BritNed, a joint venture between National Grid and TenneT, is developing a subsea electricity link between Great Britain and The Netherlands. The BritNed cables have a capacity of 1000 MW and are 260 km long. The link is laid beneath the North Sea and runs between the Isle of Grain in Kent in the UK and the Maasvlakte, near Rotterdam, in The Netherlands.
ABB High Voltage Cables AB is contracted to supply and install a HVDC power cable link. The interconnector link consists of two high voltage direct current (HVDC) submarine cables designed to transmit bidirectional electrical power across the North Sea.
ABB is subcontracting Visser & Smit Hanab to perform the required landfall and near shore works n the summer of 2009 at the Maasvlakte in The Netherlands.
The scope of work consists of the following:
● Engineering the landfall;
● Designing and building Special Tools;
● Coordinating between offshore and onshore;
● Installing two PE dune/beach crossings with Horizontal Directional Drilling;
● Extending PE pipes 300 meters into the sea;
● Designing, mobilising and demobilising the Separation Pontoon;
● Floating HVDC cables in from the Cable Lay Vessel "Team Oman" to the Separation Pontoon;
● Pulling HVDC cables in from the Separation Pontoon into the joint bay;
● Accurately placing cables 20 meters apart on the seabed;
● Burying HVDC cables in the shallow water section;
● Filling the HDD ducts with cable grout.
The Visser & Smit Hanab-owned, 30 ton pulling winch is used to pull in the HVDC cables to the Separation Pontoon and the two 40 ton winches are used to simultaneously pull both HVDC cables, in two 900 meter long ducts, to the joint bay on land.
Construction of the Maasvlakte port extension is the complicating factor, as this causes changing water depths, sedimentation and strong tidal currents. To allow for these conditions Visser & Smit Hanab's Engineering Team is developing special tools such as over-boarding structures and cable push frame for an anchor handling vessel.
Another challenge is the required 20 meter space between the cables under the future landreclamation area of Maasvlakte II right out to 600 meters offshore. From this point on the cables are bundled and placed on the seabed, upto the CLV "Team Oman".
Visser & Smit Hanab is also contracted to subsequently bury the cables from the shoreline to 10 meters water depth, up to 3000 meters off the coast.
Thanks to close co-operation between all inter-company and external parties, the near shore cable works are completed to the satisfaction of ABB.