What is the purpose of oil in transformer cooling systems?

Oil removes heat from the windings and core and transports it to radiators or coolers where it is released to air or water. It also improves thermal contact by filling voids and ensuring uniform temperature distribution. By keeping hot spot temperature under control, oil protects cellulose insulation from accelerated aging and preserves transformer loading capability. In addition, oil circulation supports cooling during transient overloads and helps stabilize operating temperature across varying ambient conditions.