National Grid’s first report into the causes of Britain’s biggest blackout in more than a decade is expected to blame a string of avoidable faults at electricity generators, networks and rail companies.
On Friday the company, which is responsible for keeping the lights on, will submit an interim report to the energy regulator detailing the cause of the widespread chaos triggered by last week’s grid outage.
The system operator will also face questions from the energy minister, Kwasi Kwarteng, who will visit the National Grid control room on Friday.
A full report will be published in about three months. The National Grid is also facing a separate government probe by the energy emergencies executive committee.
Kwarteng told the BBC Radio 4 Today programme that the “resilience” of the energy system is more important than last week’s individual power plant shutdowns in making sure that the “unacceptable” blackout chaos does not happen again.
He said: “I think it’s extremely unlikely that it will happen again.” The minister added that the International Energy Agency had “said that the UK has an exemplary energy network and we must make sure that what happened last week does not happen again”.
A National Grid spokesman declined to comment on the report findings.
It is widely expected to confirm that the outage occurred during rush hour last Friday evening because of a steep drop in the grid’s overall frequency – or energy intensity – which National Grid is supposed to keep at about 50Hz.
The frequency fell to below 49Hz in a matter of seconds after the “near simultaneous” shutdown of a gas-fired power plant, owned by the German utility RWE, and an offshore wind farm owned by the Danish energy firm Ørsted because of faults with their equipment.
Both companies have said relatively minor shutdowns are not uncommon.
National Grid is understood to be investigating whether a lightning strike to the grid near RWE’s gas plant in the Bedfordshire area could be to blame for the shutdown of the two electricity generators.
A strike could, theoretically, have sent a false reading to both power generation sites causing their automatic systems to shut down as a safety precaution.
Ørsted said its Hornsea offshore wind farm, off the east coast of England, experienced a technical fault which caused the wind farm to shut down and pulled 800MW of electricity from the grid.
It said National Grid would normally have been able to cope with a shutdown of this size.
RWE said it was still investigating the shutdown of its Little Barford gas plant, which had a 730MW capacity, but believed its automatic control system “detected an abnormality and initiated a safety shutdown of the plant”.
A spokesman at the grid said: “Such events are not uncommon in power stations. 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.”
The twin shutdowns have raised questions over whether National Grid should be better prepared for near-simultaneous outages on the grid.
The Guardian revealed that the system operator weathered three of its most severe frequency losses of recent years in the three months leading up to the blackout because of unexpected outages.
Thomas Edwards, an analyst at energy consultancy Cornwall Insight, confirmed that experts had observed the grid’s frequency fluctuations were “getting wider”.
He said: “Frequency levels are less clustered around 50Hz compared with three years ago, and we can see a clear trend of higher volatility in the system.”