The announcement of the Fenno-Skan 2 link, due for completion in 2011, has given renewed impetus to international co-operation in the sharing of power resources. The new 800MW high-voltage direct current (HVDC) connection between Sweden and Finland builds on the success of the existing 572MW link, which came into service in 1989 and was upgraded in 1998.
ABB delivered the original link and will be supplying two HVDC converter stations for the new connection. HVDC is a technology that enables power to be transmitted over long distances with minimal transmission loss. ABB pioneered HVDC more than 50 years ago, with the first link connecting the Swedish island of Gotland with the mainland. Since then, HVDC systems have been installed around the world, with the vast majority being built by ABB. The company has participated in a total of 60 HVDC projects worldwide with a total capacity of more than 48,000MW.
In recent years, there have been a growing number of cross-border and undersea HVDC projects, including the NorNed and the BritNed links in Europe.
The North-South divide
The Finnish and Swedish power transmission are part of the Nordic Nordel joint grid.
Both countries have similar challenges with power generation and distribution. While power consumption is largely focused in the south, hydro power generation is centered in the north. The existing AC connections are also in the north, resulting in long transmission distances between the two nations. By using HVDC interconnections in the south, overall power capacity is greatly increased with easy redistribution of load flows between the networks, which in turn reduces the losses in the Nordel grid as a whole.
First steps
Fenno-Skan 1, a monopolar 500MW HVDC interconnection across the Gulf of Bothnia, came into service in November 1989. It was the world’s first 400kV HVDC interconnection, and at the time was also the world’s longest submarine interconnection.
Special control modes have meant that the link has had a beneficial effect on the northern AC connections between the two countries. This has been achieved by increased damping of electromechanical oscillations, a higher transient stability limit and increased capacity on sections of the Swedish grid.
The link was upgraded in 1998 to provide a maximum continuous capacity of 572MW with a short (one-hour) overload capability of 600MW. On-line temperature measurements are fed into the cable load prediction system to calculate the current transmission capability.
The total length of the cable connection is 200km, with 198km undersea and 2km on land. The maximum depth is 117m, with an average depth of 80m.
The seven-section cable was laid in two parts and jointed at sea.
Fenno-Skan 2
For Fenno-Skan 2, ABB will supply two HVDC converter stations as part of an 800MW power link. The contract is part of a larger scheme that includes a 400kV AC substation in Finnböle, a 70km DC overhead line in Sweden, and a 200km submarine cable. The new Swedish converter station will be considerably further inland than the existing one.
For the Fenno-Skan 2 project, ABB will be responsible for system engineering, including design, supply and installation of the two HVDC converter stations. The system is scheduled to be in operation by the end of 2011.