In this diagram [math]E_0[/math], [math]V_{1f}[/math], [math]I[/math] and [math]j X_s I[/math] are the phasors related to the no-load e.m.f., the grid voltage, the armature current and the synchronous reactance drop voltage, respectively (phase quantities). [math]\Delta \omega[/math] is the possible difference of the angular frequencies of [math]E_0[/math] and [math]V_{1f}[/math] (it could be [math]≠0[/math] during transients, i.e. phase swinging)