The £660 million project by SSEN Transmission will involve constructing a 260km subsea cable from Shetland to Noss Head in Caithness, connecting Shetland to the main GB energy system for the first time, supporting Shetland's future security of supply as well as enabling the connection of renewable energy generation.
The first phase of boulder relocating work along the proposed subsea cable route has been completed by Principal Contractor NKT, lead Contractor for all cabling works, which involved clearing a 100m-wide corridor along the proposed consented cable route to move any obstacles from its path. Subsea equipment deployed from specialist vessel the Seawell was brought in to help safely manoeuvre boulders away from the Shetland HVDC cable route along its 260km route.
Prior to the boulder clearance work taking place, a UXO survey was carried out in a bid to identify if any unexploded ordnance (UXOs) were in the cable route of the subsea HVDC cable being installed between Shetland and the mainland at Noss Head, Caithness. While multiple marine seabed surveys have been completed as part of the project, the additional specialist UXO survey was carried out as standard practice and identified no UXOs within the cable corridor, meaning work could continue as planned. While no UXOs were identified, the survey located various items such as scrap metal and other debris along the cable route, which were recovered by the vessel. These objects have now been safely disposed of, helping to clean-up the seabed and reduce unnecessary marine debris and any associated risk they may cause.
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Back on land, the team completed horizontal directional drilling (HDD) work to the south of Noss Head lighthouse where the subsea cables will make landfall, marking a major milestone for the project. HDD is a drilling method used to install ducts beneath the ground through which cables can be pulled, providing minimum disturbance to the surrounding area.
The HDD works took around three months to complete with teams working continuously to carefully execute the drilling scope and then install the new ducts, preparing for when the cable will be pulled through from the seabed through to the transition joint bay where it will tie-in to the land cables which will be connected to the switching station. The operation required multiple activities including diving operations and marine surveys in order to support the land-based HDD effort.
Teams are now preparing to begin work on the first subsea installations this summer, which will involve specialist vessel NKT Victoria installing the first cable length.
Reflecting on the project achievements so far, SSEN Transmission Lead Project Manager Chris Finnigan said: "We've made some really excellent progress in recent months with regards to the Shetland HVDC link which allows us to move forwards on connecting Shetland to the mainland and opening up a clean-energy corridor for transporting electricity to and from the islands.
"Completing the HDD work was a crucial milestone, and the team has worked tirelessly to overcome major challenges including working through the complex geological make-up of the ground conditions at the Noss Head cliffs, as well as safely mobilising and demobilising the drilling spread and the vessels required for the supporting marine operations. It's a huge achievement and one that those involved with the works should be proud of.
"The first stage of subsea boulder clearance marks another integral step ahead of the HVDC cable being installed, and the team from NKT and their subcontractor Helix, including all those onboard the Seawell vessel, did a fantastic job in creating a safe subsea corridor for the future cable.
"As is standard practice we carried out specific surveys in order to check for UXOs along the cable route, and we're pleased that no UXO targets were identified within the cable installation route. The survey did however identify some scrap metal debris on the seabed, and although this would not have impacted our project we worked with our contractor NKT to remove these items and have them disposed of properly onshore. As a responsible developer we aim, where possible, to leave a positive impact on the environment in which we operate and small actions like this are something we aim to achieve whenever we can.
"In general the project continues to make great strides forward and teams are now gearing up ahead of our first subsea installation campaign which is scheduled to begin this summer.
"We thank the local community and stakeholders for their cooperation and understanding while we continue with this crucial project, and as ever we'll work to keep informed as we move through the pre-construction phases of the Shetland HDVC link project."
The Shetland HVDC subsea link project is on track to be completed by 2024.
