Adaptive ratio of current forcing of synchronous generators with thyristor self-excitation system

The voltage decreases significantly at the generator leads if a short circuit occurs near the power rails of a power plant. In this case thyristor self-excitation system that use rated algorithms and forcing-state parameters in some cases might not be able to force by raising the voltage and the excitation current. Voltage collapses, and the generator loses its excitation and turns off. It is not difficult to alter the forcing algorithm in microprocessor-controlled systems. It is therefore interesting to find out whether it is possible to save the generator in the power system by using a higher-than-2x current-forcing ratio or a ratio that adapts to the resulting system impedance. The paper investigates how generator-lead voltages depend on the resulting system impedance in case of short-circuits; analysis is done for various current-forcing ratios, with analyzed generators varying both in power and by the excitation system type. It is shown that ratios or current-forcing durations might be altered to expand the zone wherein short-circuits do not result in voltage collapse and excitation loss. Altering the generator forcing ratio can make power plants and systems generally more reliable.