Use of surface resistance for assessing vulnerability of HV outdoor insulators to contamination flashover

This paper describes the use of surface resistance under wet conditions to evaluate the vulnerability of HV outdoor insulators to flashover in contaminated locations. The insulators evaluated include porcelain, silicone rubber and EPDM rubber composite insulators. The experiments were performed in the laboratory on clean and artificially contaminated insulators utilizing different modes of wetting, namely, salt-spray, clean-fog and fog produced by ultrasonic devices. It has been shown that there is a critical value of surface resistance below which flashover invariably occurs. This value can be used to assess the likelihood of imminent flashover in the field. Several insulators removed from the field from contaminated locations were evaluated to validate the findings.