Voltage 3rd harmonic in generator stator winding at changes in generator load conditions

The influence of changes in load of the generator-transformer unit on the operating conditions of the 100% ground-fault protection based on the 3rd harmonic voltages feeding stator ground-fault protection using comparison of the voltages 3rd harmonic in generator neutral and at the generator terminals was analyzed. The 3rd harmonic voltages were determined on the base of the experimental tests (measurements) run in real conditions at changes of active and reactive power. It was found that generator active power influences the voltage feeding the measuring element of ground-fault protection. Therefore determining operating conditions of ground-fault protection the influence of the generator load should be deeply considered. This can ensure the proper operation of the ground-fault protection in the whole range of the changes in generator load. Considering the influence of changes in generator load on the 3rd harmonic voltages feeding measuring element of the protection system will allow elimination of irregular generator tripping as a result of unselective operation of these protections.