In a constant V/f induction motor drive, the slip at the maximum torqu...
In an induction motor operating at any voltage Vr, frequency f, slip for max torque = r2 / x2 where x2 = 2πL2 f.
Now; if frequency is changed (irrespective of whether v/f is constant or not) x2 changes proportionally. So slip for maximum torque is inversely proportional to frequency. Synchronous speed is directly proportional to frequency. Hence slip of maximum torque has an inverse relation with synchronous speed.
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In a constant V/f induction motor drive, the slip at the maximum torqu...
Slip in a Constant V/f Induction Motor Drive
Slip is defined as the difference between the synchronous speed and the actual rotor speed of an induction motor. In a constant V/f induction motor drive, the frequency (f) of the stator voltage is kept constant while the voltage (V) is varied with the load. At the maximum torque, the slip has an inverse relation with the synchronous speed.
Explanation
As per the torque equation of an induction motor, the torque is directly proportional to the slip. At the maximum torque, the slip is also maximum. The maximum torque is achieved when the rotor impedance is equal to the rotor reactance. This condition is also known as the breakdown torque. At this point, the slip has an inverse relation with the synchronous speed.
The formula for slip is given by:
Slip = (Ns - Nr) / Ns
Where Ns is the synchronous speed and Nr is the actual rotor speed.
At the maximum torque, the rotor speed is less than the synchronous speed, hence the slip is positive. As the synchronous speed decreases, the slip increases. This is because the rotor impedance increases with decreasing speed, which causes an increase in slip. Therefore, the slip has an inverse relation with the synchronous speed at the maximum torque.
Conclusion
In conclusion, the slip at the maximum torque in a constant V/f induction motor drive has an inverse relation with the synchronous speed. This is because the rotor impedance increases with decreasing speed, causing an increase in slip.