A new index based on proximity of inter-area oscillation to UEP point for predicting proper time of controlled islanding

In emergency condition due to unstable inter-area oscillations, controlled islanding is considered as the final defensive strategy against system forced splitting. Applying the strategy at the proper time is vital for preserving system security. In this respect, determining the right time for applying the controlled islanding is a crucial task. Predicting the time of uncontrolled system splitting can be used as a sign for arming the controlled islanding strategy efficiently in the right time. In this paper, based on the concept of center of inertia, two oscillating areas are represented as a generalized single machine infinite bus system (GSMIB). For the GSMIB system, based on the on-line measurement data, the locus curves of the power-angle variations of the oscillating areas are evaluated from which by means of weighted least-squares technique, the equivalent power-angle curve is estimated. For predicting the proximity of the unstable inter-area oscillation to the point of out-of-step, based on the power-angle curve of the GSMIB model an equivalent unstable equilibrium point (UEP) is evaluated. The proximity of inter-area oscillation to UEP is regarded as a new instability index. The proposed approach is demonstrated on the 39-bus New England test system and Iran 1063-bus power system with promising results.