My theory is that the smoke you saw, & the bang you heard was an overload protection device exploding, you probably didn't notice it, it might have been a short distance away, they mostly are, my father was an industrial electrician, & he used to tell me of some amazing things that he'd seen happen, they can be very noisy as I have seen, it happened in a town near where I live, I'll tell you the details if you like, I was in that town at the time.