Methodology of risk assessment and decomposition in power grid applications

The most common approach to risk assessment for power systems is based on the N - 1 principle. Nevertheless, the economic rationale suggests its relaxation in cases where the consequences are relatively minor and exacerbation when they are large. This study addresses this need by proposing an alternative operational risk assessment methodology that is based on both probabilities and costs of possible contingencies. The foundations are built on listing all possible contingencies that may be considered by the transmission system operator (TSO). As only a subset of these contingencies can be examined in reasonable time, the upper and lower risk boundaries are introduced to quantify the risk underestimation. The ratio of those limits is used as an accuracy indicator, which - according to the desired level - may help the TSO to identify the required number of contingencies that have to be analysed. Furthermore, several approaches to improve the reduction of the number of simulated contingencies are discussed and the results obtained basing on the dynamic IEEE39 model are presented.