Infrared characteristics of surface discharges in dynamic dropping test for hydrophobicity evaluation of polymeric insulator

Hydrophobicity performance of polymeric insulator in severe condition has caused more concern about reliability of power system, which increasingly requires the evaluation method for the surface hydrophobicity. In this research, based on the dynamic dropping test (DDT) method, infrared characteristics of surface discharges induced by dynamic behaviors of water droplet were investigated to carry out the hydrophobicity evaluation for different ageing levels of silicone rubber insulator. Both the dynamic morphology of water droplet and the induced discharge phenomena on the sample surface were captured by using an infrared camera to establish the relationship between the infrared radiation along the sample surface and the surface hydrophobicity. Methods of image processing and fractal dimension were employed to quantitatively analyze the infrared images. It is found that the maximum temperature and thermal distribution of discharges increase with the decrease of hydrophobicity. The increasing tendency in discharge strength and fractal dimension of thermal pattern can reveal the decrease of hydrophobicity. The results obtained indicate that the infrared characteristics of discharges in DDT method are sensitive to the hydrophobic properties, which can be applied as non-contact method for hydrophobicity evaluation of polymeric insulators.