Correct transformer and primary wiring sizing

[Coastalguy1]

I am looking for confirmation on a transformer sizing and primary wiring sizing.

incoming primary voltage=34.5kv
building load= 800amps @ 277/480v
transformer size=750kva 34.5kv pri-277/480v sec
primary wire size= 4-1/c 4/0 34.5kv EPR w/ 133% insulation.

Correct?
:?

 

[bob]

500 kva/(34.5kv x 1.73) = 8+ amps. Did you mean to install 4/0 primary? Possibly you meant #4 primary. That may be the smallest you can get. Max secondary load on transformer is 602 amps.

 

[masterinbama]

Are you sure you need 4 wires on your primary?

 

[Coastalguy1]

Are you sure you need 4 wires on your primary?

Yes

 

[Coastalguy1]

500 kva/(34.5kv x 1.73) = 8+ amps. Did you mean to install 4/0 primary? Possibly you meant #4 primary. That may be the smallest you can get. Max secondary load on transformer is 602 amps.

A 4/0 primary is the standard smallest conductor for our area of application. Our secondary load is like I said about 800amps. I was sizing the transformer a little larger for what possibly could be another building project added to it.
Thanks for the reply Bob.

 

[masterinbama]

Just seemed odd to me, we rarely see a Y-Y transformer. Most are Delta-Y

 

[erickench]

500 kva/(34.5kv x 1.73) = 8+ amps. Did you mean to install 4/0 primary? Possibly you meant #4 primary. That may be the smallest you can get. Max secondary load on transformer is 602 amps.

I think he wrote 750KVA. Thus 750/(34.5 X 1.73)= 12.56 Amps on the primary.
The secondary would be 750K/(277 X 3) = 902.53 Amps on the secondary.

 

[bob]

Thanks Eric for that correction.

 

[Coastalguy1]

Just seemed odd to me, we rarely see a Y-Y transformer. Most are Delta-Y

to clarify, the 4th conductor is a spare in the event of failure to one of the other conductors which would allow for a faster fix.

 

[masterinbama]

to clarify, the 4th conductor is a spare in the event of failure to one of the other conductors which would allow for a faster fix.

Do you pull the spare in the same conduit with the 3 phase conductors, or do you run 1 conduit per phase?

 

[JoeStillman]

Our POCO requires 34.4 kV customer-owned transformers to be Y-Y. When one phase is lost, there is more risk of overvoltage due to ferroresonance on the primary circuit with a delta connected transformer.