Corona loss is an important influence factor for ultra-high voltage alternating current (UHVAC) transmission line construction. At high altitude

due to the low air pressure and the strong ultraviolet light

the corona discharge around the energized conductors is more likely to occur

and the corona loss control has become very important. At present

there are little research on corona loss level of multi-bundled conductors over 4000 meters above sea level

where the conductor can be used in UHV AC transmission project. In this paper

the corona loss characteristics of three important conductors

8×LGJ1000

8×LGJ1250

and 10×LGJ630

are investigated by using the integrated photoelectric corona loss measurement system under dry

rain

and wet conditions. The tests are based on the UHV corona cage in Yangbajing Test Base in Tibet at an altitude of 4 300 m. The corona loss performances with different electric field intensity are obtained

and the influence of rainfall and electric field intensity on the corona loss is analyzed. After that

taking the 1 000 kV UHV single circuit transmission project for instance

the corona loss levels of different conductor bundles at 4 300 m altitude of are calculated. The research results can provide reference for the construction of UHV AC transmission lines in the high-altitude area of China.