Influence of manufacturing tolerances and eccentricities on the unbalanced magnetic pull in permanent magnet synchronous motors

Abstract

Eccentricity is an inevitable fault in electric motors and hence its diagnosis is an important topic. Thus, the influence of static and dynamic eccentricities on the harmonics of the frequency spectra of the unbalanced magnetic pull is analyzed. In this article, dimensional tolerances of the rotor and the stator are also considered. All parts have dimensional tolerances in their designs and their real magnitudes vary to some extent from the theoretical values after the manufacturing process. Thanks to analytical calculations and finite element simulations, verified with experimental results, it is observed that the deviations originated by the manufacturing tolerances produce changes in the amplitudes of some harmonics and also additional and characteristic harmonics in the frequency spectra of the unbalanced magnetic pull. These are not negligible and must be taken into account when robust eccentricity detection procedures are defined. Otherwise, harmonics originated by tolerances and by eccentricities can be misidentified. Finally, after decoupling the effect of tolerances and eccentricities, the frequency harmonics that are indicators of rotor tolerances are determined, and a new methodology based on ratios of amplitudes of adjacent harmonics is proposed to identify eccentricities.