Electromagnetic force on a whirling cage rotor

The forces acting between the rotor and stator of a cage induction motor, when the rotor is performing cylindrical circular whirling motion, are measured. Time-stepping finite-element analysis is used for solving the magnetic field, and the forces are calculated from the airgap field based on the principle of virtual work. The forces are measured with a test motor equipped with active magnetic bearings. The magnetic bearings are used to generate the whirling motion and to measure the forces. The computed and measured forces show good agreement. The effects of the magnetic forces on rotor dynamics are briefly discussed.