Section 14.5: Performance of a Round-Rotor Synchronous Generator
The synchronous generator is a non-ideal AC voltage source and, as such, it has a (per-phase a) Thevenin equivalent circuit as indicated below
The Thevenin voltage and impedance are E and Zs = Ra + jXs respectively
Usually, Ra << Xs so Zs » jXs (Xs = synchronous reactance)
N.B.: Vt = Line-to-neutral terminal voltage