The blackout was caused by a power surge with multiple factors:
- the system had insufficient voltage control capacity,
- oscillations occurred that affected the operation of the system
- power generation facilities were disconnected, in some cases apparently improperly.
The Vice President and Minister for Ecological Transition and Demographic Challenge, Sara Aagesen, presented to the Council of Ministers of the country the report of the Committee for the analysis of the circumstances surrounding the electricity crisis of April 28, 2025, approved this morning by the National Security Council. The document concludes that the incident had multiple causes, with a cascade of events that progressively destabilized the system and culminated in a peninsular blackout due to overvoltage. It also includes a series of recommendations ranging from improving the control and supervision of the behavior of agents to increasing the level of interconnection with France.
OVER 300 GB OF INFORMATION ANALYSED
The Committee had two working groups, the Cybersecurity and Digital Systems Working Group and the Electricity System Operation Working Group, which analysed over 300 GB of information. The former has conducted the largest cybersecurity investigation in Spain’s history; with the participation of more than 75 experts, it has analyzed 133 GB of data and ruled out the possibility that the incident was the result of a cyberattack, either at the System Operator’s facilities, the control centers, or the generation centers analyzed. The Operations Working Group, for its part, made 770 requests for information and analyzed 170 GB of data..
CHRONOLOGY OF THE INCIDENT
The Committee has identified a sequence of events that allows us to establish a chronology of the incident, from which several conclusions can be drawn.
- PHASE O: Voltage instability. During the days prior to the incident, there were voltage disturbances, and on the morning of the 28th, the voltages varied more intensely than normal.
PHASE 1: System oscillations (12:00 p.m. – 12:30 p.m.). At 12:03 p.m., an atypical oscillation of 0.6 Hz was recorded, which caused large voltage fluctuations for 4.42 minutes. This oscillation forced the System Operator to apply the protocol measures to dampen it, such as increasing the grid meshing—restricted by low demand—or reducing the interconnection flow with France. All these actions dampened the oscillation, but had the side effect of increasing voltages. At 12:16 p.m., the same oscillation was recorded again, smaller in size, and at 12:19 p.m., another oscillation of 0.2 Hz was recorded, in this case with the usual characteristics of these European phenomena. The System Operator applied the same measures to dampen it, which also contributed to increasing the voltage. - PHASE 2: Generation losses (12:32:57 – 12:33:18). The voltage began to rise rapidly and steadily, and numerous and progressive disconnections of generation facilities were recorded in Granada, Badajoz, Segovia, Huelva, Seville, Cáceres, and other provinces.
PHASE 3: Collapse (12:33:18 – 12:33:30). The progressive increase in voltage produced a chain reaction of disconnections due to overvoltage that could not be contained, as each disconnection contributed to further increases in voltage. There was also a drop in frequency, which led to the loss of synchronism with France, the tripping of the interconnection with the rest of the continent, and a blackout on the peninsula.
FAST RESTORATION OF SUPPLIES
Supplies began to be restored thanks to energy supplies from interconnections with France and Morocco, as well as from autonomous power plants (hydroelectric) in the Duero River basin and other points on the peninsula. As a result, at 22:00, almost 50% of the country’s consumption was met with electricity, and this coverage continued to increase to 99.95% by 7:00 on the 29th.
Although the recovery process followed an international model, the Committee’s analysis identified opportunities for better practices.
KEY CONCLUSIONS OF THE REPORT
The Committee’s analysis of the incident leads to the conclusion that the power failure was caused by multiple factors, combining three elements:
- The system showed insufficient ability to control the oscillation for two reasons. Firstly, on the 27th, the day before the incident, the system operator programmed the operation of 10 synchronous power plants with voltage regulation capacity on the 28th in accordance with its instructions. The final number of synchronous power plants connected was the lowest since the beginning of the year. Second, several of the power plants capable of regulating voltage – and specially remunerated for doing so, as they were programmed for this purpose due to technical constraints – did not respond adequately to the system operator’s instructions to reduce it; some are even producing reactive energy, contrary to instructions, which is contributing to the problem.
- Fluctuations occur. The fluctuations – the first of which, unusually, occurred in a plant on the Iberian Peninsula – required a change in the system configuration, making it difficult to stabilise the voltage. After the second fluctuation, the system operator requested a power plant capable of helping to regulate the voltage, but this proved technically impossible before the collapse.
- Power plants were shut down, some of them in an apparently unjustified manner. Some of the power plant shutdowns were carried out before the voltage thresholds set in the relevant regulations (between 380 kV and 435 kV in the transmission network) were exceeded, while others were carried out after these limits had been exceeded in order to protect the installations. Once the chain reaction started, the normal protective mechanisms of the electricity system failed to stop or limit the process. Some of these protective mechanisms, such as load shedding devices, even contribute to overvoltage by shedding even more lines, contributing to voltage increases because they act to compensate for the drop in production rather than to control voltage.
In short, there is a lack of voltage control measures, either because they are not sufficiently programmed, because those that are programmed are not adequately implemented, or because of a combination of both, but not because they are lacking in the country.
KEY RECOMMENDATIONS
Based on the conclusions of the analysis,
the Committee proposes a number of measures to prevent a similar incident from recurring, among which the strengthening of supervision and enforcement of obligations by all participants in the electricity system, as well as technical measures to strengthen voltage control and protection against system fluctuations, stand out. At this point, it is crucial that PO 7.4 be implemented, which is in the hands of the National Commission for Markets and Competition (CNMC), which will enable asynchronous installations to implement power electronics solutions for voltage fluctuation management and may contribute to cost savings through the introduction of more competitive technologies.
In addition, it is proposed to increase the demand and flexibility of the electricity system. This will be helped by the 2025-2030 Electricity Plan, which will prioritise industrial consumption, increasing storage capacity, and reviewing regulation services and technical constraints on the system.
The government’s priority to increase the level of interconnection with neighbouring countries should also be maintained.
With regard to cybersecurity, it is proposed to accelerate the transposition of European legislation and to implement network controls and segmentation, as well as to introduce event detection and correlation systems that provide a higher level of monitoring.
In early June this year, ENTSO-E (the European Network of Transmission System Operators) announced that it was continuing to collect data and determining the next steps in the investigation into the power outage on the Iberian Peninsula.
In addition, ENTSO-E has launched a special web page that will serve as an information portal for stakeholders during the investigation. It provides a preliminary timeline of events on the day of the power outage, as well as information on the restoration process, the composition of the expert group and other important aspects. The website will be updated as the investigation progresses and new information becomes available. The information published is based on preliminary findings and analyses and is subject to change at any time.
Additional information in the report of the system operator RED Electrica.
