On the Number of System Separations in Electric Power Systems

Electric power systems subjected to large and/or unexpected disturbances can become unstable and suffer from system separations and cascading outages. A major objective of smart-grid development is to maintain power system stability under high-penetration of renewable energy. Critical system separations (due to faults cleared immediately after the critical clearing time) have important applications in transient stability analysis and relay setting, and in devising corrective measures to efficiently reduce the detrimental impacts of large disturbances. Such system separations have practical physical consequences. As the main result, an upper bound on the number of possible critical system separations is derived for the power system with n generators. The analytical results are illustrated in the last section, by using the IEEE power system test cases with 9 and 57 buses, respectively, and an efficient numerical scheme is described to compute different system separations.