The European Network of Transmission System Operators for Electricity (Entso-E) has released an updated analysis regarding the significant electricity blackout that occurred on April 28, 2025. The investigation, while still ongoing, suggests that the established defense plans in Spain and Portugal were activated but were unsuccessful in preventing the collapse of the Iberian electricity system.

The report emphasizes the need to assess the management of interconnections with France, particularly after noting two significant system fluctuations in the 30 minutes leading up to the outage.

Entso-E's findings state, "The defense plans for the systems of Spain and Portugal, developed according to legal obligations, were activated but failed to prevent the collapse of the Iberian electricity system." This indicates lessons may be drawn for future similar events.

Despite a second fluctuation that resulted in increased voltage, Spain continued to export energy to France, a move that Endesa indicated could have been counterproductive.

Following the second fluctuation, international exchanges from Spain were recorded as 1,000 megawatts (MW) to France, 2,000 MW to Portugal, and 800 MW to Morocco.

The analysis notes that just prior, the second fluctuation had been effectively mitigated through measures related to the interconnection with France, but the voltage increased again shortly thereafter.

While this increase was within operational margins, it has been included in Entso-E's ongoing investigation for the first time.

The investigation indicates that the loss of synchronism, crucial for system stability, was a significant factor.

Experts have suggested that a more effective defense involving conventional gas or nuclear plants could have potentially prevented the failure, noting that operational readiness was at its lowest that month.

Entso-E has not yet delved into all details surrounding the incident but has detailed a timeline of events leading up to the blackout.

Critical occurrences included:

- At 12:32:57 to 12:33:17 Central European Time (CET): Generation outages were observed in southern Spain, initially amounting to an estimated 2,200 MW. No similar outages were recorded in Portugal or France during this period.

The result was an observed increase in voltage in Spain, which was mirrored in Portugal, leading to a decrease in frequency.

- Between 12:33:18 and 12:33:21 CET: A sharp voltage increase was noted in southern Spain and consequently in Portugal.

This overvoltage triggered a cascade of generation losses causing a drop in the frequency of the Iberian Peninsula's electrical system.

- At 12:33:19 CET: The Iberian Peninsula began losing synchronism with the broader European system.

- Between 12:33:19 and 12:33:22 CET: The automatic load shedding and the defense plans activated for the systems of Spain and Portugal failed to prevent the collapse of the Iberian electrical system.

- At 12:33:21 CET: The alternating current lines between France and Spain were disconnected by protective devices in response to the loss of synchronism.

- At 12:33:24 CET: All parameters of the electrical systems of Spain and Portugal collapsed, and high-voltage direct current (HVDC) lines between France and Spain ceased to transmit energy.

In a point of commendation, Entso-E acknowledged the restoration process following the system collapse.

The swift restoration of supply in both Spain and Portugal demonstrated the preparedness and efficiency of the affected transmission system operators, Red Eléctrica in Spain and REN in Portugal, along with support from the French transmission system operator, RTE, and Morocco's ONEE.