Siemens installs platform to connect wind farms to German power grid

Siemens installed the HelWin1 offshore platform in the North Sea, marking the completion of a stage in German grid connection projects. HelWin1 will link the two offshore wind farms Nordsee Ost and Meerwind to the mainland.

The HelWin1 HVDC platform has a capacity of 576 MW. Because of the efficient direct-current technology employed, the total transmission losses for this connection are less than four percent.

Starting in 2014, this will enable the network operator and purchaser TenneT to supply clean electricity to more than 500,000 German households on the mainland. The land-based station, also supplied by Siemens to TenneT, is located northwest of Hamburg in Büttel, where electricity will be converted back into the alternating current power required for feeding into the power grid.

Using the Siemens technology installed on the platform, the alternating current power generated by the wind turbines is transformed into low-loss direct current for transmission onto land.

The network operator TenneT contracted the consortium consisting of Siemens and the Italian cable specialist Prysmian for the HelWin1 offshore grid connection in 2010. This consortium is implementing a total of four North Sea grid connection projects for TenneT; HelWin1 and HelWin2 off of Helgoland, BorWin2 off of Borkum and SylWin1 off of Sylt.

After seven days of transport at sea and four days of installation on site, the HelWin1 platform was anchored at its final position northwest of the island of Helgoland on August 23. Siemens had installed the platform’s support substructure at this location in June in the 23-meter-deep North Sea.

Ten steel pilings up to 3.4 yards in diameter and with a wall thickness of three inches were anchored in the seabed for attachment of the structure. With a length of up to 109 yards, these pilings are as tall as London's Big Ben. The platform is installed 24 yards above sea level to protect it against giant waves. HelWin1 is designed for decades of operation in the North Sea.

At 12,000 tons, the HelWin1 platform weighs more than 20 loaded and fully tanked Airbus A380 super airliners. The surface area of the platform, at 82 by 54 yards, is more than half the size of a soccer field. The platform’s seven decks, spanning a total height of 29 yards, accommodate 16 cabins for crewmembers with a total of 24 berths, a galley, sanitary facilities, a multi-purpose room equipped with sports equipment and a day room with satellite TV, in addition to housing all the technology and equipment required for HVDC transmission.

Now, the two subsea cables from the well-established cable specialist Prysmian are also to be connected. Siemens’ consortium partner has supplied and laid in bundle the two cables, each with a length of 80 miles, for transmission of 250 kV DC voltage in the future. The cable route covers 52 miles at sea and 28 miles over land. Both 4.3-inch thick cables, with its protective steel armoring wire layer and a copper conductor, weighs about 66 pounds per meter.

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