Van Oord’s underwater robot ‘Deep Dig-It’ successfully crossed the Rotterdam Maasmond last Tuesday with the third cable for the grid connection Hollandse Kust (zuid). The underwater robot is now on its way to the recently installed Beta jacket in the Hollandse Kust (zuid) wind area.
At approximately 18 km off the coast of the province of Zuid-Holland, energy company Vattenfall is building the 1.5 GW Hollandse Kust Zuid offshore wind farm with 140 Siemens Gamesa 11 MW wind turbines. Grid operator TenneT is responsible for the offshore grid connection. This grid connection Hollandse Kust (zuid) consists of two of TenneT’s standard 700 MW transformer substations (Hollandse Kust (zuid) Alpha and Beta). The jacket foundation for each offshore substation has already been placed. From each station, the power generated by the wind turbines will be transported to land via two 220 kV alternating current cables.
Van Oord-Hellenic Cables
The Van Oord – Hellenic Cables consortium has been contracted by TenneT to realise the connection. The four offshore (export) cables will be buried in the North Sea bed. For the first ten kilometres of the offshore cable route, these cables will be sunk 5.5 metres into the seabed to cross the busy Rotterdam “Maasmond”. The connection to the Hollandse Kust (zuid) Alpha transformer station was completed in September 2020. The cable interlinking the two offshore transformer stations has also been completed. The consortium is now working on the connection to the Hollandse Kust (zuid) Beta offshore station.
The preparatory work was completed during the past few days. The cable that will be installed to the Beta jacket has been pulled ashore through the jackets to the newly built onshore transformer station on the Maasvlakte. Now, the consortium combination will lay the cable with a total length of 34 kilometres to the wind area Hollandse Kust (zuid). Van Oord developed the Deep Dig-It, a gigantic, remote-controlled underwater trencher, especially for this project.
Deep Dig-It underwater robot
Van Oord’s Deep Dig-It is a Tracked Remotely Operated Vehicle (TROV) that travels on the seabed unmanned, making a deep trench for the cables by liquefying the seabed. At the same time, this underwater trencher lays the cables in the trench and closes it. The Beta cables weigh approximately 100 kilograms per metre and consist of three cores. These three cores are made of aluminium and the cable has a diameter of 30 centimetres. Both cables were loaded onto spools on the cable vessel “Living Stone”. This cable vessel runs on liquid gas (LNG), which reduces emissions. The installation of the 34 kilometres of cable route will take about four weeks and is expected to be completed by mid-September.
The topside for the Alpha station will be installed at the end of this year. The topside for the Beta station is expected to follow early next year. Once the topsides are lifted onto the jackets, the last systems will be connected, tested and put into operation. TenneT has built a new high voltage substation and is expanding the high-voltage ‘Maasvlakte 380 kV’ substation. From this high-voltage substation, offshore wind energy will be fed into TenneT’s Randstad 380 kV South ring. The wind farm is expected to be fully operational in 2023. Source: TenneT