DC Flashover Characteristics Of Natural Environment Insulators Covered With Ice

The decline in the electrical performance of natural iced insulator strings is one of the main causes of grid accidents.Domestic and foreign experts and scholars have done a lot of research on the characteristics of insulator flashover.The insulator flashover has many influencing factors and strong randomness,and the simulation parameters of physical characteristics such as temperature,wind speed,water droplet subcooling,and particle distribution of artificial icing differ greatly from the natural environment.The analysis of the process does not completely characterize the natural ice flashover phenomenon.In recent years,ice flashover has still occurred in UHV/UHV lines.Therefore,it is of great significance to carry out the DC flashover characteristic test of natural ice-covered insulators（long）strings.It is useful for the natural ice-covered state and its ice-flash prediction,the improvement of artificial ice-covered test methods and the design of UHV DC external insulation in ice-covered areas Experimental support and theoretical basis.In the Xuefeng Mountain Natural Ice-covering Test Base,a long string of insulators were analyzed for the surface icing characteristics,and the DC flashover characteristics of a long string of natural icing insulators were experimentally explored.A three-dimensional model of the rain icing insulator was established.The influence of water film conductivity on the electric field distribution of ice-coated insulator strings.The main conclusions are as follows:（1）When the surface of the insulator is covered with icy ice,the natural environmental temperature of Xuefeng Mountain is generally between-5～0℃,the daily cumulative rainfall is greater than 10mm,and the wind speed is usually between0～7m/s.The natural icy ice-coated insulator string has the feature that the lower ice coating is longer than the middle ice coating ice edge.Composite insulators have the fastest ice coverage in the early stages.Ice coating is a special type of pollution.The surface salt density of the insulator is equivalent to the existence of iced water conductivityγ₂₀.（2）When the string length N≤15,the string length of the insulator is basically linearly related to the ice flash voltage,the coefficient e of the nonlinear relationship is between 0.9104 and 0.9775.Air pressure has no significant effect on the nonlinear relationship index e between the string length N and the ice flash voltage.As N increases,the non-linearity between the string length N of the iced insulator and the DC ice flash voltage increases.In the natural ice coating environment,the non-linearity between the insulator string length and the DC ice flash voltage is greater than that of artificial ice coating.（3）The DC flashover voltage of the suspension-type insulator long string with natural icing gradually decreases with the increase of the pollution degree SDD before icing.Glass and porcelain insulators have obvious polar effects,and composite insulators have no obvious polar effects.Glass and porcelain insulators have a positive DC ice flash voltage of 8.1%～18.1%higher than a negative DC ice flash voltage.The degree of DC ice flash voltage dispersion obtained by the artificial icing test is smaller than that of natural icing.Under the same test conditions,the DC ice flash voltage of the artificial ice coating test is 6.27%～14.81%lower than the natural ice coating.The flashover voltage of iced insulators decreases with the increase of ISP.Under the same ISP value,the flashover voltage of natural iced is higher than that of artificial iced.（4）By shooting the flashover test process of mixed maggots and rain maggot ice-covered insulators,the development law of the arc during the discharge of the insulator under different icing conditions is obtained.The flashover path of the hybrid concrete insulator is mainly along the edge of the insulator umbrella skirt,while the arc path of the rain insulator is drifting away from the ice surface of the insulator and penetrating in the air,and the arcing phenomenon is serious.The three-dimensional electric field distribution of the rain-covered ice insulator shows that the longer the insulator ice edge,the larger the electric field distortion at the tip of the ice edge,and the more easily the air gap breakdown.As the length of the string increases,the voltage difference of the insulator withstand voltage at different positions of the ice-coated insulator string increases,and the unevenness of the electric field distribution of the ice-coated insulator string increases.