Framework for trajectory‐based probabilistic security assessment of power systems

Transmission system operators prepare against threats to system security through preventive actions and the planning of corrective actions. Required actions are determined by performing security analyses according to some reliability management approach and criterion. Probabilistic approaches have been proposed as an alternative to the deterministic N  − 1 approach, by using a probabilistically filtered contingency list. This study begins by formally defining system trajectories, as a means of connecting the initiating contingency to the system response, corrective control, and restoration activities. A system trajectory considers the realisation of exogenous variables, as well as a sequence of contingencies and the subsequent system response and control behaviours. Using this definition, it is argued that the system trajectory should be modelled until service and component outages are resolved, rather than only modelling its reaction to the initiating contingency. The authors then propose some simplifying assumptions to achieve a scalable approach to probabilistic real‐time security assessment. To support this argument, contingency‐based and trajectory‐based probabilistic security assessments are compared in terms of their residual risk (the risk associated with future system trajectories that are not modelled). This comparison shows that security assessments based on trajectories allow for previously implicit assumptions on modelling accuracy to be made explicit.