ACER and ENTSO-E to investigate the 8 January system separation

2 March 2021

National regulators along with the European Agency for the Co-operation of Energy Regulators, ACER, have joined ENTSO-E’s Expert Panel investigating the electricity system separation of the Continental Europe synchronous area on 8 January. ENTSO-E’s preliminary report was published immediately after the separation occurred, and its Interim Report on 26 February.

The Expert Panel, which is charged with identifying the causes and making recommendations in a Final Report, has now begun its investigation and will hold its first meeting on 4 March.

Based on preliminary data from TSOs, the system separation of the Continental Europe synchronous area, which lasted just over an hour, is classified as a scale 2 (or “extensive”) incident on ENTSO-E’s Incident Classification Scale. 

The Interim Report contains the data gathered, and initial findings on the sequences of events and timeframes, and will form the basis for Expert panel’s formal investigation.

The Final Report will describe the sequence of events and violations of operational security limits. It will explain the causes and have recommendations to prevent such incidents in the future. 


On Friday, 8 January 2021 at 14:05 CET, the Continental Europe Synchronous Area was separated into two areas (the North-West area and the South-East area) due to cascaded trips of several transmission network elements. Immediately after the incident occurred, European TSOs started to resolve it and resynchronised the continental Europe power system at 15:08 CET. It was a fast and co-ordinated approach, and as a result no major loss of load, or damages were observed in the power system.

In the immediate aftermath, Euro­pean TSOs in close collaboration through the ENTSO-E body decided to start a joint process to collect all relevant facts regarding the incident. The watchword was transparency.

During the incident, the TSOs which were impacted most by the event activated several system states in the ENTSO-E Awareness System (EAS). This allowed all TSOs in Europe to be aware of the seriousness of the ongoing incident. Both the North and South co-ordination centres set alarms for frequency deviations according to the conse­quences in their co-ordination zones.

According to the established procedures, EMS (Serbia) acted as frequency leader in the South-East separated area, to co-or­dinate the return of the system to 50 Hz. Amprion (Germany) acted in the same manner as the frequency leader in the North-West area due to its role as Synchronous Area Monitor (SAM). This allowed the resynchronisation to take place as quickly as possible. Each separated area subsequently took appropriate control actions, mostly on the production side, to balance its area.

After stabilising both areas with automatic defence actions as well as manual countermeasures, the resynchronisation process started with HOPS (Croatia) acting as the resynchro­nisation leader.

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