架空输电线路（OTL）一直以来都是电力传输的主要方式。随着输电电压和输电容量的迅速提高，输电杆塔的尺寸也随之增加，造成土地资源的大量占用。考虑到线路复合绝缘子的优异性能，复合横担有望成为这一问题的解决方案。在本文中，作者制备了一个安装有复合横担的全尺寸交流（AC）500 kV输电杆塔，并施加了不同极性的雷电过电压。借助高速相机记录了流注-先导放电的过程，确认了闪络的主要路径。通过测量闪络电压并根据空气密度和湿度对结果进行修正，证实了放电的极性效应。继而，根据杆塔结构和闪络特性计算了杆塔的耐雷水平。基于全尺寸试验的结果与分析，确认了复合横担的可行性，并提出了结构优化方案。

Overhead transmission lines (OTLs) have always been the major means of power delivery. With the significant increase of transmission voltage and transmission capacity, the dimensions of transmission towers are increasing accordingly, resulting in extensive occupation of land resources. Towers with composite cross arms are a promising solution to this problem, considering the remarkable performance of composite line insulators. In this research, a full-scale alternating current (AC) 500 kV model of a transmission tower with composite cross arms is manufactured and applied under a lightning overvoltage of different polarities. The developing process of streamer-leader discharge is recorded with a high-speed camera, and the major path of the flashover is identified. The flashover voltages are measured and corrected to standard conditions while considering the air humidity and air density, and clearly confirm the polarity effect. The tower's lightning-withstand level is calculated based on the tower structure and the flashover characteristics. Based on the results obtained from full-scale experiments, the feasibility of composite cross arms is confirmed, and a structural optimization is proposed.