Risk, reliability, cascading, and restructuring

Restructuring of the electric utility sector introduces unprecedented uncertainty in transmission planning and operations practices. To cover the uncertainty and to provide robust solutions, it is necessary to consider a significant number of different situations and scenarios, and to base the decision-making on characteristics reflecting all this variety. The crisis caused by inadequacy of the old methodology to the new environment becomes increasingly evident, especially in transmission planning. Adequately handling the uncertainty should be based on risk assessment, multi-scenario analysis, and probabilistic methods. The stress posed on transmission systems due to the power flow diversity is also enormous and results in shrinking reliability margins. The lack of investments and fully adequate strategies to the development of open-access transmission systems also contributes to this problem. New incentives, methodologies, indices, and standards need to be developed. This paper introduces the new risk assessment indices and comprehensive reliability assessment technology developed by Southern Company. The indices include the risk and sharpness of transmission problems and the expected energy not produced (EENP). The risk and sharpness indices allow estimating the likelihood of thermal and voltage problems and the degree of locality of these problems in different parts of the grid. They also pinpoint the most affected facilities. The EENP reflects the annual expected energy that cannot be injected into the grid due to transmission constraints. It is used to evaluate the existing and proposed generation sites. The reliability assessment technology evaluates the expected unserved energy, system minutes of interruption, ASIDI and ASIFI indices. Reliability metrics are computed for all sources of unreliability including protection group outages, islanding, and network problems. The Southern Company/EPRI TRELSS software is used as the main tool. Studies include forecasting reliability trends and goal performance, identification of "weak elements", in-depth analysis of reasons and mechanisms of unreliability events, impacts of hotter-than-expected weather, reliability effects of across-system power transfers, reliability impacts of budgeted transmission projects, probabilistic risk analysis of thermal and voltage problems. Southern Company has developed a unique methodology to analyze hundreds of cascading failure scenarios, determine their expected consequences, and rank the scenarios according to their severity and likelihood of occurrence. Cascading studies are also conducted to analyze vulnerability of the system to acts of sabotage. The paper contains examples of real-life studies and their discussions.