Downstream Equivalent "Utility" Model

[ThePunisher]

Hi all,

I am currently modeling the power system of a new facility that we are working on to be connected to an overall power system. However, the overall power system is still currently being designed by OTHERS. The contractor of the overall engineering will not provide me their software model (in ETAP) due to "liability" reasons.

In this case, I would be requesting them instead to provide me simulated data at our "interconnection" point and then I would model that as "utility" for our new facility. I would identify to them (OTHERS) which part of the SLD I would be interconnecting from.

In this regard, I would ask them the following:

For Short Circuit:
a. Equivalent Phase and Zero Sequence P.U. Impedances (Based on Max and Min S.C.) at interconnection point,
b. Maximum and Minimum MVA Short Circuit at interconnection point,
c. Equivalent X/R Ratio (based on Max and Min S.C.)

HOWEVER, I seem to be not quite sure what to ask for Load Flow purposes...as the data for short cirucit simulation purposes may differ for that for load flow at the interconnection point.

Can I say 1 P.U. voltage at the interconnecting point or I will have them simulate load flow and use whatever voltage magnitude they would have at the interconnecting point and use that as the actual voltage to start with (Max and Min loading)?

Now, how will the short circuit impedances play if I do this as the program may place these impedances after the voltage input (have to verify with ETAP).

Any experience opinion will help. Thanks

 

[jghrist]

It depends on the characteristics of the overall power system. If there is local generation, the short circuit impendances will have subtransient reactances and will not be the same as the impedance for load flow. If there is no local generation, then the short circuit impedance will be mostly transformer impedances and cable impedances that don't change with time. In this case, you could treat it like a utility source. If there are any voltage regulators in the overall power system, these need to be considered.