低气压下空气间隙电弧对覆冰绝缘子串直流闪络的影响

覆冰绝缘子串在直流闪络过程特别是低气压条件下中易产生空气间隙电弧形成"飘弧"现象,飘弧易桥接覆冰绝缘子串,且空气间隙电弧和冰面电弧具有不同的伏安特性,而传统的覆冰绝缘子串直流闪络模型由冰面电弧和剩余冰层电阻构成,没有考虑空气间隙电弧,在低气压下计算结果与实际情况相差较大。为了解此一现象,首先从理论上分析了飘弧对低气压下覆冰绝缘子串直流闪络电压的影响,建立了考虑和忽略空气间隙电弧的覆冰绝缘子串直流闪络模型,根据理论模型计算了相应的闪络电压,并与试验结果进行了比较分析。试验与理论计算结果表明,飘弧现象随着气压的降低和绝缘子串覆冰及污秽的程度增加而增加,低气压下进行绝缘子串直流闪络建模、预测和特性试验时应考虑空气间隙电弧及其飘弧的影响。

Influence of Arc Levitation on DC Flashover Performance of Iced Insulators Under Low Air Pressure

Part of DC arcs may levitate from the iced insulator’s surface to form air-gap arcs in the process of flashover,especially in the low air pressure.The levitation of arc from iced surface can easily lead to the bridging of ice insulators.The air-gap arc and ice surface arc have different U-I characteristics.Traditional model of dc flashover for iced insulator string is composed of ice surface arc and residual ice layer,its calculation results are far from practical results under low air pressure as a result of ignoring air gap arcs.Consequently,we analyzed the influence of arc levitation on the dc flashover voltage of iced insulator string firstly.Then we developed the flashover model of iced insulator string with and without considering the influence of air-gap arc and calculated dc flashover voltages correspondingly.The comparison of calculated results and experimental results show that the lower air pressure and the more severity of pollution or icing,the more arcs levitating from the iced insulator string surface.So the air gap arc should be considered in modeling,forecasting and evaluating the dc flashover performance of iced insulator under low air pressure.