61. Satisfactory commutation of D.C.
machines requires
(A) brushes should be of proper grade and
size
(B) brushes should smoothly run in the
holders
(C) smooth, concentric commutator
properly undercut
(D) all of the above
Ans: D
62. Open circuited armature coil of a D.C. machine is
(A) identified by the scarring of the
commutator segment to which open circuited coil is connected
(B) indicated by a spark completely
around the commutator
(C) both (A) and (B)
(D) none of the above
Ans: C
63. In a D.C. machine, fractional pitch winding is used
(A) to increase the generated voltage
(B) to reduce sparking
(C) to save the copper because of shorter
end connections
(D) due to (B) and (C) above
Ans: D
64. For the parallel operation of two or more D.C. compound
generators, we should ensure that
(A) voltage of the incoming generator
should be same as that of bus bar
(B) polarity of incoming generator should
be same as that of bus bar
(C) all the series fields should be run
in parallel by means of equalizer connection
(D) All of the above
Ans: D
65. D.C. series generator is used
(A) to supply traction load
(B) to supply industrial load at constant
voltage
(C) voltage at the toad end of the feeder
(D) for none of the above purpose
Ans: C
66. Following D.C. generator will be in a
position to build up without any residual magnetism in the poles
(A) series generator
(B) shunt generator
(C) compound generator
(D) self-excited generator
Ans: D
67. Inter-pole flux should be sufficient to
(A) neutralise the commutating self
induced e.m.f.
(B) neutralise the armature reaction flux
(C) neutralise both the armature reaction
flux as well as commutating e.m.f. induced in the coil
(D) perform none of the above functions
Ans: C
68. D.C. generator
generally preferred for charging automobile batteries is
(A) series generator
(B) shunt generator
(C) long shunt compound generator
(D) any of'the above
Ans: C
69. In a D.C.
generator the number of mechanical degrees and electrical degrees will be the same
when
(A) r.p.m. is more than 300
(B) r.p.m. is less than 300
(C) number of poles is 4
(D) number of poles is 2
Ans: D
70. Permeance is the
reciprocal of
(A) flux density
(B) reluctance
(C) ampere-turns
(D) resistance
Ans: B
71. In D.C. generators
the polarity of the interpoles
(A) is the same as that of the main pole
ahead
(B) is the same as that of the
immediately preceding pole
(C) is opposite to that of the main pole
ahead
(D) is neutral as these poles do not play
part in generating e.m.f.
Ans: A
72. The e.m.f. generated in a D.C. generator is directly
proportional to
(A) flux/pole
(B) speed of armature
(C) number of poles
(D) all of the above
Ans: B
73. In a D.C. generator the magnetic neutral axis coincides
with the geometrical neutral axis, when
(A) there is no load on|he generator
(B) the generator runs on full load
(C) the generator runs on overload
(D) the generator runs on designed speed
Ans: A
74. In a D.C. generator in order to reduce sparking at
brushes, the self-induced e.m.f. in the coil is neutralised by all of the
following except
(A) interpoles
(B) dummy coils
(C) compensating winding
(D) shifting of axis of brushes
Ans: B
75. In D.C. generators on no-load, the air gap flux distribution
in space is
(A) sinusoidal
(B) triangular
(C) pulsating
(D) flat topped
