Siemens hands over world’s largest offshore grid connection to TenneT

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Siemens has handed over SylWin1, the third North Sea grid connection this year, to its customer TenneT. The German-Dutch transmission grid operator has now put the world’s most powerful grid connection to date into commercial operation. The offshore platform of the SylWin1 grid connection is located around 70 kilometers west of the island of Sylt. The electricity generated by wind power is transmitted over a more than 200 km subsea and underground cable link to the land-based station B├╝ttel. Up to 864 MW of green electricity can now be transmitted with this grid connection – enough to supply more than a million German households.

The three offshore wind farms DanTysk, Butendiek and Sandbank, each with a capacity of 288 MW, are linked to SylWin1. DanTysk and Butendiek both consist of 80 Siemens wind turbines, each rated at 3.6 megawatts. Sandbank will be realized with 72 Siemens wind turbines in the 4-megawatt class. At present, more than 100 wind turbines are already linked to the grid connection, with new turbines being connected almost on a daily basis. Under optimal wind conditions, such as those which the low-pressure storm front Niklas brought with it recently, a capacity of 350 MW was already transmitted via the SylWin1 grid link.

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The fourth grid connection HelWin2 is scheduled to take up commercial operation in the first half of 2015 as well. Siemens received its latest order for a grid connection in the North Sea, BorWin3, in a consortium with Petrofac in the spring of 2014. Commissioning of this fifth grid connection from Siemens is scheduled for 2019. The grid connections implemented by Siemens for TenneT will have a total transmission capacity of more than 3.8 gigawatts (GW), providing electricity from offshore wind power to supply nearly five million households.

Thanks to the Siemens high-voltage direct-current (HVDC) technology, transmission losses for each grid connection, including cable losses, are less than four percent. This Siemens HVDC technology is installed on the offshore platforms and in the land-based converter stations. The wind-based electricity is transmitted as alternating current to the converter platform, transformed into direct current and fed to the mainland via a subsea cable. The land-based station converts the direct current back into alternating current and feeds the electricity into the extra-high voltage grid. HVDC is the only efficient transmission solution for cable lengths of more than 80 km.

The HVDC Plus technology used by Siemens is less complex and extremely compact, making it predestined for use in sea-based applications. In contrast to classic HVDC technology used in a vast majority of land links, systems equipped with HVDC Plus feature self-stabilization. As fluctuations in the grid must always be reckoned with for wind-based power generation, grid stability and reliability is enhanced considerably through the use of the Siemens HVDC Plus technology.