Abstract
Silicone rubber (SiR) is used as covering material for polymeric outdoor insulators, which has an advantage of surface hydrophobicity that may suppress the discharges under wet contaminated condition. Dynamic Drop Test (DDT) is suggested in CIGRE for the evaluation of stability of hydrophobicity of polymeric insulating material under combined electric and electrolytic pollution stress. In this paper, the mechanism of the hydrophobicity loss of SiR in DDT has been studied experimentally using newly devised electrode. The setup of the experiments enabled to examine the effects of charged water drops and the electric field separately. The effect of test liquid drop sliding down the surface on the hydrophobicity loss was also examined. Through these experiments, the process of the hydrophobicity loss in DDT has been explained by dividing the process into three phases. It is concluded that the effects of charged water drops and the electric field that governed the results of DDT caused the reduction of the hydrophobicity of SiR surface before the discharges, which introduce the reorientation of polar groups.
