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Free download in PDF Polyphase Induction Motors General Knowledge Objective Type Questions & 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.
(21)
Which of the following component is usually fabricated out of silicon steel ?
[A]
Bearings
[B]
Shaft
[C]
Statorcore
[D]
None of the above
(22)
The ‘crawling” in an induction motor is caused by
[A]
high loads
[B]
low voltage supply
[C]
improper design of machine
[D]
harmonics developed in the motor
Answer: harmonics developed in the motor
(23)
The speed of a squirrel-cage induction motor can be controlled by all of the following except
[A]
changing supply frequency
[B]
changing number of poles
[C]
changing winding resistance
[D]
reducing supply voltage
Answer: changing winding resistance
(24)
DOL starting of induction motors is usually restricted to
[A]
low horsepower motors
[B]
variable speed motors
[C]
high horsepower motors
[D]
high speed motors
Answer: low horsepower motors
(25)
In a three-phase induction motor, the number of poles in the rotor winding is always
[A]
zero
[B]
more than the number of poles in stator
[C]
less than number of poles in stator
[D]
equal to number of poles in stator
Answer: equal to number of poles in stator
(26)
In three-phase squirrel-cage induction motors
[A]
rotor conductor ends are short-circuited through slip rings
[B]
rotor conductors are short-circuited through end rings
[C]
rotor conductors are kept open
[D]
rotor conductors are connected to insulation
Answer: rotor conductors are short-circuited through end rings
(27)
The maximum torque in an induction motor depends on
[A]
frequency
[B]
rotor inductive reactance
[C]
square of supply voltage
[D]
all of the above
(28)
An induction motor is
[A]
self-starting with zero torque
[B]
self-starting with high torque
[C]
self-starting with low torque
[D]
non-self starting
Answer: self-starting with low torque
(29)
If any two phases for an induction motor are interchanged
[A]
the motor will run in reverse direction
[B]
the motor will run at reduced speed
[C]
the motor will not run
[D]
the motor will burn
Answer: the motor will run in reverse direction
(30)
For which motor the speed can be controlled from rotor side ?
[A]
Squirrel-cage induction motor
[B]
Slip-ring induction motor
[C]
Both (a) and (b)
[D]
None of the above
Answer: Slip-ring induction motor
31
In the circle diagram for induction motor, the diameter of the circle represents
[A]
slip
[B]
rotor current
[C]
running torque
[D]
line voltage
32
Rotor rheostat control method of speed control is used for
[A]
squirrel-cage induction motors only
[B]
slip ring induction motors only
[C]
both (a) and (b)
[D]
none of the above
Answer: slip ring induction motors only
33
Stepless speed control of induction motor is possible by which of the following methods ?
[A]
e.m.f. injection in rotor eueuit
[B]
Changing the number of poles
[C]
Cascade operation
[D]
None of the above
Answer: Changing the number of poles
34
It is advisable to avoid line-starting of induction motor and use starter because
[A]
motor takes five to seven times its full load current
[B]
it will pick-up very high speed and may go out of step
[C]
it will run in reverse direction
[D]
starting torque is very high
Answer: motor takes five to seven times its full load current
35
When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be
considered
[A]
in series
[B]
in parallel
[C]
in series-parallel
[D]
in parallel with stator
36
The torque developed in the cage induction motor with autostarter is
[A]
K2 x torque with direct switching
[B]
k2/torque with direct switching
[C]
k/torque with direct switching
[D]
K x torque with direct switching
Answer: K2 x torque with direct switching
37
The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
[A]
star connected only
[B]
delta connected only
[C]
(a) and (b) both
[D]
none of the above
38
The crawling in the induction motor is caused by
[A]
low voltage supply
[B]
high loads
[C]
harmonics develped in the motor
[D]
improper design of the machine
Answer: harmonics develped in the motor
39
Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ?
[A]
By changing the number of stator poles
[B]
Rotor rheostat control
[C]
By operating two motors in cascade
[D]
By injecting e.m.f. in the rotor circuit
Answer: By changing the number of stator poles
40
The injected e.m.f. in the rotor of induction motor must have
[A]
zero frequency
[B]
the same frequency as the slip frequency
[C]
the same phase as the rotor e.m.f.
[D]
high value for the satisfactory speed control
Answer: the same frequency as the slip frequency
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