Failure Analysis of Field-Aged Composite Insulator Used in Traction Systems

Outdoor insulators are one of the most essential parts of the electrical power system. They provide mechanical support as well as electrical isolation to the transmission line elevated to high voltages. Composite insulators, often called non-ceramic insulators, have various advantages over their ceramic counterpart and have been widely employed in the last two decades. Polymeric housing, such as silicone rubber (SR), is used in composite insulators to protect the fiberglass reinforced plastic (FRP) core rods from environmental weathering. Despite all the advantages, polymeric material in composite insulators is prone to degradation due to aging when used in outdoor conditions. In this paper, real service life samples are taken for study used in electric traction with 25 kV applied voltage. Material-based investigations of high-temperature vulcanized (HTV) SR housing are presented. Due to thermal and ultraviolet (UV) radiation, the chemical composition of SR changes over time when exposed to external environmental stresses, as observed and reported. With aging, the SR loses its fundamental properties and turns more crystalline and, hence, more prone to forming cracks on its surface due to electrical discharges. Such prolonged gradual degradation of SR housing is observed with aging results in complete failure which is correlated with physico-chemical measurement.