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近年来，多条特高压直流线路建成投运，还有多条直流输电线路正在规划，山火严重威胁到输电线路的绝缘安全和可靠运行，研究火焰条件下间隙的直流电压击穿特性和放电机理具有重要意义，但国内外在山火条件下间隙直流电压击穿特性方面的研究较少。间隙在山火条件下击穿机理涉及火焰温度、电导率和灰烬等个因素，不同植被的燃烧特性决定了这3种因素触发放电的影响程度不同，因而击穿电压存在较大的差异。文中研究典型植被的火焰特性，利用模拟山火对不同影响因素条件下的导线-板间隙直流电压放电特性进行试验研究，分析了山火条件下间隙击穿机理。研究发现间隙在火焰中绝缘强度下降到纯空气的20%左右，直流电压下间隙的击穿存在明显的极性效应。“,”Hill fire is a serious threat to the reliability of UHV DC transmission lines and security of power grids. So, it is very important to study the DC voltage breakdown characteristics and discharge mechanism of gap under fire conditions. However, there has been few researches on the DC gap voltage discharge characteristics under fire conditions at home or abroad. Gap breakdown in forest fire is related with flame temperature, conductivity and ashes and different vegetation’s combustion characteristic result in the different influence degree of the three factors on triggering discharge, thus breakdown voltage has great diversity. This paper studied the flame characteristics of typical vegetation, DC voltage breakdown characteristics of wire-plate gap under different affecting factors using simulated forest fire, and then analyzed the gap breakdown mechanism in the forest fire conditions. Experimental results show that the gap’s insulation strength in the flames is down to about 20% of pure air, and the gap breakdown in DC voltage has obvious polarity effect.