Following the grid connections for the offshore wind farm clusters BorWin2 and HelWin1, Siemens Energy will also install a turnkey grid connection in the North Sea for the SylWin cluster. The purchaser is the Dutch-German transmission grid operator TenneT. In a consortium with the Italian cable manufacturer Prysmian Powerlink, Siemens will connect DanTysk, located west of the island of Sylt as the first wind farm to be connected via the SylWin collective connection. Equipped with 80 Siemens wind turbines, DanTysk will have a total capacity of 288 MW and supply up to 500,000 German households with clean electricity.

The wind farm will be connected to the mainland grid via a high-voltage direct-current (HVDC) transmission link using subsea and underground cable. Including its internal efforts, TenneT estimated the total investment volume at nearly one billion euros. More than a quarter of this sum has been awarded to Prysmian for supply of the cables. The Siemens share is significantly higher. The grid connection is scheduled to be ready for operation by early 2014.

“With this order we’re once again underscoring our market leadership in grid connections for offshore wind farms. For SylWin, too, we’re contributing our know-how and many years of experience – particularly in the field of high-voltage direct-current transmission,” said Udo Niehage, CEO of the Power Transmission Division of Siemens Energy.

Siemens is erecting the DanTysk wind farm as part of the SylWin cluster approximately 70 kilometers west of the North Sea island of Sylt in the vicinity of the maritime boundary with Denmark. Through the connection of more windfarms it will be possible to transmit a total of 864 MW via the cable link to the grid, which would be enough to supply up to 1.5 million German households with wind-generated power. This offshore link will have the highest transmission capacity, for which an order has been placed to date. The Siemens HVDC system HVDC Plus will be deployed. With a length of 160 kilometers the subsea cable will be the longest ever used to connect offshore wind farms. A further 45 kilometers of underground cable will be deployed.

The HVDC system, transformers and gas-insulated high-voltage switchgear will be installed on an offshore substation platform for energy-efficient transmission of the electrical energy generated by the wind farm to the mainland. The alternating current produced by the wind turbines will be converted to direct current on the platform, which will be later be located directly adjacent to the wind farm in the North Sea. The direct current will be brought to a transmission voltage of 320 kV. The power will then be transmitted to Büttel, which is located in the estuary of the river Elbe. This is the grid feed-in point on the coast, where the electricity will be converted back from direct to alternating current in a converter substation.

HVDC significantly reduces transmission losses. For high-voltage cable links covering distances of more than 80 km HVDC is necessary for power transmission because a large amount of the electrical energy in the form of reactive power would be lost in a three-phase line of that length. Siemens has developed its new HVDC system HVDC Plus for applications like this. This technology features a new generation of converters based on voltage-sourced converter technology in modular multilevel converter (VSC MMC) design. The modular, multilevel VSC technology reduces system complexity and thus space requirements – key requirements for deployment on offshore platforms. HVDC Plus ensures an almost ideal sinusoidal AC waveshape and smoothed direct voltage along the transmission line. That makes the installation of high-frequency and harmonic filters practically superfluous