Overgrown vegetation is the culprit of 21 June Balkan blackout

A power outage struck Bosnia and Herzegovina, Montenegro, Albania and part of Croatia on June 21 this year. Electricity was out for hours, causing many companies to halt operations, with some areas also left without water. This week, the European Network of Transmission System Operators for Electricity ENTSO-E released a preliminary report on the analysis of this incident.

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This is the first step in analyzing the regional system breakdown, classified as a third-level event according to ICS methodology, requiring a detailed report by an expert panel. The preliminary report contains only a factual account of events without a detailed analysis of causes, potential deficiencies, conclusions or recommendations.

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The disturbance included multiple outages at different 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 happened on the 400 kV Zemblak – Kardia transmission line at 12:21:30. It was confirmed that both incidents were caused by insufficient clearance from vegetation, which led to outages on several other transmission lines and a voltage collapse in Bosnia and Herzegovina, Montenegro, Albania and Croatia, according to the report.

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They note that the event caused significant loss of load and generation, with a total generation loss of 2,214 MW and significant load losses for various transmission system operators within minutes.

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Transformer control switches responded to the voltage drop, with automatic voltage regulation observed mainly in the control areas of CGES (Montenegro), HOPS (Croatia), and NOSBiH (Bosnia and Herzegovina), while OST (Albania) did not have automatic regulation.

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The report states that the network was considered secure, no major issues were detected in the affected area, and no safety warnings were issued for relevant network elements. No significant safety risks were identified, and the network was rated as N-1 secure.

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One of the conclusions is that the Regional Coordination Centers communicated effectively during the incident.

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The expert panel, comprising representatives of affected and unaffected transmission system operators, RCCs, ICS working group representatives, 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.

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