Characteristics Of Surface Discharge For Hydrophobic Evaluation Of Polymer Insulator Based On DDT

With the wide application of polymer insulators in UHV and EHV transmission lines, the decrease of hydrophobicity becomes one of the prominent factors to affect the stability and reliability of power system. In this paper, based on DDT method, pulse current method and an antenna were utilized to receive the surface discharge signals in the experiment for hydrophobicity evaluation of polymer insulators. The main innovations are as follolws:Based on pulse current method, the characterizations of surface discharge on the aged samples, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, had been analyzed to evaluate the surface hydrophobicity. It is found that the characteristic patterns of surface discharges apparently show the increasing tendency with the decrease of hydrophobic level. The similarity degree between the discharge characteristic methods and the traditional contact angle method is analyzed to obtain the higher similarity coefficients, while this method presents intuitive, clear, accurate, reliable and easy to operate.Based on non-liner theory, surface discharge signals were analyzed, and an antenna was utilized to receive electromagnetic signals, which were induced during the surface discharge on the sample surface. The wavelet theory was applied to obtain 3-D images and 2-D contour line spectra of surface discharge. The fractal dimensions and lacunarity were computed to assess the severity of surface discharge quantificationally, and the recurrent plot technique was applied to analyze the symmetry of the discharge signals. The result shows that the method has a high similarity compared with the traditional contact angle method, as well as high accuracy, reliability and promotion.