Caithness-Moray Link

The Caithness-Moray HVDC Project is a major infrastructure development in northern Scotland, representing a £1.1 billion capital investment by Scottish Hydro Electric Transmission. This project is the first HVDC scheme in the region and is a key component of the largest renewal of northern Scotland's electricity network since the 1950s.

Project Overview

The project involves the installation of a 113km submarine HVDC cable beneath the Moray Firth, connecting Spittal in Caithness to Blackhillock in Moray. The cable uses ±320kV HVDC technology and can transmit up to 1,200 MW of electricity, enough to power approximately two million Scottish homes. The submarine cable is complemented by 48 km of underground cross-linked polyethylene cable at both ends.

Technical Specifications

The HVDC link consists of two converter stations: one rated at 1,200 MW at Blackhillock in Moray and another rated at 800 MW at Spittal in Caithness. The project employs HVDC Light® technology, which allows for efficient transmission of large volumes of electricity over long distances with reduced visual impact compared to overland alternatives.

Project Components

In addition to the submarine cable, the Caithness-Moray project encompasses work at eight substations and two overhead line reinforcement projects. Key elements include the Spittal substation and HVDC converter station, Blackhillock substation and HVDC converter station, Dounreay to Mybster reinforcements, and Loch Buidhe to Beauly reinforcements. The project also involved the construction of a high voltage direct current (HVDC) switching station north of Wick in Caithness, which connects to the HVDC system between Caithness and Moray and utilizes available capacity in the Caithness-Moray Subsea Cable.

Project Significance

The Caithness-Moray HVDC Project is designed as a multi-terminal scheme, allowing for future expansion to connect the Shetland Isles and other renewable generation sources. It enables the export of electricity from one of Europe's most productive renewables areas and demonstrates how a multi-terminal grid can be developed without HVDC breakers.

Technical Challenges

The project faced several technical challenges, including connecting to a weak AC (275kV) network in northern Scotland, designing for multi-terminal operations, and potential for multi-vendor extensions. To address these challenges, the project utilized Replicas of control panels to test system operation under various conditions, with a detailed representation of the AC network.

Economic and Social Impact

The Caithness-Moray project has had a substantial economic impact on the UK and Scottish economies. It has created job opportunities and positively affected local businesses in the north Highlands and Moray. The project also awarded the largest ever Living Wage contract, benefiting employers and employees across the supply chain.

Completion and Future Prospects

The Caithness-Moray HVDC Link was officially completed in January 2019, under budget at £970 million. As the project moves into its operational phase, it continues to play a crucial role in accommodating the export of renewable energy from Caithness and supporting the UK's transition to a low-carbon network. The successful implementation of this project paves the way for future developments in offshore grids and multi-terminal HVDC systems. It has also justified the establishment of a National HVDC Centre for modeling and simulating multi-vendor HVDC systems while protecting the intellectual property of equipment suppliers.