Electrical Machines(DC Machines) Part-03:
51. Two 4
pole d.c. machines of identical armature, one with wave winding and other with
lap winding are wound. Then
a. The lap wound machine will have
more generated voltage
b. Wave
wound machine will have more generated voltage
c. Both
will have same generated voltage
d. None
of these
52. The armature in d.c. machines are always placed
on rotor
a. Otherwise commutation will
not be possible
b. Otherwise
there will not be any induced emf
c. Otherwise
current will not flow
d. All
of these
53. In a d.c. machine, the commutator provides
a. Half wave rectification
b. Full wave rectification
c. Semi controlled rectification
d. Uncontrolled
rectification
54. To have perfect neutralization of armature mmf under
the pole shoe, the ampere conductors of compensating winding must be
a. Not equal to the total armature
ampere conductors under the pole shoe
b. Equal
to the total armature ampere conductors under the pole shoe
c. Half
of the total armature ampere conductors under the pole shoe
d. Twice
of the total armature ampere conductors under the pole shoe
55. Ampere turns per pole for compensating winding in d.c.
machines is equal to
a. (pole arc / pole pitch) *
armature ampere turns per pole
b. (pole
pitch / pole arc) * armature ampere turns per pole
c. (pole
arc / pole pitch) * total ampere conductors per pole
d. None
of these
56. The compensating windings are used to neutralize the
armature reaction in d.c. machines. These windings are connected
a. Across armature
b. In
series with armature
c. Both
(a) and (b)
d. None
of these
57. The armature reaction effect in d.c. machines can be
completely neutralized by using
a. Only compensating winding
b. Only
interpoles
c. Both
compensating winding and interpoles
d. None
of these
58. Practically in d.c. machines, it may happen that the
emf induced in different parallel paths may not be same. This will cause
inequality in brush arm currents and will give rise to copper losses. These
effects can be avoided by using
a. Compensating windings
b. Interpoles
c. Equalizer
rings
d. All
of these
59. In d.c. machines, equalizer connections are provided
in
a. Only wave winding
b. Only
lap winding
c. Both
wave winding and lap winding
d. None
of these
60. If in the d.c machine, the reversal of current in the
coil is faster than ideal or linear commutation then the commutation is said to
be
a. Retarded commutation
b. Under
commutation
c. Accelerated
commutation
d. Ideal
commutation
61. In d.c. machines, the interpoles have tapering shape
which results in
a. Simpler design
b. Reduction
in the weight
c. Increase
in acceleration of commutation
d. All
of these
62. The generating action and motoring action in d.c.
motor is determined by
a. Fleming’s left hand rule, Fleming’s right hand
rule
b. Both
by Fleming’s left hand rule
c. Both
by Fleming’s right hand rule
d. Fleming’s
right hand rule, Fleming’s left hand rule
63. In a practical motor, to reverse the direction of
rotation
a. Reverse the direction of main field produced by
the field winding
b. Reverse
the direction of current passing through the armature is reversed
c. Either
(a) or (b)
d. None
of these
64. A 220 V, d.c. motor draws an armature current of 20 A.
Its armature resistance is 0.6 ohm. Then the induced emf in the motor will be
a. 195 V
b. 202
V
c. 208
V
d. 215
V
65. If the flux is increased by 50% and speed is reduced
by 50% of a d.c. motor (keeping the other parameters constant), then its back
emf will become
a. 50 % of the original back emf
b. 0.75
% of the original back emf
c. 100
% of the original back emf
d. 150
% of the original back emf
66. If Eb is the back emf of d.c.
motor and V is the terminal voltage, then the condition for maximum power is
a. Eb = V
b. Eb =
2V
c. Eb =
( V / 2 )
d. Eb =
V ∧ 2
67. A 4 pole, lap wound d.c. motor drawing an armature
current of 20 A has 360 conductors. If the flux per pole is 0.015 Wb then the
gross torque developed by the armature of motor is
a. 10.23 N-m
b. 15.56
N-m
c. 17.17
N-m
d. 19.08
N-m
68. If the no load speed of d.c. motor is 1350 rpm
and full load speed is 1150 rpm, then its voltage regulation is
a. 11.56 %
b. 15.36
%
c. 17.39
%
d. 19.39
%
69. As the load on d.c. motor increases, the current drawn
by motor
a. Increases
b. Decreases
c. Remains
same
d. None
of these
70. If the back emf of a d.c. motor is doubled and
flux is halved (keeping other parameters constant) then its speed will become
a. Double of the original speed
b. Square
of the original speed
c. Four
times of the original speed
d. Half
of the original speed
71. Keeping the field excitation constant, the constant of
proportionality between back emf and armature speed of d.c. motor is
a. Twice of the proportionality constant between
developed torque and armature current
b. Half
of the proportionality constant between developed torque and armature current
c. Same as that of proportionality
constant between developed torque and armature current
d. None
of these
72. D.C. shunt motor is also called as
a. Constant flux motor
b. Constant
voltage motor
c. Variable
voltage motor
d. Constant
current motor
73. The torque developed in d.c. shunt motor is
a. Directly proportional to the armature current
b. Directly
proportional to the square of the armature current
c. Inversely
proportional to the armature current
d. Inversely
proportional to the square of armature current
74. For a constant torque load, if the armature
resistance of shunt motor is doubled (keeping the shunt field constant) then
the armature current will
a. Double
b. Get
halved
c. Remain
same
d. None
of these
75. A 4 pole, 220 V, 10 H.P, d.c. shunt motor is rotating
at a speed of 320 rpm. Then the developed useful torque is
a. 210.647 N-m
b. 215.547
N-m
c. 219.484
N-m
d. None of these
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