"Doc" wrote in message
oups.com

The transformer - if that's the correct term for it - big
gray basically cylindrical unit on top of a power pole -
near my house blew once. Powerful **BOOM** and a huge
column of flame.

Been there, seen that, from a few blocks away. The boom was audible and the
fire was visible from that distance.

The old transformer in my back yard smoked for several hours, but neither
exploded nor emitted flames. The replacements were appreciably larger!

Not sure what the fuel for the flame
was, do they have oil in them?

Yes, most pole transformers are filled with some kind of insulating,
heat-transferring oily liquid. It may contain nifty stuff like PCBs, though
hopefully those have all been removed.

Also a bit disconcerting
since anyone nearby surely would have been in jeopardy
from flaming debris.

There's a reason why they don't put these things in people's houses!

In fact oil-filled transformers are commonly put in dedicated rooms in
commercial buildings, but they have appropriate design and safety features.

Needless to say, power was out for a while on that one.

We had a transformer blow in a local substation, and had rotating blackouts
for about a week. It was about the size of a small house, and the
replacement had to be trucked in from out of state.