Photo: Image by Markus Distelrath from Pixabay
Overvoltage was the main reason for the blackout on May 18 last year in North Macedonia, according to the final report of the European Network of Transmission System Operators for Electricity.
The final report of an expert panel established to investigate the three-hour blackout that occurred on May 18, 2025 in North Macedonia identifies the causes and outlines recommendations to strengthen the resilience of Europe’s interconnected electricity system.
The European Network of Transmission System Operators for Electricity (ENTSO-E) said that the investigation concluded that the blackout in North Macedonia resulted from operating the transmission system above the defined voltage limits of 420 kV.
On May 18, the circumstances most exacerbated the underlying issue
Overvoltage led to the tripping of all 400/110 kV transformers, resulting in the 400 kV network being separated from the 110 kV network and causing the blackout in the region, ENTSO-E explained.
The experts stressed that such situations – overvoltage and excess of reactive power – had been occurring beforehand, but the blackout only occurred on a specific day when the circumstances most exacerbated the underlying issue.
The report noted that on May 18 at 04:59 CET, the power system of North Macedonia experienced an overvoltage episode that led to a separation of the 400kV and 110kV voltage levels. The separation led to a loss of stability, supply, and load in the 110kV transmission network, resulting in a blackout across the entire 110kV system, to which all the demand is connected, the report reads.
Throughout the event, the 400 kV transmission network remained operational.
MEPSO, the transmission system operator (TSO) of North Macedonia, immediately activated measures, and the system was restored by 07:47 on May 18.
The final report was prepared by an 18-member panel comprising representatives from transmission system operators (TSOs), the European Union Agency for the Cooperation of Energy Regulators (ACER), and national regulatory authorities (NRAs). The panel was chaired by an expert from 50Hertz, a TSO outside the affected area.
The third blackout in Europe in two years
Based on these causes, the expert panel has set out recommendations addressing each of the factors identified in the report, with the aim of preventing similar events in the future.
These include a recommendation to establish an action plan for the entire South-East Europe region to mitigate high-voltage conditions, as well as a recommendation for stronger alignment among TSOs on operational voltage control measures, supported by Regional Coordination Centers (RCCs) and ENTSO-E.
This was the third blackout in Europe in the last two years.
The first one, in 2024, left Bosnia and Herzegovina, Albania, Montenegro, and parts of Croatia without power supply for three hours.
In April 2025, power systems of Spain and Portugal experienced the most severe and unprecedented blackout in Europe in the past 20 years.
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