Risk Assessment and Mitigation of Cascading Failures Using Critical Line Sensitivities

Security concerns have been raised about cascading failure risks in evolving power grids. This paper reveals, for the first time, that the risk of cascading failures can be increased at low network demand levels when considering security-constrained generation dispatch. This occurs because critical transmission cor-ridors become very highly loaded due to the presence of central-ized generation dispatch, e.g., large thermal plants far from de-mand centers. This increased cascading risk is revealed in this work by incorporating security-constrained generation dispatch into the risk assessment and mitigation of cascading failures. A se-curity-constrained AC optimal power flow, which considers eco-nomic functions and security constraints (e.g., network con-straints, 𝑵−𝟏 security, and generation margin), is used to pro-vide a representative day-ahead operational plan. Cascading fail-ures are simulated using two simulators, a quasi-steady state DC power flow model, and a dynamic model incorporating all fre-quency-related dynamics, to allow for result comparison and ver-ification. The risk assessment procedure is illustrated using syn-thetic networks of 200 and 2,000 buses. Further, a novel preventive mitigation measure is proposed to first identify critical lines, whose failures are likely to trigger cascading failures, and then to limit power flow through these critical lines during dispatch. Results show that shifting power equivalent to 1% of total demand from critical lines to other lines can reduce cascading risk by up to 80%.