Effects of eccentricity on external magnetic field of induction machine

This paper deals with the analysis of external magnetic field of three-phase induction motor in order to diagnose the air gap asymmetry caused by eccentric rotor. Dynamic eccentricity produces low frequency air gap flux components, however they can be observed in stator current only under mixed eccentricity. Unlike MCSA (motor current signature analysis), described method allows to detect purely dynamic eccentricity or to detect dynamic eccentricity under mixed eccentricity with a minimal effect of static eccentricity. Although many papers have been focused on external magnetic field analysis, they have usually decribed other types of faults. In this paper the amplitudes of characteristic frequency components are predicted using FEM and some obtained results are verified by measurement. Both purely dynamic and mixed eccentricities are taken into account as well as saturation of magnetic circuit due to its significant influence on calculated spectrum.