Some questions and answers about DC Generators
Part 2==>>
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
81. Number of tappings for each equilizer 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
82. A D.C. generator can be considered as
(a)
rectifier
(b)
primemover
(c)
rotating amplifier
(d)
power pumpAns: c
83. In any rotating machine that part which houses the
conductors and in which e.m.f.
induced is to be utilised is called
(a) rotor
(b) stator
(c) field
(d) armature
Ans: d
84. In a D.C. machine stray loss is the sum of
(a) total
copper loss and mechanical loss
(b) armature
copper loss and iron loss
(c) shunt
field copper loss and mechanical loss
iron loss and mechanical lossAns: d
85. Lap 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: a
86. In a D.C. generator in case the resistance of the
field winding is increased, then output voltage will (a) increase
(b) decrease
(c) remain
unaffected
(d) fluctuate
heavily
Ans: b
87. An exciter for a turbo generator is a
(a) separately
excited generator
(b) shunt
generator
(c) series generator
(d) compound generator
Ans: b
88. In case of a flat compounded generator
(a) voltage
generated is less than the rated voltage
(b) generated
voltage is proportional to the load on the generator
(c) voltage
remains constant irrespec¬tive of the load
(d) speed
varies in proportion to the load on the generator
Ans: c
89. Which of the following generator will have negligible
terminal voltage while running on no-load ?
(a) Series
generator
(b) Shunt
generator
(c) Compound
generator
(d) Separately
excited generator
Ans: a
90. Which of the following D.C. generators 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) None
of the above
Ans: d
91. In over compounded generator, full load terminal voltage
is
(a) almost
zero
(b) less
than noload terminal voltage
(c) more
than noload terminal voltage
(d) equal
to no-load terminal voltage
Ans: c
92. In a level compounded D.C. generator, full load
terminal voltage is
(a)
negligibly low
(b)
equal to no-load terminal voltage
(c)
more than no-load terminal voltage
(d)
less than no-load terminal voltage
Ans: b
93. The terminal voltage of a D.C. shunt generator
drops on load because of all of the following reasons except (a) armature
reaction
(b) armature
resistance drop
(c) field
weakening due to armature reaction and armature
(d) commutation
Ans:
d
94. In a D.C. generator
(a) external
resistance = internal char-acteristic - armature reaction
(b) internal
characteristic = magnetisation characteristic - ohmic drop
(c) external
characteristic = magnetisation characteristic - ohmic drop - armature reaction
(d) magnetisation characteristic = external characteristic
Ans: c
95. A sinusoidal voltage of 5 Hz is applied to the field of
a shunt generator. The armature voltage wave
(a) will
be zero
(b) will
be of 5 Hz
(c) willbeof5xiVHz
(d) will
be of v Hz 5
Ans: b
96. 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
97. 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
98. 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
99. 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) damagnetising
the centre of all poles
(d) magnetising
the centre of all poles
Ans: a
100. Following energized winding of a D.C. machine
should not be opened as it would produce high inductive voltage which may be
dangerous to personnel and may cause its own insulation failure.
(a) Series
field
(b) Compensating
field
(c) Inter
pole field
(d) Shunt
field
Ans: d
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