It wasn't me, I was nowhere near that area yesterday. Actually, I was but just passing by on the M4. I would guess Rockingit is right. If a 132kV TX goes down it'll take out all the subs until things can be rerouted.
@Dan yes, there are auto fire systems, or deluge systems, on transformers. Larger transformers are normally surrounded with those little glass bulbs that break at certain temperatures. Once they break they set off the system. You wouldn't want to be in a transformer enclosure when that goes off. You wouldn't be able to breathe.
At a guess I would say lack of maintenance could be an issue. I remember years ago before the UK olympics UKPN had a mad panic of servicing the tap changers on transformers all around London. They hadn't had proper maintenance for years and were worried they may have failures due to extra loading. We were really busy that year!
@Dan, in answer to your orange smoke take a look at these. Pretty old videos but fun!