Multi-speed control of cage Induction Motor
Essentially a squirrel cage induction motor can never keep up with the synchronous speed due to a few physical factors. The main reasons being friction and drag from load. So the rotor always lags behind the rotating field in the stator. At no load the motor will turn closer to synchronous speed as there is little load on the rotor. The speed on the nameplate is the speed at full load. This applies to all induction motors, single, three, multi-speed, etc.