Testing of WAMS-based Supervised Zone-3 Distance Relay Protection Scheme using a Real-Time Digital Simulator

Power swings, load encroachment, and low voltage conditions can cause false tripping due to the Zone-3 backup protection feature of a distance relay. To avoid this, a distance relay can be supervised using the measurements from Phasor Measurement Units (PMUs) of a Wide Area Measurement System (WAMS). The algorithm and software for this purpose was developed. Through the monitoring of differential currents of the backed-up lines, the software generates Block and Trip signals which are communicated to the relay. This paper presents the results of testing of this scheme using a real-time digital simulator. Different fault scenarios in a four-machine ten bus system were simulated. The results indicate that the scheme is effective in preventing the false tripping of distance relays.