Subsea cable specialist, Offshore Marine Management (OMM) has successfully completed operations to install the HVAC cables connecting the Bard Offshore 1 and BorWin alpha platforms (BorWin1 project) for TenneT Offshore GmbH (formerly Transpower Offshore GmbH).
BorWin1, the world's first HVDC connector for offshore wind farms, is 120 km off the coast of Germany, and OMM's role was to install the two one kilometre long HVAC cables (208mm OD) between the principle platforms at a water depth of approximately 40m. From the BorWin alpha platform the DC-export cables run to the Island of Norderney and onward cables to Diele where power will enter the German grid.
All operations were conducted between late August and early November 2010 from the MV Seabed Worker, a state-of-the-art and multi purpose DP2 vessel with OMM survey, cable and pull-in teams and sub-contracted WROV and trenching spreads, bringing new partners into the renewable energy sector. Hallin Marine, Modus and Aquatic were chosen as OMM's partners for the supply of the specialised vessel, Seabed Group, subsea vehicles (CT1 and Triton XLX35) and cable equipment.
The scope of work included the inspection of the J-tubes, mudline dredging, visual route surveys, pre lay grapnel runs and full preparatory topside works on both platforms for the J-tube pull in operations. This was followed by cable installation with associated pull-ins, trenching and post trench depth of burial surveys.
Both cables were installed and buried to protected depth to the satisfaction of TenneT, with a 1.5m burial criteria and three trenching passes..
Additional extensive work included a total of 150km of WROV depth-of-burial inspection operations on the BorWin1 DC export and the alpha ventus AC export cables. Also a general visual inspection of the BorWin alpha connector platform jacket structure and mudline scour survey.
Benjamin Hühnerbein, TenneT Project Manager said that OMM proved to be a flexible and capable partner for offshore cable installation.
"The company has worked according to high industry standards from engineering to final reporting and of course the installation itself," he said.