The Caithness ring has been completed

Scottish and Southern Electricity Networks Transmission, the wholly-owned subsidiary of SSE plc, has completed the construction, commissioning and energisation of the new Caithness-Moray link. It represents the largest single investment ever undertaken by the SSE Group and is the most significant investment in the north of Scotland electricity transmission system since the hydro projects of the 1950s. Total spend for the project has been around £970 million, out of a total investment of nearly £1.1 billon.

It is part of a major strengthening of its power network by SSE in the north of Scotland to accommodate the rapid growth in generation of electricity from renewable sources.

The link uses HVDC technology to transmit 1200 MW of power through a 113 km subsea cable beneath the Moray Firth seabed between new converter stations at Spittal in Caithness and Blackhillock in Moray. Constructed over a period of four years, the project also involved work at eight electricity substation sites and has also required two overhead electricity line reinforcement projects.

The decision was taken to route the cables across the Moray Firth rather than over land to ensure greatly reduced visual impact. Reinforcement of the onshore transmission network between Dounreay and Mybster in the north and between Loch Buidhe and Beauly further south will also optimise the existing network in combination with the new cable.

Completed on time and within the allowance approved by regulator Ofgem, the Caithness- Moray link provides capacity to transmit power from the increasing sources of renewable energy from across the far north of Scotland.

The link has already enabled turbines from Beatrice offshore wind farm (588 MW on completion) and Dorenell onshore wind farm (177 MW on completion) to connect to the national grid with a further 100 MW of onshore generation in Caithness and Ross-shire due to connect in the coming months.

Asset value

The completion of the link and other electricity transmission projects is expected to help take the Regulatory Asset Value (RAV) of SSEN Transmission to around £3.3bn as of 31 March 2019. In the remaining years of the RIIO-T1 Price Control the business has a pipeline of planned capital investment of around £640m, as at 1 January 2019, meaning that it remains on track to increase its RAV to around £3.6bn by March 2021.

Complex project

Dave Gardner, who led the project as SSEN’s Director of Transmission, said:

“The successful energisation and commissioning of the Caithness-Moray link, on time and within budget, is a significant achievement for SSEN and everyone involved in the project.

“Caithness-Moray has been a highly complex project, requiring very high standards of project design, development, construction and commissioning. It will support deployment of renewable energy in the north of Scotland for many years to come. 

Creating the link

ABB was contracted to design, engineer, supply and commission two landbased 320 kV HVDC Light VSC (voltage source converter) converter stations, one rated 1200 MW at Blackhillock in Moray and another rated 800 MW at Spittal in Caithness. ABB’s scope of supply also includes submarine and underground cables, for a total transmission length of nearly 160 km.

The link benefits from a five year service agreement, which includes 24/7 phone support, training, remote access, grounds maintenance, spare parts and facility management, and preventive and corrective maintenance.

ABB, which has already delivered 13 of the 14 commissioned VSC links in the world. was awarded the £500 million contract in 2014, by Scottish Hydro Electric (SHE) Transmission plc, part of the SSE Group. This followed a favourable decision by Ofgem (Office of Gas and Electricity Markets), an independent National Regulatory Authority, on the need for the link.

The generation of electricity from renewable sources in the north of Scotland has been growing fast in recent years. That growth is forecast to continue in the years ahead, with proposed wind, wave and tidal generators contracted to connect. As a key element in the needed reinforcement, SHE identified the need for a subsea power link, capable of carrying up to 1200 MW between Caithness and Moray.

Further reinforcement

Reinforcement of the onshore transmission network between Dounreay and Mybster in the north, and between Loch Buidhe and Beauly further south will further improve the use of the existing network in combination with the HVDC link.

Under the contract SSE also has an option for a future HVDC link to Shetland. The equipment delivered under the Caithness–Moray contract has the capability to handle the multi-terminal set-up that would be required.