Coatings for outdoor high voltage insulators

As the range of transmission voltage increases, the pollution severity of the site becomes the most important factor in determining the insulation level of the system. Flashover on polluted insulators poses a serious threat to the reliability of the system and leads to system outages. There are many remedial measures to minimize the flashover of a porcelain insulator under pollution conditions. One such method is the application of hydrophobic coatings such as Room Temperature Vulcanizing Silicone Rubber (RTV- SiR) and Grease coatings on the surface of ceramic insulators. A recently proposed solution for contaminated outdoor insulators consists of the application of the Nanocoating “Voltshield” onto the surface of the insulator. This thesis reports a comparative assessment of the performance of these coating systems. Laboratory testing of coated porcelain insulators has been undertaken based on the solid layer method of IEC 60507 (artificial pollution- clean fog testing) and IEC 60587 (the inclined plane tests and constant voltage-liquid contaminants) to evaluate the coatings’ resistance against tracking and erosion. The performance of these coatings was assessed by monitoring the leakage current on the insulator surfaces. The applied voltage and the leakage current signals were acquired throughout the tests and saved for further analysis. The effect of UV radiation on the coatings has also been investigated. In addition, hydrophobicity tests were performed on the coated insulators. It was found that the Nanocoating reduces the leakage current by 90% whilst the energy absorbed on the insulator surface is reduced by 98% when compared to an uncoated insulator. The Nanocoating showed good resilience to sand blasting, but under long exposure to sand blasting, the surface began to degrade and showed pockmarks. The Nanocoated insulator showed good stability under UV exposure in terms of leakage current suppression. However, Nanocoated insulator lost its hydrophobicity on exposure to fog, and has lower flashover voltage than the uncoated insulator by 12.5%. Similar observations were made for the RTV coatings, where the current magnitude reduced by 92%, the energy absorbed on the insulator surface is reduced by 99% when compared to uncoated insulator and the flashover voltage is increased by 50%. RTV coating materials showed good resistance against tracking and erosion even after UV exposure. The electric field and voltage distribution along the leakage surface of coated and uncoated ceramic insulators under clean and polluted conditions were studied using finite element analysis COMSOL Multiphysics®. The electric field peaked at both the HV electrode and the ground electrode, and the presence of pollution in the form of water droplets on the coated insulator increased the electric field at the HV electrode. This study shows that the application of protective coatings to HV outdoor insulators significantly improves their performance. A reduction in surface current and power dissipation is observed, and a reduction in surface heating results in less dry-band arcing. A reduction in dissipated energy can make a contribution to reducing the total loss on the power system. In addition it showed the ability of coatings to resist tracking and erosion which leads to longer coating life under severe weather conditions. The coatings also increased the flashover voltage of the insulators which leads to more stable power system.