Using Momentary of Interrupting fault values when provided for fault contribution

[philly]

When performing a short circuit analysis and external fault contribution is provided from either the utility or another part of the system with both momentary and interrupting values provided which value do you want to use as the contribution? I understand that these fault values are derived from different impedance networks and use for different evaluation criteria.

As an example....If I'm modeling a new part of a system and I'm looking at an existing study for the existing system that feeds my new system and find the available fault current at the existing bus which my new system will connect to. The fault current at this bus will obviously have an momentary and interrupting fault current. Which one of these is best to use as the source contribution to the new part of my system? SKM and most other software programs will only allow you to enter one value as the source contribution and doesn't allow for both inputting an interrupting and momentary value.

I'm thinking that the momentary value should be used since its the highest and occurs during the initial onset of the fault.

 

[Ingenieur]

What values did they give you?
amps, kva. Etc? Reactance?
usually the sw will calculate the response based on your system parameters

it depends on what your sw does
sub transient, asymmetrical
transient
steady state, symmetrical
???

depending on what you are doing oth can be used:withstand, inturrupting

for a typical 3 ph fault it decays to symmetric within 1/2 tp 1 cycle
well before sensing and tripping, 3-6 cycles
use steady state
the x/r to get a peaking factor