Two large offshore substations, each weighing nearly 1,000 tonnes, arrived off the North Norfolk coast at 22:00 on 3 May to be installed at the Sheringham Shoal Offshore Wind Farm. The substations will channel the energy generated by the Sheringham Shoal Offshore Wind Farm to the onshore substation at Salle for distribution into the National Grid.
The Sheringham Shoal substations each weigh nearly 1000 tonnes and have dimensions of 30.5 m x 17.7 m x 16 m. They were loaded on to the barge Dina Launcher and towed to the Sheringham Shoal Field, about 40 miles off the Norwich Coast by the ocean going vessel Union Wrestler.
Heerema, Alstrom's subcontractor, constructed the offshore substations at its yard in Hartlepool in North East England. The complex logistics operation to transport them to the Sheringham Shoal site started in November 2010 when they were transferred from the fabrication hall to an outside location.
The operation to get the substations out of the Victoria quay and on to Dina Launcher, the barge which brought the substation to site, required careful planning and precise manoeuvring.
"The conditions were potentially difficult," reports John Short, barge engineer. "There was not only concern about the swells, which measured 2.5 metres, but also about the difference between high and low tides which average 4 metres in this area. The most challenging aspect was monitoring the barge to ensure that it didn't touch the bottom at low tide."
The hand-over took 30 minutes. "It was one of the best handovers I've ever seen," the experienced barge engineer comments.
The foundations for the substations were installed on the seabed during Autumn 2010 and the substations were lifted onto their individual foundations by the state-of-the-art crane vessel Oleg Strashnov, which has already been working on site. The first substation was installed at its location at 23:32 on 8 May, and the second substation was lifted onto its foundation at 14:20 two days later.
The Oleg Strashnov is ideally suited for this major operation; at 183 metres long and 47 metres wide, it can lift up to 5000 tons and can accommodate up to 395 personnel. "The operation was well prepared and everything went according to plan," says Erik Kringland, vessel representative on the Oleg Strashnov.
Statoil's oil and gas experience in offshore installations have been a major contribution to reducing risks in the operation - both in the planning process and also when it comes to the lifting performance.
"We've had a strong focus on safe installation together with our contractors. This co-operation has been essential for a successful result," says project director Elly Kristine Bjerknes.
The successful installation of the two substations is a key milestone in the project. However, this is only the beginning. There are many challenges ahead that require detailed planning and co-ordination, and progress is dependent on good weather conditions. In early summer, the main hook-up work and commissioning of the offshore substations will start and this is expected to continue throughout the coming months. Erection and commissioning of turbines will begin during the summer and continue through the remaining year and first quarter of 2012.
When completed, the Sheringham Shoal Offshore Wind Farm will generate 317MW of electricity, enough to power 220,000 domestic homes. This electricity will be distributed from these two offshore substations via the sea bed cables to landfall at the North Norfolk coastal village of Weybourne, and from there by underground cable to a new purpose-built substation at Salle, near Norwich, before entering the National Grid.
The Sheringham Shoal Offshore Wind Farm is owned equally by Statoil and Statkraft through the joint venture company Scira Offshore Energy Limited. Statoil is the operator for the project during the development phase. Scira will operate the wind farm once completed.
For further information contact: Sheringham Shoal Offshore Wind Farm Communications Manager, Elizabeth Hancock on mobile 07557 264326 or email firstname.lastname@example.org
Issue Date: 13-05-2011