Stability assessment using synchrophasor data

Rotor angle variation during post fault period in a power system leads to power swing. Both stable and unstable swings may cause tripping of distance relays and therefore they are blocked during swinging conditions. The unstable swing if not detected early or dealt properly leads to loss of synchronism among different areas and consequently resulting in catastrophic failures such as blackouts. To avoid such incidents some of the relays placed at strategic locations have to be unblocked. An integrated approach of combining various indices derived from wide area measurement system (WAMS) data using fuzzy logic for ranking the severity of the swing has been proposed. The ranking aids in taking decisions regarding the blocking and unblocking of relays to avoid severe failures. The performances of the indices have been tested on a three-machine nine-bus system using EMTDC/PSCAD and MATLAB.