DC Generator MCQs Quiz Multiple Choice Questions & Answers Page 2

51. The material for commutator brushes is generally

1. mica
2. copper
3. cast iron
4. carbon

52. The terminal voltage of a series generator is 150 V when the load current is 5 A. If theload current is increased to 10 A, the terminal voltage will be

1. 150 V
2. less than 150 V
3. greater than 150 V
4. none of the above

53. According to Flemings right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of

1. motion of conductor
2. lines of force
3. either of the above
4. none of the above

54. In the case of lap winding resultant pitch is

1. multiplication of front and back pitches
2. division of front pitch by back pitch
3. sum of front and back pitches
4. difference of front and back pitches

55. In a level compounded D.C. generator, full load terminal voltage is

1. negligibly low
2. equal to no-load terminal voltage
3. more than no-load terminal voltage
4. less than no-load terminal voltage

56. Interpole flux should be sufficient to

1. neutralise the commutating self induced e.m.f.
2. neutralise the armature reaction flux
3. neutralise both the armature reaction flux as well as commutating e.m.f. induced in thecoil
4. perform none of the above functions

57. Flashing the field of D.C. generator means

1. neutralising residual magnetism
2. creating residual magnetism by a D.C. source
3. making the magnetic losses of forces parallel
4. increasing flux density by adding extra turns of windings on poles

58. In case of D.C. machine winding, number of commutator segments is equal to

1. number of armature coils
2. number of armature coil sides
3. number of armature conductors
4. number of armature turns

59. Number of tappings for each equilizer ring is equal to

1. number of pole pairs
2. number of poles
3. number of parallel paths
4. number of commutator segments

60. A series generator can self-excite

1. only if the load current is zero
2. only if the load current is not zero
3. irrespective of the value of load current
4. none of the above

61. Eddy currents are induced in the pole shoes of a D.C. machine due to

1. oscillating magnetic field
2. pulsating magnetic flux
3. relative rotation between field and armature
4. all above

62. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when

1. r.p.m. is more than 300
2. r.p.m. is less than 300
3. number of poles is 4
4. number of poles is 2

63. A D.C. generator can be considered as

1. rectifier
2. primemover
3. rotating amplifier
4. power pump

64. The armature of D.C. generator is laminated to

1. reduce the bulk
2. provide the bulk
3. insulate the core
4. reduce eddy current loss

65. The demagnetising component of armature reaction in a D.C. generator

1. reduces generator e.m.f.
2. increases armature speed
3. reduces interpoles flux density
4. results in sparking trouble

66. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to

1. reverse the field connections
2. increase the field resistance
3. increase the speed of primemover
4. check armature insulation resis¬tance

67. Shunt generators are most suited for stable parallel operation because of their

1. rising voltage characteristics
2. identical voltage characteristics
3. drooping voltage characteristics
4. linear voltage characteristics

68. In D.C. generators the pole shoes are fastened to the pole core by

1. rivets
2. counter sunk screws
3. brazing
4. welding

69. In any rotating machine that part which houses the conductors and in which e.m.f.induced is to be utilised is called

1. rotor
2. stator
3. field
4. armature

70. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be

1. 4
2. 8
3. 16
4. 32

71. The essential condition for parallel operation of two D.C. generators is that they have

1. same kW rating
2. the same operation r.p.m.
3. the same drooping voltage charac-teristics
4. same percentage regulation

72. Which of the following generating machine will offer constant voltage on all loads ?

1. Self-excited generator
2. Separately excited generator
3. Level compounded generator .
4. All of the above

73. An exciter for a turbo generator is a

1. separately excited generator
2. shunt generator
3. series generator
4. compound generator

74. Following energized winding of a D.C. machine should not be opened as it wouldproduce high inductive voltage which may be dangerous to personnel and may cause itsown insulation failure.

1. Series field
2. Compensating field
3. Inter pole field
4. Shunt field

75. Following D.C. generator will be in a position to build up without any residualmagnetism in the poles

1. series generator
2. shunt generator
3. compound generator
4. self-excited generator

76. D.C. generator generally preferred for charging automobile batteries is

1. series generator
2. shunt generator
3. long shunt compound generator
4. any ofthe above

77. Which of the following generator will have negligible terminal voltage while running onno-load ?

1. Series generator
2. Shunt generator
3. Compound generator
4. Separately excited generator

78. Which of the following D.C. generators will be in a position to build up without anyresidual magnetism in the poles ?

1. Series generator
2. Shunt generator
3. Compound generator
4. None of the above

79. Which generator would you prefer for feeding long D.C. transmission lines ?

1. Series generator
2. Shunt generator
3. Over compound generator
4. Flat compound generator

80. In D.C. generators, the cause of rapid brush wear may be

1. severe sparking
2. rough commutator surface
3. imperfect contact
4. any of the above

81. Which of the following generators will be preferred if they are required to be run inparallel ?

1. Shunt generators
2. Series generators
3. Compound generators
4. None of the above

82. In D.C. generators on no-load, the air gap flux distribution in space is

1. sinusoidal
2. triangular
3. pulsating
4. flat topped

83. For both lap and wave windings, there are as many commutator bars as the number of

1. slots
2. armature conductors
3. winding elements
4. poles

84. Iron losses in a D.C. machine are independent of variations in

1. speed
2. load
3. voltage
4. speed and voltage

85. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and fieldresistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the loadcircuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be

1. 270 V
2. 267.5 V
3. 265 V
4. 257.4 V

86. The number of brushes in a commutator depends on

1. speed of armature
2. type of winding
3. voltage
4. amount of current to be collected

87. Two generators are running in parallel. One of the generators may run as motor forwhich of the following reasons ?

1. The direction of that generator is reversed
2. The speed of that generator is increased
3. The field of that generator is weakened
4. That generator takes large share of loads

88. The main factor which leads to unstable parallel operation of flat and over compounded generators is

1. their rising voltage characteristics
2. unequal number of turns in their series field windings
3. unequal speed regulation of their primemovers
4. unequal series field resistances

89. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutralaxis, when

1. there is no load on|he generator
2. the generator runs on full load
3. the generator runs on overload
4. the generator runs on designed speed

90. D.C. generators are connected to the busbars or disconnected from them only under thefloating condition

1. to avoid sudden loading of the primemover
2. to avoid mechanicaljerk to the shaft
3. to avoid burning of switch contacts
4. all above

91. When two D.C. generators are running in parallel an equilizer bar is used

1. to increase the series flux
2. to increase the generated e.m.f.
3. to reduce the combined effect of ar-mature reaction of both the machines
4. so that the two identical machines will pass approximately equal currents to the load

92. When two D.C. series generators are running in parallel, an equilizer bar is used

1. to increase the speed and hence generated e.m.f.
2. to increase the series flux
3. so that two similar machines will pass approximately equal currents to the load
4. to reduce the combined effect of ar-mature reaction of both machines

93. The purpose of providing dummy coils in a generator is

1. to reduce eddy current losses
2. to enhance flux density
3. to amplify voltage
4. to provide mechanical balance for the rotor

94. The function of pole shoes in the case of D.C. machine is

1. to reduce the reluctance of the magnetic path
2. to spread out the flux to achieve uniform flux density
3. to support the field coil
4. to discharge all the above functions

95. D.C. series generator is used

1. to supply traction load
2. to supply industrial load at constant voltage
3. voltage at the toad end of the feeder
4. for none of the above purpose

96. In a D.C. machine stray loss is the sum of

1. total copper loss and mechanical loss
2. armature copper loss and iron loss
3. shunt field copper loss and mechanical loss
4. iron loss and mechanical loss

97. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C.generator is approximately

1. 40 percent
2. 25 percent
3. 10 percent
4. 5 percent

98. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by

1. using conductor of annealed copper
2. using commutator with large number of segments
3. using carbon brushes of superior quality
4. using equiliser rings

99. In case of a flat compounded generator

1. voltage generated is less than the rated voltage
2. generated voltage is proportional to the load on the generator
3. voltage remains constant irrespec¬tive of the load
4. speed varies in proportion to the load on the generator

100. For the parallel operation of two or more D.C. compound generators, we should ensurethat

1. voltage of the incoming generator should be same as that of bus bar
2. polarity of incoming generator should be same as that of bus bar
3. all the series fields should be run in parallel by means of equilizer connection
4. series fields of all generators should be either on positive side or negative side of thearmature(e) all conditions mentioned above should be satisfied