Modelling of electromagnetic excitation forces of small induction motor for vibration and noise analysis

The authors present a simple method for calculating electromagnetic excitation forces in the airgap between stator and rotor of a five horse power three-phase squirrel cage induction motor, which are significantly responsible for the noise and vibration in the high frequency range under operating conditions. The method proposed adopts the classical transformer model to represent the electromagnetic circuit in the motor and takes into account skew of the rotor slot and fluctuations of the permeance due to rotor rotations in estimating the electromagnetic excitation forces at each tooth of the stator. The effects of rotor eccentricity and slot opening on the excitation forces are then analysed. Estimated electromagnetic forces are compared with measurements obtained by placing a flux-detecting coil on a stator tooth. The capabilities of the method are illustrated