Generally in power system mostly two winding transformers are employed. But three winding transformers are employed because of some advantages:
- The most common reason for having a three winding transformer is to provide a delta connection tertiary winding
- To limit the fault level on the low voltage system of the transformer by dividing the LV infeed (in order to provide double secondary windings)
- Providing tertiary winding helps to interconnect different power system operating at different voltages (Three winding transformer helps provide power supply at two different secondary voltages, 220kV/11kV/6.6kV transformer can able to provide power at two different voltage levels (11kV and 6.6kV)
- To regulate the voltage and reactive power of the system by providing synchronous capacitor connected to one of the terminals of the transformer.