Air-gap Eccentricity Diagnosis For Induction Motors Based On Vibrational Analysis

The asymmetrical faults in the machine can affect air-gap magnetic field to induce unbal-anced magnetic pull, which lead to abnormal vibration. Thus, the vibrational signals can help to diagnose whether air gap eccentricity fault happens or not. In this paper, the vibrational sig-nal spectrum of a eccentric three-phase induction motor is analyzed in detail to diagnosis the eccentricity faults.First, based on the existing air-gap eccentric fault characteristic indexes commonly used in fault diagnosis researches, a new fault feature index is obtained through the analysis of the electromagnetic field theory, and is verified its validity by simulations and experiments. Then the amplitude of fault indicators under different fault degrees are analyzed to obtain the relationship between the amplitude of fault indicators and the fault degrees. Then the eccentric degree can be deduced according to the results.Results from the literature research tell us that there are not enough related studies about the position of the air-gap eccentric fault. According to the performance of the minimum gap position under different kinds of eccentric faults, this paper analyzes the magnitude of two forces in perpendicular direction. The results of simulations and experiments verify the effectiveness of using two forces in perpendicular direction to judge the eccentricity location.The method that using the relationship between the amplitude of fault indicators and the fault degrees speculates the fault degree has no broad applicability. Then, the idea of using artificial intelligence method is proposed.The innovations that using wavelet packet energy increment as the input vectors of the neural net do not only expand the range of application but also can judge the air-gap fault degree to a certain extent.