The German wind farm, Baltic 2 (formerly known as Kriegers Flak), is situated in the Baltic Sea approx. 32 km north of the island of Rügen. 80 wind turbines, with a capacity of 288 MW, covers an area of 27 square kilometres. Some 340,000 households will ultimately receive electricity from the wind farm. The VBMS-Boka joint-venture was responsible for installing the 150 kV Export Cable.
The export cable was installed between the respective offshore substations of Baltic 1 and Baltic 2. The cable length was approximately 57 km, and crosses the shipping lane and the Baltica telecom cable. The target burial depth was 3 m. The soil conditions en route vary from sandy silt and mud to glacial till. The cable was installed in four sections of approx. 15 km each and connected by means of joints.
The contracted work consisted of the following:
The cables were laid and buried simultaneously by the Ndurance cable-laying vessel. The subtrench 2 trenching tool was responsible for burying the 235mm cable. This trenching tool can be operated in both jetting and cutting mode. The first two sections of cable were installed from the platform Baltic 1 in the direction of Baltic 2. The other two sections were installed from Baltic 2 in the direction of Baltic 1. An omega joint was used to connect the two parts. The Ndurance, a DP2 vessel, has a turntable with a 5,000 ton capacity and a 70 t A-frame. The Subtrench is a state-of-the-art trenching tool which can generate up to 11 bar at a flow-rate of 1600 m3/hr. The jointing operation proved to be another challenge, with cables being joined at three locations. The inline joints were installed on the Ndurance during cable-laying, with the omega joint being installed when the last section was laid.
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