Synchrophasor-assisted zone 3 operation

Zone 3 operation of distance relay serves as a remote backup in case of primary failure. Conditions, such as power swing, load encroachment, and voltage and transient instability, cause incorrect zone 3 operation. The detection of faults during such stressed conditions poses a further problem. This paper proposes a synchrophasor data-based technique for correct zone 3 operations by discriminating the fault from different stressed situations. This discrimination is accomplished using impedances calculated from voltage and current signals from synchrophasors placed at strategic locations. The proposed method is tested in the IEEE 39-bus New England system and found to be accurate.