Lightning Protection of ± 500 kV Three-circuit Direct Current Overhead Transmission Lines on the Same Tower

The three-circuit flexible DC transmission line in the same tower has great advantages in saving transmission corridors, but its lightning protection design is obviously different from single-circuit or double-return overhead lines. Especially in the case of forming a DC grid, the striking flashover rate should be strictly controlled. For this reason, the lightning withstand performance of ±500kV three-circuit flexible DC transmission lines arranged on the same tower is analyzed by using electrical geometric model and traveling wave method. With such method and model the effect of polar line arrangement, grounding resistance, tower height on the lightning protection are analyzed. The computational results prove that when the lightning protection angle of overhead ground wire is designed to be -14° and the recommended E layout scheme is adopted for the pole conductor, the striking flashover rate can be controlled to be less than 0.1 times/(100km·a). The research results lay the foundation for the lightning protection design of the ±500kV three-circuit flexible DC lines arranged on the same tower.