Introduction  A lightning strike is the main cause of failure and outage in 500 kV AC transmission lines, and it is very important to carry out lightning protection assessment for transmission lines for the stable operation of the system.

  Method  In this paper, based on a 500 kV AC transmission line project under construction in China, the lightning resistance of the line was simulated and studied using the EMTP (Electro-Magnetic Transient Program) and the EGM (Electro-Geometric Model) and the lightning trip-out (flashover) rate of the line was calculated according to the basic parameters of the line. The lightning risk level of line towers was determined based on the principle of lightning risk classification. Combined with the actual operation data of the nearby lines, lightning protection measures were proposed for towers with higher lightning risk, and the effectiveness of the measures was further verified through calculation.

  Result  The simulation results show that the arrester is an effective lightning protection measure, which can significantly reduce the lightning trip-out rate of the tower and improve the lightning resistance of the line. With lightning protection measures, there is no tower with lightning risk level IV on the whole line, and the average lightning trip-out rate of the whole line has dropped to the safe level I, which meets the requirements of Guide for Lightning Protection of Overhead Transmission Lines (Q/CSG 1107002—2018).

  Conclusion  The lightning risk assessment method and the lightning protection measures proposed in this paper are correct and effective, and have somewhat engineering application and reference values for the lightning protection design of 500 kV AC overhead transmission lines.