Changing Output Voltage:

Consider an increase in generator load and, thus, a drop in output voltage.  First, the sensing circuit senses the decrease in output voltage as compared to the reference and lowers its input to the comparison circuit.  Because the reference circuit is always a constant than the comparison circuit will develop an error signal due to the difference among the reference voltage and the sensed voltage.  A error signal established will be of a positive value along with the magnitude of the signal dependent on the difference among the sensed voltage and the reference voltage. This outcome from the comparison circuit will then be amplified through the amplifier circuit and sent to the signal output circuit.  A signal output circuit then rise field excitation to the AC generator.  That increase in field excitation causes produced voltage to rise to the desired output.

The voltage output of the machine would rise if the load on the generator were decreased. The actions of the voltage regulator would then be the opposite of in which for a lowering output voltage. In that case, the comparison circuit will establish a negative error signal whose magnitude is again dependent on the difference among the sensed voltage and the reference voltage. Conclusion, the signal output circuit would decrease field excitation to the AC generator, by causing the produced voltage to decrease to the desired output.