Subsea cables for Hollandse Kust Noord, the Netherlands
Power sockets at sea
To connect these Dutch offshore wind farms with the electric grid on the mainland, our client TenneT builds transformer platforms offshore. In other words: power sockets at sea. Our job is to connect these power sockets with the mainland. To get there, we transported, installed and protected four power cables with a total length of 210 km.
Ward Mertens, Project Manager Hollandse Kust Noord and West Alpha:
This project was truly a pioneering project for Jan De Nul, as we became the first contractor in the cable industry, able to bury cables at depths of up to 8 metres under the seabed in the nearshore and inter-tidal area. Moreover, we deployed an enormous amount of work, ingenuity, knowledge and strong cooperation between all stakeholders and managed to achieve this project safely and on time.
Hollandse kust Noord and Alpha-West in numbers
Did you know?
- We designed and built our cable trenching machine ‘Moonfish’ especially for this project, to protect the cables against coastal erosion.
- The final 3 kilometers to shore, the cables were dug in 6 to 8 metres below the seabed.
- Our cable-laying vessels Isaac Newton and Connector brought the 210 km cables in three trips from South Korea to the Netherlands.
The project in detail
Before installing the cables, we first levelled the seabed. Meanwhile, our foundations expert subsidiary, Soetaert, installed four cofferdams on the beach. Thanks to these cofferdams, we were able to bury the cables seven metres down in the sand and, from there, pull them through the dunes via ducts installed by directional drilling to the onshore transition joint. After this beach pull-in, it was our cable trenching machine Moonfish’s turn. The Moonfish buried the cables from the beach 3 kilometres into the sea, at a depth of about 6 to 8 metres below the seabed. As a result, the cables are properly protected against coastal erosion.
Once our cable-laying vessels connected the cable with the offshore power sockets, we buried the cables from 3 kilometres off the coast to the offshore transformer stations, respectively 22.5 and 55 km off the Dutch coast. Finally, our multi-purpose vessel Adhémar de Saint-Venant installed cable protection systems and rocks on the crossing points between different existing cables and pipelines.
