Transformer fire at North Hyde Substation disrupts West London and Heathrow Airport

What happened

On the evening of 20 March 2025, an explosion and fire occurred at North Hyde Substation, a 275 kV transmission substation in North Hyde, near Heathrow Airport, West London, United Kingdom, at approximately 20:20 local time. The substation formed part of the country's original supergrid, commissioned in the 1950s and 1960s, with some plant several decades old. Supply was interrupted to approximately 67,000 households and businesses at peak. Heathrow Airport, supplied from the substation, lost power to two terminals, which were closed, and more than 1,000 flights were cancelled, disrupting several hundred thousand passenger journeys.

Police declared a major incident and the fire service deployed more than 70 personnel. The national energy department commissioned the independent system operator to investigate under energy legislation, in coordination with the energy regulator, and the fire service led the fire investigation under fire safety regulations. Police stated that the fire was not being treated as suspicious. National Grid Electricity Transmission operates the substation, which is owned by National Grid.

Contributing factors

Public reporting on the independent investigation described a combination of equipment, maintenance and organisational factors. Equipment: the failed transformer was reported to have been installed in 1968, making it around 57 years old at the time of failure, against an asset life expectation of 60 to 65 years in National Grid Electricity Transmission's own framework, with moisture ingress in a phase bushing reported as the technical initiator. Maintenance: the most recent basic maintenance was reported to have taken place in 2018, which placed the unit outside the intervals set out in National Grid Electricity Transmission's policy, following a 2023 revision that extended basic maintenance intervals from four to five years and major maintenance from 11 to 15 years. Planned maintenance was reported to have been deferred on several occasions, including a move from 2024 to 2025 to preserve system security while work proceeded at a neighbouring substation. Fire protection: substation fire suppression equipment at North Hyde Substation was reported as non-functional at inspections in 2022 and 2024 and had not been repaired at the time of the fire, although the fire service view reported publicly was that suppression performance would not have materially changed the outcome.

Lessons learned

1. A 275 kV transformer installed in 1968 failed after moisture ingress in a phase bushing, so operators should check bushing condition on units near 60 years old.
2. Basic maintenance on the unit last took place in 2018, outside policy intervals, so operators should avoid repeated deferral of invasive maintenance on critical ageing assets.
3. Substation fire suppression was non-functional at 2022 and 2024 inspections, so operators should repair known defects on suppression systems to a fixed timescale.

More lessons on electrical protection and isolation, maintenance, inspection and ageing assets, fire suppression and firefighting, from every incident on the register.

Not yet known

• Exact downtime duration and restoration cost
• Transformer model and full maintenance history
• Whether other sites share the same bushing failure mode

This entry is updated when these are reported. Get an alert for the next one like it.

Source

powermag.com