What are the applications of oil cooled transformer?

For multi-kilowatt high power work,This oil thermosyphons around its circuit, carrying heat to tubes external to the transformer core for dissipation.





so, as we all notice that for 3.3kv or around, natural air is used to cool, or the fan


if u increase the power = then u r increasing the heat = use oil cooled transformerWhat are the applications of oil cooled transformer?
Power Substation transformers (e.g 33kV and 11kV) and Power distribution transformers on telegraph poles.