Seen impedance by impedance type relays during power system sequential disturbances

The trajectory of the seen impedance by distance type relays during sequential disturbances was investigated. For transmission systems, distance relays are known to be the main protection. For generator protection, loss of field relays present a major element of the protection systems. These two impedance type relays are considered. A case study of the seen impedance by the healthy phases during single-phase autoreclose (SPAR) following earth faults and the seen impedance by the loss of excitation relay during simultaneous faults, an earth fault in the external system triggering another fault in the generator excitation system, were investigated using phase coordinate analysis with full machine and system representation