End-of-life characteristics of RTV coated insulators under pollution conditions

Abstract

With the ever increasing demand for electrical energy in the world today necessitates this energy transmission at higher system voltages in the EHV/UHV AC and /or DC in order to reduce the line loss and increases the power handling capacity. As the system voltage increases, the design of external insulation for both line and station depends on the pollution performance. Hence the external or outdoor insulation i.e. insulators and bushings etc.plays a vital role at the extra high voltage or ultra high voltage range. The external insulation in the EHV/UHV range is generally designed mostly on the basis of switching over voltage level and in some rare cases by lightning over voltages. Switching over voltage is of concern mainly at system voltages of 300KV and above and lightning over voltage are dominating at lower level voltages. It is clear that as the range of transmission voltage is increased switching and dynamic or lightning over voltages and with stand ability of the insulators under polluted conditions are the most important factors, which determine the insulation level of the system. The continuous operation of the system mainly depends on the environmental and weather conditions, which cause flashover on polluted insulators. This pollution flashover poses serious threat to the reliability of the system. Flashover leads to the system outages, means the reliability of the system mainly depends on the pollution performance of the system. Therefore it is necessary to check the withstand capability of the insulator by the artificial test methods under pollution conditions. There are many remedial measures to minimize the flashover of porcelain insulator under pollution condition. One of such method is application of Room Temperature Vulcanizing Silicone rubber coating on porcelain insulator. The coating is subjected to ageing phenomena over a period of time which is not felt on porcelain insulators.