New Civil Engineer
Rob Hakimian
02 July 2025
Energy regulator Ofgem has launched an enforcement investigation into National Grid Electricity Transmission (NGET) over the North Hyde substation fire that shut down Heathrow Airport, as a report into the incident has revealed continual maintenance failures in the lead up.
Heathrow Airport Ltd has also said it is considering taking legal action against National Grid.
At 11.21pm on that evening, one of the substation’s three supergrid transformers – SGT3 – experienced a fault and subsequently caught fire.
Forensic analysis by NGET and the London Fire Brigade pinpointed the cause to a catastrophic failure of SGT3’s high voltage bushings. This failure was attributed to moisture ingress, which likely caused a short circuit, sparking an electrical arc. The arc ignited the transformer’s insulating oil, sparking a fire that rapidly developed and caused extensive damage.
