Underwater robot lays sea cables at Port of Rotteram to connect wind farms at sea

TenneT is building the Hollandse Kust (zuid) offshore grid north of the Maasvlakte to connect new wind farms. For this, four cables must be buried in the North Sea bed.

For the first ten kilometers of the cable route at sea, these cables have to go 5.5 meters into the seabed to cross the busy Rotterdam Maas estuary. The installation of the cables began on September 22 with the cable being pulled ashore. The underwater robot ‘Deep Dig-It’ has successfully crossed the Rotterdam Maas estuary and is now on its way to the recently installed Alpha jacket in the Hollandse Kust (south) wind area.

The cable consortium will install the first two cables to the Alpha platform this year. The other two cables, for the Beta platform, will follow in 2021. The preparatory work has been completed in recent days.

The cable was pulled ashore with controlled drilling to the newly built transformer station on the Maasvlakte. From there, the cable with a total length of 42 kilometers to the Hollandse Kust (south) wind area will be laid.

Deep Dig-It is a so-called “Tracked Remotely Operated Vehicle”(TROV) which drives unmanned on the seabed and makes a deep trench for the cables by liquefying the seabed.

At the same time, this underwater excavator puts the cables in the trench and closes it again. This new trencher is one of the largest and most powerful of its kind. The trencher weighs 125,000 kilos, is over 17 meters long, more than 8 meters high and 11 meters wide.

The Deep Dig-It has enormous power, comparable to no less than two Leopard tanks (2,500 hp) and can therefore bury the cables to a depth of more than 5.5 meters in very hard ground.

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

The 1,400 MW high-voltage connection will be completed in 2022 and the wind farms will eventually provide enough electricity for the annual consumption of 1.6 million households.

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