What are the pros and cons of star/delta connected transformer ?

[saiet]

Hello,

What are the advantages and disadvantages of a star/delta transformer in a case which star connection is effectively grounded while delta side is grounded via zigzag grounding transformer? The voltage level is 400/33.6 kV.

Thank you.

 

[RRaghunath]

Star on 400kV side allows the winding insulation to be graded (non-uniform) reducing the cost of transformer.
The insulation level of OLTC also will be less and thus making it cheaper.
Earthed star point reduces the zero sequence impedance of 400kV system, which means improved fault levels for earth faults.
Delta on 400kV side and Star on 33kV side would eliminate zigzag earthing transformer by providing star point for earthing.
Solidly earthed 33kV neutral will improve the earth fault levels in 33kV system which may be desirable in case the 33kV distribution downstream is through overhead lines.