When the transformer is make of three winding is called Tertiary winding. It is generally connected in delta. generally Transformer have primary and secondary winding, if transformer constructed with third winding is called tertiary winding or three winding transformer.
When the fault or short circuit is occur, high circulating current will flow through the primary and secondary winding. Because of that current , overheating of transformer is produced. By using tertiary winding we can avoid that overheating. Reactant of tertiary winding is such that which can limit over current.
fig shows the three winding transformer connection,
The main advantage of used thee winding transformer is that when any fault and short circuit is occur on primary and secondary side. 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. because, A Delta connected tertiary winding reduced the impedance offered to zero sequence current. So large earth fault current flows for proper operations of protective devices.when the load is unbalanced, tertiary winding reduced third harmonic voltage and limits the unbalanced voltage. the magnetizing current is neglected.
Each winding represented by the equivalent reactance and resistance. Fig shows the equivalent circuit of three winding transformer.
Purpose to used tertiary winding:-
- A three winding transformer can be used to large load split winding generator.
- In the testing transformer it is used as the voltage coil.
- For supplying additional load which is must be insulated from the secondary winding.
- Used as different voltages operated three phase supply system.
- To supplying the voltage to device which is operated different voltage from secondary and primary voltage.
Disadvantages of tertiary winding:-
- Additional winding is used hence more copper is require, so cost is high.
- Construction is little complex .
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