Bi-national electricity transmission facility
The North Sea Link (NSL) is a new interconnector that will enable a bi-directional flow of renewable electricity between the UK and Norway. Construction on the project commenced in March 2015 and the new interconnector is scheduled to be online in 2021.
The project is being developed jointly by National Grid North Sea Link, a wholly owned subsidiary of National Grid, and Statnett, the Norwegian power grid developer and operator. The project will enable the UK to import hydropower from Norway and enable the latter to import wind power from the former.
The NSL project involves the installation of 720km of subsea cables, 10km of onshore cables, and construction of a converter station at both ends. The interconnector is touted to become the longest facility of its kind.
The overall investment in the project is estimated to be €2bn ($2.2bn). As part of the European Commission’s Projects of Common Interest (PCIs), the project received a €31m ($34m approximately) grant to support the early-stage engineering studies.
The interconnector will stretch from Blyth in Northumberland, UK, to Kvilldal in Rogaland, Norway. The twin subsea cables will be laid at a water depth of approximately 600m and will be buried at depths ranging from one metre to three metres into the seabed. The cables will operate at a voltage level of ±525kV with a rating of 1,400MW.
In the UK, the project will involve the excavation of a transition joint pit (TJP) at Cambois, south of the River Wansbeck, through which the subsea cables will be connected to the HVDC onshore underground cables.
The converter station will cover an area of approximately 5ha near Brock Lane in East Sleekburn. The converter station and ancillary buildings will be constructed with steel frames and clad with metal. The buildings will rise to a height of not more than 25m.
The converter station will be connected to the new gas-insulated switchgear (GIS) substation, proposed to be built and operated by National Grid Electricity Transmission (NGET), via six 400kV HVAC cables. The GIS substation is proposed to be constructed adjacent to the existing Blyth substation.
The onshore cable in Norway will pass through a micro tunnel and a conventional tunnel from Hylsfjorden to lake Suldalsvatnet. It will then be submerged across Suldalsvatnet and further be placed in a trench stretching from the shoreline to the converter station, located adjacent to an existing hydropower plant in Kvilldal.
The converter station will be connected to the national grid using existing facilities, which will require minor upgrades and modifications.
Prysmian has been contracted to supply and install 950km of mass impregnated (MI) paper insulation HVDC submarine and land cables, which will be manufactured from its Arco Felice factory in Naples, Italy.
Nexans will supply and install approximately 500km of mass impregnated non-draining (MIND) HVDC cables for installation in the fjord, tunnel and lake sections, as well as the onshore section in Norway.
The subsea cables to be laid by Nexans will be supplied from its Halden plant in Norway. The cables will be protected on the seabed by trenching using its Capjet system and rock dumping.
ABB has been contracted to supply the two ±525kV, 1,400MW converter stations, which will integrate its proprietary HVDC Light voltage source converter (VSC) technology.
Prysmian will install the cables deploying its cable-laying vessel Giulio Verne, whereas Nexans will install the cables deploying its cable-laying vessel C/S Nexans Skagerrak.
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