Calculation of radial magnetic forces for the analysis of noise and vibrations of squirrel-cage induction motors

This paper presents a method for computing the radial magnetic forces in squirrel-cage induction motors, which contribute to a great extent to the generation of vibrations and noise. In the calculation method the various effects which determine the modal contents of the radial force are taken into account: the spectrum of the applied voltage (in case of inverter supply), the winding arrangement, stator and rotor slotting, static and dynamic rotor eccentricity and iron saturation. For modelling the induction motor, a magnetic equivalent circuit, developed in the frequency/order domain, coupled with an electrical circuit (a set of voltage equations) is used. The calculation method is experimentally verified by means of stator tooth flux measurements in an induction motor and by noise measurements