London Heathrow Airport Shutdown

[toucana]

London Heathrow airport has been completely shut down today by a major fire in a nearby electricity distribution substation which also took out power to 62,000 local residents. Authorities say that it may take a number of days to restore power to the airport, and air travellers are being advised to avoid Heathrow completely until further notice.

https://www.bbc.co.uk/news/live/cly24zvvwxlt

The fire at the North Hyde electricity substation in Hayes began last night at 23:33 GMT with an explosion in a large transformer which set some 25,000 litres of cooling oil on fire, destroying both the transformer and a nearby backup generator. This is a nightmare scenario for firefighters, because the cooling oil is electrically conductive. You cannot fight a fire like this without first de-energising the entire substation.

One point that has already attracted the attention of power engineers is that a power distribution substation of this type has extensive monitoring equipment which is designed to detect dielectric stress or thermal overload. They are also equipped with a safety cutout known as Bucholz relay which detects the presence of gas in oil-filled transformers caused by dielectric failure. These relays quickly trigger alarms and disconnect the power feeds, and have been in use since 1940.

https://en.wikipedia.org/wiki/Buchholz_relay

In the case of a major civilian airport like Heathrow, critical systems like the ground approach radars used by the ATC tower are run on a ‘Reverse Standby’ system - meaning that those systems are normally powered at all times by special generator sets, and they only lapse back onto national grid power if the local generator sets fail. The reason why Heathrow was completely shut down was because of the large number of other systems such as check-in, ticketing, digital signage and passport control computer systems which aren’t protected by reverse standby arrangements - Terminals 2 and 4 still have no power according to latest reports.