D.C. Generators

91. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is

1. 2
2. 4
3. 6
4. 8

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92. 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

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93. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage

1. will be less than 250 V
2. will always be 250 V
3. may be greater or less than 250 V
4. none of the above

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94. 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

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95. The resistance of armature winding depends on

1. length of conductor
2. cross-sectional area of the conductor
3. number of conductors
4. all of the above

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96. The series field of a short-shunt D.C. generator is excited by

1. external current
2. armature current
3. shunt current
4. load current

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97. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except

1. armature reaction
2. armature resistance drop
3. field weakening due to armature reaction and armature
4. commutation

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98. 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

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

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99. The voltage drop for which of the following types of brush can be expected to be least ?

1. Graphite brushes
2. Carbon brushes
3. Metal graphite brushes
4. None of the above

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100. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them

1. just ahead of magnetic neutral axis
2. in magnetic neutral axis
3. just behind the magnetic neutral axis
4. none

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