20 Hz generator
In order to implement a 100 % stator earth fault protection based on sub harmonic injection, a 20Hz voltage is injected into the generator star point. The 20-Hz generator SGEN-1001 is used in combination with the Band Pass Filter SBPF-1001 in the Stator Earth fault protection. Injection can be performed by connecting the SGEN-1001 and the SBPF-1001 to the load resistor of an earthing or neutral transformer. If an earth fault occurs in the generator star point, the 20 Hz voltage drives a current through the fault resistance. From the driving voltage and the fault current, the protective relay determines the fault resistance.