Multi-zonal method for cascading failure analyses in large interconnected power systems

Most cascading failure analysis methods successfully capture cascading developments within one control zone, or region comprised of multiple control zones, controlled by a single transmission system operator (TSO). They neglect, however, the operations of multi-zonal systems. To bridge this gap, the authors introduce the multi-zonal method for cascading failure analyses of large interconnected power systems. The method accounts for all control zones in a multi-zonal system, assesses their power flows, re-evaluates the system topology after disturbances and applies frequency balancing measures in each control zone independently, thus effectively simulating the actions of multiple TSOs. To demonstrate the capabilities of this method, a case study is investigated which compares the security benefits of the multi-zonal (national) versus the single-zone (regional) frequency balancing methods in a multi-zonal system. The application to the IEEE 118-bus test system shows that the regional approach increases the security of this system in small and medium cascades, whose expected demand not served is reduced by 28% and 26%, respectively, in comparison to the national approach. However, the expected load shedding for large-scale cascading events in the regional approach is 42 times as large as in the national approach. This is mainly caused by overloads occurring in transmission lines adjacent to the cross-zonal tie lines, which are 154% higher with the regional method compared to the national in large cascading events. The capability to identify congestions is presented by devising an upgrading strategy, which makes the regional frequency balancing approach viable from a security aspect.