New Export Cable for Gwynt y Môr After Year of Cable Issues

On 14 May, Sumitomo Electric Industries reported that it was awarded an export cable supply contract for the Gwynt y Môr offshore wind farm. The news comes a few months after Ofgem ruled in favour of Gwynt y Môr OFTO plc which had filed an Exceptional Event claim for the project’s export cable failure from October 2020.

The 576 MW offshore wind farm, located some 13 kilometres off the coast of North Wales, has been put into operation in 2015. That same year the project encountered its first issues with the export cable, which then underwent repair.

Some five years later, in January 2020, an Operations & Maintenance (O&M) contractor performing a routine test of the fibres in the spare fibre optic cable (FOC) discovered that all fibres within the spare FOC within subsea export cable 3 (SSEC3) had failed. This initial FOC break was located close to the location where the repair was undertaken in 2015.

Between February and September 2020, the project’s offshore transmission system owner carried out further tests to check for any degradation of the power cores and to improve the accuracy of the location of the break.

On 15 October 2020, Gwynt y Môr OFTO plc – a consortium comprising Balfour Beatty and Equitix – discovered a second break on the spare FOC within SSEC3, in whose vicinity the main power core of the cable section failed. This second FOC break was located approximately 1.5 kilometres from the the initial FOC failure identified in January.

Gwynt y Môr OFTO reported the Transmission Services Reduction to Ofgem and filed the Exceptional Event claim, which Ofgem accepted this February.

“Based on the evidence available and submitted to date, we consider that it is likely that the the Transmission Services Reduction is the result of the failure of the spare FOC either due to an inherent defect, and/or an issue that arose as a result of a previous repair on the FOC. We note, however, that when the hotspot repair was carried out, all the tests were passed”, Ofgem stated.

The transmission system owner has appointed an expert adviser to conduct the root cause analysis, but the report will not be available until after the offshore cable has been repaired and the faulted cable has been recovered from the seabed and tested in a laboratory.

Therefore, to support its claim with Ofgem, Gwynt y Môr OFTO has also provided a report from the University of Southampton, which concludes that it is probable that the two FOCs have defective semicon sheaths and that it is very likely the hotspot repair joint, or its installation, caused a weakness in the spare FOC at the site of the repair in 2015 that subsequently led to the second FOC break and the failure of the main power core.

Gwynt y Môr features 160 Siemens Gamesa 3.6 MW wind turbines, which can together enough renewable electricity to meet the equivalent needs of approximately 400,000 average UK homes.

The wind farm is owned by RWE, Stadtwerke München, and Macquarie Infrastructure and Real Assets (MIRA).

Photo: Gwynt y Môr; Photo source: RWE