Utility Transformer Sizing

[deltawhy]

Hello, I need to size a utility transformer that will be feeding a large commercial building. My main distribution panel is rated 3000A at 120/208V. Therefore, I have sized the transformer to be 1MVA. But, the utility's customer transformer guidelines state that a 1000kVA transformer's maximum aggregate service panel size is 8800A? Whats going on here? (The transformer is oil filled)

Thanks for the input,

Daniel

 

[davidbeach]

Why do you need to size it? Sounds like the utility does the sizing. Customers have to size transformers based on hard and fast code rules, such as the NEC. Utilities, on the other hand, get to size transformers based on experience. They'll put in the transformer they think is best and if it gets to be too overloaded too often they'll replace it with a bigger one. No big deal.

 

[dpc]

It's common for utilities to install transformers smaller than the service entrance rating since their experience shows them that actual loads are generally a lot less than the calculated demand load per NEC requirements.

This where the #4/0 AL often meets the 750 kcmil copper!

As David said, the utility is taking the risk, not the customer. For a large utility, the core loss savings alone can be significant.





David Castor

http://www.cvoes.com