Source: Sharecast
Publishing its final report into incident, the National Energy System Operator said the fire had been caused by a "catastrophic failure" at the North Hyde electricity substation in Hayes, west London.
The report found moisture had entered one of the transformer's high-voltage bushings, causing the substation to catch fire. Current flows in and out of transformers via bushing equipment.
An elevated moisture level had first been detected in July 2018, the report found, "but mitigating actions appropriate to its severity were not implemented".
Ofgem said: "The root cause of the fire was a preventable, technical fault."
It will therefore now look at whether National Grid complied with the relevant legislation and licence conditions relating to North Hyde.
It will also commission an independent audit of all of National Grid’s critical assets to establish if failures at North Hyde were a one-off or more systemic.
The fire late on 20 March caused a major power outage at Heathrow. As a result, Europe’s busiest airport was forced to shut on 21 March, grounding flights and affecting thousands of passengers worldwide.
Akshay Kaul, director general for infrastructure at Ofgem, said: "The fire resulted in global disruption, impacted thousands of customers and highlighted the important of investment in our energy infrastructure.
"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 ad hold companies fully to account."
Fintan Slye, chief executive at NESO, said: "The power outage and closure of Heathrow were hugely disruptive and our report seeks to improve the way parties plan for and respond to these incidents, building on the underlying resilience of our energy system."
Ed Miliband, energy secretary, called the report "deeply concerning, because known risks were not address by the National Grid Electricity Transmission".
National Grid said in a statement that it had a "comprehensive" asset inspection and maintenance programme.
It continued: "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 testing the resilience of substations that serve strategic infrastructure."
Heathrow said: "A combination of outdated regulation, inadequate safety mechanisms and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage.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."
