# External equivalent (impedance source)

I have a wind equivalet generator, a step-up transformer, collector systems, main transformer and a swing bus linked through an ideal line to the HV trasformer bus. For voltage reference step in a plant controller: "The determination of the external system strength (source impedance) at the time of the testing was essential for obtaining a well matched result" (NERC reliability guideline). If you have P,Q and V (measured values) for the initial and final operating points, how you calculate the Xsource in order to get the suitable voltage and reactive power output in the dynamic simulation? If the external grid in too strong, V does not varies.

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Sort by » oldest newest most voted Let dQ and dV be the change in reactive power [Mvar] and voltage [pu] respectively. Assume dQ is 200 Mvar and dV is 2% = 0.02 pu. That means a change of 200 Mvar leads to a voltage change of 0.02 pu.

The short circuit power can then be estimated to Sc = dQ/dV = 200 / 0.02 = 10 000 MVA!

A short circuit power of Sc can be modeled in PSSE with a generator with Mbase = Sc and Xsorce = 1. In this example use Mbase = 10 000 MVA and Xsorce = 1.

Use model GENCLS in dynamics with parameter H = 0 and D = 0.

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