Transformer platform for offshore wind farm Sandbank goes to sea

Wednesday, 4 May, 2016 - 10:30
A 2,400-tonne giant takes a sea journey: the substation and jacket foundation for the offshore wind farm sandbank on their way to the construction site in the North Sea. (Photo: Vattenfall)
A 2,400-tonne giant takes a sea journey: the substation and jacket foundation for the offshore wind farm sandbank on their way to the construction site in the North Sea. (Photo: Vattenfall)

After approximately 16 months of construction work, the transformer substation for the offshore wind farm Sandbank is now on its way to the construction site 90 kilometres west of Sylt in the German North Sea.

The substation is the single largest technical component to be installed at the offshore wind farm Sandbank. The substation, which is approximately 20 metres high and has a footprint of 20 x 40 metres, will be accompanied by a steel jacket substructure 51 metres high and weighing 1,700 tonnes. It will serve the substation as a foundation at its installation site in the North Sea. The substation and the jacket foundation together are more than 70 metres high. The substation had previously been transported from Aalborg in Denmark, where it was manufactured, to Esbjerg.

When the substation begins normal operation, it will collect the wind power generated by all 72 wind turbines, ramp it up from an AC voltage of 33 kV to 155 kV and then pass it to a converter station. From there, the power will be transmitted as direct current over a distance of 165 kilometres to the landfall site in Büsum in northern Germany.

The substation will be positioned at sea in water 28 metres deep by the installation vessel Stanislav Yudin. More than 100 people are involved in the construction work at sea. Martin Zappe, the project manager at Vattenfall, said: "The offshore transformer station we are building in the middle of the North Sea has the dimensions of a 15-story office building. When the 2,400-tonne topside is hanging on the crane hook, it will be the heaviest crane lift of the entire project. Preparations began some time ago and were simulated during a special workshop with all relevant partners to increase the safety of those involved in construction."

Status of the Sandbank project

Work is currently in progress on the cabling within the wind farm at the construction site. Production of the nacelles, hubs and blades for the wind turbines will begin shortly. The foundations for the wind turbines were already completed in mid-February. Seventy-two 4-MW wind turbines from Siemens with an overall capacity of 288 MW will be installed.

Sandbank is scheduled to be operational in 2017. Vattenfall and Stadtwerke München (SMW) will then have a combined portfolio of 576 MW installed wind power, placing them among the largest operators of wind power plants in Germany. The total investment volume for the offshore wind farm Sandbank is approximately € 1.2 billion. Vattenfall has a 51% stake and SWM 49% in Sandbank Offshore Wind GmbH, which was founded to carry out the project.

Silke Funke / Vattenfall

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