The final report of the Expert Panel on the 4 July 2025 in the Czech Republic identifies its root causes and outlines recommendations aimed at preventing similar incidents in the future. The Expert Panel was composed of 17 representatives from Transmission System Operators (TSOs), the Agency for Cooperation of European Energy Regulators (ACER), and National Regulatory Authorities (NRAs), and was chaired by an expert from an unaffected TSO.
The investigation concludes that the incident occurred after an unexpected reduction of generation in one part of the system which followed the tripping of a 400 kV line, caused by a broken wire. A couple of minutes after the N-1 event, this unexpected reduction in generation led to increasing overloads in the transmission grid. An overloaded 220 kV line was disconnected, triggering the tripping of the two remaining connection points in the affected area, which was subsequently islanded. Due to the large generation-load imbalance in this area, the automatic under-frequency load shedding was unable to prevent the frequency drop, leading to the immediate collapse of the islanded area.
Based on these findings, the Expert Panel has developed a set of recommendations addressing each of the factors identified in the report to help prevent similar incidents in the future and further strengthen system resilience.
Read the full report here.
About ENTSO-E
ENTSO-E, the European Network of Transmission System Operators for Electricity, is the association for the cooperation of the European transmission system operators (TSOs).
The 40 member TSOs, representing 36 countries, are responsible for the secure and coordinated operation of Europe’s electricity system, the largest interconnected electrical grid in the world.
Press contact: media@entsoe.eu