Start-up analysis methods for the diagnosis of rotor asymmetries in induction motors-seeing is believing

This article presents a qualitative analysis of different methods proposed for the diagnosis of broken rotor bars using the stator current during start-up operation. The slip dependent components, caused by the asymmetry, which is created by the breakage of rotor bar(s) and especially the left sideband harmonic (LSH) component, can create a distinctive pattern in a time-frequency plane. Short Time Fourier Transform, Wavelet analysis, and Wigner-Ville Distribution are evaluated using signals from motors operating in real industrial settings. The corresponding analysis presents the pros and the cons of these approaches for their potential application under realistic industrial conditions using the larger number of real life cases encountered in the literature.