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.Management Sciences
Category: Polyphase Induction Motors
In a three-phase induction motor_______________?
A. iron losses in stator will be negligible as compared to that in rotor
B. iron losses in motor will be neg¬ligible as compared to that in rotor
C. iron losses in stator will be less than that in rotor
D. iron losses in stator will be more than that in rotor
The rotor of an induction motor runs at__________?
A. synchronous speed
B. below synchronous speed
C. above synchronous speed
D. any of the above
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
An induction motor can run at synchronous speed when____________?
A. it is run on load
B. it is run in reverse direction
C. it is run on voltage higher than the rated voltage
D. e.m.f. is injected in the rotor circuit
The starting torque of a 3-phase squirrel cage induction motor is____________?
A. twice the full load torque
B. 1.5 times the full load torque
C. equal to full load torque
It is advisable to avoid line starting of induction motor and use starter because____________?
A. it will run in reverse direction
B. it will pick up very high speed and may go out of step
C. motor takes five to seven times its full load current
D. starting torque is very high
The torque of a rotor in an induction motor under running condition is maximum__________?
A. at the unit value of slip
B. at the zero value of slip
C. at the value of the slip which makes rotor reactance per phase equal to the resistance per phase
D. at the value of the slip which makes the rotor reactance half of the rotor
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
In induction motor, percentage slip depends on__________?
A. supply frequency
B. supply voltage
C. copper losses in motor
D. none of the above
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
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