Polyphase Induction Motors General Knowledge Quiz | Polyphase Induction Motors General Knowledge MCQs & Answers

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Questions
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
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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

Answer: slip ring type
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

Answer: 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

Answer: R2 = sX2
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

Answer: shaft diameter

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