1. Classified by purpose: there are power transformers, special transformers (electric furnace transformers, rectifier transformers, power frequency test transformers, voltage regulators, mining transformers, audio transformers, intermediate frequency transformers, high-frequency transformers, impulse transformers, instrument transformers, electronic transformers, reactors, transformers, etc.).
2. Classified by structure: there are double winding transformers, three winding transformers, multi winding transformers, and autotransformers.
3. Classified by cooling method: there are oil immersed transformers and dry-type transformers.
4. Classified by cooling methods: there are natural cooling, air cooling, water cooling, forced oil circulation air (water) cooling, and water internal cooling.
5. Classified by iron core or coil structure: core type transformer (plug-in iron core, C-type iron core, ferrite iron core), shell type transformer (plug-in iron core, C-type iron core, ferrite iron core), ring type transformer, metal foil transformer, radiation type transformer, etc.
6. Classified by the number of power phases: single-phase transformer, three-phase transformer, multiphase transformer.
7. Classified by conductive materials: there are copper wire transformers, aluminum wire transformers, and semi copper and semi aluminum, superconducting transformers, etc.
8. Classified by voltage regulation method: it can be divided into non excitation voltage regulating transformers and on load voltage regulating transformers.
9. Classified by neutral insulation level: there are fully insulated transformers and semi insulated (graded insulation) transformers.