Could a different sequence of operator actions have avoided the blackout?

Ascertain whether any alternative sequence of real-time operator actions—specifically energizing parallel 400 kV circuits, switching off shunt reactors, and configuring the Spain–France HVDC interconnection in fixed-power mode—would have prevented the April 28, 2025 Iberian cascading overvoltage blackout under the prevailing conditions of low synchronous-machine share and inadequate voltage regulation.

Background

The paper emphasizes that operators followed established protocols to damp oscillations by meshing 400 kV circuits, switching reactors, and placing the HVDC link in fixed-power mode. These actions likely reduced natural reactive absorption and stiffened corridors, contributing to voltage rise.

Despite the replication-based analysis, the authors state it remains unclear whether a different ordering or combination of these actions could have averted the cascade given high IBR penetration and observed shortcomings in dynamic voltage control.

References

While some of these actions may have decreased the system's ability to absorb reactive power, further raising voltages and narrowing voltage control margins, it remains unclear whether a different sequence of actions would have avoided a blackout, particularly given the low share of synchronous machines and their inadequate voltage regulation, and the fact that several trip causes and oscillation triggers remain unknown and the reports characterize the event as a multifactor overvoltage cascade under active investigation.

— The Iberian Blackout: A Black Swan or a Gray Rhino? A Thorough Power System Analysis  (2511.17433 - Albustami et al., 21 Nov 2025) in Section 6 (Replication Results: Cascade Onset and Progression)