When I first found it and scratched a little of the dirt off, I could see high voltage, large HV leads and 60 kVDC on the spec plate, so I assumed rather quickly that it was a 60kVDC power supply. Later when I got home and tested it carefully through a variac it was acting weird and I feared it was internally shorted.
But cleaning the spec plate properly revealed that it was infact a 240VAC isolation transformer with a 60 kVDC rated insulation between sides.
It suddenly became a much more rare find than just another HV supply :)