Moyle Interconnector

For much of its life the Moyle Interconnector could send only 80 MW from Northern Ireland to Scotland. The cable was rated at 500 MW, but transmission constraints on the National Grid side limited exports to a fraction of that. Coordinated work raised the export limit to 250 MW and then, in 2021, to the full 500 MW.

Moyle crosses the North Channel between Auchencrosh in South Ayrshire and Ballycronan More in County Antrim. The route is 63.5 km long and 55 km of it is subsea. Both ends are in the United Kingdom, so it is not a cross-border link in the strict sense, but it connects two separate electricity markets: Great Britain and the all-island Irish market that Northern Ireland shares with Ireland.

It went into service in 2001 as a dual monopole at 250 kV, with the return conductors built into the cables. That design caused most of the trouble that followed. In August 2011 the link went out of service; it returned in February 2012 at 450 MW. The integrated return conductors failed, and new separate metallic return conductors were installed in 2016 to restore the full 500 MW. In February 2017 one high-voltage cable developed a further fault, halving capacity to 250 MW until September 2017. A major refurbishment of the control and protection systems followed in 2022, carried out one pole at a time. The Moyle Interconnector article sets out the sequence.

A second link on almost the same crossing is now planned: LirIC, from Hunterston to Kilroot, would add 700 MW by 2032. Siemens built Moyle’s converters and Nexans its cables, and the link is owned by Mutual Energy. For how cable faults like these are found and repaired, see subsea power cables. LirIC’s planned 700 MW is more than Moyle’s full rating, on a crossing roughly twice as long at 142 km.