A New Strategy for Detecting Unstable Power Swing Using Fault Impedance Trajectory and Its Impacts on Performance of the Impedance Distance Relay

Distance relays are among the most significant components of electrical protection systems since their function is based on detecting the apparent impedance between the relay and the fault location in order to locate and isolate it rapidly.However, distance relays may encounter considerable hurdles as a result of power swings, which are caused by sudden and severe disturbances in large grids, such as faults or unexpected heavy load changes.A complex network of generators, transmission lines, transformers, and loads make up the power systems that serve as the basis for distance relays.However, the operational stability of these systems is heavily reliant on constantly balancing generation and loads.This paper investigates the impact of power swings on impedance distance relay performance.It gives a solution to keep the system in a stable region by monitoring the impedance trajectory and determining the change in time of crossing the suggested stability limit curve and the relay-characterized area.The research strategy proposes the use of three times out of four, which are the times of intersection of the measured instantaneous impedance path (trajectory) with the proposed stability curve and with the characteristics of the impedance distance relay, where the time difference (T3-T2) indicates the sensitivity to faults and the difference (T4-T2) gives a clear indication of stability.The results give a good indication to avoid unstable circumstances, with a time difference of 70-90 ms between T4 and T2 in critical power swing cases, depending on fault location and resistance.