Nexans, the worldwide leader in the cable industry, has been awarded an €87m contract by Energinet and Statnett, the state-owned transmission systems operators (TSOs) in Denmark and Norway, to deliver the subsea power cable for Skagerrak 4 (SK 4), the fourth HVDC power interconnector between the two countries. SK 4 is scheduled for completion by the end of 2014.

The new 700MW SK 4 cable will improve security of supply in Denmark and Norway as well as contributing to an increased exchange of environmentally-friendly power with other countries via the common Nordic electric power market. In combination with SK 1-3, also delivered by Nexans, the new cable will raise the total capacity of the Skagerrak interconnector to 1,700MW, facilitating the export of renewable energy (especially hydro-electric generation) produced in Norway as well as helping to stimulate an increase in wind power production in Denmark.

Subsea power and fibre optic cables

For the SK 4 project, Nexans will design, manufacture and install the new 140km subsea cable across the Skagerrak strait between the Jutland peninsula of Denmark and Norway. The 500kV HVDC cable, to be produced by the Nexans facility in Halden, Norway will be of the mass-impregnated non-draining (MIND) type and will be laid at sea-depths of up to 530m by Nexans’ own cable-laying vessel, the C/S Nexans Skagerrak. At the same time, Nexans will also install a separate fibre optic subsea cable produced by its factory in Rognan, Norway.

Cable protection

As an integral part of the SK 4 project, Nexans will protect the power and fibre optic cables on the seabed by burying them to a depth of around 1m using its sophisticated Capjet water-jetting trenching system.

Underground cables

In common with the existing SK 1-3 cables, SK 4 will connect into the local onshore transmission grids at HVDC converter stations in Tjele, Denmark and Kristiansand, Norway. On the Norway side, Nexans is also providing the 12km underground land cable that will link the subsea cable with the Kristiansand station.

Existing Skagerrak HVDC interconnections – in operation for over 30 years

Nexans deployed the first two Skagerrak HVDC subsea cables (SK 1-2) between 1976 and 1977 in a ground-breaking project that, at the time, made them the longest DC cables ever installed. Operating at 250kV, they have provided an efficient and reliable 500MW interconnector between Denmark and Norway for well over 30 years. In 1993, the interconnector was upgraded with Nexans delivering a third cable (SK 3), operating at 350kV, to provide an additional 500MW capacity.

“Winning this very significant contract for the Skagerrak 4 cable has enabled Nexans to make a flying start to 2011 and we are delighted to be working with Energinet and Statnett to help upgrade this strategic interconnector,” said Yvon Raak, Nexans senior corporate executive vice president. “An important element in our favour was that the three existing cables have provided a perfect reference for the quality and long-term reliability of our cable technology in this very demanding application.”