The North Sea Link Interconnector project involves the construction of the world’s longest subsea high-voltage direct current (HVDC) transmission line between Norway and the United Kingdom.

The project is being developed by North Sea Link, a 50:50 joint venture of UK’s National Grid, and the Norwegian transmission system operator Statnett.

The project involves laying two parallel HVDC cables between Kvilldal in Rogaland, Norway, and Blyth in the UK. The length of the subsea route of the interconnector is approximately 720km. The transmission capacity of the interconnector will be 1.4GW at a voltage level of ±525kV.

Estimated to cost approximately £1.43bn ($2.22bn), the NSL project will be the first direct transmission line between Norway and the UK.

Scheduled to commence operations in 2021, the cross-border interconnector will facilitate the integration of renewable energy and enable grid stabilisation in Norway and the UK.

The North Sea Link Interconnector project development

The interconnector project development includes the laying of two parallel HVDC cables both onshore and offshore and the building of two converter stations. The converter stations are located at Cambois in Northumberland County, UK, and Kvilldal, Norway. The Cambois converter station received seven electrical transformers in March 2020.

The cable laying work in the UK part of the project was started in 2018, while that in the Norwegian side was started in 2020.

In the Norwegian part of the project, subsea cables were laid along a route length of 2.8km in Lake Suldalsvantnet in 2020. A floating platform, 43m-long and 15m-wide, was constructed to lay high-voltage cables through the Lake Suldalsvatnet. The water depth in the area is up to 210m.

In another section in Norway, the HDVC cable passes through a 2.35km-long mountain tunnel which was constructed between Hylsfjorden and Lake Suldalsvatnet in March 2017.

The next stage involves the laying of the subsea cables along a route of approximately 100km from Hyldfjorden to the North Sea in 2020.

Project finance

Sace and Simest joined hands with BNP Paribas Corporate & Institutional Banking to provide export financing worth £415m ($519 million) for National Grid in December 2016. The loan was provided to National Grid in order to finance a contract awarded to Prysmian for the North Sea Link project.

The European Union’s Connecting Europe Facility provided a grant of approximately £25m ($42m) for the project in the initial stages of development which included technical design studies for the cable equipment and converter stations.

Contracts awarded

Prysmian Group was awarded a contract worth approximately £393m ($609m) for the manufacturing and installation of cables for the project in July 2015. The scope of work included the delivery and installation of approximately 950km  of cables along a route length of 470km spanning both offshore and onshore.

Prysmian’s Arco Felice factory in Naples, Italy, manufactures the single-core cables with mass impregnated paper insulation for the project. Prysmian’s cable-laying vessel Giulio Verne will be used for this project.

Nexans was awarded a contract worth approximately £243m ($377m) to design, manufacture and install the cable on the Norwegian side in July 2015. The work scope included the Fjord submarine section, the mountain tunnel and lake, and underground cable for the onshore connection on the Norwegian side.

Nexans’ plant in Halden, Norway, manufactures the mass impregnated non-draining (MIND) HVDC cables with a total length of approximately 500km for the project. Nexans’ cable-laying vessel Nexans Skagerrak will be used for this project.

Fugro provided remotely operated vehicle (ROV) survey and monitoring support services to Nexans for the transmission line sections through the mountain between Hylsfjorden and Lake Suldalsvatnet, and along the Lake Suldalsvatnet in Norway in 2020.

ABB secured a £290m ($450m) contract to set-up high-voltage direct current (HVDC) converter stations for the project in July 2015. The scope of the contract included the design, engineering, supply and commissioning of two ±525 kV, 1,400 MW converter stations. The converter stations will be built based on ABB’s voltage source converter (VSC) technology HVDC Light.

Implenia Norway, part of Switzerland-based Implenia Group, was contracted by Statnett for groundwork and tunnel work in Norway in June 2015. The scope of the work included excavation and blasting work, tunnel operation, as well as the construction of quays and landslide protection.

Next Geosolutions received the contract to conduct a marine survey for cable route design and engineering in December 2016. The survey included nearshore and offshore marine geophysical and geotechnical surveys, remotely operated vehicle (ROV) inspection, unexploded ordnance (UXO) survey and topographic survey.

WSP, formerly WSP Parsons Brinckerhoff, secured a contract to provide cable manufacturing quality and inspection services for the cable manufactured in Prysmian’s Arco Felice factory in March 2017.