Discrete Wavelet Transform analysis under non uniform contaminated conditions for pollution severity estimating

In this paper, we present results of scientific investigations dealing with the impact of the non uniformity distribution of polluted layer on the 1512 L plane model behaviour. This kind of insulator is largely employed by the Algerian Company of Gas and Electric Power (SONELGAZ). We have particularly examined the influence of both position and width of the non uniform polluted layer on frequency characteristics of the leakage current obtained with the DWT (Discrete Wavelet Transform) decomposition. The applied voltage level is maintained constant for each width of the polluted layer. The STD-MRA (Standard Deviation- Multi Resolution Analysis) representation is used in order to analyze clearly frequency bands of the leakage current for both width and position characterization of the pollution layer. This polluted layer is once situated near the high voltage electrode (HV) and once in the middle of the plane model. Reported results show that the low frequency band containing the third harmonic of the leakage current increases significantly when electric discharges occur in the clean air gap at a critical width of the polluted layer. In the case of HV polluted band, only the low frequency component of the leakage current increases with increasing of the polluted layer width. In contrast, in the case of the middle polluted band, the magnitude of high frequency components increases according to the increase of the conducting layer width.