Supervising Vulnerable Third Zone Distance Relay to Enhance Wide-Area Back-Up Protection Systems

Under dynamic stressed situations, distance relays are quite prone to zone-3 mal-trippings which are recognized as one of the primary causes for cascaded tripping in power systems and recent power black-outs. Our proposed algorithm enhances the zone-3 back-up protection logic by ensuring secure distance relay operation during such stressed scenarios. A parameter namely relay vulnerability index (RVI) is estimated using phasor information to rank the vulnerable relays in real time based upon the intensity of stressed conditions. Once the set of highly vulnerable relays (HVR) are recognized, an intelligent relaying logic using wide area information monitors these HVR relays. Thus, the proposed scheme effectively supervises the traditional zone-3 relay to identify fault under stressed situations. Performance analysis on IEEE 39 bus New England power system network has demonstrated high accuracy for various stressed and faulted conditions where conventional zone-3 relays mal-operate. Efficacy of the suggested scheme is validated by implementing it on RTDS platform as a part of Controller Hardware-in-Loop testing. Our proposed algorithm efficiently enhances the back-up protection operation of transmission network and significantly improves the security of distance relays without affecting the dependability.