Following the blackout incident in the Iberian Peninsula on 28 April, ENTSO-E and its member transmission system operators (TSOs), the Agency for the Co-operation of Energy Regulators (ACER), National Regulatory Authorities (NRAs), and Regional Co-ordination 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 to collect and analyse all available data on the incident and determine and publish its causes, and second, a final report establishing recommendations to help prevent similar incidents in future.
All information published to date, including the present communication, is subject to the results of the detailed investigation on the incident. The investigation will be subject to the legal framework specified by EU Regulations. ENTSO-E will present the results of the investigation to the European Commission and Member States through the Electricity Co-ordination Group and will subsequently publish them.
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.
Sequence of events
During the half hour preceding the incident, two periods of oscillations 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 programmes of Spain were 1000 MW to France, 2000 MW to Portugal and 800 MW to Morocco.
Data so far have yielded the following sequence of events.
- Starting at 12:32:57 CET and within 20 seconds afterwards, a series of different generation trips was registered in the south of Spain, accounting to an initially estimated total of 2200 MW, but not in Portugal and France. As a result the frequency decreased and a voltage increase is observed in Spain and Portugal.
- 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.
- At 12:33:21 CET, the AC overhead lines between France and Spain were disconnected by protection devices against loss of synchronism.
- At 12:33:24 CET, the Iberian electricity system collapsed completely and the HVDC lines between France and Spain stopped transmitting.
Immediately the affected TSOs worked together to restore power in the affected regions – all Spain and Portugal, and a small area of SW France.
The main steps of the restoration
Starting at 12:44 CET, a series of restorations steps took place.
First a 400 kV line between France and Spain was re-energised in the west, then at 13:04 CET, the interconnection between Morocco and Spain was re-energised, and from the start until about 13:30 CET, several hydro power plants in Spain with black-start capability launched their black-start processes. At 13:35 CET, the eastern part of the France-Spain interconnection was re-energised, at 16:11 and 17:26 CET, two power plants with black start capability in Portugal succeeded in their start up process, allowing to initiate restoration in Portugal with two islands, and at 18:36 CET, the first 220 kV tie-line between Spain and Portugal was re-energised speeding 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 the restoration process of the transmission grid was completed in Portugal, and at around 04:00 CET, restoration process of the transmission grid was completed in Spain.
The Expert Panel will be led by Klaus Kaschnitz (APG, Austria) and Richard Balog (MAVIR, Hungary).
