Interface Failure Analysis of Service Aged Composite Insulators Used in Electric Traction

In the present study, failure analysis of silicone rubber (SR) based composite insulators employed in electric traction have been carried out. The degradation of the interface between the housing material and the Fibre-reinforced Plastic (FRP) of service failed insulators is investigated. Test specimens collected from the same geographical location are visually inspected and found to be failed under exposure to similar environmental conditions. Few failed samples show clear track formation over the surface, whereas others are visually in good condition but electrically failed. Comparative analysis has been conducted with fresh/unaged samples. The material characterization is carried out using physicochemical analysis. For assessing the interfacial condition between the SR and FRP, dye penetration tests and water diffusion tests are conducted. In addition, a Finite Element Method-based simulation study is carried out to analyse the electric field distribution near the HV metal end fittings of the insulator within the bulk. Based on the results obtained in this study, it is inferred and presented that the cause of insulator failure is the formation of a conducting water channel at the rod-housing interface due to the degradation of sealant at the triple point junction, field intensification due to the sharp edges of metal end fittings, and the voids at the rod-housing interface. The development of possible failure mechanisms and preventive measures are reported.