Ac and dc performance of polymeric housing materials for HV outdoor insulators

An experimental study was conducted to investigate the performance of several polymer outdoor insulator formulations under ac and dc electrical stresses. The performance of the polymers was evaluated in terms of their charge accumulation and decay characteristics as a function of humidity, and their tracking and erosion resistance. The results obtained from this study indicate that significant differences exist in surface charging phenomena between ac and dc. A likely contribution of dc polarization processes leading to hydrophobicity loss is believed to influence additionally the performance of materials subjected to pollution and dc electrical stresses. A substantial reduction in the tracking and erosion resistance of the polymeric materials is observed with dc stresses, in comparison to ac. The poorer electrical performance of the materials stressed with dc voltage was found to be due to higher magnitudes and longer duration times of the discharge current.