Has anyone else had trouble getting fault current values from Xcel Energy? We were told all that would be provided on secondary metered services would be infinite bus calculations. I am not a big fan of doing calculations for arc flash based off infinite bus numbers.

I have not had to deal with Xcel Energy but a long time ago I did have an issue with a utility as all they would give were infinite bus. I solved the issue by:
1. Pointing out that IEEE 1584-2002 states to obtain utility max and min available fault current
2. Explained that infinite bus could lead to employees having inadequate PPE since an infinite bus in not necessarily conservative for arc flash analysis.
3. After 6 months of going back and forth with utility, I explained that I was at the point where I needed to file a complaint with the regulators (Public Utility Commission)

Shortly after I stated my only option left to protect employees was Item 3, I received the necessary information.

Thanks for the reply Barry. Its sad that you have to threaten to get information that you know more than likely they have in a model and they just flat out wont give it to you. We have been dealing with them for a while on these two locations and were pretty much told today that it was the company policy not to give the data out on secondary metered services.

According to Xcel Energy's 'Standard for Electrical Installations and Use' handbook:



I would bet that 90% of utilities actually do what Xcel does, they just don't publish the information.
Our firm's policy is to run several scenarios using different fault current values in an effort to create a 'worst case' value.

I am in XCEL territory and they have a policy to only provide fault currents that they have published. You can find this directly from them if you know the size of the transformer. If you do not know anything on the power system the account holder must find this out (and engineering firm or other must have a letter giving permission to get that info)

here is where you can get the info http://www.xcelenergy.com/Start,_Stop,_ ... r_Builders

Here is an update to get the XFMR data:
https://www.xcelenergy.com/staticfiles/ ... /Corporate PDFs/XcelEnergy_Standard_For_Electric_Installation_and_Use2014.pdf

We have frequently received the same reply from utilities. We typically will travel the nearby substation and look at the transformer types to estimate. Infinite bus is really a liability to the utility. They are saying they "guarantee" infinite bus? So their breakers will trip really fast and protect you and the fault current is really high so your devices will trip fast? That is unlikely. When you explain that to the utility engineer they will typically come back with a min/max level. They have this information in every case we've been able to dig into so it is just a matter of getting min/max. Never depend on them clearing as the upstream breaker since most utilities don't do regular breaker exercising or maintenance except in the power plants and crucial operations which have negotiated low down time.

Having headed up the short circuit studies group for a very large public utility in a past life, it really depends on the utility's staff, capabilities (and the lawyers) We would provide pretty detailed information and also provide line out contingency conditions as well as attempt to project for the future based on the company's future plans. We also then surrounded this information with legal disclaimers about how the data is based on normal conditions, the system can change, etc. etc.

The infinite bus case "might" be the worst case for the arc flash assuming the minimum case doesn't cause devices to time delay but there is no way to know for sure without the data. A few weeks ago I did a webinar about utility data and one of the areas I touched on was how to deal with a lack of utility data.

WEBINAR - Utility Short Circuit Data

The short summary is you begin with an infinite primary source (assumes 0 source impedance) and run the study using the transformer secondary short circuit results. As an example, a 1500 kVA transformer with a 480 volt secondary and 5.75 percent impedance has a secondary short circuit current of 31,374 Amps (excluding motor contribution).

Run the study with this value an see if the arc rating of the PPE is sufficient. Then reduce the current in 5 or 10 percent increments and continue to rerun the study and verify the arc rating is still sufficient. At some point, the SC current will become too low and you will see incident energy values increase dramatically.

At this point you have found the minimum fault current where the PPE results are valid. This isn't a perfect answer but it gives you a range of currents where the calculations indicate the PPE arc rating is sufficient.