D.C Generator: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive]
71. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two commutator bars
(6) Insulation failure between two turns of a coil
(c) Two of more turns of the same coil getting grounded
(d) All of the above
Ans: d
72. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) all of the above factors
Ans: d
73. Number of tapings for each equalizer ring is equal to…
(a) number of pole pairs
(b) number of poles
(c) number of parallel paths
(d) number of commutator segments
Ans: a
74. A 220 V D.C. generator is run at full speed without any
excitation. The open circuit voltage will be
(a) zero
(b) about 2 V
(c) about 50 V
(d) 220 V
Ans: b
75. In a
separately excited generator supplying rated load the armature reaction,
(a) is always present
(b) is always absent
(c) may be sometimes present
(d) none of the above
Ans: a
76. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be
(a) zero
(b) small
(c) the same as rated voltage
(d) high
Ans: a
77. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of
trailing pole tip
(b) demagnetisation of trailing pole tip and magnetisation of
leading pole tip
(c) demagnetising the centre of all poles
(d) magnetising the centre of all poles
Ans: a
78. Wave winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple of poles + 2
(d) that even number which is exact multiple of poles
Ans: c
79. The critical resistance of the D.C. generator is the resistance of
(a) field
(b) brushes
(c) armature
(d) load
Ans: a
80. When two D.C. series generators are running in parallel, an equalizer bar is used
(a) to increase the speed and hence generated e.m.f.
(b) to increase the series flux
(c) so that two similar machines will pass approximately equal
currents to the load
(d) to reduce the combined effect of ar-mature reaction of both
machines
Ans: c
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