One of the convertor stations of the SuedLink transmission project will be located near the Leingarten substation in Heilbronn, Baden-Württemberg, in south Germany. Image courtesy of TransnetBW.
The SuedLink HVDC project will involve approximately 2,500km of 525kV underground cables. Image courtesy of NKT.
The SuedLink line will facilitate the transmission of wind power from north to south Germany. Image courtesy of Jacobs.

The SuedLink high-voltage direct current (HVDC) transmission line to be developed in Germany is expected to be the longest underground HVDC power cable in the world.

Covering a total route length of 750km, the 525kV underground power line will be capable of transmitting up to 4GW of offshore wind power from north to south Germany while also facilitating the transmission of solar energy from south to north Germany.

The SuedLink HVDC line will also be connected to the 525kV NordLink HVDC subsea interconnector that brings hydropower from Norway to Germany.

The SuedLink transmission project will be developed and operated by German electric transmission system operators TenneT and TransnetBW.

The key contracts for the £8.9bn ($11bn) underground HVDC transmission project were awarded in the second quarter of 2020 with the start of operation expected in 2026.

The SuedLink project is being developed in line with Germany’s goal of feeding at least 80% of its power supply by renewable energies by 2050.

SuedLink HVDC transmission project background

TenneT is responsible for the northern section of the SuedLink transmission project, whereas TransnetBW is responsible for the development and operation of the southern corridor of the transmission system along with the converters.

TenneT and TransnetBW conceived the SuedLink underground cable power transmission corridor in 2017, while TenneT submitted the plan approval application for the northern corridor of the project to Germany’s Federal Network Agency (Bundesnetzagentur) in early 2020.

The SuedLink HVDC has also been identified as a Project of Common Interest (PCI) as part of the European Union’s (EU) Trans-European Network (TEN) initiative.

Route details

The SuedLink underground power cable corridor will run from the northernmost federal state of Schleswig-Holstein through western Lower Saxony, northern Hesse, and southern Thuringia to Bavaria and Baden-Württemberg in South Germany.

The transmission system will comprise two 525kV underground HVDC cables both originating from Schleswig-Holstein. Both the routes will run parallel along the central trunk. One route will originate in Wilster in Schleswig-Holstein and lead to the Grafenrheinfeld area in Bravia, while the other one will stretch from Brunsbüttel in Schleswig-Holstein to Großgartach in Baden-Württemberg. 

SuedLink cable design and converter details 

Both the 2GW underground lines of SuedLink will comprise plastic-insulated 525kV power cables. The total cable length of the transmission system over a route length of 700km will be approximately 2,500km. The underground route has been chosen in order to have minimal impact on the landscape.

The cables will be laid in four parallel trenches with a distance of 10m from each other in the central trunk of the transmission system. The trenches will be excavated up to 2m-deep beneath the ground.

The converter stations in Schleswig-Holstein, Bavaria, and Baden-Württemberg for the SuedLink transmission system will be designed to operate both as rectifier and inverter depending on the direction of the flow of electricity transmission.

The self-commutated convertors on the SuedLink will also be capable of regulating the grid voltage independently.

TenneT is responsible for the operation of the converters in Schleswig-Holstein and Bavaria, while TransnetBW is responsible for the converter in Baden-Württemberg.

TransnetBW received approval from the Heilbronn Regional Council for building a converter in the premises of the Leingarten substation in Baden-Württemberg in January 2019.    

Contractors involved 

NKT was awarded a contract worth more than €1bn ($1.1bn) for the design, supply, and installation of high-tension underground cables for one of the 2GW lines of the SuedLink over a route length of 750km in June 2020.

In the same month, Prysmian Group won a contract worth more than €800m ($900m) to design, supply, and install the other 2GW line of the SuedLink over a route length of 700km.

ILF Consulting Engineers was engaged for detailed route design, soil investigation, and planning services for the SuedLink power transmission project.

Jacobs was contracted to provide the technical project management services for the SuedLink HVDC power transmission project in September 2019.