In order to input different voltages, the input winding also use multiple windings to adopt different input voltage.Three separate windings which connected by different ways that fed into a three-phase ac power supply, which called three-phase transformer.
Three phase transformer is a combination of three single - phase transformers with the same capacity.It has three iron core columns, each of which is wound around two coils of the same phase, one is a high-voltage coil, and the other is a low-voltage coil.Three-phase transformer is a generator with the same amplitude, the same frequency and the phase difference of 120° which is called three-phase generator.Three phase generator as a power source known as three phase power.The circuit supplied by three phase power supply is called three phase circuit.U, V, W is called three phases, the voltage between phase and phase is line voltage, the voltage is 380V. Between phase and center line is called phase voltage. The voltage is 220V.When the ac voltage is applied to the primary winding.The ac current flows into the winding which generate excitation effect. The alternating flux is generated in the core. This alternating flux not only passes through the primary winding, but also the secondary winding.At this time, if the secondary side is connected with the load of the external circuit, there will be an ac current outflow, so there is an output of electrical energy.Transformers have different operating conditions, installation areas, different voltage levels and capacity levels, different structural forms and cooling methods. So they should be classified according to different principles.