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d c generators MCQs

Practise focused d c generators questions with marked answers for exam preparation and subject revision.

d c generators Mcqs
1. In a D.C. generator the critical resistance can be increased by_____________?
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A. decreasing its speed

B. increasing its field resistance

C. increasing its speed

D. decreasing its field resistance

2. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage____________?
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A. may be greater or less than 250 V

B. will be less than 250 V

C. will always be 250 V

D. none of the above

3. The series field of a short-shunt D.C. generator is excited by_______________?
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A. armature current

B. shunt current

C. external current

D. load current
4. Which generator would you prefer for feeding long D.C. transmission lines ?
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A. Flat compound generator

B. Over compound generator

C. Shunt generator

D. Series generator

5. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by______________?
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A. Blv

B. Blv2

C. Bl2v2

D. Bl2v

6. The purpose of providing dummy coils in a generator is__________________?
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A. to reduce eddy current losses

B. to provide mechanical balance for the rotor

C. to amplify voltage

D. to enhance flux density

7. For the parallel operation of two or more D.C. compound generators, we should ensure that_______________?
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A. polarity of incoming generator should be same as that of bus bar

B. series fields of all generators should be either on positive side or negative side of the armature

C. all the series fields should be run in parallel by means of equilizer connection

D. all conditions mentioned above should be satisfied

E. voltage of the incoming generator should be same as that of bus bar

8. Magnetic field in a D.C. generator is produced by_______________?
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A. electromagnets

B. permanent magnets

C. both A. and B.

D. none of the above

9. D.C. generator generally preferred for charging automobile batteries is______________?
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A. any ofthe above

B. series generator

C. shunt generator

D. long shunt compound generator
10. Satisfactory commutation of D.C. machines requires______________?
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A. brushes should be of proper grade and size

B. smooth, concentric commutator properly undercut

C. brushes should smoothly run in the holders

D. all of the above
11. Wave winding is composed of_______________?
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A. that even number which is exact multiple of poles

B. any odd number of conductors

C. any even number of conductors

D. that even number which is exact multiple of poles + 2
12. The field coils of D.C. generator are usually made of_____________?
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A. mica

B. carbon

C. copper

D. cast iron

13. In a D.C. machine stray loss is the sum of_____________?
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A. armature copper loss and iron loss

B. total copper loss and mechanical loss

C. shunt field copper loss and mechanical loss

D. iron loss and mechanical loss
14. The resistance of armature winding depends on
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A. length of conductor

B. number of conductors

C. all of the above

D. cross-sectional area of the conductor

15. In the case of lap winding resultant pitch is____________?
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A. division of front pitch by back pitch

B. difference of front and back pitches

C. multiplication of front and back pitches

D. sum of front and back pitches

16. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ?
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A. Commutator

B. Dummy coils

C. Eye bolt

D. Equilizer rings

17. In D.C. generators the pole shoes are fastened to the pole core by_____________?
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A. rivets

B. welding

C. brazing

D. counter sunk screws
18. Compensating windings are used in D.C. generators______________?
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A. to neutralise the cross-magnetising effect of the armature reaction

B. none of the above

C. to provide path for the circulation of cooling air

D. mainly to reduce the eddy currents by providing local short-circuits

19. D.C. series generator is used_________________?
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A. to supply industrial load at constant voltage

B. to supply traction load

C. voltage at the toad end of the feeder

D. for none of the above purpose

20. 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______________?
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A. compensating winding

B. shifting of axis of brushes

C. dummy coils

D. interpoles

21. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when____________?
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A. r.p.m. is less than 300

B. number of poles is 2

C. number of poles is 4

D. r.p.m. is more than 300

22. Which of the following generating machine will offer constant voltage on all loads?
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A. Level compounded generator

B. All of the above

C. Separately excited generator

D. Self-excited generator

23. The voltage drop for which of the following types of brush can be expected to be least ?
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A. Graphite brushes

B. None of the above

C. Carbon brushes

D. Metal graphite brushes
24. An exciter for a turbo generator is a_____________?
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A. series generator

B. separately excited generator

C. compound generator

D. shunt generator
25. Welding generator will have____________?
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A. delta winding

B. wave winding

C. lap winding

D. duplex wave winding

26. The bearings used to support the rotor shafts are generally______________?
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A. magnetic bearmgs

B. needle bearings

C. ball bearings

D. bush bearings

27. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except:_____________?
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A. armature reaction

B. commutation

C. armature resistance drop

D. field weakening due to armature reaction and armature

28. In a four-pole D.C. machine____________?
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A. two north poles follow two south poles

B. all the four poles are south poles

C. alternate poles are north and south

D. all the four poles are north poles

29. The insulating material used between the commutator segments is normally_____________?
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A. mica

B. paper

C. insulating varnish

D. graphite

30. Which of the following statement about D.C. generators is false ?
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A. Compensating winding in a D.C. machine helps in commutation

B. In a D. C. generator interpoles winding is connected in series with the armature winding

C. Back pitch and front pitch are both odd and approximately equal to the pole pitch

D. Equilizing bus bars are used with parallel running of D.C. shunt generators
31. The rapid wear of brushes takes place due to____________?
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A. all of the above factors

B. high mica insulation between com-mutation bars

C. excessive spring pressure

D. abrasion from dust

E. rough commutator bars

32. In D.C. generators, the cause of rapid brush wear may be___________?
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A. any of the above

B. imperfect contact

C. severe sparking

D. rough commutator surface

33. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be__________________?
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A. 4

B. 16

C. 8

D. 32

34. Eddy currents are induced in the pole shoes of a D.C. machine due to______________?
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A. relative rotation between field and armature

B. all above

C. pulsating magnetic flux

D. oscillating magnetic field

35. The number of brushes in a commutator depends on______________?
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A. amount of current to be collected

B. speed of armature

C. voltage

D. type of winding

36. The armature of D.C. generator is laminated to_______________?
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A. provide the bulk

B. reduce the bulk

C. reduce eddy current loss

D. insulate the core

37. To avoid formation of grooves in the commutator of a D.C. machine?
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A. None

B. the brushes of same polarity should track each other

C. brush position has no effect on the commutator grooving

D. the brushes of opposite polarity should track each other
38. 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.
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A. Compensating field

B. Series field

C. Inter pole field

D. Shunt field
39. Flashing the field of D.C. generator means:______________?
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A. creating residual magnetism by a D.C. source

B. making the magnetic losses of forces parallel

C. neutralising residual magnetism

D. increasing flux density by adding extra turns of windings on poles

40. The material for commutator brushes is generally_______________?
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A. carbon

B. mica

C. cast iron

D. copper

41. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be________________?
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A. cross magnetisation only

B. cross magnetisation as well as magnetisation

C. crossmagnetisation as well as demagnetising

D. demagnetisation only

42. Which of the following generators will be preferred if they are required to be run in parallel?
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A. Compound generators

B. Series generators

C. Shunt generators

D. None of the above

43. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
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A. The field of that generator is weakened

B. That generator takes large share of loads

C. The speed of that generator is increased

D. The direction of that generator is reversed

44. For both lap and wave windings, there are as many commutator bars as the number of_____________?
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A. armature conductors

B. poles

C. winding elements

D. slots

45. The purpose of providing dummy coils in a generator is____________?
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A. to enhance flux density

B. to amplify voltage

C. to reduce eddy current losses

D. to provide mechanical balance for the rotor
46. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f___________ ?
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A. Lap winding

B. Depends on other features of design

C. Wave winding

D. Either of A. and B. above

47. In D.C. generators, current to the external circuit from armature is given through_____________?
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A. slip rings

B. commutator

C. none of above

D. solid connection

48. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when_______________?
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A. the generator runs on full load

B. the generator runs on designed speed

C. the generator runs on overload

D. there is no load on|he generator
49. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be_____________?
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A. about 2 V

B. zero

C. about 50 V

D. 220 V

50. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be_______________?
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A. E/2

B. E

C. slightly less than E

D. 2E