An investigation by the Spanish government has revealed that the blackout affecting the Iberian grid, which serves both Spain and Portugal, in April was triggered by a series of interconnected issues. The report outlines how measures taken to rectify a minor instability inadvertently escalated the situation, leading to a self-perpetuating cascade where high voltage levels caused various power plants to disconnect from the grid, exacerbating the voltage increase.
The complete report will be made available later today; however, a summary has been released in advance. This document contains a detailed timeline of the events leading to the blackout and provides an analysis of the failures in grid management that allowed it to escalate. Additionally, a concurrent investigation ruled out any possibility of a cyberattack being responsible for the disruption.
Oscillations and a cascade
The report indicates that the Iberian grid was experiencing voltage fluctuations for several days prior to the blackout. These fluctuations, resulting from a supply and demand imbalance, were managed without incident until April 28, just after noon, when an unexpected frequency oscillation was detected. This oscillation has been linked to a specific facility within the grid, although the report does not disclose its identity or type, referring to it merely as an “instalación.”
In an effort to address the oscillations, the grid operators implemented a response that suppressed them, but inadvertently raised the grid’s voltage levels. Approximately 15 minutes later, a diminished version of the initial oscillation occurred again, followed closely by oscillations of a different frequency, characterized by patterns typically observed in European grids. This prompted further corrective measures, which led to an additional increase in the grid voltage.
According to the report, the Iberian grid is designed to manage such incidents; however, on that day, the grid operator had only scheduled 10 power plants for voltage regulation, marking the lowest commitment for 2025 thus far. The report criticizes the performance of several of these plants, noting that many did not respond adequately and some even exacerbated the escalating voltage levels.
