So I'm studying synchronous machines and what happens when load is increased. In case of alternator(synchronous generator) if the load is increased, like more lamp is added in parallel, then the armature current would increase. But where does this extra current come from? The rotor cannot go faster because: there is locking between rotor magnetic field and armature rotating magnetic field. If the rotor accelerates, then the armature rotating magnetic field also accelerates, that means the frequency of output current changes. that can't happen as bus is assumed to be at constant voltage and constant frequency? What exactly happens and where does this extra load current come from? In case of sync motor when the shaft is loaded, the resultant air gap flux is behind leads the field flux. So when the shaft is loaded(load torque increased), the speed reduces and the air gap flux is a bit more in phase with field flux. Since the rotor has to move at constant speed, the air gap flux has to go back to initial position(leading field flux), so it draws more armature current. Armature flux leads the air gap flux. Air gap flux is phasor addition of armature flux and field flux. If armature flux is increased, air gap flux goes back to initial position. What actually happens when alternator load is increased? And if the rotor does speed up how does it know it has to speed up?