Unexpected shutdowns at a 740MWe gas plant and then at Hornsea One within minutes of each other, just before 5pm on 9 August caused wide-spread power cuts across the UK, affecting a million households and key transport infrastructure.
National Grid, the UK TSO, explained other generators on the network should have responded by increasing their output, but due to the scale of the losses, this was impossible.
Instead, a backup protection system was triggered, "which disconnects selected demand across Great Britain", the TSO said.
Such systems are designed to ensure power is maintained for the "vast proportion" of the country, the National Grid’s director Duncan Burt told broadcaster, the .
Investigations
The UK government commissioned its Energy Emergencies Executive Committee to launch an investigation into the incident.
Meanwhile, energy regulator Ofgem has ordered National Grid to work with local distribution networks and affected power stations and generators on its own internal review into the power outage.
A spokesperson from project developer Ørsted said: "During a rare and unusual set of circumstances affecting the grid, Hornsea One experienced a technical fault which meant the power station rapidly de-loaded – that is it stopped producing electricity.
"Normally the grid would be able to cope with a loss of this volume (800MW). If National Grid had any concerns about the operation of Hornsea One we would not be allowed to generate.
"The relevant part of the system has been reconfigured and we are fully confident should this extremely rare situation arise again, Hornsea One would respond as required."
The National Grid’s Duncan Burt also told the BBC the TSO did not believe that "too much wind" was to blame for the power cut.
"The event that we saw yesterday had really nothing to do with changes in wind speed or the variability of wind," he said.
Burt added National Grid would look at its "automatic grid protection systems", and whether these were initiated correctly and whether they could further minimise the disruption caused by generation losses.
Lessons
Meanwhile, a spokesman for trade body RenewableUK said: "Friday's disruption underscores the need to invest in a flexible, modern system that can respond rapidly to changes in supply and demand.
"We need to prioritise regulation, markets and infrastructure that helps the grid respond rapidly and builds in flexibility to the system — from storage to smart technology, and from balancing markets to charging reform.
"That is the lesson of last week — and it will need a collective effort from Government and industry to deliver it."
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