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Ensuring reliable operation of large power systems subjected to multiple outages is a challenging task because of the combinatorial nature of the problem. Traditional approaches for security assessment are often limited by their scope and/or speed, resulting in missing of critical contingencies that could lead to cascading failures. This paper proposes a two-component methodology to enhance power system security. The first component combines an efficient algorithm to detect cut-set saturation (called the feasibility test (FT) algorithm) with real-time contingency analysis (RTCA) to create an integrated corrective action (iCA), whose goal is to secure the system against cut-set saturation as well as critical branch overloads. The second component only employs the results of the FT to create a relaxed corrective action (rCA) to secure the system against post-contingency cut-set saturation. The first component is more comprehensive, but the latter is computationally more efficient. The effectiveness of the two components is evaluated based upon the number of cascade triggering contingencies alleviated, and the computation time. The results obtained by analyzing different case-studies on the IEEE 118-bus and 2000-bus synthetic Texas systems indicate that the proposed two-component methodology successfully enhances the scope and speed of power system security assessment during multiple outages. [ABSTRACT FROM AUTHOR]

During major power system disturbances, when multiple component outages occur in rapid succession, it becomes crucial to quickly identify the transmission interconnections that have limited power transfer capability. Understanding the impact of an outage on these critical interconnections (called saturated cut-sets) is important for enhancing situational awareness and taking correct actions. This paper proposes a new graph theoretic approach for analyzing whether a contingency will create a saturated cut-set in a meshed power network. A novel feature of the proposed algorithm is that it lowers the solution time significantly making the approach viable for real-time operations. It also indicates the minimum amount by which the power transfer through the critical interconnections should be reduced so that post-contingency saturation does not occur. Robustness of the proposed algorithm for enhanced situational awareness is demonstrated using the IEEE-118 bus system as well as a 17,000+ bus model of the Western Interconnection (WI). Comparisons made with different approaches for power system vulnerability assessment prove the utility of the proposed scheme for aiding power system operations during extreme exigencies. [ABSTRACT FROM AUTHOR]

A method of applying network flow analyses during real time power system operation, to provide better network connectivity visualization, is developed and presented. Graph theory network flow analysis is capable of determining the maximum flow that can be transported between two nodes within a directed graph. These network flow algorithms are applied to a graphical representation of a power system topology to determine the minimum number of system branches needed to be lost in order to guarantee disconnecting the two nodes in the system that are selected. The number of system branches that are found serves as an approximate indicator of system vulnerabilities. The method used in these connectivity analyses makes use of well known graph theory network flow maximum flow algorithms, but also introduces a new algorithm for updating an old network flow solution for the loss of only a single system branch. The proposed new algorithm allows for significantly decreased solution time that is desired in a real-time environment. The value of using the proposed method is illustrated by using a detailed example of the 2008 island formation that occurred in the Entergy power system. The method was applied to a recreation of the 2008 event using a 20,000-bus model of the Entergy system to show both the proposed method's benefits as well as practicality of implementation. [ABSTRACT FROM PUBLISHER]

An island formation identification scheme utilizing both phasor measurement unit (PMU) measurements and supervisory control and data acquisition (SCADA) information, in conjunction with an analytical method, is developed and presented. The motivation for this work came from the investigation of the islanding event in the Entergy, Louisiana power system in 2008. During Hurricane Gustav in September of 2008, 14 transmission lines were lost which led to the formation of a large electrical island containing much of Baton Rouge and New Orleans. This work proposes a method for identifying any specific area of the transmission system that is vulnerable to islanding as the result of losing a system branch. PMU measurements are then utilized to verify SCADA reports that a system branch has been lost. The proposed identification scheme is called the one line remaining (OLR) algorithm. The proposed algorithm identifies potential island formations based on the criteria that a single bus, or a number of buses, are connected to the rest of the system by only a single branch as a direct result of a branch outage. The OLR algorithm is detailed and applied to several small test systems to motivate and validate the approach. The OLR algorithm is then applied to a large Entergy test system for the Gustav islanding event and correctly identifies the last tie line that was lost and created the island. [ABSTRACT FROM AUTHOR]