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Free download in PDF Polyphase Induction Motors General Knowledge MCQs & Answers for competitive exams. These short objective type questions with answers are very important for Board exams as well as competitive exams. These short solved questions or quizzes are provided by Gkseries.
81
Insertion of resistance in the stator of an induction motor
[A]
increases the load torque
[B]
decreases the starting torque
[C]
increases the starting torque
[D]
none of the above
Answer: decreases the starting torque
82
The rotor of an induction motor runs at
[A]
synchronous speed
[B]
below synchronous speed
[C]
above synchronous speed
[D]
any of the above
Answer: below synchronous speed
83
The torque of an induction motor is
[A]
directly proportional to slip
[B]
inversely proportional to slip
[C]
proportional to the square of the slip
[D]
none of the above
Answer: directly proportional to slip
84
In a star-delta starter of an induction motor
[A]
resistance is inserted in the stator
[B]
reduced voltage is applied to the stator
[C]
resistance is inserted in the rotor
[D]
applied voltage perl stator phase is 57.7% of the line voltage
Answer: applied voltage perl stator phase is 57.7% of the line voltage
85
Slip ring motor is preferred over squirrel cage induction motor where
[A]
high starting torque is required
[B]
load torque is heavy
[C]
heavy pull out torque is required
[D]
all of the above
Answer: high starting torque is required
86
Reduced voltage starter can be used with
[A]
slip ring motor only but not with squirrel cage induction motor
[B]
squirrel cage induction motor only but not with slip ring motor
[C]
squirrel cage as well as slip ring induction motor
[D]
none of the above
Answer: squirrel cage as well as slip ring induction motor
87
A squirrel cage induction motor is not selected when
[A]
initial cost is the main consideration
[B]
maintenance cost is to be kept low
[C]
higher starting torque is the main consideration
[D]
all above considerations are involved
Answer: higher starting torque is the main consideration
88
Less maintenance troubles are experienced in case of
[A]
slip ring induction motor
[B]
squirrel cage induction motor
[C]
both (a) and (b)
[D]
none of the above
Answer: squirrel cage induction motor
89
In a squirrel cage motor the induced e.m.f. is
[A]
dependent on the shaft loading
[B]
dependent on the number of slots
[C]
slip times the stand still e.m.f. induced in the rotor
[D]
none of the above
Answer: slip times the stand still e.m.f. induced in the rotor
90
The purpose of using short-circuit gear is
[A]
to short circuit the rotor at slip rings
[B]
to short circuit the starting resistances in the starter
[C]
to short circuit the stator phase of motor to form star
[D]
none of the above
Answer: to short circuit the rotor at slip rings
91
Temperature of the stator winding of a three phase induction motor is obtained by
[A]
resistance rise method
[B]
thermometer method
[C]
embedded temperature method
[D]
all above methods
Answer: all above methods
92
For driving high inertia loods best type of induction motor suggested is
[A]
slip ring type
[B]
squirrel cage type
[C]
any of the above
[D]
none of the above
93
Insertion of resistance in the rotcir of an induction motor to develop a given torque
[A]
decreases the rotor current
[B]
increases the rotor current
[C]
rotor current becomes zero
[D]
rotor current rernains same
Answer: rotor current rernains same
94
Insertion of reactance in the rotor circuit
[A]
reduces starting torque as well as maximum torque
[B]
increases starting torque as well as maximum torque
[C]
increases starting torque but maxi-mum torque remains unchanged
[D]
increases starting torque but maxi-mum torque decreases
Answer: reduces starting torque as well as maximum torque
95
The low power factor of induction motor is due to
[A]
rotor leakage reactance
[B]
stator reactance
[C]
the reactive lagging magnetizing current necessary to generate the magnetic flux
[D]
all of the above
96
In case of a double cage induction motor, the inner cage has
[A]
high inductance arid low resistance
[B]
low inductance and high resistance
[C]
low inductance and low resistance
[D]
high inductance and high resistance
Answer: high inductance arid low resistance
97
When /?2 is the rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running conditions will be
[A]
sR2X2 = 1
[B]
sR2 = X2
[C]
R2 = sX2
[D]
R2 = s2X2
98
In induction motor, percentage slip depends on
[A]
supply frequency
[B]
supply voltage
[C]
copper losses in motor
[D]
none of the above
Answer: copper losses in motor
99
In an induction motor if air-gap is increased
[A]
the power factor will be low
[B]
windage losses will be more
[C]
bearing friction will reduce
[D]
copper loss will reduce In an induction motor
Answer: the power factor will be low
100
The torque developed by a 3-phase induction motor least depends on
[A]
rotor current
[B]
rotor power factor
[C]
rotor e.m.f.
[D]
shaft diameter
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