41. In a dc machine, fractional pitch winding is employed to
- increase generated voltage
- reduce sparking and save copper
- improve cooling
- all of these
42. Aluminium is not used as winding wire in dc machine armature as it
- is costlier
- is of low resistivity
- is of lower thermal conductivity
- require large winding space
43. Short circuiting is caused in the armature winding due to
- failure of insulation between two turns of the coil
- failure of insulation between two commutator bars
- grounding of two or more turns of the same coil
- any of the above
44. In a lap wound dc generator, the equalizer rings are provided to
- neutralize the armature reaction effect
- avoid short circuiting
- avoid unequal distribution of currents at brushes
- avoid harmonics generated in the emf
45. Number of tappings to each equalizer ring is equal to the number of
- poles
- pole pairs
- parallel paths
- commutator segments
46. In a lap wound dc generator having P poles and Z conductors, the maximum number of equalizer rings will be
- Z/P
- 2Z/P
- Z/2P
- Z/4P
47. A frog leg winding is used in a dc machine to eliminate
- the use of equalizers in lap winding
- the use of compensating winding
- the use of drum winding
- reactance voltage produced due to commutation
48. In a dc machines, the air gap flux distribution in space at no load is
- sinusoidal
- triangular
- flat topped
- pulsating
49. The armature MMF waveform of a dc machine is
- pulsating
- rectangular
- triangular
- sinusoidal
50. The armature MMF of a dc machine has
- triangular space distribution and rotates at the speed of armature
- trapezoidal space distribution and is stationary in space
- stepped distribution and rotates at the speed of armature
- triangular space distribution and is stationary in space
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