HV Riffgat Offshore Project

Riffgat, Germany

Turnkey solution including planning, material production, installation and testing for a wind farm in the German North Sea - 51 km total length

Key Facts

Client

TenneT Offshore GmbH

Total cable route length

48 km

Location of the project

North Sea, Germany

Duration

2011 - 2014

Quantity of order

A turnkey 155 kV HVAC cable system solution with a 108 MW power rating

Scope

  • Cable system including 51 km of 155 kV export submarine cable and offshore joints
  • Design and engineering
  • Planning and project management
  • Cable-laying and installation
  • Final testing
HV Riffgat Offshore Project
HV Offshore Cable for Riffgat Project

The project

The Borkum Riffgat offshore wind farm needed an efficient link to the German electricity grid.

The wind farm is situated 15 km northwest of the island of Borkum and consists of 30 wind turbines. These turbines have a total capacity of 108 MW (megawatts), which is enough to provide clean energy for around 120,000 households.

NKT was selected by the transmission system operator TenneT to implement the connection. The export cable route runs from the wind farm through the Osterems (the eastern estuary of the river Ems) and to the landing point on the German mainland at Pilsum. This meant dealing with a range of challenges arising as a result of the varying environments where work had to take place.

Working in tidal areas requires particular consideration with regards to safety and emergency planning, and special attention was needed for operations involving the transition from offshore cable-laying on the seabed to onshore underground cable-laying via horizontal drilling.

Part of the cable route runs through the UNESCO world heritage and environmental protection areas in the Wadden Sea National Park. Additionally, the cable route had, prior to the involvement of NKT, been planned to cross a World War II ammunition dumping site.

These factors demanded a high level of expertise and specialised methods.

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The solution

We delivered a complete turnkey solution for the entire export cable system project.

Our scope included planning, project management, engineering, manufacturing and installation, including final testing. We delivered all the materials and high-voltage accessories, with 51 km of 155 kV export cable being produced at our state-of-the-art factory in Cologne.

All installations, both onshore and offshore, were executed by our installation teams together with our partners in all marine works involved in this project, marine specialists Bohlen & Doyen.

Tidal mud flats make it difficult to move personnel, materials and equipment between sea and shore at low tide. We built wooden walkways to enable free movement regardless of tide levels.

A substantial number of explosive objects were detected in the ammunition dumping site. Together with Bohlen & Doyen, we developed special processes to allow operations to continue in safety. Professional input from all involved parties was utilised to identify the best procedures for ensuring the job could be performed safely.

With the final high-voltage test, we demonstrated that we had successfully completed the work. The particular challenges gave us an opportunity to show that we are able to handle large, complex and challenging turnkey projects with professionalism and total dedication.

“Our solution included everything from manufacturing and cable-laying through to final testing.”

HV Riffgat Offshore Project

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