Diagnosis of rotor bar breakages based on the Hilbert Transform of the current during the startup transient

The Hilbert transform (HT) can improve the resolution of motor current signature analysis (MCSA), especially at very low slip, because it converts the supply frequency into a continuous component, which can be easily removed to better detect fault harmonics. This paper proposes its application also during speed transients, with two key advantages: first, it allows an easy filtering of the transient current component corresponding to the mains, and, second, the HT can be use to generate the Hilbert spectrum (HS), as a replacement of the Fourier spectrum for the analysis of non-stationary signals, like those that appear in a transient regime. The performance of the proposed method is compared with other methods such as the discrete wavelet transform (DWT) and the empirical mode decomposition (EMD), and is validated through experimental analysis of a 1.1 kW three-phase squirrel-cage commercial induction motor with one broken bar.