WATCH: Jan De Nul to carry out ‘industry’s first’ simultaneous multi-cable installation for TenneT

Belgian offshore contractor Jan De Nul plans to install three subsea power cables and a fiber optic cable simultaneously on several upcoming offshore grid connection projects for TenneT, introducing what the company describes as an industry-first installation approach.

The work relates to the BalWin4, LanWin1, LanWin5 and BalWin5 grid connection projects in the German North Sea. Jan De Nul will begin the first of the four subsea cable projects this summer.

Across the four projects, around 2,000 kilometers of cable will be transported, installed and protected to connect future offshore wind farms to the onshore grid.  

According to information published by Jan De Nul, the projects will see three power cables and a fiber optic cable installed simultaneously on the seabed, which has not been done before in the offshore cable installation sector. Part of the installation work will take place in the environmentally sensitive Wadden Sea, where shallow water depths and intertidal conditions require specialized installation methods and equipment.  

To carry out the work in the Wadden Sea, the contractor built a dedicated cable-laying barge platform, named Waadrinner, consisting of three interconnected pontoons, each fitted with a cable carousel. The pontoons can operate together as a single installation platform, allowing the cables to be laid simultaneously over a section of around six kilometres while keeping equipment lightweight to minimize seabed pressure in the shallow environment.  

The company also upgraded its cable burial machine Sunfish to bury three power cables and a fiber optic cable at the same time. The system uses high-frequency vibrations to install the cables into the seabed, a technique described as less invasive than conventional cutting or high-pressure jetting methods.

After the nearshore installation phase scheduled for 2026, the offshore sections in deeper North Sea waters are planned to be installed from 2027 using Jan De Nul’s cable-laying vessels Fleeming Jenkin and William Thomson.  

The projects are part of a long-term framework agreement between TenneT and a consortium consisting of Jan De Nul, LS Cable & System and Denys, signed in 2023.

Under the agreement, the consortium was awarded contracts covering the design, manufacturing, transport, installation, protection and testing of 525 kV HVDC cable systems for the BalWin4, LanWin1, and LanWin5 grid connections in 2023, and received a letter of allocation (LOA) from TenneT for the supply of high-voltage direct current (HVDC) cables for the BalWin5 grid connection project in 2024.

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