TERTIARY WINDING (Third Winding)

Tertiary / Stabilizing Winding:

In transformers there are two windings primary and secondary, but in some case you may see in addition to them one more winding named as tertiary winding.

This winding details were discribed in BS: 171-1959 as a delta winding used at a Star - Star Connected transformer or Auto transformer for any of the following usages;

1. Used to reduce the interference with communication circuit due to third harmanic currents in the lines and earth.
2. Used for facilitate the flow of Zero Phase Sequence Current
3. To reduce the third harmonic voltages in system and transformer
4. Injecting the reactive power for maintain the certain voltage level.( Tertiary connected with static capacitors or with synchronous condenser)
5. Auxiliary supply requirement at system which lower than primary and secondary winding voltages.

Its rating may be less apprx. 33.33% of main winding. This delta connected winding may be loaded or unloaded as per requirement. If it unloaded it called as stabilising winding. The design of tertiary based on the fault conditions.