Automatic Voltage Regulator (AVR) — Generator
An electronic control system that keeps the output voltage of a synchronous generator constant under varying load by continuously adjusting the excitation current of the rotor field (the exciter) based on a measured feedback signal from the stator voltage. When the load increases, the generator terminal voltage temporarily dips due to the larger voltage drop across the internal impedance of the windings; the AVR detects this dip within tens of milliseconds to a few hundred milliseconds and increases the excitation current to bring the voltage back to the set value, in accordance with the performance requirements of IEC 60034-1 for synchronous machines. When multiple generators operate in parallel on the same network, the AVR also works together with a droop control to proportionally share reactive power between the generators; an incorrectly set or defective AVR can lead to voltage instability, excessive reactive power circulation between parallel-operating generators, or, in extreme cases, loss of excitation during a sudden load step.
Bij het opstarten van een grote motor op een noodstroomaggregaat zakt de generatorspanning kortstondig weg; de AVR corrigeert dit binnen enkele honderden milliseconden zodat de overige belastingen geen onderspanning ondervinden.
Bij parallelbedrijf van twee generatoren de droopinstelling van de AVR's identiek maar zonder onderlinge afstemming configureren — een kleine afwijking in de spanningsreferentie tussen beide AVR's kan leiden tot een aanhoudende, ongewenste blindvermogenscirculatie tussen de generatoren.