Levelling wind turbines in which the turbine foundations come in two parts: a monopile (MP) and a transition piece (TP).
The Dudgeon Offshore Windfarm will be constructed off the coast of Norfolk, East England. The wind farm comprises of 67 monopile foundations on which 6 MW capacity turbines will be placed. The project is a joint venture from Statoil (70%) and Statkraft (30%).
The foundations are formed by two large steel structures: a monopile (MP) that is driven into the seabed, and a transition piece (TP) that is fitted on top of the MP. Six to twelve pre-installed hydraulic cylinders inside the TP make it possible to align the TP - which weighs over 300 tons - to a precise position, even if the MP was not completely levelled out in the first place. This ensures that the turbine will generate maximum yield. Another pole - holding the actual turbine - is then positioned on top of the foundation. In their full glory, the wind turbines rotate approximately 60 metres above sea level. The complete constructions need to be able to stand the heavy conditions at sea.
For the precise levelling of the TP on the foundation pile, Holmatro supplied 408 aluminium spring return cylinders, each with a capacity of 220 tons and a stroke length of 150 mm.
Holmatro have already developed and delivered hydraulic cylinders for the creation of offshore wind parks; such as Belwind in the North Sea off the Belgian coast, and the British projects Walney and London Array. The space available for the positioning of cylinders inside a TP is very limited. Holmatro’s cylinders have such a large lifting capacity - the maximum operating pressure is 720 bar - that this type of relatively small and compact cylinder can be used to jointly do the job. They are easy to use and corrosion-resistant, which makes them ideal for offshore applications.