The regulator, Ofgem, said Hornsea One Ltd, RWE and UK Power Networks have agreed to pay the sum for failing to remain connected after the lightning strike that caused the outage, and for a technical breach of rules.
On Aug. 9 last year the combined loss of two large generators and a smaller loss of generation at a local level together triggered a disconnection and loss of power that disrupted supplies to more than one million consumers.
Ofgem said two large power stations - Hornsea One Ltd, co-owned by Orsted, and Little Barford, operated by RWE - became disconnected after a lightning strike.
They have agreed to make a voluntary payment of 4.5 million pounds each into Ofgem’s redress fund.
Ofgem found that local network operators disconnected and reconnected consumers in response to the loss of power as expected.
However, UK Power Networks began reconnecting customers without being asked to do so, which could have potentially jeopardised recovery of the system.
Although this had no impact on Aug. 9, it is a technical breach, and the company has agreed to pay 1.5 million pounds into the Ofgem fund.
Ofgem's investigation has also raised questions about how the National Grid's Electricity System Operator manages the system.
The regulator had already announced a review into the structure and governance of the ESO, during which it will consider a number of options for how the system operator is structured, governed and managed.
Also on Friday, the government said it will implement an action plan to help prevent future power disruptions.
That will include assessing the need for improvements to the governance, monitoring and enforcement processes for large and smaller generators, and reviewing the pros and cons of the ESO holding additional back-up generation.
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