Cable suppliers NKT and Prysmian have won the contract for the first out of three so-called transmission super-highways to connect Germany’s windy north to consumer centres and industries to the south of the country, the energy transition’s largest grid expansion project.

The companies will supply underground power lines for the 500km-long SuedOstLink high voltage direct current (HVDC) connection between Wolmistedt near Magdeburg in Saxony-Anhalt state and Isar near Landshut in Bavaria, which transmission system operators TenneT and 50Hertz are implementing jointly.

Once built, SuedOstLink, which will have a transmission capacity of 2GW, will involve around 1,000km of the plastic-insulated 525kV underground cable. The TSOs are investing around €5bn ($5.42bn) in the project.

“The underground cables are the heart of SuedOstLink. By placing the order for the underground direct current cables, we have made good progress in implementing this important connection for the energy transition,” said TenneT managing director Tim Meyerjürgens.

“We will use the innovative, plastic-insulated 525kV underground cables for the first time worldwide and will thus set new standards in technology and the reduction of environmental impact.”

SuedOstLink is one of three delayed HVDC links that after heavy Nimby’ protests in states such as Bavaria will be mostly built underground, and are slated to be ready in 2025 – provided they are granted approval by federal network agency BNetzA. Without the ‘transmission super-highways’, the German government has claimed it will be difficult to boost wind capacity in the north and offshore at a pace, without having to resort to heavy curtailment.

With the higher voltage level now being employed, the cables can transmit more power than conventional 320kV cable systems, at lower energy loss, meaning fewer cables to transmit the same volumes of electricity using a layroute that can be narrower and fewer civil engineering works during the construction phase, 50Hertz said.

Italy’s Prysmian said it has been awarded a contract worth about €500m to design, manufacture, supply, lay, joint, test and commission part of the 2GW underground cable system.

“This award confirms our ambition to play a strategic role in the shift towards a low-carbon economy and to drive the energy transition forwards with smarter, more reliable and more sustainable solutions,” Prysmian Group chief executive Valerio Battista said.

“It gives us great satisfaction to be involved in the development of this vital infrastructure project and to set this milestone in the upgrading of the EU power transmission grid.”

NKT chief executive Alexander Kara said: “I am very pleased that we have booked our largest high-voltage DC order ever by getting a significant part of the SuedOstLink projet.

“We have worked with 50Hertz on a number of large high-voltage power cable projects over the years, and I am excited that our leading expertise and know-how within 525kV XLPE high-voltage DC technology is once again recognized by one of our key customers.”