中文摘要：

超特高压输电线路雷电屏蔽模型对线路的防雷设计有着重要的指导意义。为此研究了一种基于分形理论的输电线路绕击先导发展模型，首先从雷云电荷分布、上行先导起始、上下行先导发展和最终判据等方面研究了分形先导发展模型计算流程中的关键问题。并根据分形理论研究了上下行先导发展的电介质击穿模型DBM以及实现方式，通过雷电先导发展过程中空间电场的计算，得出了先导向空间各可能击穿点发展的概率分布，实现了雷电先导发展过程的分形生长。基于分形先导发展模型，还给出了超特高压输电线路绕击耐雷性能的评估方法，结合雷电流空间概率分布和由分形先导模型计算得出的绕击概率分布，可计算得出输电线路的绕击率。此方法在±800kV特高压输电线路上的绕击耐雷性能评估中的应用表明，该方法不仅能获得较精确的绕击率，同时使先导发展过程中既保持了沿最大场强发展的概率最大这一确定性因素，也呈现了先导发展的随机性因素。

英文摘要：

The lightning shielding model is very important for the lightning protection design of the EHV and UHV transmission lines. In this paper, a stochastic probability model based on the fraetal theory for estimating lightning shielding performance of transmission lines was introduced. Firstly, the key factors of the fractal leader progression model, such as the charge distribution in the descending leader, the criteria of the upward leader initiation, the progression path and the final jump criteria, were discussed. Then, the DBM model based on fraetal theory was employed to simulate the leader progression. Based on the space electric field calculation during the lightning progression, the probability distribution of possible breakdown point was obtained, which could be applied to the fractal growth of the lightning leaders. Moreover, a method to estimate the lightning shielding performance of EHV and UHV transmission lines based on the fractal leader progression model was put forward. Through the combination of the lightning current space probability with the lightning shielding failure probability from the fractal leader progression model, the lightning shielding failure rate of the transmission lines could be obtained. The application of the method to estimate the lightning shielding performance of 800 kV UHV DC transmission lines shows that the accurate results can be obtained. At the same time, this method can consider not only the factor that the leader progresses in the direction of the maximum electric field strength, but also the factor that the progression of leader is random.