Siemens Power Transmission and Distribution (PTD) has won an order from China Southern Power Grid Company, Guangzhou, 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 together with Chinese partners.

The system will transmit electricity at a DC voltage of +/- 800 kV. At the same time this project will have a power transmission capacity of 5000 MW. The Siemens value of the order in total is more than 300 million euros. The system is scheduled to commence commercial service by mid-2010.

The additional electric power from Yunnan is intended to supply the rapidly growing industrial region of the Pearl River delta in the province of Guangdong and the megacities of Guangzhou and Shenzhen. In future the electricity generated by several hydro-electric power plants will be transported from Yunnan via 1,400 km to Guangzhou over this long-distance HVDC link. Hydro-electric power generation is economically, environment-friendly and does not emit any CO₂. This HVDC link will save the emission of more than 30 million tons of CO₂ a year. That is how much of the gas which is harmful to the climate would be produced otherwise, for example through the construction of additional fossil fired conventional power plants in the province of Guangdong to serve the regional grid.

Together with Chinese partners, Siemens designs the complex HVDC system and supplies HVDC main components, among other things 10 800-kV and 10 600-kV converter transformers as well as DC filters and 800 kV DC components. Furthermore Siemens 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, twelve-pulse valve groups per pole, in which light-triggered thyristors are used. This scheme improves the reliability and flexibility of the power transmission.

For Siemens Power Transmission and Distribution this long-distance HVDC link between Yunnan and Guangdong is already the fifth system in China. The first was the “Ge-Sha“ HVDC interconnector linking Gezhouba and Shanghai (1200 MW, +/- 500 kV over a distance of 1040 km), which went into operation in 1989. “Tian-Guang“, the second project, which has been in service since June 2001, links Tianshengqiao in southwest China with Guangzhou (1800 MW, +/- 500 kV over 960 km). The third project, the “Guizhou-Guangdong I” interconnector between Anshun in Guizhou Province and Zhaoqing in Guangdong Province (3000 MW, +/- 500 kV over 940 km) entered operation in late September 2004. Number four is the “Guizhou-Guangdong II” project (3000 MW, +/- 500 kVover 1225 km) which will go into service before the end of 2007.

The steep rise in demand for power in China’s industrial centers means that huge amounts of electricity have to be conveyed over distances of one thousand kilometers and more. HVDC transmission is the only expedient method, in terms of both technology and efficiency. High-voltage direct-current transmission 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 due 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.