Characterization of surface discharge as indicator for hydrophobicity evaluation of silicone rubber insulators

A Dynamic drop test (DDT) has been employed for hydrophobicity evaluation, which has proven the occurrence of different discharge phenomena in relation to the hydrophobicity variation. In this paper, based on DDT method, the characterization of surface discharges, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, have been analyzed to evaluate the surface hydrophobicity of silicone rubber insulator. It is found that with the decrease of hydrophobicity, these characteristics apparently show an increasing tendency. The characteristic pattern of discharge pulse and discharge magnitude presents a twin-peak shape, in which both the increase of the discharge magnitude and the discharge pulse number of higher magnitude reflect the decrease of surface hydrophobicity. The characteristic pattern of adjacent discharge magnitude and discharge magnitude emerges to be an 'X' shape composed by the discharge spots, in which the larger value in both the spot density and the shape expansion reveals the decreasing hydrophobicity. The characteristic pattern of next time interval and discharge magnitude demonstrates the frequency of surface discharges increases with the decrease of surface hydrophobicity. Furthermore, the comparability between the discharge characteristic methods and the contact angle method is analyzed to obtain the higher similarity coefficients. Obtained results indicate that the characteristic of surface discharge in DDT method can be utilized to the hydrophobicity evaluation.