31. The dummy coils in dc machines are useful to
- increase the efficiency
- improve the commutation
- reduce the cost of the machine
- maintain mechanical balance of armature
32. A homopolar generator usually has
- high voltage and high current
- low voltage and high current
- low voltage and low current
- high voltage and low current
33. In a dc generator, the ripples in the direct emf generated are reduced by employing
- commutator with large number of segments
- equalizer rings
- carbon brushes
- graphite brushes
34. The coil span
- must be exactly equal to pole pitch
- can never be equal to pole pitch
- may or may not be exactly equal to pole pitch
- none of the above
35. The commutator pitch for simplex lap winding is
- +1
- -1
- +1 or -1
- average pitch
36. The commutator pitch for simplex wave winding is equal to
- +1 or -1
- twice average pitch
- average pitch
- half average pitch
37. In a dc machine armature winding, the number of commutator segments is equal to the number of armature
- coils
- coil sides
- conductors
- turns
38. How many segments will be there for the commutator of a 6-pole dc machine having a simplex wave wound armature with 72 slots?
- 73
- 72
- 71
- 70
39. For both lap and wave windings, there are as many commutator bars as the number of
- armature conductors
- winding elements
- poles
- slots
40. In a drum type dc armature windings, the back pitch and front pitch in terms of coil sides must be
- even and odd respectively
- odd and even respectively
- both even
- both odd
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