1. According to the number of phases: 1. Single-phase transformer: used for single-phase load and three-phase transformer group. 2. Three-phase transformer: used for voltage rise and fall of three-phase system. 2. According to the cooling method: 1. Dry-type transformer: rely on air convection for natural cooling or increase fan cooling, mainly used for power consumption of small-capacity transformers such as high-rise buildings, high-speed toll stations, local lighting, and electronic circuits. 2. Oil-immersed transformer: Oil is used as the cooling medium, such as oil-immersed self-cooling, oil-immersed air-cooled, oil-immersed cooling, forced oil circulation, etc. 3. Classification by use: 1. Power transformer: used for rising and falling voltage of power distribution system. 2. Transformers for instruments: measuring such as transformers, converters, instruments and relay protection devices. 3. Test transformer: It can generate high voltage and conduct high voltage test on electrical equipment. 4. Special transformers: electric furnace transformers, rectifier transformers, adjustment transformers, electrostatic capacitance transformers, phase-shifting transformers, etc. Fourth, according to the winding form: 1. Double winding transformer: used to connect the two working voltage levels of the power supply system. 2. Three-winding transformer: generally used in substations in power system areas to connect three voltage levels. 3. Autotransformer: used to connect power systems with different voltages. It can also be used as an ordinary step-up or step-down transformer. V. According to the form of iron core: 1. Core type transformer: a power transformer used for high voltage. 2. Amorphous alloy transformer: The amorphous alloy core transformer is made of new magnetically conductive material, and the no-load current is reduced by about 80%. 3. Shell transformer: used for electric furnace transformers, electric welding transformers and other special transformers for high current electronic equipment and power transformers for TVs and radios. A transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are primary coil, secondary coil and iron core (magnetic core). The main functions include voltage conversion, current conversion, impedance conversion, isolation, stabilization (magnetic saturation transformer), etc. According to the use, it is divided into power transformers and special transformers (electric furnace transformers, rectifier transformers, commercial frequency test transformers, transformers, mining transformers, audio transformers, intermediate frequency transformers, high frequency transformers, impact transformers, instrument transformers, electronic transformers, reactors , transformers, etc.).