The fire that caused the chaotic shutdown of Heathrow airport in March was likely caused by a “catastrophic” failure of a crucial component at an electricity substation that should have been prevented, Britain's National Energy System Operator (NESO) said in a report on the incident on Wednesday.
Regulator Ofgem today said it will launch a further investigation of the missed opportunities by National Grid to maintain the substation properly and could take enforcement action.
“This review has seen evidence that a catastrophic failure on one of the transformer’s high voltage bushings at National Grid Electricity Transmission’s 275kV substation in Hayes caused the transformer to catch fire,” the report by the National Energy System Operator said.
“This was most likely caused by moisture entering the bushing, causing an electrical fault.”
The electricity likely then "arced" which combined with air and heat to ignite the oil, resulting in a fire."
The fire led to a loss of electricity to Britain’s biggest airport, resulting in its total closure for most of Friday March 21, as well as to more than 70,000 other customers. Around 270,000 passenger journeys were cancelled or redirected.
The airport’s £3.2 million a year chief executive Thomas Woldbye was criticised for going to bed and turning his phone to silent on the night of the shutdown, leaving the chief operating officer, Javier Echave, to take key decisions,
The report said “forensic analysis” carried out by National Grid Electricity Transmission and London Fire Brigade uncovered he cause of the blaze.
However it said an “elevated” level of moisture had been detected in oil samples taken as long ago as July 2018 “ but mitigating actions appropriate to its severity were not implemented.”
A decision to defer vital maintenance in 2022 also meant that “the issue went unaddressed”
National Grid’s own internal technical guidance dictated that if elevated moisture samples are detected at a substation, it should be put out of service until the bushing can be replaced, or mitigating actions put in place.
But the report said: “While the reading was recorded, the mitigations appropriate to its severity, as set out in National Grid Electricity Transmission’s relevant policy, were not actioned at the time.”
Once the fire had broken out it “was not possible to keep either the North Hyde 275kV or 66kV substation sites operational because of the effects of heat and smoke from the fire, and the need to fight the fire safely.”
Energy Secretary Ed Miliband said: “Following the North Hyde Substation fire which caused widespread disruption, the government took rapid action to commission the National Energy System Operator (NESO) to investigate the incident.
“The report is deeply concerning, because known risks were not addressed by the National Grid Electricity Transmission, and Ofgem has now opened an official enforcement investigation to consider any possible licence breaches relating to the development and maintenance of its electricity system at North Hyde.
“There are wider lessons to be learned from this incident. My department, working across government, will urgently consider the findings and recommendations set out by NESO and publish a response to the report in due course.”
A Heathrow spokesperson said: "Heathrow welcomes this report, which sheds further light on the external power supply failure that forced the airport’s closure on 21st March. A combination of outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage.
“We expect National Grid to be carefully considering what steps they can take to ensure this isn’t repeated. Our own Review, led by former Cabinet Minister Ruth Kelly, identified key areas for improvement and work is already underway to implement all 28 recommendations."
Akshay Kaul, Director General for Infrastructure at Ofgem, said: “The North Hyde substation fire resulted in global disruption, impacted thousands of local customers, and highlighted the importance of investment in our energy infrastructure.
"As a result of the report’s findings, we have opened an investigation into National Grid Electricity Transmission (NGET). We have also commissioned an independent audit of their most critical assets.
“Ofgem will also further examine the incident and its causes and take further action as appropriate.
“We expect energy companies to properly maintain their equipment and networks to prevent events like this happening. Where there is evidence that they have not, we will take action and hold companies fully to account.
“Britain has one of most reliable energy systems in the world and thankfully incidents like this are rare. We must continue to invest in the system to maintain that resilience.”
A National Grid spokesperson said: As NESO’s report sets out, in Great Britain we have one of the most reliable networks in the world, and events of this nature are rare. “National Grid has a comprehensive asset inspection and maintenance programme in place, and we have taken further action since the fire. This includes an end-to-end review of our oil sampling process and results, further enhancement of fire risk assessments at all operational sites and re-testing the resilience of substations that serve strategic infrastructure.
“We fully support the recommendations in the report and are committed to working with NESO and others to implement them. We will also cooperate closely with Ofgem’s investigation. "There are important lessons to be learnt about cross-sector resilience and the need for increased coordination, and we look forward to working with government, regulators and industry partners to take these recommendations forward."
Fintan Slye, Chief Executive Officer, NESO said: “NESO’s final report into the North Hyde Substation outage sets out the root cause and a clear set of recommendations to further improve the resilience of Great Britain’s energy system, and the resilience of its critical national infrastructure
.“Whilst the power outage and closure of Heathrow airport were hugely disruptive, all parties responded quickly and professionally. This report seeks to improve the way parties plan for and respond to these incidents, building on the underlying resilience of our energy system and the wealth of expertise and commitment across the sector.
