Step Up Transformers 3

[markjp]

I have a question regarding step up transformers if someone could help please. I have searched the threads and not able to get an answer to my query. Our plant has 33kV distribution from utility and we need to install emergency standby generators in case utility supply is lost. We are considering 4 parallel 1MVA 415V generators each with 415V/33kV step up transformers to connect to 33kV switchboard. My question is what would be the preferred winding configuration and earthing for the step ups. The 415 generator wye to be direct earthed and considering the step up transformer to be wye/wye with the 33kV side direct earthed. Does this sound feasible. Could have delta on the 33kV side and separate earthing transformer, but looks unnecessarily complicated. The 33kV is distributed through the plant feeding a number of delta/wye step down transformers. Are there any potential issues using the wye/wye step ups with the direct earthing on 33kV side?

 

[waross]

I prefer delta connected transformers on the 415V side and impedance grounded generator wye points. The impedance grounding limits possible damage from 415V ground faults. The dela/wye will translate 33kV gropund faults into 415V line to line currents that the generator may be better able to withstand.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

I would go with 415 delta to 33 kV wye step up transformer. That provides you a means to ground 33kV side source.

Wye-Wye are best avoided. You can search for that topic on this website. You may also be best advised to engage services of a professional engineer, experienced in this area (MV systems and generator paralleling).

Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

Yep, what they said, delta on the 415, with the generators impedance grounded, and wye on the 33kV side with the grounding compatible with the existing 33kV grounding. Always the best arrangement if you aren't tying loads directly to the generator terminals.