Self-healing in power systems: An approach using islanding and rate of frequency decline based load shedding

This dissertation provides a self-healing strategy to deal with catastrophic events such as simultaneous loss of several generating units or major transmission lines when power system vulnerability analysis indicates that the system is approaching an extreme emergency state. In our approach, the system is adaptively divided into smaller islands at a slightly reduced capacity with consideration of quick restoration. The basis for forming the islands is to minimize the load-generation imbalance in each island, thereby facilitating the restoration process. Then a carefully designed load shedding scheme based on the rate of frequency decline is applied to limit the extent of the disruption and expedite the restoration process. A slow coherency based islanding theory is provided. Issues regarding the linear and nonlinear applicability of the theory are discussed in detail. R-Rdot out of step relay is deployed to form the islands. The function of the relay can be enhanced with the help of phasor measurement technology and decision tree knowledge. An overall scheme including a new two-level load shedding scheme is proposed. The proposed scheme is tested on a 179-bus, 29-generator sample system and shows very good performance.