Introduction  Lightning strike is the primary cause of failures of ±800 kV UHVDC power transmission lines, and the lightning protection assessment of power transmission lines is critical to the safe and stable operation of the system.

  Method  Based on a ±800 kV power transmission line project under construction in China, the conductor and ground wire types were selected according to the design and use conditions of the project, and the typical towers were determined according to the altitude and meteorological area distribution along the line. After comprehensive consideration of the distribution ratio of ground inclination, soil resistivity, thunderstorm days, meteorological zone, etc. of towers along the line, the lightning protection performance of the line was evaluated and specific lightning protection measures were proposed in respect of the lighting characteristics of the project. In addition, the calculation differences between the two methods regarding terrain considerations in the EGM were compared.

  Result  The calculation results show that the comprehensive lightning flashover rate doesn’t meet the requirements of design reference value and mainly protect against shielding failure. Thunderstorm days and the terrain conditions on the positive side of tower are the key factors for lightning protection.

  Conclusion  After adopting the -15° tower protection angle, the line located in lightning areas with C level and above whose positive side ground inclination angle is ≥25° can meet the lightning protection requirements that the lightning flashover rate is not more than 0.10 fl/(100 km·a·40 d). The lightning protection performance and actual operating data of this project and adjacent ±800 kV as-built lines are compared and analyzed, which verifies the rationality of the calculation method and results in this paper.