Dry-type transformers are primarily classified based on the thermal rating of their insulation system (insulation grade), cooling method, and winding conductor material. The most common classification is by insulation grade, which determines the transformer's maximum temperature tolerance during long-term operation and is directly related to its overload capacity and service life. Key grades include B (130°C), F (155°C), and H (180°C), with F being the market mainstream due to its excellent balance of performance and cost. Cooling methods also include natural air cooling (AN) and forced air cooling (AF), the latter of which significantly increases the transformer's output capacity in a short period of time. Another important classification is based on winding material, primarily splitting into traditional epoxy resin cast windings and more advanced impregnation (VPI process) non-encapsulated windings. Each has its own unique characteristics in terms of heat dissipation, environmental friendliness, maintainability, and short-circuit resistance.