Southwest China’s Xizang Autonomous Region has officially entered the ultra-high voltage (UHV) era as its first UHV power transmission project began operation on Thursday. The milestone was marked by the successful completion of a 168-hour trial run at the Karmai converter station, located at an altitude of 3,720 meters in Mangkam County, Qamdo City.
With this, a major direct current (DC) transmission project has been fully completed and has started supplying clean electricity to central China.
Electricity generated from a 750,000-kilowatt hydropower station on the Jinsha River below the converter station can now be transmitted some 1,900 kilometers to Hubei Province in just about six milliseconds.
The ±800 kV UHV DC transmission project, built with an investment of 34.3 billion yuan (around 4.9 billion U.S. dollars), is designed to deliver up to 40 billion kilowatt-hours of clean electricity annually. Mainly powered by hydropower and supplemented by solar and other renewable sources, the project is expected to replace more than 12 million tonnes of coal each year and cut carbon dioxide emissions by roughly 30 million tonnes.
According to Dong Ran, deputy project manager at the Karmai converter station, the sending end of the line consists of two ±400 kV converter stations—one in Xizang and the other in neighboring Sichuan Province.
Together, they form the sending end of the ±800 kV transmission line, making it the world’s first such UHV project built in a high-altitude environment. Operating UHV equipment at high altitudes poses challenges due to thin air and reduced insulation performance.
To address this, engineers increased ground and tower clearances during the design phase to ensure safe and stable operation. UHV technology typically refers to alternating current (AC) projects of 1,000 kV and above, and direct current (DC) projects of ±800 kV and above.
Compared with conventional transmission lines, UHV DC systems can carry electricity over longer distances with higher capacity and lower losses, functioning like an “expressway” for power transmission. The Karmai station is also equipped with advanced monitoring technologies, including cameras, track-based inspection robots and robotic dogs, enabling round-the-clock automated inspections and significantly reducing the need for manual work at extreme altitudes, said Gu Pen, the station’s deputy head.
Xizang is one of China’s key clean energy bases, endowed with abundant hydropower, wind and solar resources. Wang Bingqiang, a manager at State Grid Xizang Electric Power Company Limited, said the project’s full operation will further integrate the plateau region into the national power grid, optimize regional energy structures and support China’s “dual carbon” goals of peaking carbon emissions by 2030 and achieving carbon neutrality by 2060.
The project also showcases China’s technological strength and innovation in UHV development under complex, high-altitude conditions. In recent years, China has accelerated the construction of UHV transmission lines to channel electricity from energy-rich western regions to the fast-growing eastern areas and boost the use of clean energy. So far, State Grid has put 42 UHV projects into operation—22 AC and 20 DC—enabling an inter-regional and inter-provincial transmission capacity of 370 million kilowatts.
