I've personally watched two locomotives when the regulator shorts. It does yield spectacular smoke for a very short time! 
The one was at our club, the 10-wheeler went in the long tunnel smoking normally, when it came out, it was AMAZING. The owner was perplexed when I went for the kill switch as soon as I saw it and realized what had happened. Ended up replacing the smoke unit PCB impeller, fan motor, and of course, the voltage regulator. It took no more than 15-20 seconds max to totally destroy the smoke unit.
Did I mention the smoke is IMPRESSIVE for a very short time? 
Oh, and yes, a couple years later, I can still smell the burnt fiberglass from the smoke unit on his 10-wheeler.
Diesels are much more serious as the other regulator I saw go was a diesel, and I was able to save the shell by killing the power in that instance as well. I've also gotten one for repair where the owner wasn't so lucky, and the shell has a large melted spot right under the smoke unit.
