Different the amount of recent in the stationary exciter field coils varies the 3-phase output in the exciter. This output is rectified by a rotating rectifier assembly mounted within the rotor, along with the resultant DC provides the rotating discipline of the leading alternator and as a result alternator output. https://iwatchsteelband76319.blogdigy.com/new-step-by-step-map-for-alternator-parts-53669288