What are the key differences between dry and oil type transformer designs?

Oil type transformers use liquid insulation and cooling, enabling compact high voltage and high MVA ratings with strong thermal performance. Dry type transformers use air and solid insulation (often cast resin) and are preferred indoors where fire and spill risk must be minimized. Oil designs usually offer lower cost per kVA at higher ratings but require containment, oil maintenance, and fire mitigation. Dry types can have higher upfront cost and larger size at equivalent ratings.