Major Outage

In the early hours of Tuesday 14 May 2024, just after 01:00, both the East West Interconnector (EWIC) and the Moyle Interconnector tripped almost simultaneously while importing in excess of 90% of their combined maximum capacity. The interconnectors had been importing more than 900 MW since approximately 20:00 the previous evening, meeting around 25% of all-island demand at the time of the event, and levels of wind generation were low at approximately 600 MW. The sudden combined loss caused the system frequency to fall to a nadir of about 49.65 Hz, well below the normal operating band of 49.9–50.1 Hz. Battery storage and other fast-frequency response assets supported recovery. The Moyle Interconnector returned to importing in excess of 400 MW within three hours of the event, indicating a relatively quick restoration. EWIC, however, remained offline for the rest of the working day and only returned to service late on the evening of 14 May 2024, after approximately 18 hours out of service. The dual trip was one of a number of short forced outages on EWIC contributing to the 2024 availability of 98.7% recorded in the All-Island Transmission System Performance Report 2024.