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Cascading failure in electric power systems is a complicated problem for which a variety of models, software tools, and analytical tools have been proposed but are difficult to verify. Benchmarking and validation are necessary to understand how closely a particular modeling method corresponds to reality, what engineering conclusions may be drawn from a particular tool, and what improvements need to be made to the tool in order to reach valid conclusions. The community needs to develop the test cases tailored to cascading that are central to practical benchmarking and validation. In this paper, the IEEE PES working group on cascading failure reviews and synthesizes how benchmarking and validation can be done for cascading failure analysis, summarizes and reviews the cascading test cases that are available to the international community, and makes recommendations for improving the state of the art.

Various methodologies exist for assessing the risk of cascading outage in power systems, differing in the cascading mechanisms considered and in the way they are modeled. These methodologies can be classified in three groups: static computation (QSS methodologies), dynamic computation (dynamic methodologies), or a combination of both (hybrid methodologies). The objective of this paper is to benchmark the performance of several widely used QSS cascading outage methodologies. For that purpose, they are applied on a unique system, the RTS-96, and the results are compared. Several metrics and indicators are used for that comparison: expected demand loss, distribution of demand loss, distribution of lines outaged and critical lines. Results show common trends but also discrepancies between methodologies. It implies that there is not yet a standardized way to analyze the risk of cascading outage in power systems, and that the specific tool used by a power system engineer can impact the recommendations. KeywordsCascading outage, Blackout, Power system security, Power system reliability, Risk analysis RightsPersonal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Authors

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this paper is a result of ongoing activity carried out by Understanding, Prediction, Mitigation and Restoration of Cascading Failures Task Force under IEEE Computer Analytical Methods Subcommittee (CAMS). The task force's previous papers [1, 2] are focused on general aspects of cascading outages such as understanding, prediction, prevention and restoration from cascading failures. This is the second of two new papers, which extend this previous work to summarize the state of the art in cascading failure risk analysis methodologies and modeling tools. The first paper reviews the state of the art in methodologies for performing risk assessment of potential cascading outages [3]. This paper describes the state of the art in cascading failure modeling tools, documenting the view of experts representing utilities, universities and consulting companies. The paper is intended to constitute a valid source of information and references about presently available tools that deal with prediction of cascading failure events. This effort involves reviewing published literature and other documentation from vendors, universities and research institutions. The assessment of cascading outages risk evaluation is in continuous evolution. Investigations to gain even better understanding and identification of cascading events are the subject of several research programs underway aimed at solving the complexity of these events that electrical utilities face today. Assessing the risk of cascading failure events in planning and operation for power transmission systems require adequate mathematical tools/software.

Interconnected power grids throughout the world are very reliable but occasionally suffer massive blackouts with multibillion dollar costs to society. Cascading failures present severe threats to power grid reliability, and thus reducing their likelihood, mitigation and prevention is of significant importance. This paper is one in a series presented by Cascading Failures Task Force, under the IEEE PES Computer Analytical Methods Subcommittee (CAMS) with primary focus on mitigation and prevention of cascading outages. The paper presents the basic methodologies for mitigation, summarizes currently deployed special protection schemes, and lists cases of successful and unsuccessful mitigation of cascading outages and lessons learned. Future developments and challenges in the area of mitigating cascading outages are also discussed.

This paper is a result of ongoing activity carried out by Understanding, Prediction, Mitigation and Restoration of Cascading Failures Task Force under IEEE ComputerAnalytical Methods Subcommittee (CAMS). The task force's previous papers are focused on general aspects of cascading outages such as understanding, prediction, prevention and restoration from cascading failures. This is the first of two new papers, which extend this previous work to summarize the state of the art in cascading failure risk analysis methodologies and modeling tools. This paper is intended to be a reference document to summarize the state of the art in the methodologies for performing risk assessment of cascading outages caused by some initiating event(s). A risk assessment should cover the entire potential chain of cascades starting with the initiating event(s) and ending with some final condition(s). However, this is a difficult task and heuristic approaches and approximations have been suggested. This paper discusses different approaches to this and suggests directions for future development of methodologies. The second paper summarizes the state of the art in modeling tools for risk assessment of cascading outages.