Controlled islanding algorithms and demonstrations on the WECC system

Cascading outages have resulted in significant disruptions to power systems all over the world. Controlled islanding can provide a corrective measure of last resort to alleviate the impact of large disturbances. This dissertation provides detailed demonstrations of using slow coherency based controlled islanding to prevent cascading outages in bulk power systems.;First, a brief description of slow coherency theory and its application in power systems is provided. Some improvements and extensions over existing slow coherency theory are developed. In the extended theory, the number of slow modes does not have to be equal to the number of groups, and the weight of each slow mode is considered. A tightness index is introduced to exclude boundary or loosely coherent machines from identification. The impact of the initial conditions on slow coherency determination is also discussed.;In addition, an integrated algorithm is provided to identify cutsets for large scale power systems for the application of slow coherency based controlled islanding schemes. The large scale power system is represented as a graph and a simplification algorithm is used to reduce the complexity of the system. Generators belonging to the same slowly coherent group are collapsed into a dummy node, and a graph partition library is used to split the graph into a given number of parts. Some extra islands formed by the partition library are merged into their adjacent large islands and the original cutset of the actual power system is recovered from the highly simplified graph. A software package was developed based on the algorithm, and dynamic simulations were run on the Western Electricity Coordinating Council (WECC) system to verify the effectiveness of the cutsets obtained.;Finally, to test the islanding performance, four extreme contingencies under two different operating conditions of the WECC system are tested using the time domain simulations. The cutsets used in the controlled islanding cases are obtained from the software package developed using the graph partition library. The time domain simulation results for the four contingencies with controlled islanding and uncontrolled islanding are shown, and the dynamic performance in each case is analyzed. Further analyses are conducted to examine the amount of load shed in each case, and a discussion of the cutset sensitivity and time sensitivity of islanding are provided. Finally, a discussion of practical implementation issues and conclusions are provided.