Steady progress on Caithness-Moray transmission link

2nd April 2015 from Andrew Williams - Maritime Journal

In recent months, steady progress has been made on the £1.2 billion scheme to install a new electricity transmission link across the Moray Firth between Caithness and Moray.

So, what work has been carried out on the link so far? What work is currently being carried out? And what tasks remain before the project is completed?

The development of the project and its journey through the planning and regulatory processes has been under way for several years, but the Ofgem decision last year to grant approval for the large-scale Scottish Hydro Electric (SHE) Transmission infrastructure project paved the way for the main high voltage direct current (HVDC) and alternating current (AC) contracts to be awarded to Swiss automation and power multinational ABB (HVDC) and UK construction giant BBES (AC) in the beginning of August 2014.

As part of its contract, worth more than $800 million (£540 million), ABB will design, engineer, supply and commission two 320 kilovolt land-based HVDC Light converter stations, one rated at 1,200 megawatts (MW) at Blackhillock in Moray and another rated at 800 MW located at Spittal in Caithness. The ABB supply contract also relates to the provision of submarine and underground cables covering a total transmission length in the region of 160 kilometres.

In early March 2015, another major milestone was reached, as Scottish company Ecosse Subsea Systems announced that it had signed an agreement to carry out a seabed clearance and trenching project to ‘prepare the route for the 100-mile interconnector cable’ at the centre of the project.

As part of the agreement, ESS will conduct boulder clearance operations and pre-lay trenching, helping to clear the way for the laying of the transmission cable that will run between the converter stations at Spittal and Blackhillock. Once the transmission cable is installed by main contractors ABB, ESS will then complete back-fill operations to ‘safely conceal and protect the cable.’

Subsea Cable

SHE says that the new link, which will include more than 100 miles of underground and subsea cable, will be capable of carrying large volumes of electricity from renewable energy generation sites in the north of Scotland to the main UK electricity transmission network.

Construction work on the initiative, which forms part of a ‘transformational programme of investment in electricity transmission infrastructure to support the transition to lower carbon electricity generation, increasing security of supply and promoting economic growth’ is slated for completion in 2018.

According to Lisa Marchi, Major Project Liaison Manager at SHE, the early stages of construction work are ‘well underway’ on the main AC substations at Spittal in Caithness and at Blackhillock in Moray, as well as at some of the other planned AC substation sites in Ross-shire and Sutherland. This includes ‘enabling works’ for the HVDC converter stations and DC land cable, which will be constructed later in the programme.

“At the Caithness landfall at Noss Head, north of Wick, a trial drill was carried out towards the end of last year for the Horizontal Directional Drill process which will be used. This proved to be very successful in confirming the landing point ahead of the main onshore cable work beginning next year,” she said.

“The main work to install the subsea cable itself will be carried out in 2017 and the project as a whole is expected to be complete and operational by the end of 2018,” she added.


Although she admits that a ‘wide range of challenges’ have to be considered when planning a scheme of this type, Marchi is confident that the variety of company’s making up the project consortium are more than capable of facing up to the challenges posed in undertaking such a large scale subsea project.

“Our development team has been working for several years with the relevant planning and regulatory bodies, local communities and affected landowners to plan the project, address any concerns and obtain all the consents required,” she said.

Marchi says that the Caithness-Moray cable project represents SHE Transmission’s first experience of working with HVDC technology as an integral part of its network, and she admits that this presents a number of new challenges - particularly as the project moves into the construction phase, which she points out presents a ‘new range of practical and technical challenges’ that are still being tackled by the SHE in house team, as well by the principal contractors.

In view of the fact that the installation process for the marine cable and its landfalls also present ‘particular issues,’ Marchi says that SHE has also already completed a range of environmental and geological surveys to ‘plan the route in meticulous detail.’ 

“As part of this work, a great deal of information has been collected on Scotland’s largest known horse mussel bed, which is located close to the Caithness landfall. Due to requirements to minimise disturbance to this species, the cable cannot be trenched or rock protected in this area, so the proposed solution is to bundle the cable into a Uraduct [a cable protection system produced by companies including Trelleborg and Maritech] or similar for this 1km section,” she added.

Ultimately though, Marchi believes it is difficult to overstate the importance of the project to the ongoing and future development of the offshore renewable energy sector across the entire northern region of Scotland. Once complete, she highlights the fact that the transmission link will provide around 1200MW of additional capacity on the electricity transmission network serving the north of Scotland.

“It is essential to the continuing development of onshore renewable energy resources in the northern Highlands of Scotland, but is also a critical stepping stone to future development of Scotland’s island and marine energy resources,” she said.


Andrew Williams - Maritime Journal:

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