Expert Panel Begins Investigation into Iberian Peninsula Blackout

An investigation has been launched into the widespread power outage that affected the Iberian Peninsula on 28 April 2025. A joint Expert Panel has been established by the European Network of Transmission System Operators for Electricity (ENTSO-E), in coordination with its member Transmission System Operators (TSOs), the Agency for the Cooperation of Energy Regulators (ACER), National Regulatory Authorities (NRAs), and Regional Coordination Centres (RCCs). The panel includes experts from both affected and unaffected TSOs and is chaired by representatives from TSOs not directly impacted by the incident.

The investigation will follow a two-phase approach in line with the “Incident Classification Scale Methodology.” The first phase involves the collection and analysis of relevant data to reconstruct the sequence of events and identify the causes of the blackout. Findings from this phase will be compiled into a factual report. The second phase will focus on developing recommendations to reduce the risk of similar events in the future, to be published in a final report.

The process is being conducted within the framework of European Union Regulation (EU) 2017/1485 on the System Operation Guideline. Final results will be shared with the European Commission and EU Member States through the Electricity Coordination Group before being published.

Preliminary Timeline of Events

On 28 April 2025 at 12:33 CET, a blackout occurred across Spain and Portugal, with a limited impact in a small area of southern France. The broader Continental European power system remained unaffected.

In the 30 minutes prior to the incident, two intervals of system oscillations (in power and frequency) were observed in the Continental European synchronous area: between 12:03–12:07 CET and 12:19–12:21 CET. Measures were taken by the Spanish (Red Eléctrica) and French (RTE) TSOs in response. At the time of the blackout, system conditions were within normal operational ranges, and no oscillations were reported.

At the time, Spain was exporting 1,000 MW to France, 2,000 MW to Portugal, and 800 MW to Morocco.

Based on currently available data, the following sequence of events occurred:

At 12:32:57 CET, a series of generator trips occurred in southern Spain, resulting in an estimated 2,200 MW of lost generation. No generator trips were reported in Portugal or France. These events led to a frequency drop and a voltage increase in Spain and Portugal.
By 12:33:21 CET, the frequency had fallen to 48.0 Hz, prompting the activation of automatic load-shedding mechanisms in both Spain and Portugal.
At the same time, AC transmission lines between France and Spain were disconnected by protection systems responding to a loss of synchronism.
At 12:33:24 CET, the electricity system in the Iberian Peninsula fully collapsed, and HVDC connections with France ceased operation.

Restoration efforts began immediately. Key steps included:

12:44 CET: The first 400 kV transmission line between France and Spain was re-energised.
13:04 CET: The interconnection between Morocco and Spain was restored.
Around 13:30 CET: Spanish hydro power plants with black-start capability initiated restoration procedures.
13:35 CET: The eastern France-Spain interconnection was re-energised.
16:11 and 17:26 CET: Two black-start capable power plants in Portugal successfully started, initiating localized restoration.
18:36 CET: A 220 kV tie-line between Spain and Portugal was re-energised, accelerating Portugal’s recovery.
21:35 CET: A southern 400 kV tie-line between Spain and Portugal was restored.
00:22 CET, 29 April: The transmission system in Portugal was fully restored.
Around 04:00 CET: The transmission system in Spain was fully restored.

Expert Panel Leadership and Participants

The Expert Panel is co-led by Klaus Kaschnitz (Austrian Power Grid, Austria) and Richard Balog (MAVIR, Hungary). Participants include experts from ENTSO-E, RCCs, and TSOs. Key ENTSO-E expert convenors are: