WHAT will happen if you run oil transformer with out oil?
As well as providing a cooling medium, transformer oil is also
used to insulate a transformer. As its dielectric strength (how
well it insulates) is much higher than air, it means that
components within a transformer that are at different potentials
can be placed much closer together if they are immersed in oil. So,
operating an oil-filled transformer without oil will likely cause
insulation breakdown within the transformer.