what is Tertiary winding

What is Tertiary Winding? What is Three Winding Transformer?
In some high rating transformer, one winding in addition to its primary and secondary winding is used. This additional winding, apart from primary and secondary windings, is known as Tertiary winding of transformer. Because of this third winding, the transformer is called three winding transformer or 3 winding transformer.

Advantages of Using Tertiary Winding in Transformer
Tertiary winding is provided in electrical power transformer to meet one or more of the following requirements-

a.) It reduces the unbalancing in the primary due ato unbalancing in three phase load.

b.) It redistributes the flow of fault current.

c.) Sometime it is required to supply an auxiliary load in different voltage level in addition to its main secondary load. This secondary load can be taken from tertiary winding of three winding transformer.

d.) As the tertiary winding is connected in delta formation in 3 winding transformer, it assists in limitation of fault current in the event of a short circuit from line to neutral.

Rating of Tertiary Winding of Transformer:
Rating of tertiary winding of transformer depends upon its use. If it has to supply additional load, its winding cross - section and design philosophy is decided as per load, and three phase dead short circuit on its terminal with power flow from both sides of HV and MV.
In case it is to be provided for stabilizing purpose only, its cross-section and design has to be decided from thermal and mechanical consideration for the short duration fault currents during various fault conditions single line to ground fault being the most onerous.

Purpose of Transformer Core

In an electrical power transformer, there are primary, secondary and may be tertiary windings. The performance of a transformer mainly depends upon the flux linkages between these windings. For efficient flux linking between these windings, one low reluctance magnetic path common to all windings should be provided in the transformer. This low reluctance magnetic path in transformer is known as core of transformer.