The validity of tracking chamber tests in testing silicone rubber insulators

Silicone rubber insulators have shown superior field experience compared to porcelain and EPDM insulators in high contamination areas because silicone rubber can prevent water sheeting on the surface (hydrophobicity). On the other hand silicone rubber insulators don't perform as well when they are tested in the tracking chambers although the tracking chamber testing has been revised to accommodate the surface hydrophobicity of the insulators. This paper discusses the reasons behind that discrepancy. The data presented in this paper demonstrates that tracking chamber tests do not reflect the actual stress conditions that silicone rubber products normally encounter in the field. The tracking chamber tests only can be used to compare products to each other. However, the present tracking chamber tests must be significantly improved to predict the actual long-term performance of the silicone insulator. This paper describes one way to do that.