Application of synchrophasor for protection co-ordination in an interconnected grid

Abstract

Historically Real time vis-a-vis Post facto Analysis of Grid Events had always been carried out across control centers of Indian ISO, POSOCO through array of non-chronologically arranged relays from site complemented with control room available analogue/digital data and Sequence of Events (SoE) from SCADA/EMS and time stamped Disturbance Records (DR) / Event Logger Records (EL). However holistic post-dispatch forensic were limited with issues of data latency, gradualness of updation and skewedness of SCADA data and time drift among the digital recorders due to paucity of absolute time synchronization. Advent of Synchrophasor technology with beaming of time synchronized voltage or current phasors brought a paradigm shift in post-dispatch analysis. Any tripping or switching action or oscillation in a large interconnected complex grid like India have their global foot print not only on local but distant PMUs situated thousands of kilometers away from the loci of event. So each type of fault and resultant response of relaying and protective gear to isolate the fault generate unique signature on voltage, current, frequency or bus angle plots of local and neighboring PMUs. Analysis of signature can reveal instantly any discrepancy in Zone co-ordination of Distance protection or settings of Overflux relay or failures in Auto reclosing. This paper through case studies of PMU signatures envisages ways to detect on real time basis any mal functioning of relaying and protection including wrong settings and coordination.