Out-of-Step Protection Based on Equal Area Criterion

This paper proposes a novel self-tuning and response-based method for estimation of a single generator instability after large disturbances in multimachine power systems. The proposed method takes advantage of the equal-area criterion and least-squares method. The instability is determined by monitoring the cumulative acceleration and deceleration areas in the power-angle plane. These areas are continuously computed in order to determine whether or not the rotor angle reaches the unstable equilibrium point (UEP). A real-time curve-fitting algorithm based on the least-squares method is suggested to estimate the UEP. The generator rotor angle is calculated readily using three-phase voltages and currents taken at the generator terminal, and no further information such as fault clearing instant is required. The algorithm is independent upon changes in network parameters and only needs locally measured quantities. Self-tuning and response-based operation are the main advantages of the proposed algorithm over the other existing algorithms. The performance of the proposed algorithm and its independence from the network configuration are successfully validated and compared with that of impedance-based out-of-step protection relays.