How does power transformer oil support cooling and insulation at high voltages?

Oil supports cooling by carrying heat away from windings and core to the tank walls, radiators, and forced cooling systems. It supports insulation by filling voids and providing dielectric strength that reduces electric stress and partial discharge. At high voltages, oil also helps maintain insulation coordination by improving breakdown margins around conductors and bushings. Proper oil quality and dryness are essential because moisture and contaminants lower dielectric strength and accelerate insulation aging under electrical stress.