North Macedonia’s May 2025 blackout was a voltage-control failure, and Europe should read it that way

ENTSO-E’s final report on the Grid Incident in North Macedonia on 18 May 2025 turns what could look like a local technical failure into a broader system warning. At 04:59 CEST, North Macedonia’s power system split between the 400 kV and 110 kV networks, leaving the 110 kV system in blackout while the 400 kV network stayed operational. MEPSO restored the system by 07:47, and the wider Continental Europe system saw no major disturbance. The report therefore matters not because it describes a large geographic event, but because it exposes how voltage stress can cascade into a full loss of supply in a part of the grid that planners had already marked as vulnerable.

The key point is that this was not a surprise in the narrow sense. The factual report says MEPSO had already identified recurring nighttime overvoltage during the spring and autumn low-load season and had introduced countermeasures, including transformer-protection optimisation and the disconnection of one internal 400 kV overhead line. Even so, some 400 kV substations were still operating above the normal band, with voltages reaching 430-437 kV and, in some places over the preceding months, peaking even higher. In other words, the network was already being managed at the edge of its voltage envelope before the incident occurred.

Topology of the transmission system of North Macedonia

The report also shows that regional security tools did not flag an imminent crisis in the way operators would have liked. RCC analysis before the incident judged the grid secure based on the information available, yet it also detected that all 400 kV nodes in the MEPSO control area were expected to exceed acceptable voltage limits. At the same time, MEPSO did not deliver the individual grid model for 18 May, so the backup model used by the RCC relied on the last submission from 13 May. That combination – a system that was already voltage-stressed, plus imperfect visibility in the planning chain – is exactly the kind of operational blind spot the report is trying to highlight.

The final report’s diagnosis is structural, not accidental. Its root causes point to operating the system above defined voltage limits, reduced awareness of overvoltage risk in operational planning, insufficient reactive-power reserves with adequate activation time, and limited availability of effective voltage-control assets. That is an important distinction. The event was not simply about “too much generation” or “too little demand”; it was about a system that lacked enough fast, effective, and coordinated tools to absorb reactive power and hold voltage within bounds during a low-load operating regime.

That diagnosis is already driving a policy and investment response. The report points to three layers of recommendations: continuation of ENTSO-E work on voltage and reactive-power modelling quality and operationally useful KPIs; new regional SEE measures for monitoring voltage-limit violations and coordinating action among TSOs, RCCs and ENTSO-E; and MEPSO-specific changes to its System Defence Plan, including broader low-load and high-renewable scenarios and clearer coordination between TSOs and DSOs. The same logic is visible in the post-incident actions: MEPSO has moved to improve reactive-power support, including a 150 MVAr shunt reactor in SS Dubrovo, expected to be finalised by 2027.

For the wider European power sector, the lesson is straightforward. Security of supply in a more renewable, more dynamic grid is no longer only about enough megawatts and enough interconnection capacity. It also depends on voltage discipline, reactive-power capability, modelling quality, and the speed with which operators can see and correct abnormal conditions. North Macedonia’s blackout shows that a grid can remain “adequate” on paper and still fail in practice if voltage-control assumptions are too optimistic or if the operational toolkit is too thin. That is why this report should be read not as a post-mortem for one country, but as a warning for the entire South-East European system and, by extension, for any grid entering a lower-load, higher-renewables operating era.