Complete Bounding Method for AC Contingency Screening

The analysis of the effects of hundreds of outages on line flows and bus voltages is required for the real-time security analysis and contingency enumeration. This increases the demands on the speed, accuracy and adaptability of the solution methods. Ideally, an ac power flow should be solved for each contingency, followed by a check for limit violations and major shifts from the initial system conditions. Such an approach is not feasible for practical systems consisting of hundreds of buses. To cope with this computational barrier, various approximate methods have been developed based on the idea that the vast majority of outages does not cause major shifts/violations. There are two classes of such methods, explicit and implicit techniques, which ease the computational burden by identifying cases with severe system limit violations. The explicit methods do not identify or solve for specific violations. Rather, they quantify the severity of each outage by a scalar index by which all the contingencies can be ranked. The explicit methods are not completely reliable since they are prone to masking errors. Specifically, a contingency with a few severe violations can be ranked equally with one with many minor violations or even worse, with one without violations. The implicit methods, though more demanding in CPU resources, permit the identification of actual violations/ major shifts and, therefore avoid masking errors. This paper describes a new contingency analysis technique which overcomes the deficiencies of existing methods. This technique has been implemented in a production-grade program designed for real-time applications.