Why transformer oil is used for both cooling and insulation?

The same liquid can do both because its chemistry and dielectric behavior support high electric field withstand while also providing strong convective heat transfer. Oil circulates through internal ducts, removing heat from copper and paper insulation and carrying it to external radiators or coolers. Simultaneously, it fills voids and increases breakdown strength in critical clearances. This dual function enables compact, efficient transformer designs and reliable operation across load cycles.