Why are oil filled transformers commonly used in distribution networks?

Oil filled transformers offer strong dielectric insulation and efficient heat removal, allowing compact designs and good overload capability. They tolerate outdoor environments well, handle thermal cycling, and can be built for high kVA ratings with reasonable footprint. Utilities also benefit from established maintenance practices like oil testing, filtration, and DGA trending. While dry type units improve fire behavior indoors, oil filled designs remain common outdoors because they are cost effective, robust, and efficient for medium voltage distribution.