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

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To the north of the Maasvlakte, TenneT is building the Hollandse Kust (zuid) offshore grid  to connect new offshore wind farms. Four cables will have to be buried into the North Sea seabed for this purpose. For the first ten kilometres of the cable route at sea, these cables will have to be buried more than 5,5 meters into the seabed in order to cross the busy shipping route  Rotterdam Maasmond. The installation of the cables started on September 22nd  by pulling the cable ashore. The Deep Dig-It trencher crossed the Rotterdam Maasmond successfully and is on its way to the recently installed offshore Alpha jacket in the Hollandse Kust (zuid) wind farm area. 

The Van Oord/Hellenic Cable 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 contractor combination Van Oord - Hellenic Cables. For this purpose, Van Oord has specially developed 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. The trencher weighs 125,000 kilos, is over 17 meters long, more than 8 meters high, and 11 meters wide. The Deep Dig-It is very powerful, comparable to no less than two Leopard tanks (2,500 hp) and can bury cables more than 5,5 meters 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.

Project net op zee Hollandse Kust (zuid)
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 wind energy is then fed into the national high-voltage grid to the electricity consumers in the Netherlands.

In 2018, TenneT commissioned the Van Oord-Hellenic Cables consortium to build the offshore connection for the net op zee Hollandse Kust (zuid) project. The consortium will install and bury the sea cables that cross the entrance to Europe's busiest freight port, the port of Rotterdam. 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 realized.

Offshore wind until 2030
After Hollandse Kust (zuid) Alpha and Beta the next project of the offshore grid will be the connection of Hollande Kust (noord). TenneT uses the same type of 700 MW transformer platform five times for the grid connection. The platforms are located close to the offshore wind farms. The offshore cable is also five times the same type of 220kV cable connection. This standardization enables TenneT to build these projects more efficiently, faster and cost effectively. TenneT will realize another 6.1 GW of high-voltage connections for wind farms in the Dutch North Sea until 2030. In the German North Sea TenneT has already realized 7.1 GW and the capacity of TenneT's offshore grid connections in Germany will be increased to approximately 17 GW in 2030.

About Van Oord
Van Oord is a Dutch family-owned company with 150 years of experience as an international marine contractor. The focus is on dredging, oil & gas infrastructure and offshore wind. Its head office is in Rotterdam. Van Oord employs 5,000 staff, who worked in 2018 on 190 projects in 46 countries. The fleet consists of more than one hundred vessels. Marine ingenuity is characteristic of Van Oord. By using innovative, smart and sustainable solutions, it wishes to contribute to a better world for future generations.

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Jorrit de Jong

Media Relations

+31 026 373 26 00


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