Transformer is a device which USES the principle of electromagnetic induction to change the ac voltage. The main components are primary coil, secondary coil and iron core. The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer) and so on. It can be divided into power transformer and special transformer (furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mine transformer, audio transformer, intermediate frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer, reactor, mutual transformer, etc.) according to its USES. Circuit symbol T is often used as the beginning of a number. Example: T01, T201, etc.