A lightning strike on the UK transmission system has been identified as a contributing factor in the loss of two large power generators, including an offshore wind farm, that led to a power blackout across large parts of the country.
National Grid in a preliminary report said “de-loading” of the 1.2GW Hornsea 1 wind farm off Yorkshire and the Little Barford CCGT plant were “associated” with a strike that occurred at 16.42 on Friday 9 August. Over one million people were left without power for up to 50 minutes after the incident.
“As generation would not be expected to trip off or de-load in response to a lightning strike, this appears to represent an extremely rare and unexpected event,” stated the report.
Hornsea, which is under construction but still exporting power, lost 737MW less than a second before 641MW went down at the gas-fired plant, stated National Grid. Earlier speculation suggested Little Barford had de-loaded first.
Orsted told National Grid that equipment at Hornsea “saw a system voltage fluctuation with unusual characteristics coincident with the lightning”, according to the report.
“The initial reaction from Hornsea’s systems was as expected in attempting to accommodate and address the system condition, but very shortly afterwards as the reaction expanded throughout the plant, the protective safety systems activated.
“Following an initial review, adjustments to the wind farm configuration, and fine tuning its controls for responding to abnormal events, the wind farm is now operating robustly to such millisecond events.”
National Grid is continuing its investigation and will report to regulator Ofgem by 6 September.
The latter has meanwhile launched an investigation into the incident after receiving the report.
The probe will look into whether any of the parties involved, including the generators Orsted and RWE, “breached their licence conditions”.
Executive Director of Systems and Networks Jonathan Brearley said: “The power cuts of Friday 9 August caused interruptions to consumers’ energy and significant disruption to commuters. It’s important that the industry takes all possible steps to prevent this happening again.”
He added: “Having now received National Grid ESO’s interim report, we believe there are still areas where we need to use our statutory powers to investigate these outages. This will ensure the industry learns the relevant lessons and to clearly establish whether any firm breached their obligations to deliver secure power supplies to consumers.”