Reacción a "Final blackout report by European operators confirms event was caused by multiple factors, recommends improving oversight and coordination"

My assessments are based on the executive summary (Management Summary) of the Final Report (Final Report) drawn up by the Expert Panel for the investigation of incidents on the electricity grid (classified as severity 2 and 3 according to the ICS (Incident Classification Scale) methodology for ENTSO-E (European Network of Transmission System Operators for Electricity).

Although the Executive Summary evaluated here summarises the main findings and conclusions drawn by the experts, it omits certain details that are expected to be included in the full report. It is therefore a preliminary assessment, pending a more detailed analysis of the complete final report.

The final report published by ENTSO-E is based on the factual report prepared by the same panel and published by the same body on 3 October 2025. Thus, this report is primarily based on the same data as the factual report, although it adds some specific data that was not available in the previous report. Furthermore, it includes two new chapters of great relevance. The new Chapter 4 delves deeper into the analysis carried out to identify the causes of the incident. Meanwhile, the new Chapter 9 presents the findings of the investigation and the panel’s recommendations to prevent a recurrence of the situation.

In general terms, this report highlights that the incident was not due to a one-off failure or a single cause, but rather points to a structural problem in the provision and control of ancillary services, particularly voltage regulation, in a system with increasing penetration of converter-based generation. It is observed that existing technical and economic mechanisms are no longer aligned with the system’s actual needs.

Is the report based on sound data and methods? 

The report expressly states that the Expert Panel has requested from the affected transmission system operators (TSOs), as well as distribution system operators (DSOs) and other relevant network stakeholders (large generators, large consumers, inverter manufacturers and owners of self-consumption installations) all the data necessary to carry out a forensic analysis of the incident, including meter readings, trip orders, alarm logs, etc.

However, some data that could be relevant could not be obtained, such as, for example, the tripping of certain generators prior to the blackout (the response from the owners of the installations is that they do not record such events). This may constitute a limitation on the report’s conclusions.

What new insights does it provide?

Although the description of the events and the data presented are not significantly new, the added chapters are of great interest. The new Chapter 4 analyses in detail the phenomena observed and their impact on the incident, whilst Chapter 9 proposes measures and actions aimed at preventing or mitigating similar situations in the future.

What results/data would you highlight?

I believe the experts’ conclusions regarding the causes of the incident are highly significant; these can be summarised as follows:

1. The (synchronous) generators responsible for providing voltage support to the system were not operating as expected. The report notes that several generators failed to meet the reactive power reference in at least 75% of the hourly samples, which is the compliance rule. However, the reason for this situation is not clarified.
2. Renewable generation plants were operating with a fixed power factor. Consequently, their reactive power exchange was linked to active power, thus limiting their ability to participate flexibly in voltage regulation. Furthermore, the operating framework did not impose sufficient restrictions on the rate of change (ramps), which can exacerbate transients and interactions with voltage regulation.
3. Small-scale generators connected to distribution networks made a limited effective contribution to overall voltage control, which proved insufficient and uncoordinated with the system’s needs. Furthermore, many of them were suddenly disconnected when the inverters’ overvoltage protections were triggered, drastically increasing the net demand that had to be met by the rest of the system.
4. Certain devices relevant to voltage control, such as shunt reactors, required manual operation, which entails decision-making and operating times incompatible with the control requirements demanded by the incidents that occurred (events with dynamic components significantly faster than manual response times).
5. The permissible voltage range for transmission (400 kV) in the Spanish system is very wide (greater than in neighbouring countries). This allows operation at high voltages, which reduces the operational margins against overvoltages.
6. The existence of two oscillation episodes prior to the blackout is confirmed: one forced by power converter-based generators (0.63 Hz), and another natural inter-area oscillation (0.2 Hz), which are indicative of a dynamic weakness in the system. Their exact role in the incident is unclear, but the panel notes that some generators did not have, or did not have properly adjusted, the systems that could have dampened them (PSS: Power System Stabilizer).
7. The system entered an operational state in which, although contingency plans were implemented in a timely and appropriate manner, it was no longer possible to prevent the system from collapsing.
8. Although the system restoration plan was effective, experts have identified certain problems associated with the start-up of specific generation units and the stable maintenance of certain electrical areas. One of the main problems identified is the lack of information and management capacity regarding generators connected to the distribution network.

From the above observations, it can be concluded that:

1. Although it is not clear why some generators were not providing the required reactive power support for voltage regulation, the researchers emphasise that the regulatory framework in force at the time of the incident did not provide for penalties for failure to provide reactive power support, which is indicative of a structural weakness in that framework. Furthermore, the protocol did not establish dynamic specifications, i.e., regarding response speed. In other words, the report identifies that the system does not incorporate the value of reactive power or dynamic control. In the current context of the electricity system, this misalignment with the system’s actual needs reduces the robustness of voltage control and increases the risks of instability.
2. The report highlights instability phenomena associated with power converters. Whilst it is not stated that these were the sole cause of the incident, it has been observed that these phenomena interacted with other generation equipment in the area, revealing limitations in the design and coordination of the system’s dynamic control.
3. The operational requirements of renewable energy facilities and distributed resources are playing an increasingly significant role, and their role in the overall regulation of the system must be thoroughly reviewed.
4. The sequence of events that took place led to a situation in which, with the defence mechanisms available, it was no longer possible to prevent the collapse. Contingency plans must be reviewed to avoid reaching critical situations such as the one that occurred.
5. The incident demonstrates that traditional voltage control and auxiliary service schemes have significant limitations for modern electrical systems dominated by power electronics-based generation.

What practical recommendations can we make or highlight based on this report?

The recommendations and proposed measures are included in the full report, but are not present in the executive summary analysed. However, based on the analysis of the main causes of the incident identified by the investigators, the need to review and update the operating procedures relating to the provision of voltage regulation services stands out, as does the role of renewable generators in the electricity system.

Although the incident had multiple causes, the panel suggests that the event was not a mere anomaly, but a manifestation of the structural limitations of the current design of the electricity system. However, with the appropriate analysis, the operational framework can be adapted to meet the new grid requirements arising from the increased presence of power converters.

Summary

The report by the ENTSO-E expert panel concludes that the blackout was not the result of a single failure, but rather the outcome of multiple factors that highlight structural limitations of the current electricity system. In particular, deficiencies are identified in voltage regulation, associated with insufficient reactive power contribution from conventional generators, the operation of renewable plants with limited control capacity, and poor coordination of distributed resources. Added to this is the existence of poorly damped dynamic phenomena, including oscillations prior to the incident and possible interactions associated with power converters. The report also highlights shortcomings in the regulatory framework, which did not adequately incentivise voltage support nor set out stringent dynamic requirements. As a result, the system reached an operational state in which, even though the defence mechanisms functioned correctly, it was not possible to prevent the collapse. Overall, the incident highlights the need to adapt the design and operation of the electricity system to an environment with high penetration of power electronics-based generation.