• Major step forward for the offshore expansion of the German power grid
• North Sea platform can transmit wind power to supply more than 800,000 German households using efficient direct current technology
Siemens has installed the BorWin2 offshore platform in the North Sea northwest of the island of Borkum. This marks Siemens’ achievement of the second crucial milestone in the German grid connection projects under contract with the German-Dutch network operator TenneT. Siemens had already erected its first converter platform for the HelWin1 connection off Heligoland in the North Sea in August 2013. The BorWin2 transmission capacity of 800 megawatts (MW) is enough to meet the power demand of some 800,000 German households. On the platforms, the alternating current generated by the wind turbines is transformed into low-loss direct current for transmission to the mainland by using Siemens technology. The BorWin2 onshore converter station, likewise supplied to TenneT by Siemens, is located in Diele. There the electric power from the connected wind farms is converted back into the alternating current required to feed into the power grid.
“Once more we have mastered the challenging offshore installation part. We are now in the final stretch to achieve commissioning in the first half of 2015, as promised. When the two platforms yet installed by us go on line, they will be able to supply more than 1.3 million households,” states Karlheinz Springer, CEO of the Power Transmission Division within the Energy Sector of Siemens AG. “We are proud of having successfully tackled these highly complex tasks,” says Lex Hartman, member of TenneT management. “We are set to make major progress in expanding our offshore capacity in the coming months,” continues Hartman, “and that brings the German government’s offshore expansion targets within reach.”
In mid-2010 the grid operator TenneT had placed the order for the BorWin2 offshore grid connection with a consortium comprising Siemens and the Italian cable specialist Prysmian. In all, Siemens is realizing five North Sea grid link-ups for TenneT: HelWin1 (576 MW) and HelWin2 (690 MW) off Heligoland, BorWin2 (800 MW) and BorWin3 (900MW) off Borkum, and SylWin1 (864 MW) off Sylt. The first four platforms HelWin1 and HelWin2, BorWin2 and SylWin1 are to commence commercial operation in rapid succession between the second half of 2014 and the first half of 2015. In April 2014, Siemens won the order for the fifth grid connection in the North Sea., BorWin3, in a consortium with Petrofac. It is scheduled to go on line in 2019. Once commissioned, the grid connections installed by Siemens will have a total transmission capacity of over 3.8 gigawatts (GW). Thanks to Siemens’ efficient high-voltage direct current (HVDC) technology, transmission losses per link are less than three percent, not including cable losses.
The converter technology used by Siemens is called HVDC Plus, and is essentially a voltage-sourced converter of the modular multi-level converter type (VSC MMC). Siemens is a leading pioneer of VSC MMC technology in this field. By contrast with the conventional HVDC version, which can only be used in networks with sufficient short-circuit capacity, systems using HVDC Plus make it possible to start up island networks from scratch. This is an important prerequisite for operation of the offshore network. The modular VSC technology reduces complexity and thus the space required for the installations – an essential precondition precisely for use on offshore platforms. What is more, HVDC Plus ensures a nearly ideally sinusoidal AC voltage and a smooth voltage in the DC circuit. This eliminates the need for harmonic filters.
