Study On The Ground Flash Distribution Of Mesoscopic Terrain In Mountainous Area

The lightning have caused great harm to personal safety and the safe operation of electric power,transportation and other industries.Because of the high altitude and the changeable internal terrain,the mountain area has become a serious lightning hazard area.The main object of current research on ground flash distribution is macroscopic terrain,without considering the terrain changes within the study area;the impact of microcosmic terrain on shielding failure rate is considered in the calculation of shielding failure trip-out rate of transmission lines,while the influence of microcosmic terrain on ground flash distribution is neglected.Therefore,it is of theoretical significance and engineering value to study the ground flash distribution of the mesoscopic terrain with scale between macroscopic terrain and microcosmic terrain.This article focuses on the following aspects:The ground flash distribution coefficient is defined.Based on the striking distance theory,the ground flash distribution coefficient theoretical calculation formulas of the typical mountainous terrain are derived.The influence of the lightning current amplitude,the mountain slope and the terrain width on the ground flash distribution coefficient is analyzed.The theoretical calculation results and the statistical results of actual ground flash data in mountainous terrain are compared and analyzed.It is found that the ground flash distribution in mountainous terrain meets the rule that Ngpeak>Nghillsid>Ngvalley.Based on the difference in the ground flash distribution on the mountainous terrain,the shortage that using fixed ground flash density in the calculation of shielding failure trip-out rate of transmission lines is analyzed,and the mesoscopic terrain is defined.The variation of ground flash distribution in flat areas is studied.It is found that the ground flash distribution in flat area shows uniform distribution.The variation coefficient of the ground flash density is used as the criterion for the division of mesoscopic terrain.The method to devide mesoscscopic terrain was propound in this paper,and the feasibility of the method was verified by the example of the division of mesoscopic terrain.The influence of the mountainous height and the mountainous slope on the division of mesoscopic terrain is studied.The study shows that the higher the mountain height,the larger the mountain slope,the larger the scale of mesoscopic trrrain,and the scale of mesoscopic trrrain ranges from several hundred meters to several kilometers.Based on fractal theory,a fractal simulation model of lightning downward leader is established.The ground flash distribution rules of mesoscopic trrrain and flat area are compared.The influences of the mountain slope and mountain height are studied..The study found that when the starting position of lightning downward leader is fixed,compared with the normal distribution curve of the flat area,the typical mesoscopic terrain ground flash distribution curve have the characteristics of three-peak distribution which shows a concave part;the higher the mountain height,the larger the mountain slope,The scope of concave part in ground flash distribution curve is larger.The simulation results of the typical mesoscopic trrrain ground flash distribution and the statistical results of actual ground flash are compared in this paper.This study found that both the statistical results and the simulation results have obvious concave curves at the mountain foot and the surrounding flat areas.The higher the mountain height,the larger the mountain slope,the larger the range of concave curves.The number of ground flash increases with the increase of mountain height in hillside.