Power system security assessment. Identification of critical contingencies and outage distance by a zone filter

摘要

Power system security assessment is analysis performed to determine constraint violations caused by contingencies, and the severity of such violations. This thesis is devoted to the topic of security assessment with the authors's contributions and new approaches. Power system operation states are described as a discrete state model in order to formulate and visualize system security. The arc connecting two states represents a planned or unplanned event which causes a transition between the states. This brings about the concept of ''outage distance'' - the minimum number of outages between the existing operating state and a state within the unacceptable quality region. The size of modern power systems has resulted in a tremendously long list of contingencies to be assessed. A general strategy for power system security assessment is proposed: Starting from a complete list of single and double contingencies, use an effective heuristic approach to obtain a small set of critical contingencies. Evaluate them to finally assess security level. A helpful tool, zone identification, is developed. A generation zone and a load zone associated with a selected ''attacked'' line can be defined by a topological and line-flow based search. The key point for the zone identification is its filtering effect: the single line outages within the generation zone and load zone do not significantly contribute to the increase of attacked line loading compared with the outages outside the zones, hence they can be excluded from the candidate list of critical contingencies. Three approaches are proposed and implemented: the stepwise search, the cut-set, and a heuristic approach. They are tested on a model network (IEEE Reliability Test System) and on the southern part of the Norwegian main grid. 63 refs., 38 figs., 43 tabs.