d c generators MCQs – Page 4

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

d c generators Mcqs

61. Brushes of D.C. machines are made of_________?
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A. hard copper

B. all of above

C. soft copper

D. carbon

62. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly_______________?
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A. 150 V

B. 240 V

C. 290 V

D. 175 V

63. In case of D.C. machines, mechanical losses are primary function of____________?
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A. current

B. speed

C. voltage

D. none of above

64. In a level compounded D.C. generator, full load terminal voltage is______________?
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A. equal to no-load terminal voltage

B. more than no-load terminal voltage

C. negligibly low

D. less than no-load terminal voltage

65. In D.C. generators the polarity of the interpoles_____________?
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A. is opposite to that of the main pole ahead

B. is neutral as these poles do not play part in generating e.m.f.

C. is the same as that of the main pole ahead

D. is the same as that of the immediately preceding pole

66. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately______________?
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A. 25 percent

B. 40 percent

C. 5 percent

D. 10 percent

67. Lap winding is composed of_____________?
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A. any even number of conductors

B. that even number which is exact multiple of poles

C. that even number which is exact multiple of poles + 2

D. any odd number of conductors

68. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles?
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A. Series generator

B. None of the above

C. Shunt generator

D. Compound generator

69. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them?
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A. just behind the magnetic neutral axis

B. none

C. in magnetic neutral axis

D. just ahead of magnetic neutral axis

70. A series generator can self-excite:______________?
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A. only if the load current is zero

B. none of the above

C. only if the load current is not zero

D. irrespective of the value of load current

71. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will____________?
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A. decrease

B. fluctuate heavily

C. remain unaffected

D. increase

72. The essential condition for parallel operation of two D.C. generators is that they have ________________?
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A. the same drooping voltage characteristics

B. same kW rating

C. the same operation r.p.m.

D. same percentage regulation

73. The commutator segments are connected to the armature conductors by means of___________?
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A. copper lugs

B. insulation pads

C. brazing

D. resistance wires

74. While applying Flemings right-hand rule to And the direction of induced e.m.f., the thumb points towards___________?
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A. direction of flux

B. direction of motion of the conductor if forefinger points in the direction of generated e.m.f.

C. direction of motion of conductor, if forefinger points along the lines of flux

D. direction of induced e.m.f.

75. In D.C. generators, the brushes on commutator remain in contact with conductors which_________________?
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A. lie under interpolar region

B. are farthest from the poles

C. lie under south pole

D. lie under north pole

76. A shunt generator can self-excite:_________________?
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A. none

B. irrespective of the value of the resistance in the field circuit

C. only if the resistance of the field circuit is greater than critical value

D. only if the resistance of the field circuit is less than critical value

77. D.C. generators are connected to the busbars or disconnected from them only under the floating condition________________?
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A. to avoid mechanicaljerk to the shaft

B. all above

C. to avoid burning of switch contacts

D. to avoid sudden loading of the primemover

78. In D.C. generators on no-load, the air gap flux distribution in space is______________?
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A. triangular

B. pulsating

C. sinusoidal

D. flat topped

79. 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_____________________?
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A. 257.4 V

B. 270 V

C. 265 V

D. 267.5 V

80. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be_______________?
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A. 3 : 1

B. 2:03

C. 1:03

D. 3:02

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