Slip- Whenever 3 supply is given to the stator RMF will be developed around the rotor. Since the supply is constant so RMF speed is constant and is known as synchronous speed(NS).If the rotor rotates at synchronous speed flux linkage will be zero. So the rotor rotates just below the synchronous speed and is named as rotor speed(N).
The difference between synchronous speed to rotor speed is known as Slip speed.
S=synchronous Speed-Rotor speed/synchronous speed
Percentage slip = (NS-N/NS)*100
At no load slip is 0.5% and at normal speed slip is 2-5%.
With increase in load, rotor speed(N) decrease so slip is increase. So induction motor rotates at constant speed and plays a role of a DC shunt motor.
At stand still
At synchronous speed
At stand still percentage slip is 100% at No load it is 0.5% and at load it is 2-5%.