Van Oord’s Deep Dig-It trencher buries cables to 5,5 metres depth for offshore grid connection

September 24, 2020

Van Oord’s Deep Dig-It trencher crossed the busy shipping route Rotterdam Maasmond successfully and is on its way to offshore Alpha jacket in the Hollandse Kust (zuid) wind farm area. TenneT is building the Hollandse Kust (zuid) offshore grid to connect new offshore wind farms. 4 cables will have to be buried into the North Sea seabed for this purpose. For the first 10 kilometres of the cable route, these cables will have to be buried more than 5 metres into the seabed in order to cross the busy shipping route Rotterdam Maasmond.

The Van Oord-Hellenic Cables consortium will be installing 4 subsea 220 kV AC cables that will connect 2 offshore platforms to the onshore electricity grid. The first 2 cables to the Alpha platform will be installed this year. The other 2 cables, meant for the Beta platform, will follow in 2021. The last few days the preparatory work has been completed. The cable was pulled ashore via a direct drill to the new transformer substation that is being built on the Maasvlakte. From this point, the cable with a total length of 42 kilometres to the wind zone Hollandse Kust (zuid) will be laid by the Deep Dig-It, a large remote-controlled trencher.

Deep Dig-It

Van Oord’s Deep Dig-It is a so-called ‘Tracked Remotely Operated Vehicle’ (TROV) that drives unmanned over the seabed and creates a deep trench for the cables by liquefying the seabed. At the same time, the trencher inserts the cables into the trench and seals them again into the seabed. This new trencher is one of the largest and most powerful of its kind and can bury cables more than 5 metres deep in very hard soil. The Deep Dig-It is controlled at Van Oord’s offshore installation vessel MPI Adventure, which is also equipped with a crane to launch and take out the Deep Dig-It.

Hollandse Kust (South) grid connection

The Hollandse Kust (zuid) offshore wind farm is located 22 kilometres off the coast of the Dutch province of Zuid-Holland. The sea cables connect the two offshore platforms with the Maasvlakte high-voltage substation and the Randstad 380 kV South ring.

The 1,400 MW grid connection will be completed in 2022 and will eventually provide electricity for 1.6 million households. The offshore wind farm contributes significantly to the Dutch government’s objective of having a total of 3.5 GW installed offshore wind energy capacity by 2023. With the commissioning of Borssele Alpha and Beta this year, the first 1.4 GW has been realised.