500kV输电线路的山火击穿特性及机制研究

Study on Forest Fire Induced Breakdown of 500kV Transmission Line in Terms of Characteristics and Mechanism

近年来中国森林火灾频繁发生,严重威胁到输电线路的绝缘安全和可靠运行。结合500kV输电线路山火事故录像以及棒-板间隙在木垛火条件下的放电特性,分析了500 kV输电线路在山火条件下的击穿特性和机制。结果表明:1)火焰的绝缘电阻随火焰高度的增加而增大;2)在木垛火焰条件下,棒-板间隙的工频击穿强度降低为纯空气间隙下的23%;3)火焰温度、火焰电导率和颗粒等能够促进放电的发展,并导致间隙的绝缘水平下降;4)导线对火焰顶部的预放电能促进燃烧,电弧则能够增强山火燃烧的强度并抬升火焰的高度,导致击穿电压降低。由试验与分析可知,输电线路因山火击穿是由火焰温度、电导率以及灰烬与烟雾等3个因素促进放电发展的结果,并指出提升导线高度,控制线路走廊附近的植被种类、高度和密度能够有效地提高线路在山火条件下的绝缘水平。

Forest fires near power transmission lines always threaten the reliability of transmission lines and safety of power grids.Combining video record of the 500kV transmission line fire induced flashover and breakdown characteristics of rod-plane gap under wood crib fires,the flashover mechanism of 500kV line under forest fires was investigated.Results are as follows： the dielectric resistance increases with the height of flame due to temperature that affects the thermal ionization of alkali mental salts;the breakdown strength of rod-plane gap under wood crib fire is reduced to 23% of that air gap under standard atmosphere;flame temperature,conductivity and particles such as smokes and flying ashes promote the electronic avalanches and streamers development and lead to the dielectric strength reduction of the transmission gap acutely;pre-discharges initiated by flying ashes and smoke are connected to flame tip and promote the burning of fire.Electrical arc enhances the fire intensity and lifts the height of flame.Based on field records and experimental results,it is concluded that flame temperature,flame conductivity and flying ashes are ascribed to factors leading to transmission line flashover due to fire.Measures to reduce transmission line breakdown under forest fire such as increasing height of transmission line conductors above ground,restricting the vegetation species,height and density near transmission line corridors are proposed.