FEM: How to calculate impedance in stator circuit for loaded generator

I am modeling a synchronous generator and in the stator circuit consisting of 3 phases at the alternator output, I have resistances and inductances of the end windings. Thus I have a 3D approximation of my current 2D approximation.

Now I am considering a generator with load. S = 50 kVA or 50 kW with p.f.unity. We have the formula $$Z = V^2/S$$. But which V to use? It is only after doing the simulations of the FE model that I get the output voltage V at the stator terminals. It's a chicken and egg situation. If I want to add an impedance or resistance for my loaded generator, I need to know V but V is only computed afterwards in the FE simulation.

The approximation which I can have is to use a V which I get from a no-load simulation and then use this V in the formula Z= V^2/S to obtain the impedance Z to put in the stator circuit next to the end winding resistances and inductances in order to simulate a loaded generator.

As you can see, this is confusing to me. Looking forward for your comments. Thanks.

If I consider the voltage regulation formula, then I do not know my $V_{rated}$.

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Don't you know the AC mains voltage for which you'd be using this generator? 208 / 440 / ??? It's usually specified as line-to-line, RMS voltage. –  Jason S May 21 '12 at 13:38
Heard that the line voltage RMS is 156 V but my simulations are giving a higher voltage i.e. 184 V. –  yCalleecharan May 22 '12 at 7:34
Is this a homework problem? –  madrivereric May 22 '12 at 18:40