71. If a D.C. generator fails to build up the probable cause could not be
(a) imperfect brush contact
(b) field resistance less than the critical resistance
(c) no residual magnetism in the generator
(d) faulty shunt connections tending to reduce the residual magnetism
Ans: b
72. Flashing the field of D.C. generator means
(a) neutralising residual magnetism
(b) creating residual magnetism by a D.C. source
(c) making the magnetic losses of forces parallel
(d) increasing flux density by adding extra turns of windings on poles
Ans: b
73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
(a) 640 V
(b) 620 V
(c) 600 V
(d) 580 V
Ans: d
74. In a D.C. generator the critical resistance refers to the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b
75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis
Ans: a
76. Armature coil is short circuited by brushes when it lies
(a) along neutral axis
(b) along field axis
(c) in any of the above positions
(d) in none of the above positions
Ans: a
77. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt
(c) cumulatively compounded short shunt
(d) differentially compounded short shunt
Ans: b
78. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other
(b) the brushes of same polarity should track each other
(c) brush position has no effect on the commutator grooving
Ans: a
79. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two com-mutator 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
80. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) high mica insulation between com-mutation bars
(e) all of the above factors
Ans: e
(a) imperfect brush contact
(b) field resistance less than the critical resistance
(c) no residual magnetism in the generator
(d) faulty shunt connections tending to reduce the residual magnetism
Ans: b
72. Flashing the field of D.C. generator means
(a) neutralising residual magnetism
(b) creating residual magnetism by a D.C. source
(c) making the magnetic losses of forces parallel
(d) increasing flux density by adding extra turns of windings on poles
Ans: b
73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
(a) 640 V
(b) 620 V
(c) 600 V
(d) 580 V
Ans: d
74. In a D.C. generator the critical resistance refers to the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b
75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis
Ans: a
76. Armature coil is short circuited by brushes when it lies
(a) along neutral axis
(b) along field axis
(c) in any of the above positions
(d) in none of the above positions
Ans: a
77. A cumulatively compounded long shunt generator when operating as a motor would be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt
(c) cumulatively compounded short shunt
(d) differentially compounded short shunt
Ans: b
78. To avoid formation of grooves in the commutator of a D.C. machine
(a) the brushes of opposite polarity should track each other
(b) the brushes of same polarity should track each other
(c) brush position has no effect on the commutator grooving
Ans: a
79. The following constitute short-circuit in the armature winding.
(a) Insulation failure between two com-mutator 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
80. The rapid wear of brushes takes place due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) high mica insulation between com-mutation bars
(e) all of the above factors
Ans: e
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