SIGNIFICANCE OF THE ELECTROMAGNETIC FORCES ON THE MECHANICAL RESONANCES OF STATOR LAMINATIONS

The laminated structure of the stator core of fractional horsepower el ectric motors consists of plates of ferromagnetic materials that can h ave unusually large deformation coefficients when an electric field is applied. The influence of the compressive stresses is the cause of si gnificant changes in the harmonics that can be explained by the effect of the stress on the harmonic content of the flux density waveform. M agnetostriction harmonics are important when considering the significa nt contribution to audible noise of electric motors. The significance of magnetostrictive forces increases when they excite the lamination p lates around their mechanical resonances. The combined effects of the radial components of the electromagnetic forces and the magnetostricti ve deformation can cause further problems of amplification of noise by setting the core and frame in motion. This study investigates the eff ects of magnetostrictive forces on the laminated mechanical structure of the stator core by referring to changes of the plate materials depe nding upon the heat treatments, magnetic properties, and the percentag e of silicon alloying that were all considered as factors which modify the effects of magnetostriction. (C) 1996 Academic Press Limited