Business and energy secretary Andrea Leadsom has said the government will commission the Energy Emergencies Executive Committee to conduct an investigation into Friday’s power cut, which left swathes of the country without electricity.
Leadsom said National Grid must also “urgently” review the incident, which “caused enormous disruption”, and report back to Ofgem.
Meanwhile, Ofgem itself has requested an “urgent detailed report” from National Grid “so we can understand what went wrong and decide what further steps need to be taken”.
The regulator said these steps “could include enforcement action.”
National Grid Electricity System Operator (ESO) responded in a statement over the weekend: “Any type of power cut can be disruptive to daily life, and the whole UK energy industry needs to understand the causes of yesterday’s power cut and also why it was able to create such significant disruption to services across Great Britain, particularly the transport network.
“The National Grid ESO is therefore very pleased that the government has commissioned the Energy Emergencies Executive Committee to consider the incident and how it played out, and we will work closely with that investigation to ensure that learnings can be reflected in industry processes and procedures going forward.
“In the meantime the ESO has already initiated its own internal review of the response, and is collaborating closely with Ofgem, local distribution networks and affected power stations /generators to understand the cause of (Friday’s) power cut.”
The event was triggered by the near-simultaneous loss of two generators – first, RWE’s 730MW Little Barford combined-cycle gas turbine plant in Bedfordshire shortly before 5pm, and then two thirds of Orsted’s 1.2GW Hornsea Two offshore windfarm a few minutes later.
“Such events are not uncommon in power stations,” said a spokesperson for RWE.
“What is now needed is for National Grid and Ofgem to investigate why the wider system issues occurred. We are very interested in the results too.”
It’s not yet clear whether the second outage was a coincident or whether it was related to the first. A spokesperson for Orsted said: “We are investigating the cause, working closely with National Grid System Operator, which balances the UK’s electricity system.”
The outages resulted in the total loss of nearly 1.5GW of generation from the transmission network. Both brought large drops in frequency, which at one point fell below 49 Hertz.
“Following the event, the other generators on the network responded to the loss by increasing their output as expected,” the ESO explained.
“However due to the scale of the generation losses this was not sufficient, and to protect the network and ensure restoration to normal operation could be completed as quickly as possible, a backup protection system was triggered which disconnects selected demand across GB.”
Power supplies were cut to hundreds of thousands of customers across the license areas of all six distribution network operators, although the effects were mainly felt in London, the South East and the Midlands.
The following is a breakdown of the number of customers affected in each area:
- Electricity North West – 82,600
- Northern Powergrid – 110,000
- Scottish and Southern Electricity Networks – 16,500
- SP Energy Networks – as yet unknown
- UK Power Networks – reportedly 300,000
- Western Power Distribution – 500,000
The ESO said it gave the “all clear” to the DNOs to start reconnecting demand within 15 minutes and that power supplies had been fully restored across the entire country by 5.40 pm – just over 40 minutes after the event started.
“We appreciate the disruption caused and will continue to investigate, with the generators involved and wider stakeholders, to understand the lessons learned,” it added.