Expert Panel
Following the blackout, on 12 May 2025, ENTSO-E set up an Expert Panel in line with Article 15(5) of the Commission Regulation (EU) 2017/1485 of 2 August 2017 establishing a guideline on electricity transmission system operation (SO GL) and the Incident Classification Scale (ICS) Methodology. The ICS Methodology is the framework for classifying and reporting incidents in the power system and for organising the investigation of such incidents and is especially relevant to the work of the Expert Panel. It is noted that the investigation of the Expert Panel was performed in line with the version of the ICS Methodology applicable at the time of the incident.
Under the legal requirements of both SO GL and the ICS Methodology, when the incident is classified according to the ICS Methodology criteria as scale 3 incident – blackout – the Expert Panel is tasked to investigate the root causes of the incident, produce a comprehensive analysis, and make recommendations in a final report, published on 20 March 2026.
The Expert Panel consists of representatives from TSOs, the Agency for the Cooperation of Energy Regulators (ACER), National Regulatory Authorities (NRAs), and Regional Coordination Centres (RCCs).
The Panel is led by experts from TSOs not directly affected by the incident and includes experts from both affected and non-affected TSOs. The Expert Panel is led by Klaus Kaschnitz (APG, Austria) and Richard Balog (MAVIR, Hungary).
ENTSO-E Bodies Convenors participating in the Expert Panel
- Olivier Arrivé – as chair of the System Operation Committees
- Robert Koch – as convenor of the Steering Group Resilient Operation
- Rafal Kuczynski – as convenor of the Regional Group Continental Europe
Experts from TSOs and RCCs participating in the Expert Panel
| Amprion (Germany) | Tilman Ringelband |
| EirGrid (Ireland) | Donna Kearney |
| Elia (Belgium) | Bernard Malfliet |
| Elia (Belgium) | Peter Van Meirhaeghe |
| Energinet (Denmark) | Bent Myllerup |
| Mavir (Hungary) | Andras Woynarovich |
| Red Electrica (Spain) | David Alvira |
| REN (Portugal) | Filipe Ribeiro |
| RTE (France) | Laurent Rosseel |
| SEleNe CC (Greece) | Maria-Faidra Katsiantoni |
| Swissgrid (Switzerland) | Bastien Grand |
| Terna (Italy) | Guido Coletta |
| Terna (Italy) | Giorgio Giannuzzi |
| Transelectrica (Romania) | Mihai Cremenescu |
Experts from ACER and NRAs participating in the Expert Panel
| ACER | Georgios Antonopoulos |
| ACER | Uros Gabrijel |
| ACER | Aleksander Glapiak |
| ACER | Maria Barroso Gomes |
| ACER | Domen Kodric |
| ACER | Zoran Vujasinovic |
| ACER | Jan Kostevc |
| ANRE (Romania) | Alina Poanta |
| ARERA (Italy) | Marco Pasquadibisceglie |
| ARERA (Italy) | Andrea Rosazza |
| BNetzA (Germany) | Jochen Gerlach |
| BNetzA (Germany) | Thomas Hoelzer |
| BNetzA (Germany) | Nicolas Krieger |
| CNMC (Spain) | Virginia Garcia Escoin |
| CNMC (Spain) | Teresa Ibanez Tarrago |
| CNMC (Spain) | Diego Roldan Cabanillas |
| CRE (France) | Martin Frédéric |
| CRE (France) | Pierrick Muller |
| CRE (France) | Sara Rami |
| CREG (Belgium) | Marijn Maenhoudt |
| CREG (Belgium) | Emilie Leroy-Biasutti |
| EI (Sweden) | Anna Carlen |
| ElCom (Switzerland) | Raffaele Bornatico |
| ERSE (Portugal) | Jose Capelo |
| ERSE (Portugal) | Paulo Oliveira |
| ERU (Czech Republic) | Pavel Simoncik |
| MEKH (Hungary) | Erika Szirmai |
| URE (Poland) | Lukasz Makos |
| URE (Poland) | Piotr Rak |
| URE (Poland) | Witold Zuchowski |
Publications & Documents
8.3 Scale of all Violations Linked to the Incident
The OB3 was the most severe criterion violated during the incident in Spain and Portugal. Several other criteria were violated before the blackout occurred, which are presented in Table 8-1 and summarised below. When an incident meets several criteria, it is classified according to the criterion with the highest priority. Additionally, all sub-criteria information (i. e., ICS violations or events) is also collected. Figure 8-2 presents a timeline view of the ICS criteria violated during the incident. It should be noted that the violations of the criteria regarding loss of generation facilities (G) and loss of load (L) have been separated into smaller violations to better visualise the sequence of events and correlate the impact of these violations with the measured frequency and voltage during the incident. The following paragraphs consolidate the violations according to the ICS methodology and therefore do not fully align with the detailed time line presented in Figure 8-2
In Spain, there was a loss of generation facilities (G0) at 12:32, followed by a transformer trip at 12:32:57, which is classified as a scale 0 loss of network element (T0) violation, and a further 355 MW of generation tripped.Approximately 20 seconds later, at 12:33:16, there were successive trips of power generation facilities. These generation trips are classified as one G2 incident as they occurred within fifteen minutes and were greater than3,000 MW. Further T incidents occurred with the loss of tie lines and transmission lines in Spain. The trip of the HVDC interconnector was classified as a T2 ICS violation due to the impact on a neighbouring TSO with OV (voltage) violations in France. The disconnections of all tie lines between France and Spain split the Iberian Peninsula from CE (involving more than one TSO with a load larger than 5 % of the total load of the synchronous area before the separation, thus violating the RS2 criterion). The loss of load (L2) criteria was met after the generation loss, as automatic TSO system defence measures were activated with the tripping of pumps and distribution load shedding.
There was high-voltage violations in Spain during the incident that contributed to the trip of generation,
although they did not meet the time threshold for a voltage violation as defined in the ICS methodology.
Voltage was above 1.1 per unit for 16 seconds, whereas the ICS methodology requires a time of greater than 30 seconds. The subsequent voltage collapse is captured under the OB3 (blackout) criteria.
Portugal experienced high voltage and – similarly to Spain – the duration did not reach the time thresholds specified in the ICS methodology, and therefore therewere no OV incidents. There was a significant loss of load (L2) as pumps and industrial consumers were disconnected, as well as the distribution load. There were two T0 events with the loss of a transformer and an overhead line. Additionally, a G2 violation was recorded at the time of the blackout, as all generation facilities were
disconnected.
The highest criteria experienced in France by RTE was scale 1 related to OV1. France also had G0 and T0 violations.
Frequency degradation (F) ICS criteria violation was abelow scale (BS) violation (FBS). The reason is that the frequency deviation magnitude thresholds were met,but – similarly to the ICS voltage criteria (OV) – the duration of the deviations were not sufficiently long to be registered at a higher scale.
Furthermore, the frequency deviations are registered at a synchronous area level,even if local anomalies might occur.
All oscillations that occurred prior to the blackout – as detailed in this report – did not cause any ICS criteria violations.
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