China is now the world's largest HVDC user.
The Three Gorges Hydroelectric Power Plant
will be the largest of its kind in the world. It will consist of 26 generating units, each with a rated power of 700 MW. The total generating capacity of the plant will be 18.2 GW. After all these units are commissioned in 2009, 6 more units will be installed in an underground power house and the total capacity of the plant will then become 22.4 GW.
500 kV AC transmission lines will deliver power from this plant to Central China and Sichuan-Zhongqing Systems. Power will also be sent to East China by three HVDC lines and to South China by one HVDC line. The East China System and the South China System are asynchronous with the Central China System, so the HVDC links also connect the large AC systems asynchronously. You can read more about the power networks and grids in China on the web site of The State Power Corporation.
The purpose of the links to East China, a distance of over 1,000 km, is to transfer electric energy from the power plant to the East China Power System during the summer. In the winter it will be used as an interconnecting tie line between the two power systems, transferring power from Central to East China during peak hours and transferring power in the reverse direction during valley hours.
The total capacity of this HVDC transmission system will be 7,200 MW. It will consist of the 1,200 MW HVDC line Gezhouba - Shanghai commissioned in 1989 by ABB and two 3,000 MW lines. The first of these lines, Three Gorges - Changzhou, has been commissioned by ABB in 2003. In 2004 ABB was awarded the converter stations for the second 3,000 MW HVDC transmission to Shanghai, that will go into operation in 2007.
The two 3,000 MW HVDC lines were compared to five 500 kV AC lines and the HVDC option was found to be the most advantageous, considering investments and losses but also land use.
Right -of-way requirement for 6,000 MW with two DC lines vs. five 500 kV AC lines
The transmission to the South China System is another 3,000 MW line, Three Gorges - Guangdong, 940 km long. There has been a rapid load growth in the south that motivated the link, which was comissioned in 2004. HVDC was chosen primarily because of the length of the transmission and that the two systems are asynchronous.
These long distance transmissions from a hydroelectric plant make it possible to avoid burning 40 - 50 million tons of coal and emitting 100 million tons of carbon dioxide (CO2) per year.