A transformer is a piece of static electrical equipment used to transform AC voltage and current to transmit AC power. It is based on the principle of electromagnetic induction to achieve electrical energy transfer. Transformers can be divided into Electrical Transformer, test transformers, instrument transformers, and special-purpose transformers according to their uses: power transformers are necessary equipment for power transmission and distribution and power user distribution; test transformers are used to withstand voltage (boost) electrical equipment. Test equipment; instrument transformers are used for electrical measurement and relay protection of power distribution systems (PT, CT); special-purpose transformers include electric furnace transformers for smelting, welding transformers, rectifier transformers for electrolysis, and small voltage regulating transformers.

　　Power transformers are classified by use: step-up (6.3kV/10.5kV or 10.5kV/110kV for power plants, etc.), liaison (220kV/110kV or 110kV/10.5kV for substations), step-down (35kV/0.4kV for power distribution or 35kV/0.4kV for power distribution) 10.5kV/0.4kV).

　　Power transformers are classified according to the number of phases: single-phase, and three-phase.

　　Power transformers are classified by insulating medium: oil-immersed transformers (flame retardant, non-flame retardant), dry-type transformers, and 110kVSF6 gas-insulated transformers.

　　The cores of power transformers are all core-type structures. The three-phase power transformer configured in general communication projects is a double-winding transformer.