Ofgem decides Gwynt y Môr cable failure was Exceptional Event

In: CablesWindfarms
12/02/2021

Ofgem has announced its decision that the cable failure at the
Gwynt y Môr offshore wind farm was an 'Exceptional Event'.

Located 8 miles from the North Wales coast in Liverpool Bay, the 576 MW offshore wind farm was built and operated by Innogy with partners Stadtwerke München and Macquarie Infrastructure and Green Investment Group. The project has been operational since 2015. Gwynt-y-Môr OFTO plc, a consortium of Balfour Beatty and Equitix, acquired the transmission assets for the project in 2015, through the Offshore transmission owner (OFTO) regime.


On 23 January 2020, during a routine test of the fibres in the spare fibre optic cable (FOC), the O&M contractor identified that all fibres within the spare FOC in subsea export cable 3 (SSEC3) had failed (the initial FOC break). The initial FOC break is located at or close to the location where a repair was undertaken in 2015 (the hotspot repair).

Between February and September 2020, the further tests were undertaken to check for any degradation of the power cores and to improve accuracy about the location of the break.

On 15 October 2020, a second break on the spare FOC within SSEC3 was discovered, located approximately 1.5 km from the the initial FOC failure. The same day, the main power core in SSEC3 failed in the vicinity of the second FOC break. Gwynt-y-Môr OFTO appointed an expert adviser to conduct the root cause analysis (RCA). The RCA report, however, 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. As the licensee, therefore, Gwynt-y-Môr OFTO also provided a report from the University of Southampton.

Gwynt-y-Môr OFTO  submitted an 'Exceptional Event' claim to the Authority on 24 November 2020, alongside details of the actions it has taken since it discovered the issue and up to 31 December 2020.

Ofgem stated in its decision today that it finds the outage to be an 'Exceptional Event' and that it was a circumstance that was beyond the reasonable control of the licensee, which caused a Transmission Service Reduction.

Ofgem outlined it has considered whether Gwynt-y-Môr OFTO could have prevented the failure by acting when it first became aware of the issues in January/February 2020. Tests undertaken by Gwynt-y-Môr OFTO in June, July and September 2020 did not identify any break in the main power core, nor the second FOC break.
In addition, Gwynt-y-Môr OFTO has explained that even if it had undertaken a repair in early 2020, it is likely that this would not have prevented the failure of the power core, as the failure location (the second FOC break) was not identified until the October 2020 fault occurred and that second FOC break may not have developed by January/February 2020.

Ofgem has directed that the Gwynt-y-Môr OFTO's reported system incentive performance be adjusted to offset the duration of the Transmission Service Reduction from 15 October to 31 December 2020 as follows: 266,200 MWh reported system incentive performance for incentive year 6 (1 January 2020 to 31 December 2020).

4C Offshore monitors subsea cable failures in its Quarterly Subsea Cables and Grid Report.
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