Cascading blackout across Albania, Bosnia and Herzegovina, Montenegro and Croatia after vegetation contact

June 2024Published 1 May 2026Responsible editor: Chief Editor

MajorElectrical

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From the recordRoot cause Failed part

Where: Albania, Bosnia and Herzegovina, Montenegro and Croatia
What: Cascading blackout after two overhead lines tripped
Cause: Vegetation contact on conductors
Outcome: Supply restored with help from neighbouring operators

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What happened

In June 2024, shortly after midday, a disturbance on the Continental European interconnected transmission system caused a cascading blackout affecting Albania, Bosnia and Herzegovina, Montenegro and Croatia. Immediately before the event the affected area was importing in the order of 2,000 MW from neighbouring systems and exporting in the order of 400 MW over a sub-sea high voltage direct current link. An overhead line tripped on a short circuit about fifteen minutes before the collapse, and a second 400 kV cross-border overhead line tripped about two minutes before it.

Together these produced an N-2 condition with violations of line loading and voltage limits, after which voltage in the south-eastern part of the synchronous area began to fall rapidly. Multiple lines then disconnected in sequence on undervoltage and overcurrent protection, the system separated, and voltage collapse led to loss of supply across Albania, Bosnia and Herzegovina, Montenegro and Croatia. The transmission system operators in these countries restored supply with assistance from neighbouring operators.

The regional coordination body for European transmission system operators convened an expert panel, joined by the European regulatory agency and the relevant national regulatory authorities, which published an interim factual report in November 2024 and a final report in February 2025.

Contributing factors

As stated in the expert panel's final report of February 2025: (1) the two initial short circuits were attributed to vegetation that had grown too close to the conductors at specific corridor sections; (2) the resulting outages affected several transmission system operators, including those in Albania, Bosnia and Herzegovina, Montenegro and Croatia, at the same time without the operators concerned having an overall view of the state of the regional grid, which the report identified as a gap in cross-border real time situational awareness; (3) the subsequent cascade reflected the reduced margin of the system under N-2 conditions together with limited local voltage support in the affected region. The report set out recommendations covering cross-border coordination, regional situational awareness tools and vegetation management practices.

Lessons learned

Vegetation contact on 400 kV overhead lines can start an N-2 condition, so operators must survey and clear growth on high voltage corridors on a risk-based cycle.
A disturbance that spans several control areas needs a shared real-time view, because operators lacked an overall picture of the regional grid state.
N-1 and N-2 checks must reflect actual import flows, since a heavily importing area lost voltage support after the line trips.

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Not yet known

Duration of the blackout in each country
Cost of lost supply and repairs
Exact locations of the vegetation contact

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Source

entsoe.eu

Published 2026-05-01. Written from public reporting. Descriptive, not investigative. See the data accuracy disclaimer.