Fire That Closed Heathrow Airport Caused By Unrepaired Transformer

London: A fire at an electrical substation that forced a shutdown at London's Heathrow Airport in March was likely caused by moisture entering electrical components, a problem first flagged in 2018, a report said Wednesday.

Water entering a transformer and causing a short circuit "most likely" started the fire, according to the National Energy System Operator (NESO) report, adding that elevated moisture readings were detected in July 2018 but "mitigating actions appropriate to its severity were not implemented".

The fire broke out at the North Hyde substation in West London, around two miles (3.2 km) north of Heathrow, at 11:21 pm on March 20, resulting in a complete loss of power supply to part of the airport's private internal electrical distribution network.

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The airport was closed for most of March 21, affecting thousands of passengers around the world and raising serious questions about the reliability of one of the UK's most critical pieces of infrastructure.

Using forensic analysis from the National Grid Electricity Transmission and London Fire Brigade, the report concluded that "a catastrophic failure" on high voltage "bushing" components caused a fire to ignite on the transformer.

"This was most likely caused by moisture entering the bushing causing a short circuit. The electricity likely then 'arced' (causing sparks) which combined with air and heat to ignite the oil, resulting in a fire," it added.

An elevated moisture reading in one of the bushings had been detected in oil samples taken in July 2018, indicating "an imminent fault and that the bushing should be replaced".

However, "controls in place were not effective and failed to identify subsequently that action had not been taken in relation to the elevated moisture reading," it said.
Energy Minister Ed Miliband called the report "deeply concerning".

"Known risks were not addressed by the National Grid Electricity Transmission, and (energy regulator) Ofgem has now opened an official enforcement investigation to consider any possible licence breaches," he said in a statement.

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