Great Belt Power Link

Until 2010 Denmark had two electricity grids that could not be joined directly. The western half, Jutland and Funen, runs in step with continental Europe. The eastern half, Zealand with Copenhagen, runs in step with the Nordic countries. Because the two systems are not synchronised, the only way to connect them is through direct current.

The Great Belt Power Link, also called Storebælt HVDC, fixed that. The decision was taken in December 2005. The route starts at the Fraugde converter station on Funen, runs 16 km underground to the coast, crosses the Great Belt in a 32 km sea cable, and continues 10 km underground on Zealand to the Herslev station. The cable was laid in July 2009 by JD-Contractor with the cable ship Henry P. Lading.

The link was commissioned in July 2010, started commercial operation in August and was inaugurated on 7 September 2010. The Wikipedia article on the link gives the cost as DKK 1.29 billion. Energinet, the Danish system operator, owns it, and Siemens supplied the converters.

Its stated purpose was practical: to make better use of the power system, share reserves, create a common market for regulating power and improve the working of the market.

The figures differ slightly by source. Wikipedia’s sections add up to 58 km, while this page gives 56 km, from the List of HVDC projects. The difference is small, but you should know it exists before quoting either.

Denmark’s two grids remain separate synchronous systems; the link is a bridge between them, not a merger. How DC makes that possible is set out in the HVDC explainer. Of the whole route, only the 32 km crossing is under water; the rest lies buried in the fields of Funen and Zealand.