81. The fall in speed of a dc generator due to increase in load can be corrected by
- cooling the armature
- increasing the excitation
- reducing the load voltage
- increasing the input to the prime mover
82. The magnetic field which initially induces emf in the armature in a self excited dc generator is because of
- permanent magnets
- armature reaction
- residual magnetism
- none of the above
83. A generator may loose residual magnetism due to
- heating
- vibrations
- over excitation
- any of these
84. In dc generators, the residual magnetism is of the order of
- 2.5%
- 10%
- 15%
- 25%
85. In comparison to the self excited generator, a separately excited generator
- is more reliable
- is amenable to better voltage regulation
- has exciting current independent of load characteristic
- has all of the above features
86. The voltage at the terminals of a dc series generator running at rated rpm and no load will be
- more than the rated voltage
- full rated voltage
- a very small voltage
- zero
87. If the field circuit resistance of a dc shunt generator exceeds its critical value, the generator
- fails to build up
- builds up a very high voltage
- exceeds its current capacity
- produces power beyond its rating
88. The factor that is not responsible for the drop in terminal voltage of a dc shunt generator on load is
- commutation
- armature reaction
- armature resistance drop
- field weakening due to (2) and (3)
89. In the dc shunt generator, the voltage build up is generally restricted due to
- armature heating
- insulation restrictions
- saturation of iron
- speed limitation
90. Over or under compounding of a dc generator is achieved by
- shunting more or less current from the shunt field
- shunting more or less current from the series field
- connecting it as long shunt
- connecting it as short-shunt
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