Variation of leakage current caused by hydrophobicity loss of silicone rubber in Dynamic Drop Test

Silicone rubber used for polymeric insulators has good hydrophobicity and recovery characteristic of it. CIGRE WG D1.14 aims to establish new test procedure, dynamic drop test. That can evaluate the property of hydrophobicity loss of silicone rubber easily and with small systems. So, we clarified the relation between processes of hydrophobicity deterioration or loss and leakage current waveform in dynamic drop test. The hydrophobic conditions were classified into three categories. In the condition of keeping hydrophobicity, pulse discharges were repeatedly observed at the time when droplets ran down. As hydrophobicity deteriorated, small water droplets remained on the surface and many pulse discharges were observed when the droplets ran down. The tendency of the current ingredient of 60 Hz became more dominant and discharge light started to be observed continuously regardless of the timing of the droplets just before when hydrophobicity lost. Then it was considered that a thin moisture layer was formed on the surface, although only droplets were observed with the naked eye. Finally, the leakage current flowed continuously.