On April 28, 2025, the Iberian mainland power system experienced a major blackout triggered by rapid voltage escalation, widespread generator disconnections, and loss of synchronism. An ENTSO-E investigation identified multiple contributing factors: inadequate voltage control coordination, reactive power constraints, fast generation ramps exceeding system response time, protection relays set without dynamic considerations, and limited visibility into distribution-level inverter-based resources. This incident highlights a fundamental operational vulnerability in modern grids: system operators lack tools to assess whether imminent disturbances—a generation trip, load ramp, topology change, or capacitor switching—will push voltages beyond relay thresholds before available controls can respond.
Researchers have developed a protection-aware dynamic voltage security assessment framework to address this gap. The approach begins with a nonlinear hybrid differential-algebraic equation model incorporating automatic voltage regulators, inverter-based resources, STATCOMs, HVDC links, protection functions, and limiter behavior. Key innovations include mode-wise finite-window voltage maps that capture transient dynamics, normalized overvoltage margin erosion metrics at protection measurement points, and time-resolved bounds on control response latency.
The methodology includes three core components: a monotone pickup cascade screen that predicts nonlinear protection activation sequences; robust data-limited certificates for cases where relay and voltage data are incomplete; and a mitigation optimization that computes minimum fast reactive support required to keep voltages below thresholds. Testing on a 2000-bus Iberian replica and standard benchmark systems demonstrates that the cascade screen successfully predicts nonlinear propagation patterns.
This framework enables operators to move beyond static voltage limits toward dynamic security assessment. By explicitly modeling protection relay response times and inverter control delays, the tool identifies vulnerabilities that conventional steady-state analysis misses. Implementation could support real-time operational decisions, guide protection coordination studies, and inform investment in fast reactive resources essential for grid stability as synchronous generators decline and inverter penetration increases.
