Locally optimized chirplet spectrogram for condition monitoring of induction machines in transient regime

The locally optimized chirplet spectrogram (LOCS) is a novel method proposed in this work for generating a high-resolution and cost-effective spectrogram of the induction machine (IM) current, suitable for the identification of fault-related harmonics in transient conditions. Its distinctive novelty is that it optimizes automatically the parameters of the analysing window used for building the current spectrogram, at each point of the time–frequency plane, with the computational cost of a conventional, non-optimized spectrogram. It is based on the definition of a large dictionary of different chirplet windows, which are combined into a single, complex time window. A single short time Fourier transform with this new window generates in parallel the spectrograms of all the dictionary windows, and the LOCS chooses among them the locally optimized values in an automatic way. The proposed technique is applied to the diagnosis of two commercial induction motors with bar breakages and mixed eccentricity faults. [Display omitted] •Chirplet spectrogram for fault diagnosis of induction machines in transient regime.•A dictionary of chirplet windows is defined with a wide range of parameters.•A single, complex time window contains the dictionary in separated frequency bands.•The spectrograms of all the dictionary windows are generated in parallel.•Highest spectrogram value at each time–frequency position is automatically selected.