IFA2 interconnector between Sellindge and France down over two months

In November 2023, National Grid issued a market transparency notification of an unplanned outage on the IFA2 (Interconnexion France Angleterre 2) high voltage direct current submarine interconnector, a link of around 1 GW between Sellindge, Kent, United Kingdom and Les Mandarins, France. The link was reported as unavailable until at least the start of February 2024 following a suspected cable fault, an expected outage of roughly two and a half months. The link is one of several interconnectors across the English Channel crossing, and its unavailability over the winter heating demand period represented a meaningful reduction in cross border transfer capability between the two countries. Flows at the time were reported as predominantly imports on the interconnectors serving that region, so alternative transfer capacity was limited. No safety incident was reported in connection with the fault. The consequences reported were operational and commercial.

The market notification characterised the immediate cause as a suspected cable fault. No further detail of the fault mechanism, such as insulation breakdown, mechanical damage from anchor or trawl interaction, or a manufacturing defect, was given in the public notification. The following is general industry context rather than reported detail: repair of a submarine HVDC cable normally requires fault location by electrical diagnostic methods over the full cable length, mobilisation of a specialist cable repair vessel equipped for the cable type and water depth, weather dependent lift, jointing and re-laying operations, and post repair commissioning testing. Fault location and vessel mobilisation each commonly take several weeks, which is broadly consistent with the outage duration indicated in the notification.

1. A submarine interconnector concentrates a large block of transfer capability in a single circuit, and loss of that circuit removes the whole block for the duration of the repair, so contingency plans should treat the full rating as a credible single loss.
2. Plan on the basis that a submarine cable repair can take of the order of two to three months from fault to return to service, and treat that as an expected rather than a worst case duration in system and market planning.
3. Where a system relies on imports through winter, capacity adequacy assessments should include scenarios in which one or more interconnectors are unavailable for a full winter peak period.
4. Anchor strike and fishing gear interaction are recognised hazards for subsea cables, so maintain ongoing engagement with maritime authorities, shipping operators and fishing bodies, including chart notation and awareness campaigns along the route.
5. Carry out periodic burial depth and route integrity surveys through the asset life and act on areas where cover has been lost.
6. Multiple links between the same pair of systems improve resilience but are not fully independent, as they can share weather, seabed and shipping exposure in the same corridor, so common mode failure should be assessed explicitly.
7. Procure fast acting frequency response sized against the loss of the largest single infeed, including interconnector trips, and review that sizing when interconnector capacity changes.
8. Hold a cable repair contingency plan that can be activated on fault detection, covering access to a suitable repair vessel, spare cable and joints of the correct type, and pre agreed fault location resources, since extended outages of this asset class are commercially material.

newpower.info/2023/11/cable-fault-takes-ifa2-interconnector-out-of-act...