What is the difference between dry type transformer and oil type transformer?

Dry type transformers use air and solid insulation, often cast resin or VPI, and do not contain liquid dielectric. Oil type transformers use insulating oil for both dielectric strength and heat removal. Oil units usually achieve higher MVA ratings, better thermal performance, and smaller footprint for the same power, but they need spill control, oil testing, and fire safety planning. Dry type units are preferred indoors and in sensitive buildings because they reduce spill risk and can be designed for lower fire load, though they may be larger and noisier.