When to island for Blackout Prevention

Cascading outages leading to large-area blackouts can be mitigated using intentional controlled islanding (ICI). An ICI scheme must define the most suitable time to split the system after a severe contingency (i.e., when to island), as well as to quickly determine the set of branches to be disconnected to create stable islands (i.e., where to island). Most of the works in the literature, however, focus on the latter and little has been done to address the “when to island” problem. To fill this gap, this paper proposes a unified methodology to determine the most suitable moment for islanding. First, the proposed methodology uses real-time information to estimate the rotor angles of generators, which, in turn, serve to define the suitable number of coherent generators and the actual coherent groups. It then adopts the concept of area-based center of inertia-referred rotor angle index to determine the actual time of islanding. The unified methodology for determining the number of islands to be created, the coherent generators, and the time for islanding is tested using the IEEE 39- and 118-bus test systems. Multiple case studies are presented to demonstrate the adaptability and effectiveness of the proposed unified methodology to different system conditions.