UK power cut triggered after simultaneous mystery outage at off-shore windfarm and gas facility more than 150 miles apart within moments of lightning strike

Report finds ‘extremely rare and unexpected event’ led to travel chaos

A simultaneous malfunction at an offshore windfarm and gas facility caused a power cut in the UK earlier this month, according to a new report.

The unexplained outages followed moments after a lightning strike, the National Grid Electricity System Operator (NGESO) said.

Officials said the lightning strike hit a transmission circuit at 4.52pm on 9 August.

Such strikes are common, and the national grid’s protection systems cleared the lightning in under 0.1 seconds.

But moments after the strike the UK lost 5 per cent of its power.

Simultaneous outages, associated with the strike, occurred independently at Hornsea offshore windfarm and Little Barford gas power station.

The two sites are more than 100 miles apart.

“The total generation lost from these two transmission-connected generators was 1,378mw,” the NGESO interim report said.

The scale of generation loss meant that the 1000mw level of “backup” power held under regulations was insufficient.

As a result, the system automatically disconnected customers on the distribution network.

Around 5 per cent of electricity demand was turned off to protect the other 95 per cent.

Such a vast outage has not occurred in more than a decade.

“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,” the report said.

The lightning strike was one of many to hit the national grid on the day.

NGESO said lightning strikes are “routinely managed as part of normal system operations”.

The power cut caused travel chaos during rush hour in London and the southeast.

Traffic lights were knocked out, flights grounded and passengers stuck on halted trains for hours, with one commuter describing the atmosphere at Clapham Junction as “like witnessing something out of an apocalyptic film”.

Euston and King’s Cross train stations were brought to a standstill, with commuters forced to use the torches on their mobile phones to exit the London Underground, which was plunged into darkness in some areas.

Train signals lost power across the south, in Bristol, Newport and Eastbourne, while passengers travelling from Edinburgh to London were stuck on a train for an extra eight hours.

The Office of Gas and Electricity Markets (Ofgem), the industry regulator, said it was launching an investigation following the report.

The probe is set to examine the national grid’s requirements to hold sufficient backup power, as well as how generators met their obligations with respect to the transmission fault, and whether distribution network operators complied with their obligations.

The regulator will also examine “whether the companies made the right decisions both in the numbers of customers disconnected and whether those customers disconnected were the right ones”.

“It’s important that the industry takes all possible steps to prevent this happening again,” said Jonathan Brearley, Ofgem’s executive director of systems and networks.

“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 clearly establish whether any firm breached their obligations to deliver secure power supplies to consumers.”

Additional reporting by agencies