Electromagnetic forces of the cage rotor in conical whirling motion

The paper deals with the electromagnetic forces in induction machines when the rotor is in cylindrical whirling motion, symmetric conical whirling motion or a combination of these. These motions describe the eccentric movements of the rigid rotor in induction machines. Time stepping finite element analysis is used for solving the magnetic field, and the forces are calculated from the airgap by a method based on the principle of virtual work. The forces are measured for a test motor equipped with active magnetic bearings. The active magnetic bearings are used to generate the eccentric rotor motions and also to measure the electromagnetic forces. The computed and calculated forces show relatively good agreement. Based on the calculated and measured results, a simple analytical model is developed to describe the electromagnetic forces of the rigid rotor motions.