HVDC cable sets standard for transmission projects

Paul Boughton
Since first being introduced in Sweden in 1954, high voltage direct current (HVDC) has became a standard method of electrical power transmission. Over 100 projects currently use HVDC, with power ranges from under 100MW to over 3000MW, both as overhead lines and undersea/underground cables.

The technology has now met another challenge, with the official opening of the largest and most powerful underwater cable in the world.

The cable connects the HVDC converter stations at Eemshaven in the Netherlands and Feda (Fig.1) in Denmark. It is 580km long, has a capacity of 700MW and cost EUR600m. The project also required 9000 tonnes of copper and 12000 tonnes of lead for the cable - giving it a total weight of 47000 tonnes - and took 10 years to complete.

The converter stations convert alternating current into direct current and vice versa. Each one is roughly the size of a soccer pitch (Fig.2).

Run by NorNed, a cooperative formed between Dutch grid manager TenneT and Nowegian equivalent Statnett, this is the first direct power link between Norway and the Netherlands, and is part of the European Union's plan to improve cross-border power infrastructure, reduce blackouts and help create more efficient power markets within Europe. The key technologies used were supplied by ABB, a forerunner of which introduced the original HVDC to Sweden 54 years ago.


The link uses the latest HVDC technology to allow TenneT and Statnett to trade power and increase the reliability of electrical supply in each country.

The Dutch grid can use Norwegian hydropower to manage peak power loads during the day and, by offering an alternative to fossil fuel-based generation, grid operators expect to reduce carbon dioxide emissions by about 1.7million tonnes per year.

The cable was inaugurated in the presence of executives from the two utilities that own the link and ABB, as well as the Norwegian minister of petroleum and energy, Terje Riis-Johansen, and the Dutch economics minister, Maria van der Hoeven.

"NorNed is a landmark feat of engineering that brings Europe even closer to the goal of creating a reliable, continent-wide electrical network with low environmental impact," said Peter Leupp, head of ABB's power systems division. "It is a significant contribution to the quality and reliability of Europe's power supply."

"I have no doubt that further steps towards market coupling will be made in the near future, benefiting all parties concerned. Most importantly, you have shown international co-operation to be the key to safeguarding security of supply, raising flexibility and maintaining affordability. Last but definitely not least, NorNed also raises the profile of Norwegian hydraulic power, helping us to 'go green'," added van der Hoeven.

NorNed started using the cable on 6th May and, with an availability of nearly 100 per cent, the sub-sea power link between the Netherlands and Norway has made what the company describes as 'a promising start'.

In the first four months of operation, "an extreme high return of EUR70million was realised," says the company. This exceeded all expectations: in the business case formulated for the NorNed cable, an annual return of EUR64million was forecast. Most of the income is being used in projects to improve and upgrade the Dutch electricity network.

p to now, more than 1.8 million megawatt hours has been supplied by means of this cable. In total 1.7million megawatt hours of Norwegian hydropower was brought to the Netherlands, and a total of 0.1 million megawatt hours was exported by the Netherlands. In the last four months the transport capacity of the cable for import was auctioned at an average price of EUR39.29 per MW, and for export at an average price of EUR1.42.

"The NorNed cable provides a significant number of advantages, for producers and consumers alike. Thanks to NorNed, the international trade will increase which will result in more stable prices for electricity in North-western Europe. The NorNed cable represents an important physical link on the road to one single, strong European power supply market," explained TenneT ceo Mel Kroon.

Kroon also used the inauguration to announce an upcoming study for a new cable connection between the Netherlands and Denmark.

Security of supply

Known initially as Cobra, the link will allow for the integration of more renewable energy into the Dutch and Danish power systems and to increase security of supply. It will also help to intensify competition on the North West European power markets.

"Strong power links between the European countries make it possible to integrate markedly more wind energy into the European power systems," said Peter Jorgensen, vice president of electricity system development with Energinet.dk, the company that owns the overall electricity and gas infrastructure in Denmark.

"In the next four years, we must integrate 40 per cent more wind energy into the Danish power system, and the Netherlands also has grand expansion plans for their wind energy. A power link between Denmark and the Netherlands will therefore be highly beneficial to both countries as we can export power to the Netherlands when we produce a lot of wind power and import power from the Netherlands when there is no wind in Denmark," he concluded.

European transmission grid

A power link between Denmark and The Netherlands is in line with the EU's ambitions for a stronger and more interconnected European electricity transmission grid and will contribute to the development of a more international, sustainable power market, which is a main priority in European energy policy.

Lex Hartman Tennet's director of corporate development, added: "This Cobra initiative is a good contribution for the many Dutch plans to construct new power plants and off-shore wind parks. A new interconnector would make it possible to increase electricity exports."

The link will be a dc cable similar to the existing power links from Jutland to Norway and Sweden and from Zealand to Germany. The Netherlands already has a power link to Norway, and another power link to Great Britain is under construction.

In the coming months, TenneT and Energinet.dk will carry out the technical and economic investigations. A business case is expected to be ready in the first half of 2009, identifying factors such as socio-economic benefits, cable capacity, investment requirement and commissioning date.