An induction or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.ince rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slower than synchronous speed. The difference, or slip, between actual and synchronous speed varies from about 0.5 to 5.0% for standard Design B torque curve induction motors.