A recently released report details the events surrounding a fire at an electricity substation that caused Heathrow Airport to shut down for almost a full day, disrupting travel for over 200,000 passengers.
The National Energy System Operator (NESO) has identified the probable cause of the fire and revealed that National Grid, the operator of the substation, had been warned about a fault seven years prior.
Here are five key findings from the report.
The NESO report has provided an answer to one of the main questions – what sparked the fire?
The device that caught fire was a “supergrid transformer” responsible for lowering the voltage of high voltage electricity from the transmission grid for use at Heathrow Airport and nearby residences.
Inspectors have determined that the most likely cause of the fire was moisture entering the high-voltage “bushing” – insulation surrounding the connections – resulting in a short-circuit and “arcing” (electric sparks similar to those in a spark plug) which ultimately led to a “catastrophic failure.”
This caused the transformer’s cooling oil to ignite, taking two transformers offline and cutting power to Heathrow.
The report also notes that signs of moisture were detected at the North Hyde location in July 2018. National Grid’s guidelines indicated that these signs were indicative of an imminent fault and should have been addressed. However, the issue was not resolved at the time.
In 2022, basic maintenance on the transformer was postponed. Several attempts were made to schedule maintenance, but none were successful.
Heathrow Airport consumes as much electricity as a small city and has three connections to the national grid. However, it was not considered a likely scenario for one of these connections to fail, and therefore, it was deemed unnecessary to spend the estimated billion pounds to fix the issue, as previously stated by Heathrow.
The NESO report suggests that having three connections to the grid presents opportunities to improve Heathrow’s supply resilience.
National Grid and the local network operator SSEN were aware that electricity from North Hyde supplied Heathrow Airport. However, they were not aware that a disruption in this supply would result in the airport’s closure.
Currently, energy suppliers do not have knowledge of whether their customers are considered “critical national infrastructure (CNI)” – industries such as transportation, defense, government, or communications. The report recommends improved communication between CNI operators and their energy suppliers to prevent interruptions in supply.
Heathrow faced significant backlash following the fire, including criticism for the fact that CEO Thomas Woldbye was asleep when the decision was made to close the airport.
The NESO report states that it was not written to assign blame, but Heathrow has announced that they are considering legal action against National Grid. According to Heathrow, the report highlights “clear and repeated failings” that could and should have prevented the fire. They expect National Grid to take responsibility for these failings.
National Grid maintains that they have a comprehensive maintenance program and will closely cooperate with the Ofgem investigation.