On 25 February, the European Network of Transmission System Operators for Electricity (ENTSO-E) published the final report of the Expert Panel on the incident that occurred on 21. On 21 June 2024, when a large part of the consumer area of Albania, Montenegro, Bosnia and Herzegovina and Croatia was left without power.
The report identifies seven direct causes, the coincidence of which on that day led to the power cut:
's missing A practical simultaneous fault (just 13 minutes apart) on two key transmission lines in the region – the 400 kV "Ribarevine – Podgorica" and 400 kV "Zemblak – Kardia" lines;
's missing The inability of transmission operators in the region to detect the inadequacy of the system in the period between two failures;
's missing Inability to detect voltage instability in the region;
's missing Cascading failure of an additional three transmission lines due to overload protection adjustments;
's missing Automatic reaction of the transformer's regulating taps to a disturbance;
's missing An insufficient amount of available reactive power throughout the region and
's missing Lack of measures to prevent voltage collapse in the region.
Based on the identified causes, the report provides 12 recommendations for improving the work of all operators in the interconnection:
's missing Review of national policies and the process of removing vegetation in transmission line corridors;
's missing Improvement of observability zones on monitoring and control systems;
's missing Regular assessment of voltage stability;
's missing Identifying key indicators that indicate the risk of tension collapse;
's missing Revision of the ENTSO-E guidelines for the adjustment of overload protections;
's missing Blocking of automatic voltage regulation in specific situations;
's missing Assessment of the adequacy of resources for voltage control;
's missing An investigation into the feasibility of introducing a concept of automatic measures for regulating voltage in pre-fire conditions;
's missing Investigating the possibility of installing undervoltage protectors for the controlled automatic disconnection of part of the consumers from the grid;
's missing Verification of the accuracy of data used for safety analyses;
's missing Timely updating of information on the availability of system elements and
's missing Verification of the accuracy of voltage drop calculations in the region.
Together with the recommendations already given from previous incidents within the ENTSO-E area, these recommendations should lead to a reduction in the likelihood of similar incidents recurring in the European electricity interconnection.
The full report, which was prepared by over 60 experts from across Europe, can be found here: ENTSO-E Report