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Wednesday, 20 January 2016

D. C. Generators - Multiple Choice Questions

D. C. Generators - Multiple Choice Questions Points : d. c. generators multiple choice questions and answers, electrical objective type question answers, mcqs 1. The armature of a d.c. machine is prepared …….. of
(i) silicon steel
(ii) wrought iron
(iii) cast steel
(iv) soft iron

2. A 4-pole d.c. machine has ……….. magnetic circuits.
(i) 2
(ii) 8
(iii) 4
(iv) none of the above

3. ………. d.c. machines are mainly common.
(i) 2-pole
(ii) 4-pole
(iii) 6-pole
(iv) 8-pole

4. The coupling field among electrical with mechanical systems of a d.c. machine is …………..
(i) electric field
(ii) magnetic field
(iii) both electric and magnetic fields
(iv) none of the above

5. The current in armature conductors of a d.c. machine is ……………
(i) pure d.c.
(ii) pulsating d.c.
(iii) a.c.
(iv) pure d.c. plus pulsating d.c.

6. Small d.c. machines commonly contain ………… poles
(i) 4
(ii)6
(iii) 2
(iv) 8

7. The yoke of a d.c. machine is prepared of ……….
(1) silicon steel
(ii) soft iron
(iii) aluminium
(iv) cast steel

8. Armature winding of a d.c. machine is put on the rotor to ………….
(i) save iron
(ii) reduce Losses
(iii) facilitate commutation
(iv) reduce armature reaction

9. The armature winding of a d.c. machine is …………. winding.
(i) an open-circuit
(ii) a closed-circuit
(iii) partly open-circuit and partly closed-circuit
(iv) none of the above

10. The yoke of a d.c. machine carry ………. pole flux.
(i) the
(ii) one-half of
(iii) two times the
(iv) none of the above

11. Carbon brushes are use in a d.c. machine as …………….
(i) carbon lubricatcs and polishes the commutator
(ii) contact resistance is decreased
(iii) carbon is cheap
(iv) none of the above

12. The real working part of a d.c. machine is the
(i) commutator
(ii) field winding
(iii) armature winding
(iv) none of the above

13. The commutator pitch for a simplex lap winding is equivalent to ……………
(i) number of poles of the machine
(ii) pole pairs
(iii) 1
(iv) none of the above

14. The armature of a d.c. machine is laminated in arrange to decrease …………..
(i) eddy current loss
(ii) hysteresis loss
(iii) copper loss
(iv) frictional loss

15. The field structure of a d.c. machine use …………
(i) salient-pole arrangement
(ii) non-salient pole arrangement
(iii) both (i) and (ii)
(iv) none of the above

16. The most eddy current loss occurs in ………….. of a d.c. machine.
(i) field poles
(ii) yoke
(iii) commutating
(iv) armature poles

17. The brush voltage drop in a d.c. machine is on …………
(i) 0.1 V
(ii) 10 V
(iii) 2.V
(iv) 20 V

18. In a wave winding commutator pitch is about equal to .........
(i) pole pitch
(ii) twice the pole pitch
(iii) thrice the pole pitch
(iv) none of the above

19. High voltage d.c. machines use .......... winding.
(i) lap
(ii) wave
(iii) either lap or wave
(iv) none of the above

20. A 6-pole lap-wound generator has 300 conductors; the e.m.f. induce per conductor being 5 V The generate voltage of generator is ………….
(i) 60 V
(ii) 1500 V
(iii) 360 Y
(iv) 250 V

21. An 8-pole. 250 V, wave-wound generator has 400 conductors. If generator is to be lap-wound. the number of conductors required is..
(i) 800
(ii) 100
(iii) 3200
(iv) 1600

22. A triplex wave winding will have ……….. parallel paths.
(i) 6
(ii) 2
(iii) 4
(iv) none of the above

23. The nature of armature winding of a d.c. machine is certain by ...........
(i) front pitch
(ii) commutator pitch
(iii) back pitch
(iv) none of the above

24. In a simplex wave winding, number of parallel paths is equivalent to …………..
(i) number of poles in the machine
(ii) 2
(iii) number of pairs of poles
(iv) none of the above

25. In a d.c. generator, armature result ……………. pole tip.
(i) weakens the flux at the trailing
(ii) weakens the flux at the leading
(iii) strengthens the flux at the leading
(iv) none of the above

26. For a given d.c. generator, the generate voltage depends upon ………….
(i) flux only
(ii) speed only
(iii) both speed and flux
(iv) none of the above

27. The number of parallel paths in a simplex lap winding is equivalent to ………….
(i) 2
(ii) number of pairs of poles
(iii) number of poles
(iv) none of the above

28. The major drawback of a d.c. shunt generator is that …………..
(i) terminal voltage drops considerably with load
(ii) shunt field circuit has high resistance
(iii) generated voltage is small
(iv) it is expensive

29. In a d.c. machine, number of commutator segments is equivalent to ………..
(i) number of conductors
(ii) twice the number of poles
(iii) number of coils
(iv) none of the above

30. For the similar rating, a d.c. machine has ……….. an ac. machine.
(i) the same weight as
(ii) more weight than
(iii) less weight than
(iv) none of the above

31. A d.c. compound generator having full-load terminal voltage equivalent to no-load voltage is call ……… generator.
(i) under-compounded
(ii) over compouded
(iii) flat compounded
(iv) none of the above

32. The armature conductors of a 6-pole, lap-wound d.c. generator are divided into
(i) 2 parallel paths
(ii) 4 parallel paths
(iii) 3 parallel paths
(iv) 6 parallel paths

33. The field winding of a d.c. shunt machine generally carries ………. of rated current of machine.
(i) 2 % to 5 %
(ii) 15 % to 20%
(iii) more than 20%
(iv) less than 0.5%

34. ……….. together are called stray losses.
(i) copper and iron losses
(ii) iron and mechanical losses
(iii) field copper loss and iron loss
(iv) frictional loss and copper loss

35. The most percentage of heat loss in a d.c. machine is due to ……………..
(i) eddy current loss
(ii) hysteresis loss
(iii) copper loss
(iv) frictional loss

36. D.C. machines which are subjected to abrupt changes of load are give by ……………..
(i) incerpole windings
(ii) compensating windings
(iii) equalizers
(iv) copper brushes

37. In a lap winding, number of the brushes necessary is equal to ………..
(i) number of poles
(ii) number of pairs of poles
(iii) commutator pitch
(iv) none of the above

38. The efficiency of a d.c. generator is most when its variable loss is
(i) equal to constant loss
(ii) equal to half of constant loss
(iii) equal to double the constant loss
(iv) none of the above

39. The generally efficiency of a d.c. generator is most when its uneven loss is equivalent to
(i) constant loss
(ii) stray loss
(iii) iron loss
(iv) mechanical loss

40. The size of a d.c. generator can be reduced through by ……………
(i) lap winding
(ii) high-resistance winding material
(iii) iron commutator
(iv) magnetic material of high permeability

41. An 8-pole duplex lap winding will have …………. parallel paths
(i) 8
(ii) 4
(iii) 32
(iv) 16

42. Wave-wound generators give
(i) less current but more voltage
(ii) more current but less voltage
(iii) more current and more voltage
(iv) none of the above

43. Stray losses consist of
(i) magnetic and mechanical losses J
(ii) magnetic and copper losses
(iii) mechanical and copper losses
(iv) none of the above

44. The efficiency of a d.c. generator means its
(i) electrical efficiency
(ii) overall efficiency
(iii) mechanical efficiency
(iv) none of the above

45. The copper loss is steady for
(I) series generator only
(ii) shunt generator only
(iii) both shunt and compound generator
(iv) none of the above

46. A 4-pole, lap-wound d.c. shunt generator has an armature winding consisting of 220 turns each of 0.004 Ω. The armature resistance is
(i) 0.5 Ω
(ii) 1 Ω
(iii) 0.025 Ω
(iv) 0.055 Ω

47. The armature reaction in a d.c. generator can be increased through increasing the
(i) field current
(ii) armature current
(iii) data is insufficient
(iv) none of the above

48. If the flux per pole of a d.c. generator is halved but its speed is doubled, its generate e.m.f. will
(i) be halved
(ii) remain the same
(iii) be doubled
(iv) be quadrupled

49. In d.c. shunt generator, the steady losses is equal to
(i) stray losses
(ii) mechanical losses
(iii) stray losses plus shunt Cu loss
(iv) none of the above

50. In a d.c. generator, eddy current power loss is
(i) directly proportional to thickness of each lamination
(ii) inversely proportional to thickness of each lamination
(iii) directly proportional to square of thickness of each lamination
(iv) none of the above

51. In a d.c. generator, the major function of compensating winding is to
(i) assist in commutation
(ii) reduce demagnetizing effect of armature reaction.
(iii) reduce distorting effect of armature reaction
(iv) eliminate reactance voltage

52. The O.C.C. of a d.c. generator is too call its ....... characteristic.
(i) magnetic
(ii) internal
(iii) external
(iv) performance

53. In a long-shunt compound-wound generator, shunt field is connected in parallel by
(i) armature
(ii) series field
(iii) parallel combination of armature and series field.
(iv) series combination of armature and series field

54. The cause of armature reaction is to …………….
(i) decrease the total flux
(ii) increase the total flux
(iii) make the air-gap flux uniform
(iv) none of the above

55. A discretely excited d.c. generator is not use as ………….
(i) it is costly
(ii) separate d.c. source is required for field circuit
(iii) voltage drops considerably with toad
(iv) none of the above

56. The armature copper loss in a d.c. generator is a
(i) constant loss
(ii) variable Loss
(iii) stray loss
(iv) none of the above

57. A shunt generator gives its most voltage at
(i) no-load
(ii) full-Load
(iii) half full-load
(iv) none of the above

58. The d.c. generator that has poorest voltage is
(i) shunt generator
(ii) over-compounded generator
(iii) flat compounded generator
(iv) series generator

59. The terminal voltage of a ………… generator vary extensively by changes in load current.
(i) series
(ii) shunt
(iii) flat-compounded
(iv) none of the above

60. The line representing critical resistance of a d.c. generator …….. its O.C.C.
(i) intersects
(ii) runs parallel to
(iii) just touches
(iv) none of the above

61. The level of compounding in a cumulatively compounded d.c. generator is usually adjusted through
(i) changing series field current
(ii) changing shunt field current
(iii) connecting it long-shunt
(iv) connecting it short-shunt

62. The physical size of 100 kW. 2000 r.p.m. generator is ………. that of 10 kW. 200 r.p.m. generator.
(i) more than
(ii) less than
(iii) about the same as
(iv) none of the above

63. The O.C.C. of a d.c. generator
(i) is similar for au types of generators
(ii) is different for different generators
(iii) may be same or different
(iv) none of the above

64. The commutator of a d.c. generator acts as
(i) an amplifier
(ii) a rectifier
(iii) a load
(iv) none of the above

65. In a practical d.c. generator, mechanical competence is
(i) less than electrical efficiency
(ii) more than electrical efficiency
(iii) equal to electrical efficiency
(iv) none of the above

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