Improvements in high frequency modelling of induction motors for diagnostics and EMI prediction

This paper shows that it is possible to apply in on-line conditions a proposed procedure to diagnosis induction motors or predict the EMI due to them. This procedure is based in high frequency measurements to obtain a high frequency model whose parameters are linked with some characteristics of the motors (ball bearing performance and others). The authors have been exploring the use of measurements of common mode impedance up to 30 MHz to adjust a Z_CM expression and identify the parameters of that model. Two different measuring methods have been described in former papers and the obtained results showed the reliability of that procedure. In this paper, measurements of common mode impedance obtained by using a third method (simply, by using standard instrumentation: an impedance analyzer working in a range of only up to 1 MHz) are presented. Firstly, these results confirm the former ones. Secondly, motor speed influence is analyzed. Being the procedure for adjusting Z_CM based on knowing resonance maximum frequencies, measurements of frequency of a particular resonance maximum for different motor speeds have been made. Results show that motor speed does not affect the frequency of this resonance maximum in the considered range of speed. Thirdly, on-line measurements of high frequency data show a strong impact of EMI from the environment. This paper shows how this noise can be filtered in an efficient way. In conclusion this paper shows that the proposed procedure to diagnose the induction motor or predict the EMI due to that load could be applied in on-line conditions.