Intelligent Out of Step Predictor for Inter Area Oscillations Using Speed-Acceleration Criterion as a Time Matching for Controlled Islanding

Inter-area oscillations is a potential threat for uncontrolled islanding leading to power system blackout. Based on the severity of inter area oscillations, three control strategies, namely: 1) device based control; 2) operational based control; and 3) structural based control approaches can be applied. Emergency controlled islanding is a structural based method consisting of three sub-tasks denoted as “when,” “where,” and “how” to intentionally separate a power system. In this paper, regarding the task of when, an intelligent out-of-step predictor for inter-area oscillation is proposed. It is shown that early prediction of power system trend toward inter area instability can be used as a criteria for handling the issue of when. For this purpose, the criterion of the speed-acceleration which is earlier developed for out-of-step of single machine is extended for out-of-step of inter-area oscillations. In this approach, based on the concept of center of inertia, coherent areas oscillating against each other are represented by two equivalent machines from which extended speed-acceleration locus curve is derived. The slope of the extended speed-acceleration locus curve can be used as a criterion for predicting system trend toward uncontrolled separation. The main feature of the proposed criterion is its independency from system modeling and just relying on on-line data obtained from WAMS. The proposed approach is applied on IEEE 39 bus test system and Iran power system with promising results.