With the large-scale development of clean energy in Qinghai-Tibet Plateau, it is necessary to construct UHV transmission lines for transmission of clean energy. Previous UHV transmission lines are mostly located at the altitude of 2000 m and below. With the increase of altitude, the air gap insulation strength decreases. How to reasonably select the air gap distance of tower is one of the key technologies to ensure the reliability and economic design of transmission lines. In order to solve the problem of gap discharge characteristics of UHVDC tower in high altitude area, the air gap impulse discharge test was carried out by using 800 kV full-size simulation tower in the test hall of 2500 m altitude area in Qinghai Province. The corresponding switching impulse and lightning impulse discharge voltage were obtained, and the dispersion of switching impulse and lightning impulse discharge voltage was analyzed. Combined with the existing discharge voltage of tower air gap in low altitude area, the altitude correction coefficient of discharge voltage in 2500 m altitude area is calculated. Finally, combined with the overvoltage calculation results of typical ±800kV project, the minimum gap distance required for switching impulse voltage of ±800kV transmission line at 2500 m and below is recommended. The results show that the relative standard deviation obtained by lifting method does not show that the altitude has no obvious effect on the dispersion of impulse discharge voltage. Under the switching overvoltage of 1.60p.u., the gap distances from 1000 m to 2500 m are 5.3 m and 6.2 m, respectively.

air gap distance;altitude correction;UHVDC;tower;discharge characteristic