Image, Alexandra Koch, Pixabay
ENTSO-E’s factual report presents a second-by-second account of the ‘whats’ of the 28 April 2025 power system blackout of the Iberian Peninsula, however the ‘whys’ still remain unknown.
This unprecedented event, the most severe blackout incident in the European power system in over 20 years, also affected a small area of France near the Spanish border for a limited duration and had major repercussions for citizens and society in Portugal and Spain.
Drawing on data from the country’s TSOs, DSOs and other significant grid users including generators, ENTSO-E through its expert panel has now compiled the most comprehensive account of the event.
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Broadly attributed to a cascading series of generation disconnections along with voltage increases over a period of less than 90 seconds, the reasons for some of these are not known and detailed analysis is now under way for a final report, including recommendations to help prevent similar incidents in the future, in early 2026.
When it started
The starting point of the incident from the report’s point of view is 12:32:00 (CEST) on 28 April, at which time the voltage of Iberian power system at the 400kV level was below 420kV and no notable oscillation with amplitude higher than 20mHz could have been observed.
From that time onwards, several important generation trips occurred. Between 12:32:00.000 and 12:32:57.000, there was a loss of 208MW identified distributed wind and solar generators in northern and southern Spain, as well as an increase in net load in the distribution grids of approximately 317MW, either due to the disconnection of small embedded generators <1 MW (mainly rooftop PV) or to an actual increase in load or to a combination of both. The reasons for these events are not known.
The next phase of major disconnection events started some milliseconds after 12:32:57 with the tripping of a generation transformer in the region of Granada due to the activation of an over-voltage protection in the 220kV side of a 400/220kV transformer connecting several renewable generation facilities to the transmission grid.
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This was followed with two sets of trips at 12:33:16.460 and 12:33:16.820, the reasons for which are not known, resulting in an additional loss of around 725MW of PV and thermo-solar facilities connected to two 400 kV transmission substations in the area of Badajoz.
After that several trips between 12:33:17 and 12:33:18.020 occurred that led to disconnection of wind and solar generation in Segovia, Huelva, Badajoz, Sevilla and Caceres for a total of approximately 930MW – some due to over-voltage protection, but most not known.
As some generation units were consuming reactive power with the effect of reducing the voltage, the disconnections of these units without adequate compensation of loss of reactive power by other resources in the system with the capability to inject/absorb reactive power meant that voltages in the system increased, not only in Spain but also in Portugal. Furthermore, the frequency decreased.
Up until then, no generation trips had been observed in Portugal or France. However, between 12:33:18 and 12:33:21, the voltage of the south area of Spain sharply increased, and consequently also in Portugal, triggering a cascade of generation losses that caused the frequency of the Spanish and Portuguese power system to decline.
At 12:33:19, the power systems of Spain and Portugal started losing synchronism with the rest of the European system and despite the activation of the automatic load shedding and system defence plans at 12:33:23.960, the electrical separation of the Iberian system was completed with the tripping of the AC interconnections to Morocco and France.
ENTSO-E’s 45-person panel that prepared the report was led by Klaus Kaschnitz of APG in Austria and Richard Balog from MAVIR in Hungary, experts from TSOs not directly affected by the incident.
Also included were panellists from both affected and non-affected TSOs, including Red Electrica from Spain, Portugal’s REN and RTE from France.
