PMU-based vulnerability assessment using wide-area severity indices and tracking modal analysis

Two techniques based respectively on the transient energy injected by the disturbance into the grid and the tracking damping level of the resulting oscillatory responses are investigated for quickly assessing the post-event vulnerability status of a multi-area power system from a Wide-area measurement systems (WAMS) record. The "Transient Energy" approach using the so-called Wide Area Severity Index (WASI) was originally developed to suit a highly reliable Dynamic Security Assessment (DSA) system which is currently being tested in actual operations. The WASI concept is extended here to provide the necessary attributes for ranking the dynamic strength of the grid after an arbitrary contingency, giving the full 10 to 60-s record from an ensemble of strategically located PMUs. It is shown that Wide Area Severity Indices over short and long windows timeframe allow for a very effective clustering of dynamic events into various categories of phenomena with embedded type and level of grid vulnerabilities. For comprehensiveness, a tracking modal analysis using the ERA method is also implemented to provide additional insight into the grid signal responses, in terms of the evolving damping level throughout the observation window. The proposed approaches are illustrated on detailed simulations of the Hydro-Quebec grid and confirmed on actual measurements recorded with the existing WAMS.