DolWin Alpha HVDC offshore converter platform

Located around 60 kilometres off the German coast in the North Sea, DolWin Alpha was one of the first offshore HVDC converter platforms built to connect German wind farms to the onshore grid. TenneT Offshore GmbH, the grid operator responsible for the HVDC network in the German North Sea, was the client for the design, manufacture and installation of the platform. Under an EPC contract awarded to ABB Offshore Wind Connections, Heerema Fabrication Group in the Netherlands was commissioned by ABB to design and construct the DolWin Alpha HVDC converter platform.

Iv was selected by Heerema to provide the complete design, including its support facilities such as the auxiliary systems, accommodation, and helideck. Iv also prepared designs for the transport and installation process, including structural workshop drawings for the grillages and other supporting structures.

At the time of its development, DolWin Alpha was among the first offshore HVDC converter platforms ever built. The main challenge was to enable efficient conversion of 155 kV AC to 320 kV DC for long-distance transmission of 800 megawatts of power. To achieve this, Iv integrated the high-voltage equipment within a compact offshore structure, including a 155 kV gas-insulated switchgear (GIS) for connecting the AC cables to the wind farm, main step-up transformers rated 155/320 kV, and a 400 kV GIS for linking and protecting the main transformers. These systems, together with the control, protection, and auxiliary systems, were designed to ensure safe and reliable operation under demanding offshore conditions.

With a transmission capacity of 800 megawatts, DolWin Alpha connects offshore wind farms in the German North Sea to the mainland grid with minimal transmission losses. As one of the first offshore HVDC converter stations, it laid the foundation for subsequent large-scale projects and contributed to the reliable integration of offshore wind into the European energy system.

Dimensions

Topside: 62 x 43,3 x 40m (excluding helicopter deck)

Jacket: 45 x 42 x 44m

Weight

Topside: 11,000 mT

Jacket: 4,000 mT       

Water depth: 27m

Accommodation: 24 persons

Input: 8 cables of 155 kV AC

Output: 2 x 320 kV DC

Throughput: 800 MW

Electricity generation: 2 x 3050 kV A/ 10 kV Diesel