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25. January 2019 | Site Reports

Environmentally friendly grid connection of offshore wind park clusters

To connect the offshore wind park clusters “Westlich
Adlergrund” and “Arkona See” in the Baltic Sea, the grid operator, 50Hertz, used the ege-com® Macroduct High-T.

For the ege-com® Macroduct High-T protective tube for high and extra-high voltage cables, trenchless installation using the horizontal directional drilling method was for a total length of 18.7 km. This way, the green energy supplied by the wind power plants and transmitted ashore results in a less severe impact on the environment.

Expanding and connecting the offshore wind parks is an important element which helps to make the energy revolution a success. In the framework of the Ostwind 1 project, two of the offshore wind parks from the cluster Westlich Adlergrund (CWA) were to be connected to the grid. This area is regarded as particularly suitable for erecting wind turbines. The grid operator and the client, 50Hertz, are the parties responsible for the realisation of the project.

To connect the offshore wind parks Wikinger and Arkona-Becken-Südost of the CWA, three approx. 90 km long submarine cables were to be installed which were placed in the floor of the Baltic Sea with the help of special ships. The onshore continuation of the 270 mm thick cables which weigh 130 kg per meter was performed via an empty conduit system beginning at a distance of approx. 400 m from the shoreline of the Greifswalder Bodden. Onshore, the cables were laid to the 50Hertz transformer station in Lubmin approx. 2.5 km away through an empty conduit system.

High and extra-high voltage cables are subject to increased temperature load. Against this background, the ege-com® Macroduct High-T PE was used for this project: a sheathed pipe made of polyethylene for high- and extra-high voltage cables of up to 380 kV. The sheathed pipe provides increased thermal stability thanks to the special PE-HD material, enabling it to withstand the high thermal stress in the long run. To minimise the impact on the environment resulting from the provision of the empty conduit system for the 220 kV cable, the pipes were installed applying the HDD (Horizontal Directional Drilling) method. Its high flexibility and unchanged behaviour at low temperatures predestines this pipe for trenchless installation. It is suitable for butt-welds able to withstand the high tension and bending stresses occurring in the context of the HDD procedure.

Onshore continuation

To continue the laying of the submarine cables onshore, the empty conduit system was installed applying the environmentally friendly horizontal flush-drilling method. Since the marked route crossed a nature reserve and the target pits were in the Greifswalder Bodden, particular environmental constraints had to be heeded. For example, any dumping of problematic substances into the waterway was to be avoided. At the seaside, six temporary sheet pile boxes were prepared as a target trench to catch the drill flushing fluids, approx. 400 m before the shoreline.

The ege-com® Macroduct High-T PE 800 x 58.5 mm was laid out in the area of Lubmin port and welded. Subsequently, the pipes were lowered into the water in the port and tugged to the
onshore connection hole by water. For these operations, Lubmin port needed to be closed temporarily. Hydraulic engineering was handled by Matthäi-Wasserbau GmbH. During the  insertion of the empty conduit to trench A, the protective tube needed to be held in place to prevent it from being misaligned by the wind and the waves. With a length of up to 700 m, the drillings for onshore continuation were the longest ones on the entire cable route.

Onshore route

The natural reserves in the areas also called for extended environmental protection measures onshore, e. g. the erection of screening walls and sound barriers for vulnerable bird species. The preparation and maintenance of the construction sites and its approaches as well as the general technical coordination was managed by Matthäi Bauunternehmen Westerstede.

From trench A, where the submarine cables terminate, the cables were conducted onshore as 3 single conductors. In view of this situation, three 250 x 22.7 mm protected pipes installed in a triangular network were used for the onshore transmission route. Their installation was also performed using the HDD method and they were guided via seven additional drilling operations to the Lubmin transformer station approx. 2.5 km away. The drilling operations on the onshore route, which totalled 42 (six cable routes involving 7 individual drilling operations each) were performed by Beermann Bohrtechnik GmbH.

In the meantime, the first submarine cable of the East Wind 1 project has arrived safely in Lubmin. The cable was inserted into the 700 m long ege-com® Macroduct High-T PE pipe with
the help of a heavy-duty winch which had been installed in trench A.

Project data

Project description: Establishment of grid connection of offshore wind power plants to the clusters “Westlich Adlergrund” and “Arkona See”.
Challenges: Installation of an empty conduit system for a 220 kV cable using the horizontal directional drilling method.
Solution: Use of ege-com® Macroduct High-T made of special PE-HD for enhanced thermal stability
Installation: Trenchless installation with the help of horizontal directional drilling
Pipe System: • 3.960 m ege-com® Macroduct High-T PE 800×58,8 mm
• 44.300 m ege-com® Macroduct High-T PE 250×22,7 mmincluding fittings
Parties involved in the project: Client: 50Hertz Offshore GmbH
Construction: ARGE HDD Lubmin
(Matthäi / Matthäi Wasserbau / Beermann)
Bore: Firma Beermann Bohrtechnik GmbH
Professional welding work: TIAS Tiesler Tief und Hochbau GmbH

Contact

Timo Mücke
Beermann Bohrtechnik GmbH
Tel. +49 5454 930525
Timo.Muecke@beermann.de 
Dipl.-Ing. Fabian Reiter
Product Management Cable Protection Systems
Tel. +49 2575 9710 432
fabian.reiter@egeplast.de

 

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