Influence of corona discharge on aging characteristics of HTV silicone rubber material

To obtain dominant parameters of material characteristics for evaluating aging state of composite insulators effectively, a comparative study was performed on the HTV silicone rubber material aged by corona discharge in laboratory and by natural environment, in regard to such parameters as hydrophobicity, surface leakage current, surface microstructure and chemical composition. Experimental results show that the characteristic parameters of the silicone rubber material under two kinds of aging conditions exhibit similar change rules. Corona aging condition decreases hydrophobicity, and increasing corona voltage or acting time leads to a sharper drop and a slower recovery or even uncompleted recovery in hydrophobicity. Hydrophobicity decline is also observed in the naturally aged specimens from HC1 level in two years to HC5 level in 15 years. In addition, surface resistivity also decreases with aging time and thus surface leakage current increases. SEM and FTIR analyses show that both corona aging and environment aging conditions induce increasing surface defect density and deepening pits, and even cracks. Moreover, aging gets the molecular chain of silicone rubber material broken and results in the generation of strong polar groups, worsening the mechanical and insulation performances of the silicone rubber.