Study on clearance optimisation and altitude correction of 750 kV AC side for UHVDC converter transformer

Abstract

AC system which ±800 kV converter station access to commonly used 500 kV voltage level. With the construction of the Northwest Energy Base, a large number of ultra-high-voltage direct current (UHVDC) project are constructing. The backbone voltage in the northwest region is 750 kV. Phase or phase-to-ground clearance the converter transformer 750 kV AC side required will affect the length of the valve hall and the highest altitude of the project close to 3000 m. In order to optimise the 750 kV AC side and meet the engineering requirements in high altitude areas, this paper carried out the true phase-to-ground and phase–phase discharge characteristics test in the gap of 750 kV AC side in Beijing and Tibet, and the gap discharge voltage was then corrected for altitude. At last, the distance at different altitudes of 3000 m and below between the phase-ground and the phase-to-phase at the AC side of converter transformer is obtained. The results provide the design of UHV converter station in Northwest China with technical support.