Mitigation of outdoor insulators failure using silicone coating

Insulator is one of the most important equipments in an electric power system. Since long time ago ceramic insulators are widely used in transmission as well as in distribution lines. As outdoor insulators, the insulators are subjected to outdoor environmental stresses such as humidity, temperature and pollution. Under polluted and wet condition, high leakage current may flow on the insulator surface. As the result a dry band arching may take place and in the long time it may degrade the insulator and initiate the insulator flash over leading to the failure of the lines. Several efforts may be taken to improve the insulator performance under polluted condition. They are increasing the number of insulator strings, modification of insulator design to increase the creepage distance and regular washing. This paper reports a proposal to mitigate the outdoor insulator failure using silicone coating. This paper explains the experimental results on the silicone compound coating on the medium voltage ceramic insulators under various environmental condition. It was found that the coating was significantly suppressed the magnitude of leakage current and drastically eliminated the harmonic content. The coating also drastically suppressed the corona on the insulator and reduced the surface temperature. The coating also significantly increased the flash over voltage of the insulator. Surface analysis indicated that increasing of the water repellence of the insulators played important role in the increase of the insulator performance.