> The cans are full of mineral oil, or sometimes vegetable oil! (Why are they full of oil? I don't know; I guess for insulation. But I could probably find out.)
> Its functions are to insulate, suppress corona discharge and arcing, and to serve as a coolant.
Isn't it also to keep a pressurized environment in the can and prevent moisture leaking in, resulting in rust? I was reading up on these too recently. Oil is also used in large circuit breakers to extinguish electrical arcs.[1]