THREE PHASE TRANSFORMER

Different combination of 3 phase transformer
1. WYE-DELTA OR STAR-STAR (Y-Y)
- This connection is most economical dor small high voltage transformer because of the number of turns/phase and the amount of insulation required is minimum. This connection work satisfactorily and if the load is balanced.

2. DELTA-DELTA (Δ-Δ)
- This connection is economical for large low voltage transformer in which insulation problem is not so urgent. Because it increases the no. of turns/phase.

3. WYE-DELTA (Y-Δ)
- The main use of this connection is at substation end of the transmission line where the voltage is to be stepped down.

4. DELTA-WYE (Δ-Y)
- This connection is generally employed where it is necessary to step up voltage as for example at the beginning of high transmission system.

5. OPEN DELTA
- It is employed (a) when the 3 phase loads is two small to warrant the installation of full 3 phase transformer bark. (b) when once of the transformer is Δ-Δ bank is disabled as that service is continued although at reduced capacity and (c) when it is anticipated that in future the load will increase necessitating he closing of open delta.

6. SCOTT CONNECTION
- This is a connection by which 3ø to 3ø transformation is accomplished with the help of 2 transformers. This connection can also be used for 3ø to 2ø transformation.