Adequacy of Generator Coherency for Online Islanding of Transmission Power Systems

Controlled Islanding is the last countermeasure for a severely disturbed power system to avoid wide-area blackouts. As generator coherency is dependent on the type and location of the disturbance, it is necessary to perform the coherency analysis and power system clustering in an online manner. The impact of generator coherency for solving power system islanding problems has been studied and compared to typical islanding requirements such as minimal power flow disruption or minimal load imbalance. The K-Harmonic Means Clustering was used to identify coherent generators online. Coherent generator groups defined the constraints of the subsequent Constrained Spectral Clustering of the transmission system to create coherent islands with minimal power flow disruption on the boundaries. A Coherency Fitness Index is introduced to study the adequacy of generator coherency and its impact on the islanding process. Results show that if coherency is completely considered, solving the islanding problem can ensure the wide-area stability of the islanded system by creating self-operating and stable island grids. A study case is performed on the IEEE 39 bus system. With less than 0.3 s needed to solve the islanding problem for the middle-sized test system, the suggested approach is assumed to be capable for real-time power system islanding.