Prediction of Dielectric Breakdown of OHTL Insulators Using Contact Angle Measurements

Abstract

Porcelain insulators used in overhead transmission lines (OHTL) are exposed to pollution when operational. To observe the effect of external pollution on these insulators, the relationship between the flashover voltage and surface contamination was studied. The flashover voltage drops sharply when contaminants in the wind are deposited on the surface of the insulators in a humid environment. Under wet conditions, the flashover voltage demonstrates a difference of approximately 10 kV depending on the contamination levels. The higher the equivalent salt deposit density, the lower the contact angle. In particular, the flashover voltage under wet conditions decreases exponentially when the contact angle is below 30°. In this case, the condensation area becomes considerably wider, thus exhibiting the difference in the area of the electrolytic conductive film layer forming the leakage path on the surface. Depending on the equivalent salt deposit density and contact angle, the area of condensation is more than doubled. To measure the level of contamination on the surface using this principle, a contact angle measurement method was adopted to predict the dielectric breakdown of the insulator.