The Comparison Between AC And DC Flashover Performance And Discharge Process Of Ice-covered Insulator Under Low Air Pressure

The electrical property of insulators will be reduced remarkably in an environment where low air pressure, icing and pollution coexist. The study on flashover performance and discharge process of insulators under such a complicated environment is valuable both academically and practically, for it can enlighten how to select external insulators in the west-east electricity transmission project and power grid construction, how to formulate strategies to prevent flashover and how to secure the function of power systems.This study, having reviewed relevant researches at home and abroad, conducted plenty of tests in the multifunctional artificial climate chamber mainly with the following procedures: XP-160 insulators were iced with both icing-water-conductivity and solid-layer methods, while LXY4-160 and FXBW4-110/100 insulators were iced only with icing-water-conductivity method; 50% flashover voltage method was applied, flashover performance and discharge process of ice-covered insulators then were studied in terms of AC and DC; discharge circuit model under low air pressure was applied to calculate the flashover voltage of 7-slice XP-160 insulators, results of which were compared with test results, arriving at the following conclusions:n, characteristic index of the influence of air pressure on 50% flashover voltage of ice-covered insulators, is greater under AC than that under DC, which means that such influence is greater under AC.a, characteristic index of the influence of pollution on 50% flashover voltage of ice-covered insulators when solid-layer method is applied, and b when icing-water-conductivity method is applied, are both greater under AC than under DC, which means such influence is greater under AC.With ice on the monitoring cylinder 10 mm thick and slices equal to or fewer than 14, there is approximately a linear relation between 50% AC and DC flashover voltage of XP-160 insulators and length of slices. Nonlinearity is found in such a condition as well. Therefore, a way to revise 50% flashover voltage of insulators influenced by the coactions of icing, pollution and low air pressure, is put forward. Arc may float in the flashover process of ice-covered XP-160 insulators under bothAC and DC, yet arc-floating tends to be more serious under DC.Δt, duration from local arc to complete flashover of ice-covered insulators, reduces with the decrease of air pressure. In the same conditionΔt under DC is smaller. The radius of arc also reduces with the decrease of air pressure. Different ways of pollution lead to differences in arc diameters and colors in the flashover process.m, characteristic index of the influence of air pressure on critical flashover current, is greater under AC than under DC, which means that such influence under AC is greater. As for porcelain and glass insulators, e, characteristic index of the influence of pollution on critical flashover current, is greater under AC, yet e of composite insulators under AC is 4.7% smaller.ΔU, deviation between calculated flashover voltage of 7-slice XP-160 insulators under low air pressure and tested voltage, ranges from 1.4% to 13.2%. Calculated n under AC is 58.1% greater, while b under AC is 10.9% smaller.