d c generators MCQs – Page 2

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

d c generators Mcqs
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