Back in the mid 1980's I worked for General Electric as Technical Support Engineer of Industrial Sales. I had to visit the Renaissance Center in downtown Detroit. Underground they had numerous large power transformers that were overheating, and some had actually exploded, and caught fire! I had to inspect them and determine why this was happening, and come up with a solution. It turned out to be rather simple. In the base of the transformer cabinets, they had large cooling fans that drew in cool air off the floor, and directed it up though the transformers. The problem was that these cooling fan motors were vented on each end, to cool themselves. They were sucking up dust bunnies, and clogging the vents, causing the cooling fan motor itself to over heat, and burn out. This stopped the cooling of the transformer, causing them to overheat, and burn up! The fix was to replace the cooling fan motors with one that was sealed, non-vented, with a higher service factor. Problem solved.
