Research of Lightning Withstand Performance for Double-circuit UHV DC Transmission Lines with Dual Voltage 800 kV/500 kV on the Same Towe

Mixed-voltage double-circuit UHVDC transmission lines on same tower can be considered for solving the contradiction between the growing electricity demand and the limited line corridor. It is of great significance to study the back flashover performance of the UHV mixed-voltage double-circuit transmission lines on same tower(UMDTL). Based on the intersection method, the insulator string flashover model is built on EMTP-ATP platform. Taking 800 kV and 500 kV transmission line for example, the impacts including different towers, the impulse ground resistances of tower and the tower heights on back flashover lightning performance are researched. The shielding failure performance under different kinds of towers and transmission lines are researched based on the improved electric geometry method. Compared with the single circuit for 800 kV lines and the doublecircuit for 500 kV lines, characteristics of lightning withstand performance are summarized for UMDTL.Results of the research show that the weak points of the lightning protection for UMDTL is the insulation of 500 kV transmission lines, and the insulation level of 500 kV transmission lines should be enhanced, however, the shielding failure performance of 500 kV transmission lines is better than 800 kV transmission lines. Compared with the second tower, the first one is more appropriate as the tower in the research on lightning withstand performance for UMDTL.