The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f) constant. At rated frequency of 50 Hz and rated voltage of 400 V its speed is 1440 rpm. What is the speed at 30 Hz, if the load torque is constant?

The speed of a 4-pole induction motor is controlled by varying the sup

1.	The speed of a 4-pole induction motor is controlled by varying the supply frequency while maintaining the ratio of supply voltage to supply frequency (V/f) constant. At rated frequency of 50 Hz and rated voltage of 400 V its speed is 1440 rpm. What is the speed at 30 Hz, if the load torque is constant?
A.	882 rpm
B.	864 rpm
C.	840 rpm
D.	828 rpm
Answer» C. 840 rpm

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