Online estimation of power system separation as controlled islanding scheme in the presence of inter-area oscillations

This paper presents an online scheme of wide area out of step protection of synchronous generators to controlled islanding of power system based on inter-area signals gathered from wide area measuring systems (WAMS) data. The proposed scheme provides an online criterion of critical splitting times for online estimation of both unstable inter-area oscillations and inter-area transient instability scenarios. In this regard, according to meaning of the center of inertia (COI), coherent generators are identified and represented as equivalent virtual generators within different oscillating areas. The proposed strategy is an extension of conventional RRdot relay from which by measuring the COI of inter-area rotor angle oscillation (δCOI) within two oscillating areas, a new adaptive δCOI-ΔδCOI locus curve is extracted. For online prediction of both inter-area transient scenarios, two different curves are provided which by extending them within unit curve, the main inter-area relay zone is developed. The proposed strategy is an online and non model-based scheme from which the emergency decisions are obtained individually according to different operational and topological conditions. The proposed approach is studied within two different cases including modified IEEE 39 bus test system and a practical Iran national power grid from which considering some typical wide area out of step scenarios, the proposed scheme is evaluated within time domain simulations. Studies indicate the promising results of wide area out of step prediction in the presence of different types of inter-area oscillations.