DolWin3

The DolWin3 project is a high voltage direct current (HVDC) link designed to transmit offshore wind power to the German mainland power grid.

Technical Specifications

DolWin3 utilizes Voltage-Sourced Converters (VSC) with DC ratings of 900 MW and ±320 kV. The total cable length spans 160 km, consisting of an 83 km subsea cable and a 79 km underground cable. The project connects the offshore converter platform DolWin gamma, located approximately 85 km offshore in the North Sea, to the onshore converter station in Dörpen/West, Lower Saxony, Germany.

Converter Technology

The project employs HVDC Voltage Source Converter (VSC) technology. VSC technology offers enhanced operational capabilities, including improved power and frequency control compared to traditional line commutated converter (LCC) technology. The VSC solution can deliver up to 900 MW of wind-produced electricity at ±320 kV.

Cable System

Prysmian Group was responsible for supplying, installing, and commissioning the HVDC ±320 kV extruded submarine and land power cable connections. The cable system includes associated fiber optic cables. The cables were manufactured at Prysmian Group's production facilities in Arco Felice, Italy; Pikkala, Finland; and Delft, the Netherlands.

Offshore Converter Platform

The DolWin gamma converter platform was installed in July 2017, the platform was constructed in Warnemünde, Mecklenburg-Western Pomerania, and transported over a six-day journey along the German and Danish coasts to its final location in the North Sea. The offshore converter station converts the alternating current (AC) generated by the connected wind farms into direct current (DC).

Onshore Converter Station

The onshore converter station, located in Dörpen/West, Lower Saxony, receives the DC power transmitted through the subsea and land cables. Here, the power is converted back to AC and fed into the German transmission grid. Construction of the onshore converter station commenced in May 2014.

Power Transmission Process

The electricity generated by offshore wind turbines is first transported via submarine cables to an AC substation, where the voltage is combined and transformed. The power is then directed to the offshore converter platform, where it is converted from AC to DC using a large series of valves. After conversion, the electricity is transported via submarine and land cables to the onshore converter station, where it is converted back to AC and fed into the German power grid.

Project Capacity and Impact

DolWin3 has a capacity of 900 MW and can supply enough power for a city of over one million people. It is part of a larger initiative to deliver approximately 6.8 GW of offshore wind energy to the German grid. The project has been operational since September 2018 and has already transmitted over 800 MW, subject to wind park availability.

Additional Features

The DolWin3 project includes enhancements to the valves and control system, which improve overall performance and reduce maintenance requirements. GE Vernova has implemented upgrades that incorporate learnings from their recently released second-generation VSC valve and eLumina control system.

Project Execution

Alstom (now part of GE) was awarded the project in February 2013 by TenneT, the Dutch-German grid operator. Alstom served as the general contractor, working in collaboration with platform constructor Nordic Yards and cable supplier Prysmian. The project was handed over to TenneT in 2017, with the grid connection becoming operational in September 2018.

Maintenance and Service

A five-year service contract was awarded alongside the turnkey contract. This service agreement covers the complete offshore converter station and platform, as well as the onshore converter system. It includes inspection, preventive and corrective maintenance, refurbishment and repair, spare parts management, and a technology support line.

The DolWin3 project represents a significant step in Germany's energy transition, contributing to the country's goal of generating 80% of energy consumption from renewable sources by 2050. It showcases the latest advancements in HVDC technology and plays a crucial role in efficiently transmitting clean energy from offshore wind farms to the mainland grid.