China Southern Power Grid Co. (Guangzhou, China) has awarded Siemens Power Transmission and Distribution (PTD; Erlangen, Germany) an 300 million euro order to construct a high-voltage dc transmission (HVDC) system between the province of Yunnan in the southwest corner of China and the province of Guangdong on the south coast of the country. The system will be the first in the world to transmit electricity at a dc voltage of ±800 kV. At the same time, this project, with a power-transmission capacity of 5000 MW, will be the long-distance HVDC link with the world's highest-ever power capacity that has been built. The system is scheduled to commence commercial service by mid-2010.

The additional electric power from Yunnan will supply the rapidly growing industrial region of the Pearl River delta in the province of Guangdong and the megacities of Guangzhou and Shenzhen. In the future, the electricity generated by several hydro-electric power plants will be transported from Yunnan via 1400 km (870 miles) to Guangzhou over this long-distance HVDC link. The economically and environmentally friendly hydro-electric power generation does not emit any CO₂; therefore, it will save the emission of more than 30 million tons of CO₂ a year (which is the amount of harmful gas that would be produced through the construction of additional fossil-fired conventional power plants in the province of Guangdong to serve the regional grid).

“This outstanding order shows that our efforts over recent years to further develop 800-kV HVDC technology to the point where it is ready for use in projects have been worthwhile. Today, we can boundlessly provide it to our customers,” says Dr. Udo Niehage, president of Siemens PTD.

Together with Chinese partners, Siemens designs the HVDC system, including ten 800-kV and ten 600-kV converter transformers, dc filters and 800-kV dc components. Siemens also supports its Chinese partners in design and manufacturing of thyristor valves, converter transformers and control systems. The converter stations operate in bipolar mode with two series-connected 12-pulse valve groups per pole, in which light-triggered thyristors are used. This scheme improves the reliability and flexibility of the power transmission.

The steep rise in demand for power in China's industrial centers requires huge amounts of electricity to be conveyed over distances of 1000 km (621 miles) and more. HVDC transmission is the only expedient method, in terms of both technology and efficiency, and it is the only technically and economically viable solution. As the current Siemens HVDC project shows, China has now increased the dc transmission voltage of new long-distance HVDC systems to ±800 kV, in response to China's need for even longer lines and more bulk transmission demand. China is the fastest-growing market in the field of power transmission and distribution, and will become the world's largest single market for HVDC transmission technology over the next 20 to 30 years.