[belter]

Old oil transformer. The insulation breaks down in old transformers. It happens sometimes. No need to involve Russian conspiracy theories at this point in time... :-)

"How to Prevent Substation Fires": https://www.oilbarriers.com/blog/suppress-substation-fires/

https://youtu.be/2np745xyQ7o

[milleramp]

Probably, but definitely check for bullet holes. https://en.wikipedia.org/wiki/Metcalf_sniper_attack

[Calwestjobs]

just check newspapers title pages in UK today.... https://www.bbc.com/news/articles/c70wylzyqw2o

[sega_sai]

It could be an old transformer, but it is not known at this time.