ACER and national regulators join ENTSO-E’s Expert Panel investigating the electricity system separation of 24 July 2021, which first meets today

The Continental Europe electricity system was separated in two resulting in transmission system outages in Spain, Portugal and the Pyrénées-Orientales region of France

The Expert Panel will identify the causes and make recommendations in a Final Report

On 24 July 2021 at 16:36 CET, due to a major incident in France, the transmission systems of Portugal and Spain, together with a small part of the French transmission system1, were disconnected from the synchronous area Continental Europe for just over 30 minutes.

Based on preliminary data of transmission system operators (TSOs), the system separation is classified as a scale 2 or “extensive” incident as per ENTSO-E’s Incident Classification Scale (ICS)2.

According to the ICS Methodology, for scale 2 incidents, a final report shall be prepared by an Expert Panel, where relevant National Regulatory Authorities (NRAs) and the European Agency for the Cooperation of Energy Regulators (ACER) may be involved upon their request. ENTSO-E has therefore set up an Expert Panel and has invited ACER and relevant NRAs to join it. The Expert Panel will first meet today, on 22 October.

The investigation of the Expert Panel will be based on the Interim Report that ENTSO-E is currently finalizing. This Interim Report, which will be published on 12 November 2021, will contain the data, initial findings on the sequence of events and timeframes related to the incident.

Expert Panel’s Final Report will have recommendations

The Expert Panel will prepare a Final Report, which shall describe the sequence of events and details of the transmission outages. It will also explain the causes and contain recommendations to prevent such incidents in the future. The Expert Panel’s Final Report shall be published in first quarter of 2022.

ACER and ENTSO-E are committed to fulfilling their legal obligations specified in the System Operations Guideline3 and ICS Methodology. In line with the provisions of those documents, the Expert Panel will be chaired by a representative of a TSO not affected by the incident whilst all the members will contribute to the deliverables assigned on equal basis in order to ensure high quality and consistency of the final report. ACER and ENTSO-E will continue together to provide timely information about the incident, published on their websites4.


  1. Figure 1 depicts the disconnection route between the two areas:

  2. Incident Classification Scale. The ICS Methodology has been developed in accordance with Regulation (EU) 2019/943 of the European Parliament and of the Council of 5 June 2019. It was updated in 2019, to fulfil the objectives of Article 15 of SO GL quoted above.
  3. Commission Regulation (EU) 2017/1485 of 2 August 2017 establishing a guideline on electricity transmission system operation (System Operation Guideline, SO GL).

  4. ENTSO-E publications - 24 July 2021: A short outage of French-Spanish interconnection on 24 July 2021

  5. ACER news - 22 October 2021: ACER and ENTSO-E investigate the 24th July 2021 electricity system separation in Spain, Portugal and parts of France.

Press contacts:

ACER,, T: + 32 (0) 484 66 85 99

ENTSO-E,, T: +32 (0) 476 97 50 93.