d c generators Mcqs
51. Copper brushes in D.C. machine are used_____________?
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A. where low voltage and high currents are involved

B. where high voltage and small cur-rents are involved

C. in both of the above cases

D. in none of the above cases

52. The demagnetising component of armature reaction in a D.C. generator___________?
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A. reduces interpoles flux density

B. reduces generator e.m.f.

C. increases armature speed

D. results in sparking trouble

53. A D.C. generator can be considered as____________?
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A. rotating amplifier

B. rectifier

C. primemover

D. power pump

54. In D.C. generators, lap winding is used for______________?
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A. high voltage, low current

B. high voltage, high current

C. low voltage, low current

D. low voltage, high current
55. In a separately excited generator supplying rated load the armature reaction.
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A. is always present

B. is always absent

C. may be sometimes present

D. none of the above

56. Armature reaction in a generator results in_____________?
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A. damagnetising the center of all poles

B. magnetising the center of all poles

C. demagnetisation of leading pole tip and magnetisation of trailing pole tip

D. demagnetisation of trailing pole tip and magnetisation of leading pole tip

57. Flemings right-hand rule regarding direction of induced e.m.f., correlates__________?
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A. magnetic flux, direction of force and direction of motion of conductor

B. magnetic field strength, induced voltage and current

C. magnetic flux, direction of motion and the direction of e.m.f. induced

D. magnetic flux, direction of current flow and resultant force

58. For a D.C. machines laboratory following type of D.C. supply will be suitable___________?
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A. synchronous motor D.C. generator set

B. rotary converter

C. induction motor D.C. generator set

D. mercury are rectifier

59. The main factor which leads to unstable parallel operation of flat and over compounded generators is_____________?
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A. unequal series field resistances

B. their rising voltage characteristics

C. unequal speed regulation of their primemovers

D. unequal number of turns in their series field windings

60. 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____________?
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A. none of the above

B. greater than 150 V

C. less than 150 V

D. 150 V

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

81. If a D.C. generator fails to build up the probable cause could not be_____________?
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A. no residual magnetism in the generator

B. field resistance less than the critical resistance

C. imperfect brush contact

D. faulty shunt connections tending to reduce the residual magnetism

82. Laminations of core are generally made of________________?
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A. stainless steel

B. case iron

C. carbon

D. silicon steel
83. In a D.C. generator the critical resistance refers to the resistance of_____________?
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A. field

B. load

C. brushes

D. armature

84. The critical resistance of the D.C. generator is the resistance of_____________?
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A. field

B. load

C. armature

D. brushes

85. The function of pole shoes in the case of D.C. machine is______________?
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A. to spread out the flux to achieve uniform flux density

B. to support the field coil

C. to discharge all the above functions

D. to reduce the reluctance of the magnetic path

86. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilized is called____________?
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A. armature

B. stator

C. rotor

D. field

87. Equilizer rings are required in case armature is_______________?
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A. lap wound

B. wave wound

C. delta wound

D. duplex wound

88. A separately excited generator as compared to a self-excited generator_____________?
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A. is amenable to better voltage control

B. is more stable

C. has exciting current independent of load current

D. has all above features
89. When two D.C. generators are running in parallel an equilizer bar is used______________?
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A. to increase the series flux

B. to increase the generated e.m.f.

C. to reduce the combined effect of ar-mature reaction of both the machines

D. so that the two identical machines will pass approximately equal currents to the load
90. In case of a flat compounded generator:
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A. voltage remains constant irrespective of the load

B. speed varies in proportion to the load on the generator

C. voltage generated is less than the rated voltage

D. generated voltage is proportional to the load on the generator

91. The following constitute short-circuit in the armature winding.
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A. Insulation failure between two turns of a coil

B. Insulation failure between two commutator bars

C. All of the above

D. Two of more turns of the same coil getting grounded

92. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is______________?
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A. 8

B. 2

C. 6

D. 4
93. Permeance is the reciprocal of______________?
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A. ampere-turns

B. reluctance

C. flux density

D. resistance

94. Armature coil is short circuited by brushes when it lies_____________?
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A. along field axis

B. in none of the above positions

C. in any of the above positions

D. along neutral axis
95. In case of D.C. machine winding, number of commutator segments is equal to______________?
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A. number of armature turns

B. number of armature conductors

C. number of armature coil sides

D. number of armature coils
96. In a D.C. generator:___________________?
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A. internal characteristic = magnetisation characteristic ohmic drop

B. magnetisation characteristic = external characteristic

C. external resistance = internal char-acteristic armature reaction

D. external characteristic = magnetisation characteristic ohmic drop armature reaction
97. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?
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A. 0.005 mm

B. 0.05 mm

C. 0.5 m

D. 5 m

98. Armature reaction of an unsaturated D.C. machine is_____________?
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A. crossmagnetising

B. none of above

C. demagnetising

D. magnetising

99. In lap winding, the number of brushes is always_____________?
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A. same as the number of poles

B. double the number of poles

C. two

D. half the number of poles

100. Interpole flux should be sufficient to_____________?
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A. neutralise the commutating self induced e.m.f.

B. neutralise the armature reaction flux

C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil

D. perform none of the above functions