SuedLink: contract awarded for two converter facilities

• TenneT and TransnetBW award contract for two converter stations to Siemens
• Significant project progress despite difficult conditions caused by the coronavirus pandemic
• Another milestone achieved towards fulfilling a key energy transition project

The grid expansion project has made another important step by awarding the contract for the converter stations for the SuedLink direct current connection in Brunsbüttel and Leingarten/Großgartach. The two responsible transmission system operators TenneT and TransnetBW have awarded the contract for the construction of two converter stations to Siemens. The project involving the two plants is worth hundreds of millions of euros, while the investment volume for SuedLink amounts to a total of around ten billion euros.

The current award relates to the scheme in Brunsbüttel in Schleswig-Holstein and Leingarten/Großgartach in Baden-Württemberg, which is referred to as Project 3 in the Federal Requirements Plan Act. A separate bidding process to be concluded by mid-2022 was launched for Project 4 with the converter stations in Wilster in Schleswig-Holstein and Bergrheinfeld in Bavaria.

Each of the direct current projects has a transmission capacity of 2,000 megawatts. A converter station is needed at each end point of the two connections to convert direct current into alternating current and vice versa. TenneT is responsible for the northern section of SuedLink and the converter stations in Schleswig-Holstein and Bavaria. TransnetBW is responsible for the southern section and the converter station in Baden-Württemberg.

“The construction of SuedLink, Germany’s largest system expansion project, is key to the success of the energy transition,” says Tim Meyerjürgens, Managing Director of TenneT. “The awarding of the contract for these converter stations is an important milestone on the road to making it a reality. It is proof that we have managed to make significant progress with SuedLink despite the difficult conditions during the coronavirus pandemic,” says Meyerjürgens.

“By awarding the contract, we have reached an important milestone in fulfilling SuedLink. Plans can now be further refined for two start and end points and the preparatory construction measures underway at the southern end point in Leingarten, Baden-Württemberg, can be pressed ahead with,” says Dr Werner Götz, Managing Director of TransnetBW.

The direct current technology makes it possible to transport electricity more efficiently over long distances by better controlling load flows and keeping transmission losses low. Converter stations are needed at the start and end points in order to integrate direct current connections such as SuedLink into the existing mains system. They convert alternating current into direct current and vice versa.

The converters will be constructed as what is known as a rigid bipole with nominal active power of 2,000 megawatts at a nominal DC voltage of ±525 kilovolts (kV). Cutting-edge modular multilevel converter (MMC) technology with half-bridge submodules will be used. Thanks to VSC technology, the converters can adapt the active power as well as the reactive power flexibly and quickly to the respective system conditions. They play an important role in system stability. With lower losses than alternating current transmission, they facilitate transport over long distances and the integration of wind power from northern Germany and solar power from southern Germany into the German transmission system.

The site of the northern converter station in Brunsbüttel, in TenneT’s part of the project, is located in an industrial area close to the Brunsbüttel substation. In February 2021, TenneT submitted the application papers for this site to the State Office for Agriculture, the Environment and Rural Areas for initial partial planning permission pursuant to the Federal Immission Control Act.

The plan is to build the southern converter in Leingarten/Großgartach on the site of the TransnetBW substation. A 220-kV switchgear system will be dismantled to create the necessary space for the converter. TransnetBW received initial partial planning permission for construction in early 2019. Preliminary building work is currently being carried out to prepare the site for the construction of the converter.

The two system operators launched a joint bidding process for the two converter stations. Detailed site-related plans will be compiled in the coming months. In the construction phase, Siemens will work together with TenneT and TransnetBW to flesh out the detailed design of the converters.