Following the blackout incident in the Iberian Peninsula on 28 April, ENTSO-E and its member Transmission System Operators (TSOs), the Agency for the Cooperation of Energy Regulators (ACER), National Regulatory Authorities (NRAs), and Regional Coordination Centres (RCCs) have set up a joint Expert Panel. The panel is led by experts from TSOs that weren’t directly affected by the incident and includes experts from both affected and non-affected TSOs. It will investigate the root causes of the blackout and will make recommendations.

In accordance with the “Incident Classification Scale Methodology”, the investigation will be split into two phases. First, the panel will collect and analyse all available data on the incident to reconstruct the events of 28 April and determine the causes of the blackout. These insights will be completed and published in a factual report.  In the second phase, the panel will establish recommendations to help prevent similar incidents in future, which will be published as a final report. 

All information published to date, including the present communication, is subject to the results of the detailed investigation on the incident. The investigation follows the legal framework under the European Union Regulation (EU) 2017/1485 of 2 August 2017 (System Operation Guideline). 

ENTSO-E will present the results of the investigation to the European Commission and Member States through the Electricity Coordination Group, and will subsequently publish them once the analysis is completed. 

First information on the chronology of events leading to the blackout

The blackout is the result of a complex sequence of events for which ENTSO-E is providing a preliminary chronology with the information known so far. An in-depth analysis by the Expert Panel will be provided in a full technical report. 

On 28 April 2025 at 12:33 CET, the power systems of Spain and Portugal suffered a total blackout. A small area in France, close to the border with Spain, was also affected by the incident, albeit for a very limited duration. The rest of the Continental European power system did not experience any disturbance.

Figure 1 – Geographic area affected by the incident of 28 April 2025.

During the half hour preceding the incident, two periods of oscillations (power and frequency swings) were observed in the Continental European synchronous area, between 12:03 and 12:07 CET and between 12:19 and 12:21 CET respectively. The TSOs of Spain (Red Electrica) and France (RTE) took actions to mitigate these oscillations. At the moment of the incident, there were no oscillations and the power system variables were within normal operation range.

Before the incident, the international exchange programs of Spain were 1,000 MW to France, 2,000 MW to Portugal and 800 MW to Morocco, all in the exporting direction.

 Data so far, have yielded the following sequence of events during the incident:

1. Starting at 12:32:57 CET and within 20 seconds afterwards, presumably a series of different generation trips were registered in the south of Spain, accounting to an initially estimated total of 2200 MW. No generation trips were observed in Portugal and France. As a result of these events the frequency decreased and a voltage increase is observed in Spain and Portugal.   
2. Between12:33:18 and 12:33:21 CET, the frequency of the Iberian Peninsula power system continued decreasing and reached 48,0 Hz. The automatic load shedding defence plans of Spain and Portugal were activated.
3. At 12:33:21 CET, the AC overhead lines between France and Spain were disconnected by protection devices against loss of synchronism.
4. At 12:33:24 CET, the Iberian electricity system collapsed completely and the HVDC lines between France and Spain stopped transmitting power.

As soon as the disruption of the electricity supply occurred, the affected TSOs worked together in a coordinated effort to restore the power in the affected region of France, as well as in Spain and Portugal.

The main steps of the restoration process were the following:

• At 12:44 CET, a first 400 kV line between France and Spain was re-energised (Western part of the border).
• At 13:04 CET, the interconnection between Morocco and Spain was re-energised.
• From the start of the restoration until approximately 13:30 CET, several hydro power plants in Spain with black-start capability launched their black-start processes to initiate the restoration of the system.
• At 13:35 CET, the eastern part of the France-Spain interconnection was re-energised.
• At 16:11 and 17:26 CET, the two power plants with black start capability in Portugal succeeded their start up process after unsuccessful previous attempts, allowing to initiate the restoration process in Portugal with two islands.
• At 18:36 CET, the first 220 kV tie-line between Spain and Portugal was re-energised, allowing to speed up the restoration of the Portuguese system.
• At 21:35 CET – the southern 400 kV tie-line between Spain and Portugal was re-energised.
• At 00:22 CET on 29 April 2025, the restoration process of the transmission grid was completed in Portugal.
• At around 04:00 CET, the restoration process of the transmission grid was completed in Spain.

Expert Panel composition

The Expert Panel will be led by Klaus Kaschnitz (APG, Austria) and Richard Balog (MAVIR, Hungary).  The ENTSO-E, RCC and TSO experts in the Expert panel are:

ENTSO-E expert Convenors:

• Olivier Arrivé – as chair of the System Operation Committee
• Robert Koch – as convenor of the Steering Group Resilient Operation
• Albino Marques – as convenor of the Regional Group Continental Europe

Experts appointed by TSOs and RCCs:

The process of appointing Expert Panel members by ACER and the NRAs is underway.

(1) The “Incident Classification Scale Methodology”, established by ENTSO-E in accordance with EU Regulations 714/2009 and 2017/1485,  is the framework for reporting and classifying incidents on the power system and for organising the investigation of severe incidents.