THREE-WINDING TRANSFORMERS
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 a Tertiary winding of the transformer. Because of this third winding, the transformer is called three winding transformer or 3 winding transformers.
TERTIARY WINDING
Tertiary-winding is generally connected in delta. Delta connected tertiary winding reduced the impedance offered to zero sequence current. A large unbalance of phase voltage may be produced, which is compensated by large tertiary winding circulating currents. Third winding is also known as stabilizing winding.
ADVANTAGES
1. The main advantage of used three-winding transformer is that when any fault and the short circuit occur on the primary and secondary side. So large earth fault current flows for proper operations of protective devices.
2. When the load is unbalanced, tertiary winding reduced third harmonic voltage and limits the unbalanced voltage. The magnetizing current is neglected.
3. The tertiary winding may be used for connecting shunt capacitors.
4. In the testing transformer, it is used as the voltage coil.
5. To supplying the voltage to the device which is operated different voltage from secondary and primary voltage.
DISADVANTAGES
1. The additional winding is used hence more copper is require, so cost is high.
2. Construction is a little complex.
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