D.C. Generators

81. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be

1. E/2
2. 2E
3. slightly less than E
4. E

View answer

82. The e.m.f. generated in a D.C. generator is directly proportional to

1. flux/pole
2. speed of armature
3. number of poles
4. all of the above

View answer

83. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be

1. 640 V
2. 620 V
3. 600 V
4. 580 V

View answer

84. 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 characteristics
4. same percentage regulation

View answer

85. The field coils of D.C. generator are usually made of

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

View answer

86. The following constitute short-circuit in the armature winding.

1. Insulation failure between two commutator bars
2. Insulation failure between two turns of a coil
3. Two of more turns of the same coil getting grounded
4. All of the above

View answer

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

1. to reduce the reluctance of the mag¬netic 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

View answer

88. The insulating material used between the commutator segments is normally

1. graphite
2. paper
3. mica
4. insulating varnish

View answer

89. 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

View answer

90. The material for commutator brushes is generally

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

View answer