Out-of-Step Protection Using State-Plane Trajectories Analysis

This paper proposes a novel out-of-step protection technique using the state-plane representation of the generator speed and power angle. The critical clearing angle is computed using the principle that the total energy of the system at the instant the fault is cleared should be equal to the maximum potential energy of the system. The critical clearing time corresponding to the value of critical clearing angle is obtained directly using the time calibration of the relative speed versus power-angle solution curve. The simultaneous calculation of the critical clearing angle and the time make the proposed approach much faster than the two-blinder scheme. The proposed state-plane prediction scheme is used to detect the first swing out-of-step condition in a two-area test system using system-wide information. The two generators are represented with a single-machine infinite bus equivalent system, and the state-plane algorithm is applied to the reduced equivalent. Electromagnetic transient simulations are carried out using ${\rm PSCAD/EMTDC}^{\rm TM}$ to test the proposed algorithm in the two-area test systems. The simulation studies show that the proposed method is computationally efficient and accurate. The technique also does not require any offline studies.