I've run across 'Potier' reactance and such several places, but not found a satisfactory explanation for what it really is. I assume it's named after someone? (always capitalized, like a proper noun). I've noticed most of the older texts did a fair number of solutions by converting to P.U. and then graphical analysis (one definitely had to know their plane geometry to follow along).
Yes, in the Navy we had MG sets where they often ran as AC synch motor and DC generator. Operating as AC synch. motor, we learned quite well the affects of field excitation. Since they were connected to 'ships service turbine-generators' for power, we could shift the reactive load from the SSTG's to the MG and back, just by adjusting MG AC-Voltage adjustment. But we normally left it split 'evenly', so the voltage of the MG AC unit would be correct should the SSTG and MG set get split apart (then the MG reversed power flow to supply the vital AC loads from the DC supply).
Thanks again. So hard to find anyone to talk this sort of 'shop' with. Most electricians are more about NEC compliance, where AFCI are required and such. Not that that is a bad thing, just not many folks interested in large machinery theory/practice.