The fire at an electricity substation that led to the shutdown of Heathrow Airport for almost an entire day in March, was caused by a fault that was discovered seven years earlier, but not acted upon.
A final report into the North Hyde substation outage by the National Energy System Operator (NESO) said a ‘catastrophic failure on one of the transformer’s high voltage bushings (insulating material used around electrical equipment) at National Grid Electricity Transmission’s 275kV substation caused the transformer to catch fire’.
The review, which used forensic analysis from the National Grid and London Fire Brigade, said the fire was ‘most likely’ caused by moisture entering the bushing, which caused a short circuit. It is then likely the electricity sparked, igniting oil in the bushing and causing a fire.
An elevated moisture reading in the bushing had been detected in oil samples in July 2018, but had not been fixed.
NESO Chief Executive Officer Fintan Slye said: “The power outage and closure of Heathrow airport 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.”
The power outage and subsequent closure of Heathrow Airport caused around 1,300 flights were grounded, disrupting up to 270,000 passengers.
In response to the report’s findings, a Heathrow spokesperson said: “A combination of outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage.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.”
