ONLINE CURRENT MONITORING AND APPLICATION OF A FINITE-ELEMENT METHOD TO PREDICT THE LEVEL OF STATIC AIRGAP ECCENTRICITY IN 3-PHASE INDUCTION-MOTORS

The introduction reviews the real practical problems of airgap eccentr icity in large 3-phase induction motors. On-line monitoring methods fo r diagnosing airgap eccentricity are also discussed and a state of the art reveiw on the application of current monitoring to detect airgap eccentricity is presented. The limitations of the classical MMF and pe rmeance wave approach for predicting the severity of airgap eccentrici ty are discussed. The time stepping finite element (FE) method and FFT analysis technique are used as 'analyses tools' to predict the freque ncy components in the current (Hz and dB) as a function of static airg ap eccentricity Excellent agreement is obtained between the measured a nd predicted frequency components (Hz) in the current spectra which ar e a function of static eccentricity. The FE method is also used to pre dict the magnitude (dB) of these frequency components in the current s pectrum with different levels of static airgap eccentricity. These pre dictions are much closer to the measured values in comparison to previ ous attempts using the classical MMF and permeance wave approach. The contents of this paper will be of particular interest to the manufactu rers and industrial users of three-phase induction motors.