Impact of In-Service Defects in Composite and Porcelain Disc Insulators on Flashover Performance of HVAC Strings

Silicone composite long rod and porcelain disc insulators strings are used in EHV/UHV transmission lines to transfer power from generating station to load centers. Integrity of insulators have considerable role in providing uninterrupted and quality power to the end users. Insulators, the vital equipment of transmission system, is either composite or porcelain disc, which may develop defects during service. Damages made by in-service defects, excluding cracks and superficial faults, may reduce the creepage distance of string considerably. Moreover, potential distribution along the string become non-linear due to local electric field concentration at that damaged portion of insulators. Both these creepage distance and non-linear field distribution will affect the flashover performance of insulator string, sometimes, insulators with these in-service defects fail to withstand normal operating voltage and leads to line outage. Bird pecking and cracks are the most common in-service defects on composite long rod insulators. Damage of shed profile commonly evolve during service on porcelain disc insulators. In this work, an attempt is made to experimentally evaluate the impact of in-service defects on flashover voltage of insulator string. Defects are deliberately developed on insulator samples. Details of defects, impact of particular fault, viz. crack or bird pecking or shed damage on porcelain along with its location of insulator string has been elaborately evaluated.