Mitigation of cascading failures by real-time controlled islanding and graceful load shedding

This paper presents an emergency control strategy, which serves to counteract a cascading disturbance in a large power system that would eventually lead to a blackout. The strategy is composed of two parts: after a disturbance, a real-time controlled islanding algorithm based on slow coherency of synchronous generators and k-means clustering splits the system into autonomously operating parts. The imbalances between load and generation are then accounted for by generator tripping in the generation-rich islands and a novel type of under-frequency load shedding in the load-rich islands, if the available primary control reserves are insufficient or too slow to stabilize the frequency. As opposed to the under-frequency relays in substations which are often used nowadays, the system considered here utilizes a “smart home” communication and control infrastructure for assigning frequency thresholds to individual appliances owned by consumers. Pervasive availability of this infrastructure is assumed. The strategy is evaluated in time-domain simulations using the IEEE 118-bus system.