Dynamic behavior of water droplet on silicone rubber surface in dynamic drop test

Stability of hydrophobicity of silicone rubber composites is considered to be important for long-term insulating performance of polymeric outdoor insulator. Recently, dynamic drop test (DDT), which could evaluate the stability of hydrophobicity under ac voltage application with good reproducibility, has been studied as a standard laboratory test in CIGRE. DDT could clear the time until the formation of continuously wetted path between the electrodes when electrolyzed droplets were dropped on the sample surface. On the other hand, the degradation mechanisms of hydrophobicity on silicone rubber surface were not clear enough. In this paper, we investigated the dynamic behavior of the water droplet on the silicone rubber surface and its influence to the hydrophobicity in DDT. As a result, we clarified that the time transition of the droplet oscillation was involved with the degradation of hydrophobicity in silicone rubber surface. These results indicated the possibility to investigate the status of hydrophobicity in silicone rubber surface from the oscillation of the water droplet in DDT.