Siemens hands over fourth North Sea grid connection HelWin2 to TenneT

With HelWin2, Siemens has handed over the fourth North Sea grid link to the customer TenneT. This marks the start of commercial operation of the grid connection by the German-Dutch transmission grid operator. All in all, there are now four Siemens grid links with a transmission capacity of over 2.9 gigawatts (GW) installed in the North Sea which together are capable of supplying around four million German households with electricity. The offshore platform HelWin2 alone, which has just gone online, can transmit up to 690 megawatts (MW) of green electricity, enough to supply nearly 900,000 German households. The offshore platform of the HelWin2 link is located about 85 kilometers off the northwest coast of the island of Helgoland from which it takes its name. The connected wind farm will be successively expanded and connected with Siemens wind turbines of the 3.6 megawatt class, with additional turbines being linked in practically every day.

"This year we've completed the first four offshore grid links of this performance class in the world using efficient direct current technology. Thanks to Siemens technology, nearly four million German households can be supplied with wind power generated offshore," said Tim Dawidowsky, CEO of the Transmission Solutions business unit within the Siemens Energy Management Division. "The completion of HelWin2 marks an important milestone for us. Step by step we are implementing the offshore development goals set by the German government", declared Lex Hartman, member of the managing board of TenneT. "The goal of the German government is to have 6.5 gigawatts of offshore wind power capacity installed by 2020. TenneT has already achieved more than 50 percent of this target."

Transmission grid operator TenneT awarded the consortium consisting of Siemens and Italian cable specialist Prysmian the order to deliver the offshore grid links for HelWin1 (576 MW) and HelWin2 (690 MW) off Helgoland, BorWin2 (800 MW) off Borkum and SylWin1 (864 MW) off Sylt. All four North Sea grid links are now in normal operation and transporting electricity generated out at sea onto land with low losses.

Siemens received its latest order for a grid connection in the North Sea, BorWin3, in the spring of 2014 in a consortium with Petrofac. This fifth Siemens grid link is due to go into commercial operation in 2019. After it is commissioned, the five installed Siemens network grids will have a total transmission capacity of 3.8 gigawatts and will transport offshore wind power for supplying theoretically 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 kilometers.

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.