Considered the field power system stabilizer (F-PSS), which reacts to change components of vector induction the resulting magnetic field in a gap and change rotor speed of the synchronous generator. For definition the change of internal rotor running-out angle it is possible to use the geometrical parties between components of an induction vector of a resulting magnetic field B in a gap of the synchronous generator, determined in a stator coordinate system X-Y . Axis Y of this coordinate system is directed in a radial direction from a rotor to stator. The direction of axis X is defined by quantity of pair’s poles р of the synchronous generator. As a reaction of active loading determining a rotor movement is directed on a bisector between the neighbours poles, we shall direct axis X under at angle.