Thanet’s 1,250-tonne offshore electrical substation was in position by mid-February, and electrical contractor Siemens is now finishing off the remaining mechanical and electrical work, says Ole Bigum Nielsen, Vattenfall’s Head of UK Offshore Projects and Project Director for Thanet.
The substation is a key part of the project, so there was concern late last year when the supplier, UK firm SLP Engineering, went into administration. But by this point the substation was 90 percent complete and the project team was able to bring it back on track, Nielsen says. The Thanet substation uses two transformers to step up the voltage from the 33 kV produced by the wind turbines to the 132 kV required by the grid. Siting substations offshore reduces power distribution losses and is becoming increasingly common as offshore wind power projects grow larger and move further out to sea.
“This is by no means the first substation offshore,” says Nielsen. “In fact, back in 2002 the world’s first large offshore wind farm [Horns Rev 1] had an offshore substation.” Since then, he says, many substations have been sited onshore for cost reasons, one example being the neighbouring 90 MW Kentish Flats project. “But when you go up to 100 turbines, as at Thanet, you definitely need an offshore substation – and there are only a few companies who can supply them.”
The Thanet substation is a three-deck structure looking rather like a miniature offshore oil or gas platform. The “topsides” housing the electrical equipment sits on a supporting “jacket” supplied by UK firm McNulty Offshore Construction. Poor winter weather was more of a problem for cable laying than for the installation of the turbines themselves, says Nielsen. As a result, energisation of the first turbines has been delayed by two months, but final completion of the project is still on schedule for October.