Isle of Grain UK BritNed - Cable Landfall

BritNed, a joint venture between National Grid and TenneT, has constructed a subsea electricity link between Great Britain and the Netherlands. The BritNed cables have a capacity of 1000MW and a length of 260 kilometres. The link has been 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.

Facts and figures

Interconnector Cable
Two high-voltage direct-current (HVDC) submarine cables
Equipment
Multipurpose pontoon Fetsy L, Transport pontoon Stemat 81, Linkflote pontoons, Winch 20 tons
Project categories

ABB High Voltage Cables AB was awarded the contract to supply and install an HVDC power cable link. The interconnector link consists of two high-voltage direct-current (HVDC) submarine cables designed to transmit bi-directional electrical power across the North Sea.

 ABB subcontracted VBMS to perform the required landfall and nearshore works at the Isle of Grain in Kent in the United Kingdom in the summer of 2010.

 The scope of work was as follows: 

  • Engineering of the landfall;
  • Design and building of special tools and equipment;
  • Coordination between offshore and onshore operations;
  • Installation of two PE flood bank crossings by HDD;
  • Design, mobilisation and demobilisation of Cable Lay Spread;
  • Design, mobilisation and demobilisation of Cable Pulling Spread;
  • Collection of two 4,200 metre HVDC cables (44kg/m) from Karlskrona, Sweden;
  • Pre-excavation and backfill, offshore on the mudflats in the Thames Estuary, of 800 metres of trench through the London clays;
  • Supply and install of two 4000 metre HVDC cables on the mudflats, pre-excavated trench and sea bed;
  • Burial of HVDC cables on the mudflat;
  • Filling of HDD ducts with cable grout.

 

The challenge of this project was the extremely soft and extensive (1000-metre) mudflat in the Thames Estuary, offshore of the Isle of Grain. To tackle this problem, VBMS's Engineering Team developed a special installation method using shallow draft vessels which could be beached at low tide.

For the collection and storage of the two HDVC cables, a special pontoon was mobilised in Rotterdam. After a round-trip of 2,750 sea miles, during which two large (8-metre) cable reels were collected in Peterhead (Scotland), the cables collected in Karlskrona (Sweden) and then installed offshore of the Isle of Grain (Kent, UK) and the reels subsequently returned to Peterhead, the pontoon arrived back in Rotterdam for demobilisation. For positioning and accommodation, the VolkerWessels-owned multipurpose barge, Fetsy-L was used. On the mudflat VolkerBrooks linkflote pontoons were deployed for excavation. The VBMS-owned 20-ton pulling winch was used to pull in the HVDC cables to the joint bay on land.

 

Thanks to close co-operation between all inter-company and external parties, the nearshore cable works were completed to the satisfaction of ABB.

 

Project location

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