In China,the power failure caused by flashover of iced insulators often occurs,and a lot of researches have been done on the flashover performance of iced insulators.But the flashover accidents occur frequently about snow-covered post insulators in recent years.Therefore,the artificial snow-covered method is used in the large scale artificial climate room in this paper.The influence of the parameters of snow cover,surface contamination and umbrella structure on the flashover voltage of the insulator in substation is studied.The snow flashover process is analyzed.The finite element method is used to calculate the electric field distribution of the post insulator under different snow conditions to explore the snow flashover process of partial arc cause.The arc temperature were measured during the development of the partial arc by plasma Emission spectra and the variation law of local arc temperature with time was studied.The main conclusions are as follows:The 50% snowing flashover voltage(U50)of post insulators decreases with the increasing of the pollution degree of snow-covered post insulators and show negative power-law relationship with the pollution degree;The pollution impact feature index of snowed insulators influenced by umbrella types.The index of the post insulator of adding creepage extenders is the maximum,which the flashover voltage decreases with the increase of the pollution degree at the soonest;The index of equal diameter umbrella post insulator is second;The index of big or small umbrella post insulator is the minimum.The snow flashover voltage of the post insulator is affected by the umbrella structure.With the increase of the distance between the umbrella,the snow flashover voltage increases by about 11.65%;With the increase of the umbrella,the snow flashover voltage increases by about 23.86%;With the increase of the diameter of the core,the flashover voltage increases by about 6.4%.The snow flashover voltage of the post insulator with silicone rubber umbrella skirt is improved significantly.Under light pollution degree condition,the booster sheds can bring higher flashover voltage about 60% on post insulator under snowing condition;Under heavy pollution,the flashover voltage will increase by about 17.5%,which is affected by the pollution degree.;The RTV coating has a better effect of anti-snow flashover,and the average of snow flashover voltage is increased by 18%.With the increase of the thickness of snow,the flashover voltage of the post insulator decreases;The flashover voltage of the post insulator decreases with the increase of the density of snow.When the density is greater than 0.6g/cm3,the influence of the snow cover density on the snow flashover voltage of the post insulator decreases gradually.The flashover voltage of the insulator decreases with the increase of liquid water,but the decrease is very small;The snow flashover voltage of the polluted post insulator that is uniformly covered by snow is higher than it that is non-uniformly covered by snow;The flashover voltage decreases with the increase of temperature.When the temperature is below 0 ℃,the change is significant.The DC snow flashover voltage of polluted post insulator is lower than the AC snow flashover voltage of that.The pre salt density characteristic index of the influence of polluted post insulator affected by voltage type.Under the condition of AC,we can consider the influence of the distance between the umbrella to make the measure of preventing the snow;Under the direct current condition,we can give priority to the influence of the umbrella extension to formulate the measures to prevent snow flashover.The local arc of snow-covered polluted post insulator is caused by air breakdown that is caused by uneven voltage distribution along the insulator surface,which the electric field distribution on the insulator surface is distorted after the snow melts.The local arc is usually found in the gap between the skirt of the leeward side of the snow-covered insulator.The development of local arc is closely related to the temperature of the arc and the arc temperature of the snow-covered insulator changes with arc development time changing.The arc temperature changes from 4207.16 K to 4728.9K before flashover.The arc temperature reaches 8389.97 K when the snow-covered insulator flashover.On the one hand,the arc temperature melte the snow and may form a continuous "waterfall",on the other hand,the arc temperature causes the air to enter the thermal ionization discharge and accelerate the development of arc.Local arc develops along the leeward side of insulator until flashover. |