The three-phase asynchronous motor consists of two basic parts, a fixed stator and a rotating rotor. The rotor is mounted in the inner cavity of the stator and supported on the two end caps by means of bearings. In order to ensure that the rotor can rotate freely in the stator, the stator and the rotor must have a gap, called the air gap. The air gap of the motor is a very important parameter, and its size and symmetry have a great influence on the performance of the motor. Figure 2 shows the components of a three-phase cage asynchronous motor.