The effect analysis and simulation test of harmonics on differential protection of Scott transformers

Most High-Speed railway systems around the world used single-phase voltage source as power supply for trains, therefore, adopted some special transformers to convert 3-phase source to single phases. The differential relays used for this situation most be restudied for understanding their operation changes in a high harmonic content environment. This research aims at the study of effects of harmonics to the differential protective differential relays for special transformers. The CA (Westinghouse) type differential relay is used to protect the selected special transformer, the Scott transformer. Different combinations of harmonics are adopted for testing. Relationship between the tripping time of the differential relay and quantity of harmonic is studied. We expect the results will be helpful and useful to the applications of differential relays for protecting special transformers.