Utility Transformer 13800 Primary

[GoldDigger]

Xcel Energy has this clause in the service book"
"If the customer?s power requirement, within six months after the installation of transformers, proves to be less than shown in the application for service, the Company may make a reduction in the installed transformer capacity and the customer will be required to pay the Company the cost of making the change.

If the customer?s power requirement, within six months after the installation of transformers, proves to be more than the installed transformer capacity, the Company may make an increase in the installed transformer capacity and the customer will be required to pay to the Company the cost of making the change."

In their territory you would not want to 'mis-size' your service on your permit application, as you did in your example, it could come back and cost you.

Regardless the point still is, that utilities have their own methods for determining the size of their service equipment.

Interesting Catch 22 they get you in there:
You give them an estimated load in your application and if you are 1kW lower than that, you might end up paying. While if you underestimate and you are still within the capacity of whatever size transformer they chose to install, then you are still OK.

But if for any reason they choose to install a transformer with a lower capacity than your stated load (as it is within their power to do) then you are still screwed if you actually use what you stated. :blink:

 

[weressl]

To add to what the others have said.

The power company does not care what the NEC based load calculations are. The power company does not care what size main breaker is being supplied. They use their many years of data to determine what the building will actually use.

They are also not opposed to using a transformer above its labeled rating for short periods of time. They rely on the thermal mass of the transformer to keep it from getting overheated during the short periods of overload.

In short what they do puzzles us but works fine the vast majority of the time and saves all of us money.

I wonder how OCPD coordination works with the customers protective devices.

 

[jim dungar]

I wonder how OCPD coordination works with the customers protective devices.

It usually doesn't.
Except for 'primary rate' customers, I have never seen a utility concerned with coordination with the customer.

 

[Open Neutral]

[POCO] are also not opposed to using a transformer above its labeled rating for short periods of time. They rely on the thermal mass of the transformer to keep it from getting overheated during the short periods of overload.

Not just them. WMATA has many traction power stations for the Metro. These are 6-9MW, taking in 13.2KV and producing 750VDC. While they are slowly upgrading the 6MW ones, they have a ways to go.

I'm told that by the end of rush hour, many of the transformer temps "are in the red" and take hours to cool down again.