Very nice report on the fire at North Hyde substation which took down Heathrow in March.
tl;dr:
* Fire was caused by moisture ingress in a high voltage bushing which was detected in 2018 but got lost in the system.
* North Hyde is an ageing substation which didn't have adequate protection against spread of fire
* Heathrow didn't think that a loss of grid feed was a plausible risk, so they assumed 10-12 hours was a reasonable recovery time from that.
@russss Was there no other sub-station which could pick up the slack due to loss the North Hyde? Was Heathrow supplied and is still supplied by a single substation?
Also how come moisture ingress that happened in 2018 resulted in a fire in 2025? I get that deferring 2022 maintenance on one of the transformers was contributing factor. But it's surprising that all 3 transformers were in such close proximity that fire in one caused a cascade failure in others.
cc @Lydie
Russ Garrett
Welkin
ℒӱḏɩę 
💾