Bank of 2 - 1425 kV BIL and 1 - 1550 BIL one phase transformers

[EddyPach]

Can somebody tell me if it is feasible in a bank of three, to replace 2 x 65 MVA, one phase, 400 kV units with 1550 kV winding BIL, and keep a third one that is 1425 kV BIL rated? It looks weird that the bank should be split in 2 transformers with 1425 BIL and 1 with 1550 kV wqinding BIL.

 

[electricpete]

I can think of no reason why the BIL needs to "match" (as long as the lower bil is satisfactory for your environment and surge protection).

Voltage ratio on the selected taps is of course a parameter you need to match very closely.

 

[EddyPach]

Thank you, electricpete. Yet, what about the coordination of insulation? Does it get affected in any way? My first thougth when seeing a bank of three single phase transformers, 2 x 1425 BIL and 1 x 1550 BIL was of astonishment!

 

[dpc]

I don't think different BIL will have any impact on operation of the bank. Just make sure surge arresters are correctly rated.

I would be much more concerned about the impedance. It is important that all three units have matching impedances.