National Grid has said it will “learn the lessons” after nearly one million people across England and Wales lost power on Friday.
But director of operations Duncan Burt told the BBC that its systems “worked well” after the “incredibly rare event” of two power stations disconnecting.
He said he did not believe that a cyber-attack or unpredictable wind power generation were to blame.
Regulator Ofgem has demanded an “urgent detailed report” into what went wrong.
It said it could take enforcement action, including a fine, after train passengers were stranded, traffic lights failed to work and thousands of homes lost power during the blackout.
An energy department spokesperson said National Grid must “urgently review” what happened and that it was awaiting its report.
Some train services continued to be disrupted on Saturday.
The power cut happened at about 17:00 BST on Friday, National Grid said, with blackouts across the midlands, the south east, south west, north west and north east of England, and Wales.
National Grid said its systems were not to blame and the power cut was caused by the loss of two generators.
Industry experts said that a gas-fired power station at Little Barford, Bedfordshire, failed at 16:58, followed, two minutes later, by the Hornsea offshore wind farm disconnecting from the grid.
Speaking to BBC Radio 4’s Today programme, Mr Burt acknowledged the “immense disruption” the blackout had caused.
He said the near-simultaneous loss of two generators was more than the grid was routinely prepared for, prompting automatic safety systems to shut off power to some places.
“We think that worked well; we think the safety protection systems across the industry, on generators and on the network, worked well to secure and keep the grid safe, to make sure that we preserved power to the vast proportion of the country,” he said.
But he said the industry needed to examine whether these safety systems were set up correctly to have “minimal impact” on people’s daily lives.
Mr Burt said the shutdown had “nothing to do with changes in wind speed or the variability of wind” and they were confident there was no “malicious intent” or cyber-attack.
On Friday evening, police officers were called to help travellers during the huge disruption on the railways with delayed passengers stranded for hours.
Disruption continued into Saturday for some rail routes.
- London North Eastern Railway, which runs between King’s Cross and the north of England and Scotland, said services were returning to normal, but a small number of trains were cancelled
- Thameslink services have returned to normal
- Great Northern services are still facing disruption and passengers are being advised to check their train’s status before travelling.
National Grid power was restored by 17:40 BST on Friday.
David Hunter, energy analyst at Schneider Electric, told the BBC that although the grid is “pretty safe and pretty reliable”, this was a “wake-up call” to the energy industry and businesses with critical infrastructure.
He said the transition to clean energy may be creating “greater stresses” on the system because energy such as wind power is less effective as a “shock absorber” to shifts in supply and demand.
RWE, owner of the Little Barford power station, said it shut down temporarily on Friday as a routine response to a technical issue, and called for National Grid and Ofgem to investigate the “wider system issues”.
And Orsted, the owner of the Hornsea offshore wind farm, said automatic systems on Hornsea One “significantly reduced” power around the same time others failed.
A spokesperson added: “We are investigating the cause, working closely with National Grid System Operator, which balances the UK’s electricity system.”
Shadow business and energy secretary Rebecca Long Bailey said the impact of the power cut was “unacceptable” at a time when National Grid reported £1.8bn in profits and increased dividends to shareholders.
Northern Powergrid said the problems had affected Newcastle airport and city’s metro system.
King’s Cross was one of the worst-hit stations, with all trains suspended for several hours.
Passenger Dayna McAlpine told BBC Radio 5 Live her train took nearly 13 hours to reach London King’s Cross from Edinburgh – a journey which would normally take less than five hours.
“By hour seven things were starting to get pretty tense,” she said. “People were threatening to self-evacuate off the train… Food ran out about five hours ago.”
Others on social media reported having travelled for 12 hours, while some rail passengers were stuck on trains until the early hours of the morning.
At the worst point of the power cut, about 500,000 people were affected in Western Power Distribution’s area – including 44,500 customers in Wales – while 110,000 Northern Powergrid customers also lost power.
In London and the South East, 300,000 people were affected, UK Power Networks said, and another 26,000 customers were without power in the North West.
BBC Radio 5 Live listener Ed, in Woodford Green, north-east London, said he felt “totally cut off” as mobile phone networks were also down.
“You heard all the alarms going off all around. Everything else was pretty eerie and quiet,” he said. “There was no way we could know anything – it could be any reason that the power had gone down.”
At Ipswich Hospital, a back-up generator which was supposed to supply power to outpatient areas did not work after the power cut, causing problems for 15 minutes before power was restored.
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