They operate on the fundamental principle of electromagnetic induction.Synchronous generators are also called the alternators.Rotors are of two types.Salient pole rotor is used in hydroelectricity.Exciter is small self-excited DC generators.
The main advantage of rotating magnetic field is that it is easier to insulate stationary armature winding for high voltage rather than rotating armature & the working principle of a synchronous generator is based on electromagnetic induction phenomenon.The speed governor is used to keep the speed of machine constant and the induced voltage is made constant by automatic voltage regulator (AVR).
With the load in alternator,terminal voltage V is less than induced voltage or emf E.For unity power factor (Resistive load) , the armature reaction is cross-magnetizing in nature. The Ovearall effect for pure inductive load (lagging), the armature reaction is demagnetizing in nature & for pure capacitive load (leading), the overall effect of armature reaction is magnetizing in nature.
The numerical value of the regulation is defined as the percentage rise in voltage when the full load at the specified power factor is switched off with speed and field current remaining unchanged expressed as a percentage of rated voltage.
The two alternators are operating in parallel so that the above requirements are satisfied, they are said to be synchronous. The operation of getting the machine into synchronism is known as synchronization and system of constant voltage & constant frequency regardless of load is known as an infinite bus.