Why are oil cooled distribution transformers widely used in grids?

Oil cooled units provide high dielectric strength and efficient heat removal at relatively low cost per kVA, making them practical for outdoor pole mounted and pad mounted service. Oil enables compact designs, good overload handling for short durations, and reliable insulation coordination for lightning and switching surges. Utilities also have mature maintenance practices for oil sampling, leak management, and condition monitoring, supporting long asset life in widespread deployments.