Report describes successive dismissals and says investigation faces challenges to investigate causes
Which hit Portugal and Spain on April 28 began with an overvoltage and spread in the waterfall, turning off mills in a few seconds. This is what a preliminary preliminary says, the European transmission operators network, released on Friday (3.out.2025).
The entity states that it was the 1st of the continent related to overtension, without relevant impacts in the rest of the European network. Here is (PDF – 1.8 MB).
The document describes 3 critical events that occurred almost at the same time. The 1st, at 12:32 pm 57s (Spanish time), was the shutdown of a transformer in the Granada region, after the overvoltage protection (355 MW injection). Then there was a loss of about 725 MW in photovoltaic and thermo-solo plants linked to two 400 kV substations in Badajoz.
The 3rd event disconnected wind and solar generation in Segovia, Huelva, Badajoz, Seville and Cáceres, totaling approximately 930 MW – could reach more than 1,100 MW as the frequency variation.
From 12h33min19s, the electrical frequency in the Iberian Peninsula fell and the Iberian system lost synchronism with continental Europe. Automatic load relief plans were even fired in Spain and Portugal, but failed to contain the failure because of the character of overtension. Two seconds later, all alternating current lines between Spain – France and Spain – Marrocco were turned off.
Klaus Kaschnitz of APG (Austrian Power Grid) and co-leader of the Entso-E expert panel, said the investigation was “Very challenging” for the difficulty of obtaining complete information from operators and generators. “Some data simply do not exist”he declared, referring to small units, such as domestic solar panels. According to him, the collection of information took 5 months and demanded about 150 formal requests, which only allowed to rebuild the incident rigorously in August.
Damian Cortinas, chairman of the Entso-and Council, emphasized that the report does not seek to point guilty but technically analyze the blackout. “Our focus is to understand the facts and use this information to prevent something similar from happening, not assigning guilt”he declared.
Kaschnitz also pointed out that the blackout showed a new phenomenon: cascade overvoltages that require local voltage control. “Voltage needs to be managed locally, close to the problem. All units, renewable or conventional, can contribute to voltage control, as long as they meet the technical requirements.”these.
The restoration was quick, with Portugal completely recovering the high voltage connection shortly after midnight and Spain at 4am the next day.
Second curtains, “The size of the interconnection had no impact on blackout or resolution. The problem was local in southern Spain. The existence of interconnections in general helped only in the recovery of the system, allowing to restore the tension in a coordinated manner, but could not have prevented the incident.”.
According to Entso-E, the episode was “The most severe in over 20 years”. The report, prepared by 45 network operators and regulators specialists from 12 countries, has a factual character. The final version, which will bring analysis of Raiz causes, performance of generators and recommendations, should come out in the 1st quarter of 2026.
