trenching/cable installation
Nordsee Ost cables completed ahead of schedule
Dividing installation of the inter-array cables on the Norsee Ost offshore windfarm into two campaigns worked well, with the project completed ahead of schedule
JUNE 2014 saw VBMS, the former Visser Smit Marine Contracting (VSMC), complete installation of the inter array cables on RWE’s Nordsee Ost offshore windfarm. The work was undertaken by the vessel Stemat Spirit, this being the vessel’s first inter-array cable installation job. A total of 30 infield cables were installed by the vessel, which has since moved to continue work as an infield installation vessel on the Butendiek project. With the inter array cables installed, the focus of attention has moved to burial work, which was expected to wrap up shortly. Termination work and testing are due to be completed in mid- October 2014. A network of more than 60km of cable was installed on the windfarm in less than four months. “We divided cable installation into two campaigns,” Marcel Sunier, project director for Nordsee Ost at RWE Innogy explained. “The first 30km of cable or so were installed and buried in 2013. The remaining cables were laid over the
in brief…
• Ecosse Subsea Systems (ESS) has been awarded a third seabed clearance contract on an offshore wind construction project. The subsea engineering specialist recently started offshore operations on the Westermost Rough development off the Yorkshire coast in the UK. The company is using its SCAR subsea boulder clearance system.
• CT Offshore in Denmark was recently awarded a cable installation contract for Dong Energy’s Gode 1 and 2 offshore windfarms. The scope of work includes cable installation and burial of 97 inter-array cables. “Although new and larger cable laying vessels are being deployed in the offshore renewables market, we believe that our years of experience and expertise in installation and burial of inter-array cables is a decisive factor,” said Jens Frederik Hansen, CEO of A2SEA and chairman of the board at CT Offshore. CT Offshore is due to start cable installation in the summer of 2015.
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Stemat Spirit wrapped up the inter-array cable installation on Nordsee Ost in June
last few weeks. The team VBMS did an excellent job, completing the work two weeks ahead of schedule.”
All 48 foundations for the turbines and the foundation of the substation were connected using the inter-array cables. The 33 kV cables have a diameter of up to 16cm and have a particularly robust sheathing to protect them from the stresses imposed by the installation process. Two different cable installation vessels were used for the project: Stemat Spirit and Normand Flower (which undertook the 2013 campaign) . The vessels were loaded with cable at Landskrona in Sweden; on arrival at the site they connected 12 foundations together in a so-called ‘loop’ – to do so the cables first had to be cut to the right length, which was done on board. Subsequently, the cable ends were pulled into the cable tunnels in the foundation, where they were fastened. The cables connecting the individual foundations were buried at a depth of around 1.5m, after which remotely operated vehicles (ROVs) surveyed the final cable position. During August the inter-array cables were connected with the
offshore substation, which transforms the electricity generated by the wind turbines at 33 kV to a transmission voltage of 155 kV so that the electricity can be transmitted via high-voltage cables to land. VSMC, which recently changed its name to VBMS to reflect the strategic joint venture between VolkerWessels and Boskalis, has secured contracts for a number of projects in recent weeks. These include the award of a €90 million contract by Sandbank Offshore Windfarm (a joint venture between Vattenfall and Stadtwerke München) for cable supply, installation, post-lay burial and termination and testing of 76 infield cables for the Sandbank project, which is in the German Bight. The project is due to start in August 2015 and will be completed by the summer of 2016. The company was also recently contracted for the design, supply and installation of the infield cables connecting 48 turbines on the Westermeerwind windfarm. The work also includes seven dike crossings, cable terminations and testing. VBMC was due to start work on this project in August 2014, followed by cable installation in April 2015. VBMC has also been awarded a €110 million contract by Dudgeon Offshore Wind Limited, which is owned by Norwegian companies Statoil and Statkraft, for the export and inter-array cabling for the Dudgeon offshore windfarm. The company will start work there in 2015, undertaking two 1,100m horizontal directional drilling campaigns at the landfall, followed by the installation of two 42km export cables in 2016.. OWJ
Offshore Wind Journal I 3rd Quarter 2014 I 53
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