Cable installation offshore wind farms Hollandse Kust (noord) and (west Alpha), the Netherlands
To connect the Dutch offshore wind farms Hollandse Kust (noord) and (west Alpha) with the electric grid on the mainland, TenneT called on the consortium Jan De Nul Group and LS Cable & System. Jan De Nul Group was responsible for the transport, installation and protection of the electricity cables. LS Cable & System took care of cable design and production, as well as connection and testing of circuits.
Both wind farms were connected to a transformer platform by two 220 kV high voltage cables. In total, four cables, with a total length of 210 km, establish the connection with the Dutch electric grid near Beverwijk, just north of the port of IJmuiden. With a production capacity of 1.4 GW, these wind farms supply 1.4 million households for a whole year with green power.
To ensure the success of this challenging project, Jan De Nul deployed a multifunctional fleet of in-house cable installation equipment.
Our cable-laying vessels Isaac Newton and Connector brought the 210 km cables in three trips from South Korea to Wijk aan Zee and installed them on the seabed. This was first levelled by our amphibious crane Starfish and our trailing suction hopper dredger Alexander von Humboldt.
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. The long sword of the Moonfish is fitted with powerful waterjets. The Moonfish uses these to make a deep trench in the seabed, in which the cable is laid at the same time up to an 8-metre depth. The trench is backfilled immediately. As a result, the cables are properly protected against possible future coastal erosion.
Jan De Nul designed and built this innovative machine entirely and specifically for the Hollandse Kust (noord) and (west Alpha) project.
Moonfish in numbers
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The teams of our colleagues Dries Poelman (Works Manager) and Arne Baeyens (Project Engineer) worked closely together for 1.5 year to make this machine. In the video below, they present the Moonfish.
Once our cable-laying vessels connected the cable with the Hollandse Kust (noord) and (west Alpha) offshore platforms, the submarine vehicle UTV1200 took over from the Moonfish. This machine 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.
Ward Mertens (Project Manager Hollandse Kust (noord) and (west Alpha))