D.C. Generators

61. In D.C. generators, the cause of rapid brush wear may be

1. severe sparking
2. rough commutator surface
3. imperfect contact
4. any of the above

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62. In lap winding, the number of brushes is always

1. double the number of poles
2. same as the number of poles
3. half the number of poles
4. two

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63. In over compounded generator, full load terminal voltage is

1. almost zero
2. less than no load terminal voltage
3. more than no load terminal voltage
4. equal to no-load terminal voltage

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64. In the case of lap winding resultant pitch is

1. multiplication of front and back pitches
2. division of front pitch by back pitch
3. sum of front and back pitches
4. difference of front and back pitches

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65. Interpole flux should be sufficient to

1. neutralise the commutating self induced e.m.f.
2. neutralise the armature reaction flux
3. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
4. perform none of the above functions

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66. Iron losses in a D.C. machine are independent of variations in

1. speed
2. load
3. voltage
4. speed and voltage

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67. Laminations of core are generally made of

1. case iron
2. carbon
3. silicon steel
4. stainless steel

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68. Lap winding is composed of

1. any even number of conductors
2. any odd number of conductors
3. that even number which is exact multiple of poles + 2
4. that even number which is exact multiple of poles

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69. Magnetic field in a D.C. generator is produced by

1. electromagnets
2. permanent magnets
3. both (a) and (b)
4. none of the above

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70. Number of tappings for each equilizer ring is equal to

1. number of pole pairs
2. number of poles
3. number of parallel paths
4. number of commutator segments

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