[belter]

It's not looking good and the other alternative airports in the UK are at full capacity:

"Heathrow Doesn't Know When Power Will Be Back, Days of Disruption Expected" - https://www.newsweek.com/heathrow-airport-fire-counterterror...

If the entire transformer is lost, procuring replacement transformers for substations can take from several months to years. Insulation failures are relatively common in older power substations. It seems someone should have done a better job preparing disaster recovery scenarios for Heathrow.

Edit:

BBC reporting "some power" restored on a "interim basis" as the power company is now using a different substation. It would be curious if the increased effort on other substations would then cause further power failures...A bit like the postmortems of global cloud providers, where taking a node out, causes increased stress on other nodes...

[quickthrowman]

One would hope the utility would have a spare transformer or two sitting around, I guess that’s not guaranteed tho. MV and HV transformers have extremely long lead times like you said.

[blibble]

the utility are expecting to go back on at 3pm...

(edit: and are back)

[belter]

Yeap: https://www.nationalgrid.com/incidents