The sequence of events that preceded the major outage of the power system of Albania, Montenegro, Bosnia and Herzegovina and Croatia on June 21 this year began in Montenegro with the disconnection of the Podgorica 2 - Ribarevine transmission line at 12:09 p.m. due to a short circuit that occurred due to insufficient of the distance between the transmission line and the vegetation below it, when the switch turned off the transmission line, according to a preliminary report of the European Network of Transmission System Operators for Electricity (ENTSO-E).
The report also states that this does not have to be the cause of the breakdown of the energy system in four countries, but that in Montenegro it was the first failure of the transmission system that day, and that the final report will be available by the beginning of 2025, which will determine the causes and make recommendations.
The analysis is not yet complete
Montenegrin transmission lines are managed by the majority state company Crnogorski elektroprenosni sistem (CGES), which, when asked by "Vijesti", said that the analysis of the cause of the collapse of the energy system in four states on June 21 is not final but preliminary, as well as that the contact of transmission lines with vegetation caused the outage of this transmission line, not the entire system.
"Only the preliminary report of ENTSO-E was published, which listed the events of importance for the collapse of the system. Only one of the events recorded that day was the outage of the Podgorica - Ribarevina transmission line. A detailed analysis of the real causes of the collapse of the system is still underway, and the report will be published, most likely, at the beginning of next year", CGES stated.
There was contact between vegetation and power lines...
When asked if it is true that insufficiently cleared vegetation near the Ribarevina - Podgorica transmission line is the cause of the power system outage in four states, the CGES denied this.
"No, it is not true that insufficiently cleared vegetation near power lines is the cause of the outage. The contact between the conductor and the vegetation is the cause of the outage of that particular transmission line, not the collapse of the system. Namely, the preliminary report already stated that 'the results of various analyzes carried out by the regional coordination centers before the incident of June 21, 2024 show that the network was considered safe and that no major problems were detected in the affected area'. This means that the outage of any single transmission line could not have caused the entire incident. That is why a detailed analysis is being done, which ENTSO-E will introduce to the public as soon as it is completed", CGES stated.
When asked what CGES can do and what they will do to prevent similar situations from recurring, they said that they are constantly working to improve the quality of work.
"Regarding a specific event, CGES will certainly follow up all the recommendations from the report, once it is completed," the company stated.
The chain collapse started after the breakdown in Albania
According to the mentioned details from the ENTSO-E report, after this outage on the Podgorica 2 - Ribarevine transmission line at 12 hours and nine minutes, the voltage in the system in Montenegro and the region stabilized.
"This outage caused an initial voltage drop in the affected region, but voltages stabilized quickly. The second interruption was the disconnection of the transmission line Zemblak - Kardia (Albania - Greece) at 12 hours and 21 minutes. The short circuit that led to the failure was caused by too little distance to the vegetation under the transmission line, the same as the first interruption," the report stated.
The first and second outages occurred 12 minutes apart, and the cause of the second breakdown on the Albania-Greece transmission line was not related to the first breakdown in Montenegro, as it was caused by a short circuit between the transmission line and vegetation.
The sequence of outages shows that after the failure of the Albania-Greece transmission line that occurred at 12 hours, 21 minutes and 33 seconds, there was a series of connected outages of the energy system in the region. Ten seconds later, at 12:21:43, the Fierze-Prizren transmission line went out of the system, five seconds after that, at 12:21:48, the Dubrovnik hydropower plant went out, and three seconds after that, the Trebinje hydropower plant.
Entire systems collapsed in three minutes
After that, with a difference of only a few seconds, 17 energy facilities - transmission lines, transmission substations and large power plants - went out of operation, so that in 12 hours and 24 minutes, the entire area of Albania, most of Montenegro and Bosnia and Herzegovina and a large part of Croatia. Most of this region received power in the next two to three hours.
"During the incident, automatic voltage regulation was applied as described in subsection 3.3 and all transformers reacted properly. There was no manual change of the transformer switch or manual disconnection of the load. The affected relay protection systems of each high-voltage element worked in accordance with the set parameters," the ENTSO-E analysis stated.
A final investigation will provide causes and recommendations by early 2025.
The final report of the ENTSO-E Expert Council, as explained, will not only present an analysis of the incident, but will also provide recommendations to prevent similar occurrences in the future.
“The investigation will focus on several key aspects, including a general and specific analysis of the collapse of the energy system, particularly in the context of: technical reviews of the incident; an investigation into the primary causes and other critical factors contributing to the event as well as a conclusion with any recommended actions based on the findings of the investigation,” the report stated.
They expect the final results of the investigation to be published on ENTSO-E by the beginning of 2025. The key questions to be addressed by the investigation are what were the root causes of the incident and why they could not have been prevented, what other significant factors during the disruption should be taken into account, what defense measures were effective in preventing further outages within the power system and whether all regulations and procedures were followed during these events or whether some irresponsibility contributed to this incident.
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