How does transformer oil circulation support cooling?

Circulating oil carries heat away from windings and the core into radiators or coolers where it is rejected to air or water. In natural circulation, density differences between hot and cool oil drive flow; in forced oil systems, pumps increase flow to reduce hot spot temperatures during high loads. Good circulation maintains uniform temperature distribution, prevents local overheating, and slows insulation aging. It also helps flush contaminants toward filters or treatment systems when conditioning is performed.