correct : C. Level compounded generator .
50. Which of the following generators will be preferred if they are required to be
run in parallel ?
Correct : A. Shunt generators
51. Two generators are running in parallel. One of the generators may run as
motor for which of the following reasons ?
Correct : D. That generator takes large share of loads
52. A D.C. generator works on the principle of
Correct : C. Faraday's law of electromagnetic induction
53. A series generator can self-excite
Correct : B. only if the load current is not zero
54. A shunt generator can self-excite
Correct : A. only if the resistance of the field circuit is less than critical value
55. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be
Correct : C. greater than 150 V
56. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
Correct : C. may be greater or less than 250 V
57. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be
Correct : B. 267.5V
58. The essential condition for parallel operation of two D.C. generators is that
they have '
Correct : C. the same drooping voltage charac-teristics
59. When two D.C. generators are running in parallel an equilizer bar is used
Correct : D. so that the two identical machines will pass approximately equal currents to the load
60. With a D.C. generator which of the following regulation is preferred ?
Correct : D. 1% regulation
61. Which generator would you prefer for feeding long D.C. transmission lines ?
Correct : C. Over compound generator
62. In a D.C. generator the critical resistance can be increased by
Correct : C. increasing its speed
63. The number of armature parallel paths in a two-pole D.C. generator having
duplexlap winding is
Correct : B. 4
64. For both lap and wave windings, there are as many commutator bars as the
numberof
Correct : C. winding elements
65. The series field of a short-shunt D.C. generator is excited by
Correct : D. load current
66. As a result of armature reaction, the reduction in the total mutual air gap flux
in aD.C. generator is approximately
Correct : D. 5 percent
67. Shunt generators are most suited for stable parallel operation because of their
Correct : C. drooping voltage characteristics
68. The main factor which leads to unstable parallel operation of flat and over compounded generators is