Nearly two months following the energy blackout that plunged Portugal and Spain into darkness on April 28, 2025, investigations into the incident are underway, revealing initial findings. The Portuguese Energy Services Regulatory Authority (ERSE) released an update on the investigation this Monday based on a report by the expert group of the European Network of Transmission System Operators for Electricity (ENTSO-E) following their latest meeting on June 23, 2025.
“On April 28, 2025, at 11:33 (12:33 CEST), the energy systems of Portugal and Spain experienced a blackout that also briefly affected a small area of France near the Spanish border. The rest of the Continental Europe’s electrical system did not experience any significant disruption,” states the document.
What is known so far?
According to information from ERSE, three critical points stand out:
- “As per ENTSO-E’s collected data, the blackout resulted from a complex sequence of events“;
- “Following its third meeting on June 23, 2025, the Expert Panel analyzed the electric system conditions before the incident and found that significant voltage and frequency variations occurred on the morning of April 28, and initial production trips happened just before the incident, causing voltage to rise beyond operational limits in much of the Spanish transmission network, ultimately leading to the blackout”;
- “Based on currently available information, the Expert Panel established a preliminary chronology of the incident. This timeline will be updated with further details as the investigation progresses”.
The established chronology reveals the following sequence of events during the incident:
- At 12:32:57, 12:33:16, and 12:33:17 CEST: “Production shutdowns were observed in the regions of Granada, Badajoz, and Seville, initially estimated at 2,200 MW. No production shutdowns were observed in Portugal and France during this period. These events resulted in a voltage rise in Spain and a similar increase in Portugal, along with a frequency drop.”
- Between 12:33:18 and 12:33:21 CEST: “Voltage in southern Spain rose sharply, consequently affecting Portugal. The overvoltage triggered cascading production losses, reducing the electric system’s frequency in both Spain and Portugal.
- At 12:33:19 CEST: “The Portuguese and Spanish energy systems began losing synchronization with the European System.”
- Between 12:33:19 and 12:33:22 CEST: “The Automatic Load-Shedding and System Defense Plans of Spain and Portugal, prepared under Regulation (EU) 2017/1485, were activated but failed to prevent the Iberian electric system’s collapse.”
- At 12:33:21 CEST: “Overhead Alternating Current lines between France and Spain were disconnected by devices protecting against loss of synchronization.”
- At 12:33:24 CEST: “All parameters of the Spanish and Portuguese electric systems collapsed, and the direct current interconnection between France and Spain ceased to transmit energy.”
The Government will present a package of measures on July 28 aimed at strengthening the national electric system’s security, following the April 28 blackout that affected millions in Portugal and Spain.
