By the principle of ac generator as we know, alternator electromotive force produced by the phase of the three-phase winding of valid values for E phi = = Ce Ф n (V)

There is Ce for generator structure constant, n as the rotor speed, Ф for rotor magnetic flux, that is to say, the generator of induction electromotive force is proportional to the rotor speed and the magnetic flux.
　　

Increases when the speed increases, E phi, the output voltage of the UB increases, when the speed increases to a certain value (no-load speed above), the output voltage of limits, to make the output of the generator voltage UB is no longer with the increase of rotational speed rise, can only be accomplished by reducing flux Ф.And magnetic flux Ф is proportional to the excitation current of the If, reduce the magnetic flux Ф also is to reduce the excitation current of the If.

communication The working principle of the generator voltage regulator Is: when the speed of the ac generator rises,Generator voltage regulator By reducing the generator field current If to reduce the magnetic flux Ф, make the output of the generator voltage UB remains the same.