The collecting point for power of the wind turbines, the offshore substation is the most complex part of the wind farm. In order to minimise the transmission losses of the wind farm, the turbine output voltage of 33 kV is transformed to 155 kV before transportation from the Butendiek substation to Tennet’s converter platform (SylWin).
The Butendiek offshore substation is built and installed by a consortium of four companies: Cofely Fabricom GDF Suez being responsible for the design, electrics and auxiliary systems, Iemants for the steel construction, CG for major electrical components and GeoSea for the installation.
Based on a jacket foundation the top side of the substation consists of four decks housing the two 33/155 kV transformers, each of a rated power of 288 kVA and the core high voltage equipment on the main deck. On the lower deck the internal cables from the wind turbines and the Tennet cables are installed for connection to the switchgear. In addition, on the lower deck, diesel generator sets and two large tanks for water and diesel are installed. The control and communication systems, office and accommodation rooms are located on the mezzanine deck. Finally the top deck harbours the crane, antennas and the helicopter landing platform.
The arrangement of the offshore substation provides full redundancy in case of single failure in the 33 kV or 155 kV equipment. Similarly an outage of one of the transformers or one of the medium or high voltage switches will not prevent the operation of a single wind turbine.