Transformer (Transformer) is the use of the principle of electromagnetic induction to change the alternating current voltage device, the main building blocks are the primary coil, the secondary coil and the iron core (magnetic core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer) and so on. According to the use can be divided into: power transformers and special transformers (furnace transformers, rectifier transformers, frequency test transformers, regulators, mining transformers, audio transformers, medium frequency transformers, high frequency transformers, shock transformers, instrument transformers, electronic transformers, reactors, mutual inductors, etc.). Circuit symbols are often used as the beginning of the T number. Example: T01, T201, etc.