Yesterday, the first steel cutting marked the start of construction of the BorWin kappa converter platform at the shipyard in Jebel Ali (Dubai, United Arab Emirates). The contract for the construction of the converter stations at sea and on land was awarded to the consortium McDermott and GEIRI/C-EPRI in February 2022. The converter station
BorWin kappa is the starting point for the offshore grid connection BorWin6, which will make an important contribution to the energy transition from 2027 with a grid connection capacity of 980 MW.
About the project
The BorWin6 project will implement a high-voltage direct current (HVDC) transmission of 980 megawatts from the offshore wind farm to the extra-high voltage grid in Büttel (Schleswig-Holstein). The wind power produced off the coast of Lower Saxony at sea is fed as three-phase current to TenneT's BorWin kappa converter platform, where it is converted into direct current and transported along the 235-kilometre (km) long cable route to the Büttel converter station. Here the electricity is converted back into three-phase current and fed into the extra-high voltage grid via the transformer station. Due to the distance and the power to be transmitted, direct current is suitable for low-loss transport.
The converter platform itself (topside) is placed on a substructure (jacket). This jacket will be built in Batam (Indonesia) from September. The topside will measure approximately 63 x 67 x 46 metres, with installation scheduled for summer 2026. The platform will be transported through the Suez Canal, the Mediterranean Sea and then through the Bay of Biscay to the location in the North Sea and set down on the jacket by "float-over". This means that the platform will be positioned exactly above the jacket and then lowered precisely onto the structure. The jacket is to be installed in the 38-metre-deep water a year earlier in the summer of 2025. At 50 x 38 metres and around 8,000 tonnes, this alone is a real heavyweight, with around 3,700 tonnes of this being made up of the total of ten piles for anchoring the jacket. The topside then accounts for another 18,000 tonnes.
The other milestones at a glance
In 2023, horizontal drilling under the land protection dike near Büsum and later under the Kiel Canal is still planned. The laying of the land cable will take place in 2024 and 2025, the laying of the submarine cable in 2025 and 2026. Nexans Norway AS has been commissioned with the production and installation of the direct current cables at sea and on land. In addition, initial construction preparation measures for the land station in Büttel have been completed, and the actual construction of the land station will begin in 2024.
Innovative direct connection with 66 kilovolts (kV)
TenneT is not only driving forward the standardisation of systems and processes. TenneT is also developing innovative technologies to make grid connections even more efficient and cost-effective. One of these innovations is the 66 kV direct connection, which is also used in the BorWin6 project. This technology enables significant cost savings, as the wind turbines are connected directly to TenneT's offshore platform via 66 kV three-phase cables. Previously, it was necessary to build a separate transformer station for each offshore wind farm and connect it to the converter station with 155 kV three-phase cables.
Facts and figures on BorWin6
- 235 km long connection using high-voltage direct current transmission technology (HVDC) with a maximum transmission capacity of 980 megawatts
- 190 km submarine cable, 45 km land cable
- Grid connection point: Büttel
- Commissioning planned for 2027
Caption:from left Roberto Cecchini (McDermott Project Director, BorWin6) and Valentin Fontana (TenneT Project Director BorWin6).
Photo credit: McDermott/TenneT
Fachkoordinatorin & Referentin Offshore Projektkommunikation
Public Affairs & Communications | Community Relations Germany | Team Nord
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