Study On Switching Impulse Flashover Performance Of 110kV Ice-covered Insulator String

The electrical performance of iced insulator string will decrease and the icing flashover accident may occur, which is a serious threat to the safety operation of power systems. The switching impulse may be a reason resulted in the icing flashover; however, there are many researches about the AC or DC flashover performance and mechanism while there are a few about switching impulse discharge performance of iced insulator string. So it is significant referenced to the requirement of external insulation design in the icing regions to study the switching impulse discharge performance of iced insulator string.Three types of insulators with different material of transmission lines are selected as test samples in the thesis. Based on the natural icing conditions simulated in the multi-function artificial climate chamber, the switching impulse discharge performance of iced insulator strings are tested and studied by the ice amount and freezing-water conductivity characterized the icing parameters. The results show that:The positive 50% switching impulse discharge voltages of porcelain, glass and composite insulators in the severe icing and higher freezing-water conductivity conditions are lower 52.85%, 43.19% and 48.59% than those in dry-clean conditions. The negative 50% switching impulse discharge voltages are lower 66.28%, 56.95% and 59.67% respectively.The positive and negative 50% discharge voltages of icing insulator strings under switching impulse are related with the icing state and parameters. The conclusion that the relation between 50% discharge voltage and ice amounts as well as that between 50% discharge voltage and freezing-water conductivity can be described by negative exponent function respectively is obtained. The statistical analysis of discharge times show that the switching impulse flashover almost occurs near the wave tail or wave crest. 50% discharge voltage is related with the time of wave tail.There is not obvious polarity effect for the iced porcelain or glass suspension insulator strings under switching impulse. While there is a certain polarity effect for the composite insulator covered with ice, namely, the positive 50% discharge voltages of composite insulator are lower than the negative ones, but the polarity effect is weakening with the increase of ice amount.The reason for the decrease of 50% discharge voltage of iced insulator string under the switching impulse is that the electrical potential along the insulator string surface is distorted, the high-voltage side of insulator string bears the higher electric field strength, the leakage resistance decline and leakage distance along the insulator string decrease.