On Monday, 4 November 2024, ENTSO-E published the Interim Factual Report on the analysis of the incident of 21 June 2024 on its website.
This is the first step in the analysis of the regional system failure, which has been classified as a Level 3 incident according to the ICS methodology, requiring a detailed report from the Expert Panel. The preliminary report contains only a factual account of the incident, without detailed analysis of the causes, any deficiencies, conclusions, and recommendations.
In the remainder of the report, the Expert Panel will analyse key aspects such as the identified voltage collapse, the technical details of the event, the root causes and the key factors. The final report will also provide recommendations, should this be deemed necessary.
The expert panel consists of representatives from affected and unaffected transmission system operators, regional coordination centres, the ENTSO-E ICS group, national regulatory authorities and ACER. The panel began its investigation in July 2024, and the final report is expected to be published on the ENTSO-E website by early 2025.in the year
Below you can read a summary of this Report, and more details HERE.
1 Report Summary
1.1 Introduction
On Friday, 21 June 2024, a significant incident occurred in Southeast Europe (SEE), which led to a major disruption in the continental European electricity system. The incident led to a significant loss of load and generation, šthat hit višand countries includedčincluding Albania (OST), Bosnia and Herzegovina (NOSBiH), Montenegro (CGES) and Croatia (HOPS). DogađIt is characterised by a series of unpredictableđThese situations in the transmission network ultimately led to the (partial) collapse of the system in these four countries.
Immediately after the incident, transmission system operators in the affected south-eastern Europe launched a coordinated response to manage the situation and restore normal operation. This brief summary provides a detailed overview of the system's state before the incident, the sequence of events during the incident, the system restoration procedure, and the communication between coordination centres and transmission system operators. The brief also includes an analysis of the incident based on the Incident Classification Scale Methodology (hereinafter: ICS methodology) and outlines the next steps for further investigation and performance improvement.
In the following chapters, the collected facts are presented, offering a comprehensive understanding of the incident and its impact on the power system in the Balkan region. In this report, all times are Central European Summer Time (CEST), which corresponds to UTC+02:00.
1.2 Systemic and market conditions before the incident
Disconnection planning is coordinated through the transmission system operator and regional coordination centres, with annual and weekly meetings to align maintenance plans. Several lines were disconnected as planned on 21 June 2024, including some of the 220 kV and 400 kV lines. Affected transmission system operators[1] They did not report any unplanned outages in the immediate preceding period. of the original fall during the incident in JIE.
In June 2024, record-high temperatures were recorded globally and in Europe, with significant heatwaves in SE Europe. In many places, temperatures over 40°C were recorded, which contributed to an increase in demand.žone for electricity and other operational challenges.
Information on organised day-ahead markets is available in three of the four affected price zones, with significant cross-border market transactions based on explicitly allocated cross-border capacity, which refers to the maximum amount of electricity that can be transmitted between two different price zones or regions without compromising the security of electricity supply.
Highest electricity price of 176.32 €/MWh was recorded in Albania.
The load patterns reflect seasonal changes and are increased due to the tourist season and similar weather conditions across the region. The daily load curve on 21 June was about 10% hišand from the average working week, with knowčany increase in total consumptionšnot
Significant differences have been recorded between planned commercial exchanges and physical flows due to the highly interlinked network and the application of bilateral calculation methodologies. capacities applied at all interconnections between the affected transmission system operators.
The day-ahead and intraday security analyses carried out by the relevant transmission system operators did not indicate any critical unforeseen situation that would lead to a possible disruption.šava of operational security. Analyses have shown that during criticalčThere have not been any major criticisms in recent times.čno failures occurred, and corrective measures have been taken for the identified overloads.
1.3 Development of systemic conditions during the event
The disturbance of 21 June 2024 involved multiple outages at various substations and voltage levels, primarily in the 400 kV and 220 kV networks. The first outage occurred on the 400 kV Ribarevine – Podgorica 2 transmission line at 12:09:16. The second outage occurred on the 400 kV Zemblak – Kardia transmission line at 12:21:30. Both incidents were confirmed to be caused by insufficient clearance from vegetation. This resulted in the outage of several other transmission lines and a voltage collapse in Bosnia and Herzegovina, Montenegro, Albania and Croatia. The event caused a significant loss of load and generation, with a total generation loss of 2,214 MW and knowčminimum load losses in variousčof the transmission system operator within a few minutes. The transformer regulation switches reacted to the voltage drop, with automatic voltage regulation observed mainly in the control areas of CGES (CG), HOPS (HR) and NOSBiH (BIH), while OST (AL) did not have automatic regulation.
1.4 Analysis Regional coordination centres before the incident
The results of various analyses carried out by the regional coordination centres before the incident of 21 June 2024 show that the network was considered safe and that no major problems were discovered in the affectedđenom područThe task of coordinating outage planning, carried out by SEleNe CC, SCC and TSCNET, did not reveal any security warnings for the relevant grid elements. The short-term adequacy analysis, led by SCC, confirmed that the available generation capacity can meet the expected demand. The security analysis performed by TSCNET, SCC and SEleNe CC did not reveal any significant operational security risks, and the network was assessed as N-1 secure. Similarly, other tasks of the regional coordination centres, such as the creation of a common grid model, coordinated capacity calculation and the assessment of the consistency of defence and system restoration plans, did not indicate any unsafe operation where and to the extent they were carried out. (capacity calculation and regional network model).
1.5 Communication of coordination centres and between transmission system operators
Communication began with TERNA notifying CGES of the fault on the Monita high-voltage direct current (HVDC) cable, which was followed by an exchange of information between CGES, NOSBiH, HOPS and OST regarding the details of the incident and offers of support. Svisgrid (Swissgrid) played a significant role in the communication following the system collapse, coordinating with Amprion, ELES and OST to offer assistance and gather the latest information on the situation. The Regional Coordination Centres communicated effectively throughout the incident. The European Awareness System (EAS) was used, which provided detailed signalling of system state changes for each affecđof the transmission system operator during an incident, including normal conditions, pre-accident conditions, accident conditions, system collapse conditions and system restoration conditions.
1.6 Procedure for the system restart
The transmission system operators affected by the incident received information via the EAS and through direct communication among the affected transmission system operators about the voltage collapse and system collapse in Albania, Montenegro, Bosnia and Herzegovina, and Croatia shortly after the disturbance, which led to the immediate planning of the system's restoration.
Interconnector lines were used for the system restoration procedure in a Top-Down manner, ensuring active power management on the interconnector lines in accordance with agreements between the transmission system operators.
HOPS began to re-establish the system's operation in the Split area at the 220 kV voltage level, as the 400 kV level was unavailable. for maintenance, which was followed by a series of reconnections and transformer activations to energise key substations.
NOSBiH coordinated with neighbouring transmission system operators and initiated the restoration of the system from the Ugljevik substation, progressively reconnecting lines and substations, and resolving high-voltage issues in the southern part of their system.
CGES focused on restoring the system's operation in the northern part of the country, starting with reconnecting key transmission lines and transformers, and resynchronising with the OST.
OST has resumed the operation of the system by energising the substations and synchronising with neighbouring networks, starting with IPTO and subsequently with KOSTT and CGES.
The procedure to restore the system to operation began with the first action at 12:33, and the procedure to restore the load for all transmission system operators was completed at around 16:00.
1.7 Classification of incidents based on the ICS methodology
The ICS methodology is based on the requirements of Regulation (EC) No 714/2009 and Commission Regulation (EU) 2017/1485 and aims to provide a realistic view of the system's state during incidents. The incident classification criteria are ranked by priority, with the highest-priority criterion determining the incident's level. An expert panel investigates incidents classified as level 2 or 3. The OB3 criterion was met on 21 June 2024 in Albania, Bosnia and Herzegovina and Montenegro, while Croatia met the L2 criterion. The incident was classified as level 3 due to a large demand loss. The RCC investigation threshold was met as multiple transmission system operators entered emergency states, and the incident was confirmed as at least Level 2. The triggering of the threshold encourages the launch of an RCC investigation by the RCC Investigation Subgroup in accordance with Article 7 of the RCC Post-Operation and Post-Disturbances Analysis and Reporting Methodology.
1.8 Next steps
The incident of 21 June 2024 has been classified as a Level 3 event according to the ICS methodology, which requires a detailed report from the Expert Commission. This will provide both a factual account and an assessment of the incident, based on available and potentially additional data identified during the investigation. Analysis of RCCs in accordance with Article 7 of the Post-Drive Incident Analysis and Reporting Methodology will be part of this report. The Commission will analyse key aspects such as voltage collapse, technical details, root causes and critical factors, and make recommendations if necessary.
The expert panel, which consists of representatives from affected and unaffected transmission system operators, RCCs, the ICS working group, national regulatory authorities and ACER, began its investigation in July 2024. The final report is expected to be published on the ENTSO-E website by early 2025.
[1] The term 'affected transmission system operators' refers to the four transmission system operators (CGES, HOPS, NOSBiH and OST) who were affected by a level 2 or 3 incident. More details can be found in chapter 7.1 of this report.šsecret