• Alpha Ventus Transformer Station
• Container Terminal CT IV
• Container Terminal Gdansk

Alpha Ventus Transformer Station

Client: Deutsche Offshore-Testfeld und Infrastruktur GmbH & Co. KG (cooperative              venture of EWE AG, E.ON Climate & Renewables GmbH and Vattenfall Europe              Energy GmbH)

Implementation: HOCHTIEF Construction AG Civil Engineering and Marine Works
                               (as technical leader in joint venture)

Dates work carried out: Jan 2008 - Sept 2008

With the alpha ventus project Germany started a new era of wind energy use. At a water depth of 30 metres a transformer station and twelve wind energy stations had to be installed under offshore conditions. With a total output of 60 megawatts the alpha ventus offshore wind farm can supply 50,000 households with energy. The designing, building and network integration of the wind farm provides vital experience with regard to the future commercial use of offshore wind energy stations; this is a reference project in every respect.

HOCHTIEF Construction Civil Engineering and Marine Works (CEM) was awarded the contract in a joint venture to produce and build the offshore transformer station. As well as being responsible for the steel construction, we were responsible for the planning and implementation of the offshore assembly.

With its own office for offshor projects, HOCHTIEF Construction CEM can draw upon many years of offshore experience, gained for example with the Messmast Amrumbank and Lillgrund offshore wind farm projects. We also have our own technical equipment for the offshore sector. Our Odin jack-up platform has been used as a secure platform for building the transformer station.

Odin was also used when the pile foundations were laid for the tripods for the wind energy stations off Borkum.

The transformer station is the logistical centre of the wind farm. Here is where the power cables for the wind energy stations converge. The electricity is transferred to the transformer station at a voltage of 110 kilovolts and fed to the mainland by submarine cable.

The design of the transformer station consists of three elements. The so-called “jacket” is a steel-framed foundation which is around 45 metres tall and weighs 580 tonnes. A further module is the “topside”, which is around 15 metres tall and houses the electrotechnical units (such as the transformer). The jacket is anchored 30 metres into the seabed by four 42-metre-long piles each weighing 110 tonnes.

The schedule was ambitious; the construction project was completed from planning to installation in only nine months and handed over on time to the operator of the farm. Besides the hig requirements concerning the quality of the steel construction and corrosion protection, the particular challenges lay in the extensive logistics involved in assembly at sea. The individual elements were transported from three ports in Northern Europe by floating crane to the construction site and installed by HOCHTIEF using its own Odin jack-up platform.