Natural Contamination and Surface Flashover on Silicone Rubber Surface under Haze–Fog Environment
Anti-pollution flashover of insulator is important for power systems. In recent years, haze-fog weather occurs frequently, which makes discharge occurs easily on the insulator surface and accelerates insulation aging of insulator. In order to study the influence of haze-fog on the surface discharge of room temperature vulcanized silicone rubber, an artificial haze-fog lab was established. Based on four consecutive years of insulator contamination accumulation and atmospheric sampling in
... sampling in haze-fog environment, the contamination configuration appropriate for RTV-coated surface discharge test under simulation environment of haze-fog was put forward. ANSYS Maxwell was used to analyze the influence of room temperature vulcanized silicone rubber surface attachments on electric field distribution. The changes of droplet on the polluted room temperature vulcanized silicone rubber surface and the corresponding surface flashover voltage under alternating current (AC), direct current (DC) positive polar (+), and DC negative polar (−) power source were recorded by a high speed camera. The results are as follows: The main ion components from haze-fog atmospheric particles are NO 3 − , SO 4 2− , NH 4 + , and Ca 2+ . In haze-fog environment, both the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) of insulators are higher than that under general environment. The amount of large particles on the AC transmission line is greater than that of the DC transmission line. The influence of DC polarity power source on the distribution of contamination particle size is not significant. After the deposition of haze-fog, the local conductivity of the room temperature vulcanized silicone rubber surface increased, which caused the flashover voltage reduce. Discharge is liable to occur at the triple junction point of droplet, air, and room temperature vulcanized silicone rubber surface. After the deformation or movement of droplets, a new triple junction point would be formed, which would seriously reduce the dielectric strength of room temperature vulcanized silicone rubber. The haze-fog is a mixture of haze and fog, but the difference between haze and fog is great. Haze is composed of dust, sulfuric acid, nitric acid, organic hydrocarbons, and other particles in the air. Fog is an aerosol system consisting of a large number of tiny droplets or ice crystals suspended in near-surface air  . The occurrence of flashover under haze-fog environment is related with insulator pollution degree, haze component, haze particle size, fog-water conductivity, and so on. It is even more complicated than other pollution flashover      . Guo et al. proposed that the fog-water conductivity is the key parameter to characterize the effect of the haze-fog on the outdoor insulation performance. With the fog-water conductivity increasing from 25.3 to 3000 µS/cm, the flashover voltage may decrease up to 27.5% . Arshad et al. proved that Arc inception and flashover voltages decreased by 50% and 52%, respectively, as the value of ESDD was changed from 0.035 to 0.4 mg/cm 2 . Studies found that silicone rubber surface attached with the droplets will lead to electric field distortion. Consequently, the initial discharge voltage of the corona is decreased and the life of insulating materials is shortened. Joneidi et al. simulated the electric field of 20 kV composite insulators with Comsol. With the influence of droplets, the electric field intensity is basically maintained at 0.1 kV/mm. The electric field intensity floats in the range of 0.01-0.24 kV/mm without the influence of droplets  . Souza studied the effect of droplet conductivity on corona initial voltage. With the increase of conductivity, the initial discharge voltage is reduced by an average of 30%. Besides, it is believed that for composite insulators, corona discharge is easier to occur in humid and polluted environments  . Xie et al. proposed that the initial discharge voltage and the temperature variations for two salt droplets closely correlated with the ionization degree of the salt, as well as the interfacial electrochemical reactions near the electrodes  . Li et al. proved that when applying a tangential electric field, water droplet on super hydrophobic surface tended to a self-propelled motion while it tended to elongate and break up on Room Temperature Vulcanized (RTV) silicone rubber surface  . However, the characteristics of the deposition on the RTV surface of transmission lines in the haze-fog environment are still unknown. The flashover performance of silicone rubber surface under haze-fog environment also needs to be studied in further. In this paper, the conditions of contamination and atmosphere for the insulators coated with RTV in transmission lines were sampled in the spring of year 2014-2017. ESDD, NSDD, contaminant particle size and fog contained inorganic ions were obtained from the field sampling data. Ansys Maxwell was used to analyze the influence of the droplets on the electrical filed strength of coated surface. Finally, by a high speed camera, the changes of the droplet attached on the surface of contaminated silicone rubber and the corresponding flashover voltage were recorded in AC field and positive (negative) polarity DC field, respectively. The research results may provide a reference for the study of the surface discharge characteristics of silicone rubber in haze-fog environment.