火焰条件下气固两相体空间合成电场数值模拟方法研究

Tripping accidents of transmission line caused by forest fire are frequent. A large number of particles are generated and charged in the vegetation fire. Then they drift into the gap under the transmission line. Some test studies show that the charged particles cause serious electric field distortion and triggering discharge is the key to cause the gap breakdown. Currently, the electric field distortion characteristics of air-solid mixture are still unclear under vegetation fire conditions. In this project, the vegetation combustion characteristics will be obtained by vegetation fire test. Statistical analysis on the sizes and shapes of the particles will be carried out. The charging mechanism of particles in the vegetation fire will be studied and the charging model will be established. The interactions between the fluid dynamics, temperature, electric field and the particulate flow will be analyzed. A numerical simulation model of the air-solid mixture under vegetation fire conditions will be established. In the model, the complex interactions between the electric field, temperature field, fluid dynamics and the particulate flow will be taken into consideration. The fluid drag force, electrostatic force and gravity will be taken into account when studying the movement characteristics and distribution rule of the charged particles. The accurate solution of total space electric field will be calculated. It will be used to analyze the electric field distortion characteristic of air-solid mixture. The research results can provide the basis for mechanism study of the gap discharge and further guide the tripping risk assessment, warning and protection of transmission line under vegetation fire conditions.

输电线路因山火跳闸事故频发，植被燃烧产生大量颗粒物在火焰中荷电并漂移到间隙中形成颗粒链。部分试验研究表明荷电颗粒链畸变电场并产生触发放电是导致整个间隙击穿的关键，但目前对火焰条件下气固两相体中电场畸变特性的研究尚不完善。本项目利用模拟山火试验平台进行试验研究，得到典型植被的燃烧特性，并对颗粒物形态、尺寸进行统计分析；研究颗粒在植被火焰体中的荷电机理，建立颗粒荷电的数学模型；分析火焰条件下流体、温度、电场、荷电颗粒之间的相互作用，研究火焰条件下气固两相体的热-流体-颗粒运动-电场耦合模型及数值模拟方法，研究荷电颗粒在流体曳力、电场力、重力等作用下的运动特性和分布规律，求解计算空间合成电场，分析火焰条件下空间电场畸变特性。研究成果可为山火条件下间隙放电机理研究提供基础，进一步指导输电线路因山火跳闸的风险评估、预警及防护。

研究火焰条件下气固两相体空间合成电场数值模拟方法对分析山火条件下电场畸变特性、间隙击穿机理有重要作用。本项目通过典型植被燃烧试验，得到植被热释放速率、火焰间隙温度分布、火焰体各部分电阻率、颗粒尺寸及荷电特性等特征参数；根据植被火焰体电阻率的分布特性确定等效高阻模型边界；基于颗粒统计数据和炭黑颗粒荷电试验，建立了颗粒荷电的数学模型。提出了火焰条件下气固两相体的热-流体-颗粒运动-电场多物理场耦合模型，结合试验获得的对应参数，仿真分析正、负极性电压下不同颗粒的受力特性和运动过程，最后结合燃烧颗粒特点分析了不同荷电颗粒分布情况下的空间电场畸变特性。本研究为不同植被燃烧情况下间隙放电的差异提供了分析依据，可进一步指导不同输电走廊环境情况下山火跳闸的风险评估及防护。