Lightning Flashover Characteristics of a Full-Scale AC 500 kV Transmission Tower with Composite Cross Arms

Abstract

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.