The Iberian Blackout: A Black Swan or a Gray Rhino? A Thorough Power System Analysis

Abstract

On April 28, 2025, the Iberian power system suffered a full blackout. It was the first documented overvoltage-driven cascade in Europe. The event sparked debate about root causes, including high renewables output, low inertia, and operator actions. This paper presents a thorough power system analysis of the incident to sort signal from noise and explain, step by step, how the blackout unfolded. Specifically, we (i) reconstruct the timeline and causal chain of the incident, (ii) present and summarize contributing factors using factual findings from incident reports, (iii) reproduce the blackout on an IEEE test system, (iv) analyze the incident from a system-theoretic, voltage-control perspective, and (v) translate our analysis into practical, technical measures that aim to mitigate and prevent similar incidents.

Figures (9)

• Figure 1: High-level chronology of the April 28 blackout.
• Figure 2: Feedback structure of the cascading overvoltage collapse. The negative feedback loop (dashed) through voltage control failed to stabilize due to limited AVR response, while the positive feedback loop (solid) through collector-level overvoltage and protection-triggered trips reinforced voltage rise. Operator actions (orange) inadvertently amplified the cascade by reducing natural reactive absorption.
• Figure 3: Effect of AVR compliance on overvoltage. Top: observed trajectory with limited AVR (red) versus generators providing continuous droop-based absorption (teal). Bottom: with compliant AVR, even higher renewable shares (60% and 100% lines) keep voltages below the relay limit across the same disturbance sequence.
• Figure 4: Block structure of the linearized DAE model in \ref{['eq:dae_linear']}. Controls $\Delta\boldsymbol u$ excite device dynamics $\boldsymbol A_{dd}$, devices and network are coupled by $\boldsymbol A_{da}$ and $\boldsymbol A_{ad}$, the algebraic network is governed by the power-flow Jacobian $\boldsymbol A_{aa}$, exogenous disturbances $\Delta\boldsymbol w$ act on the algebraic part.
• Figure 5: Meshing/energization mechanism---a simple illustration.