Ageing and degradation of silicone rubber insulators in contaminated environments is a major concern due to their organic nature. Understanding the flashover process of silicone rubber insulators under contamination is very important and needs standardized tests and procedures. Surface resistance measurement can be used as an indication of ageing and contamination severity of outdoor silicone rubber insulators. This paper presents experimental and mathematical results on surface resistance of high-temperature vulcanized silicone rubber sheets under various environmental and contaminated conditions. Rectangular silicone rubber sheets were polluted artificially in laboratory using a modified solid layer method based on IEC 60507 and tested in a climate chamber where fog rate, humidity and temperature can be controlled. Influence of non-soluble salt deposit density (NSDD), pollution severity, relative humidity, ambient temperature, dry band location and width, and multiple dry bands on surface resistance have been investigated. The obtained results show that surface resistance decreases with increase in NSDD, pollution severity and relative humidity. Increase in surface resistance was observed with the formation of dry bands. Although surface resistance was effected by all parameters, the most dominant parameter was noted Repeatability of results was confirmed by performing each test five times and concluded that surface resistance measurement can be standardized to evaluate ageing and pollution severity of silicone rubber insulators. These results along with the available literature on equivalent salt deposit density (ESDD) measurement could be used to formulate a relation between ESDD and surface resistance that could be useful for evaluating the performance of silicone rubber insulators in wet and contaminated environments.
Silicone rubber insulators are replacing the conventional ceramic and porcelain insulators rapidly in power transmission and distribution industry. Very limited field knowledge is available about the performance of silicone rubber insulators in polluted and contaminated environments and therefore need further investigation. A comprehensive analysis of silicone rubber sheets (intended for coating outdoor insulators) was carried out in this paper based on experimental results. The main performance parameters analyzed were arc inception voltage and flashover voltage. Dependence of these parameters on equivalent salt deposit density (ESDD), non-soluble salt deposit density (NSDD), relative humidity, ambient temperature, fog rate, dry band formation, dry band location and number of dry bands were investigated extensively. Insulator orientation and its effect on performance were also studied. The authors believe that this paper will provide a comprehensive knowledge about the flashover characteristics of silicone rubber insulators under humid, contaminated and dry band conditions. These results could be used in the selection and design of silicone rubber insulators for polluted environments.
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