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.Management Sciences
Category: Polyphase Induction Motors
A change of 4% of supply voltage to an induction motor will produce a change of approximately ________?
A. 4% in the rotor torque
B. 8% in the rotor torque
C. 12% in the rotor torque
D. 16% in the rotor torque
The ‘cogging’ of an induction motor can be avoided by____________?
A. proper ventilation
B. using DOL starter
C. auto-transformer starter
D. having number of rotor slots more or less than the number of stator slots (not equal)
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
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
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
Star-delta starting of motors is not possible in case of____________?
A. single phase motors
B. variable speed motors
C. low horse power motors
D. high speed motors
5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest ?
A. 730 r.p.m.
B. 960 r.p.m.
C. 1440 r.p.m.
D. 2880 r.p.m.
The shaft of an induction motor is made of_____________?
A. high speed steel
B. stainless steel
C. carbon steel
D. cast iron
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
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
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