Good Day,

We were provided utility data, but it only included system impedances (R1,X1,R0,X0-PU on 100MVA Base). The utility company considers providing the fault current values a liability. What is the recommended method, convert to SC amps (reference Jim Phillips article, Making Sense of the Numbers, Utility Company Short-circuit Data For Arc Flash Studies) or input directly into software as ‘Zpu’ fault duty units, or other method. Will each method yield the same results? Thanks - DBL

That is a pretty interesting statement from the utility. The impedance data and the short circuit data are pretty much the same thing - just need a few calculations to go from one to the other. The article that you reference did not have a case with Z0. That is used when there is a ground/non-phase path so....

For a line-to-ground fault:
I line-to-ground = (3xV) / (Z1 + Z2 + Z0) in your case (and in almost every case Z2 is the same as Z1)
I line-to-ground = (3xV) / (2xZ1 + Z0)

I show everything as a magnitude Z to make it simple. You have the better format of individual R and X values.

The utility indirectly gave you the fault current. It is a direct function of the equivalent impedance which they gave you. Many utilities simply shroud this information in legal disclaimers and go ahead and provide it.

Thanks Jim.
To confirm, one can obtain Z with individual R and X values, using Z=SQRT[R squared + X squared].

For some programs you have to enter per unit impedance. I developed a spreadsheet to convert to Per Unit impedance. I tried to paste the spreadsheet
but it was unreadable. I will be happy to provide it.

I would rather have the impedance values, most of the time I only get a fault current.