Time–frequency analyses of leakage current waveforms of high voltage insulators in uniform and non-uniform polluted conditions

This study deals with the analysis of the leakage current (LC) in both time and frequency domains, for different configurations of polluted high voltage insulators (i.e. for clean and polluted insulator surfaces). The characteristic parameters of the recorded LC waveforms up to flashover namely the peak value, the phase shift, the total harmonic distortion and the harmonic contents are investigated. It is shown that the LC peak value and the phase shift cannot be a trustworthy indication of the surface activity related to partial discharges and waveform type whereas the harmonic components magnitude can be well correlated with the LC distortions; it is shown that in the early stages, the fifth and seventh harmonics contribute to the distortion of the LC whereas for advanced stage, the third harmonic contribution is the most significant. A time-frequency analysis is also carried out to better understand the LC behaviour. The spectrogram of the different stages of LC activity is computed using Matlab toolbox. The results show that time-frequency analysis can be used as a tool for patterns recognition and classification of the LC.