Enhancing Performance of Distance Relay Zone 3 Under Stressed Conditions Using an Angle-Based Algorithm

The security of distance relays in zone 3 is critical for preventing catastrophic blackouts, especially during stressed conditions. However, the challenge lies in distinguishing between short-circuit faults and system disturbances, e.g., load encroachment, power swing, out-of-step condition, and voltage instability, which can mimic fault conditions and lead to improper relay operation. To address this issue, this article presents a new local protection method by employing three innovative indices: the out-of-step detection index, the positive-sequence impedance angle (PSIA) index, and the superimposed PSIA index. These indices are derived from theoretical principles and are tailored to effectively discriminate between faults and system disturbances. As a major novelty, the determination of indices threshold values is extracted based on the theoretical relationships and further validated through comprehensive static and dynamic analyses. The algorithm's effectiveness is evaluated under various stressed conditions through multiple simulations, showing its ability to distinguish between stressed conditions and short-circuit faults, even in the presence of inverter-based resources. This leads to enhanced power system reliability and security. The proposed method is also cost-effective as it is implemented in the local distance relay, eliminating the need for synchrophasor devices and communication infrastructure.