UK blackout
Image credit: metro.co.uk

A much-anticipated initial report by the UK’s grid operator National Grid, leaked to the UK’s Financial Times, noted findings that a lightning strike caused the failure of the UK’s largest wind farm, Hornsea 1, just minutes before the failure of the smaller, gas-powered Little Barford power station, and the blackout that left 900,000 people in England and Wales without power on 10 August, during peak Summer commuting time.

The findings, which were shared with the Financial Times by persons briefed on the report, suggest the blackout may have been the result of a lightning strike near Cambridge, which caused 300-400MW of capacity, comprised mostly of renewables, to go offline. Whilst lightning strikes are common to National Grid infrastructure, the strike occurred almost simultaneously with the collapse of the wind site off the coast of Yorkshire, where capacity fell from 800MW to zero almost instantly.

The failure at the farm may have led to it disconnecting from the grid if safety systems were set up too sensitively to drops in frequency, and power plants should not disconnect unless the frequency oscillates sharply.

Orsted has acknowledged that a “technical fault” saw the wind farm “rapidly de-loaded”, but declined to comment on whether the collapse at Hornsea had occurred before the Little Barford site's failure.

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The company said it had since made adjustments to “the relevant part of
the system”.

“We are fully confident should this extremely rare situation arise
again, Hornsea 1would respond as required.”

National Grid refused to comment.

The report is expected to indicate that the frequency of the grid didn't drop to 48.8 hertz- the level at which National Grid’s automated system automatically cuts off electricity supply except to approximately 5% of
demand, until the first generator tripped at Little Barford, joining Hornsea offline.

Other preliminary findings noted that National Grid had
just 1,000MW of rapid-response emergency power supply at the time of the blackout - only two-thirds of the power that was lost.

A broader government investigation is expected to focus, in part, on
whether the grid should have a higher reserve supply in the case of future incidents.