Simulation and experimental study of induction motor broken rotor bars fault diagnosis using stator current spectrogram

Recent advances in the field of power electronics and control circuits, have contributed to the increasing use of induction machines in electrical systems. The use of induction machines is mainly due to their robustness, and their low cost of manufacture. Still, various faults may appear in such machines. The Power Spectral Density (PSD) based on the Fourier Transform (FT), is used as a method of analysis for many years for its simplicity and its relatively low computing time. However, it is ineffective in faults detection in the case of a small slip (harmonics too near to the fundamental). In addition, the fact that this method is based on the calculation of the FT, implicitly implies that the spectral properties of the signal are stationary. With the development of variable speed applications, the spectral characteristics of the stator current become non-stationary and the spectra are much richer in harmonics. To resolve these problems, we used in this paper, a time-frequency representation called Short Time Fourier Transform or Spectrogram, giving therefore, additional information on changes of the frequencies with time in the case of a stator current signal. Several simulations and experimental results are obtained in order to illustrate the merits of the Spectrogram and validate our work.