Synchrophasor Assisted Adaptive Relaying Methodology to Prevent Zone-3 Mal-Operation During Load Encroachment

Phasor measurement unit (PMU) has uniquely blended the contributions of modern information and communication technology in terms of time synchronization and fast data transmission to emerge as the smart sensor for advanced protection methodologies in smart power grids (SPG). The latency issue associated with the functionality of PMUs has made synchrophasors assisted protection algorithms suitable for backup protection, so as to efficiently prevent events, such as maloperation of relays under load encroachment as well as other stressed situations. This paper proposes a novel methodology to prevent Zone-3 mal-operation of distance relays during load encroachment using the synchrophasor measurements obtained from PMUs installed in a widely-spread power system network. The proposed algorithm is to be implemented in transmission line protection center (TPC), where the synchronized three phase voltage and current phasors acquired from the PMUs are transferred to Phasor data concentrator (PDC) and are used to calculate the impedances seen by the relays in real time. A load encroachment situation and a faulty situation can be distinguished by comparing the impedances seen by primary and backup relays installed at different buses for protecting their respective transmission lines. Numerous case studies have been conducted in WSCC-9 bus system modeled in PSCAD/EMTDC environment to validate the proposed methodology.