Transient Stability Prediction for Real-Time Operation by Monitoring the Relative Angle with Predefined Thresholds

Under real-time operation, early detection of oscillations that lead to instability is of noteworthy importance for power system operators. This paper demonstrates how the relative angle (RA) obtained with online data from phasor measurement units (PMUs) and predefined thresholds of the relative angle (PTRA) obtained with offline simulations are valuable for the monitoring and prediction of transient stability. Primary features of the method consist of first calculating the maximum and minimum relative angles by offline simulations of different contingencies. Next, the voltage angles at buses that represent areas of the power system are measured to calculate the center of inertia (COI). Finally, the RA of the generators at each area is determined during the online operation to monitor stability behaviors and identify those that lead to a loss of synchronism. The method was validated in the New England 39-bus and the IEEE 118-bus power systems by performing contingencies, finding critical stability angles, monitoring areas and controlling the predicted unstable events with control actions, such as generation and load tripping, with enough time to return to stability.