IN Brief:
- ENTSO-E’s final report links the 18 May 2025 blackout in North Macedonia to operation above the defined 420kV voltage limit.
- The overvoltage led to the trip of all 400/110kV transformers, separating the 400kV and 110kV networks.
- The recommendations focus on stronger voltage-control coordination across South-East Europe, involving TSOs, RCCs, DSOs, significant grid users, and regulators.
ENTSO-E has published the final report from its expert panel investigation into the blackout that hit North Macedonia on 18 May 2025, setting out both the immediate technical cause of the event and a wider package of recommendations for the South-East Europe region. The panel was made up of 18 members, including representatives from transmission system operators, ACER, and national regulatory authorities, and was chaired by an expert from 50Hertz as an unaffected transmission operator.
The report’s central finding is that the incident resulted from operation of the transmission system in North Macedonia above the defined voltage limit of 420kV. That overvoltage condition caused all 400/110kV transformers to trip, separating the 400kV network from the 110kV network and triggering the blackout in Northern Macedonia. The sequence described in the report is technically direct: voltage exceeded the permitted operating envelope, transformer protections responded, and the network split across a critical interface.
The report also sets out a broader action plan. ENTSO-E says the panel has recommended measures across the South-East Europe region to mitigate high-voltage conditions, together with stronger coordination among TSOs on operational voltage-control measures, supported by regional coordination centres and ENTSO-E itself. The accompanying summary points to a need for improved cooperation between TSOs, DSOs, significant grid users, and national regulators. The incident occurred at transmission level, but the corrective actions extend across multiple layers of the system.
Voltage management often receives less attention than thermal loading, frequency response, or generation adequacy, yet it remains a core operating constraint in interconnected AC networks. High-voltage conditions can develop when topology, demand, reactive power behaviour, and cross-border flows move out of balance, particularly during lightly loaded periods or under network configurations that reduce available control margins. Under those conditions, transformer behaviour, switching decisions, and reactive compensation become central to maintaining stability.
The North Macedonia event also sits within a wider European operating context. Transmission systems are being run with changing generation mixes, increasing quantities of power-electronics-based plant, and cross-border flows that do not always resemble the patterns on which older operating assumptions were built. In those circumstances, voltage-control practices carry greater weight. Secure operation depends not only on infrastructure capacity, but on the precision with which operating limits are maintained across neighbouring systems.
The report’s emphasis on regional coordination reflects that reality. A local operating problem can become a wider synchronous-area issue where system conditions are closely coupled and operating measures are not aligned. That places greater importance on common procedures, shared operational visibility, and coordinated actions between TSOs where voltage management is concerned. It also brings transmission and distribution interfaces into sharper view where significant connected users influence network conditions.
The final report is likely to prompt a closer review of voltage-control procedures, transformer coordination, and reactive power management across the region. More broadly, it adds to the growing body of system-event analysis showing that network resilience is shaped as much by operational discipline and control frameworks as by physical expansion alone. The full document can be accessed through ENTSO-E’s report portal.