| Insulators are widely used in power transmission lines and are important components to maintain the safe and stable operation of power systems.Under icing conditions,the electrical strength of the insulator will gradually decrease,which may easily cause a long-term power outage,threaten the sustainable operation of the power system,and cause significant economic losses.At present,scholars at home and abroad have done a lot of research on the flashover characteristics,influencing factors and discharge mechanism of ice-coated insulators.However,most of the ice-coated tests are completed in an artificial climate room.The environmental conditions simulated by artificial climate chambers are quite different from the natural environment,and the operating conditions of insulators under actual conditions are also different.In addition,most of the studies on insulators at home and abroad are only short strings,and the models studied have not been verified in long insulator strings.Therefore,the research of this topic can not only supplement the model and mechanism of insulator icing discharge,but also provide reference and basis for the coordination and selection of external insulation of AC transmission lines.In this paper,a natural ice-covered AC flashover test was performed on five long strings of insulators at the Xuefeng Mountain Ice-covering Test Station,and the laws and maps of natural ice-covering of long-string insulators were obtained,as well as their different contamination levels and ice-covering degrees.The AC flashover voltage,and its discharge path,electric field distribution,and leakage current changes were analyzed,and the following conclusions were obtained:(1)Low temperatures,high wind speeds and intensive rainfall will accelerate the rate of natural icing of insulators.Insulators in natural environment show regional uneven distribution on the leeward side.The type and structure of the insulator will affect the degree of icing.(2)The flashover voltage of an ice-coated insulator string is affected by the degree of ice coating and contamination.The ice flash voltage of a long string of insulators decreases with the salt density and the weight of the ice coating.The result of the voltage has an effect.The influence index of salt density is 0.212 ～ 0.294 for glass insulators,0.184 ～ 0.322 for porcelain insulators,and 0.189 ～ 0.263 for composite insulators.(3)The combined effect of ice weight and salt density can be obtained by using the parameter ISP to measure the combined effect of ice weight and salt density.The double umbrella insulator has the largest decline with ISP,and the bell insulator has the smallest decline with ISP.The 13-string suspension insulator pollution flashover voltage is characterized by a salt density characteristic index c between 0.207 and 0.316.Except for the case of lighter ice weight,the long-chain insulator pollution flashover voltage is higher than the ice flashover voltage.(4)The ice flash process of a long string of insulators can be divided into four stages: corona generation,local arc occurrence,arc development,and complete flashover.During the discharge process and pollution flashover process of natural ice coating on long strings of insulators,the phenomenon of arc extinction and reignition is obvious,and the phenomenon of arc drift is serious.In the electric field simulation analysis of the LXY-210 insulator,when the arc starting voltage is applied,the discharge phenomenon first occurs at both ends of the insulator string.When the flashover voltage is applied,many air gaps of the insulator string are broken by the arc,which is consistent with the observed test. |
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