Electromagnetic Forces Caused by Cage Induction Motor

The paper deals with the forces acting between the rotor and stator of a cage induction motor when the rotor is performing cylindrical whirling motion. Time-stepping finite element analysis is used for solving the magnetic field, and the forces are calculated from the air-gap field based on the principle of virtual work. The forces are measured with a test motor equipped with active magnetic bearings. A simple analytic model is given for rotor dynamic analysis purposes. This model accurately predicts the behaviour of the low frequency force component also in transient situations. Finally, the effects of the magnetic forces on rotor dynamics are briefly discussed.