Understanding the Great Blackout of April 28: A Preliminary Report Analysis
Five months after the great blackout of April 28, a preliminary report from the Technological Research Institute (IIT) of the Comillas Pontifical University has shed light on the incident. The report identifies an insufficient synchronous generation program in the peninsular south as a “fundamental cause” of the electric failure. This document, commissioned by Endesa and Iberdrola and submitted to Entso-E , also questions the operational maneuvers executed by Electrica de España (REE) .
A “Collapse Due to Overtension.” The report introduces a new concept — a phenomenon characterized by uncontrollable tension rise resulting from the disconnection of renewable generation units operating under a constant power factor. According to IIT calculations, the safety margin available on the 220 kV network was 1,019 MW, but disconnections exceeded 1,600 MW.
In practical terms, this means that when a renewable plant disconnects, the tension increases. This rise initiates further disconnections, creating a vicious cycle that culminates in a total system collapse. The Comillas report asserts that this cascading reaction, unprecedented in Europe, illustrates that simply ensuring tension remains within acceptable ranges is insufficient to guarantee stability.
A Fragile and Low Inertia Network. The ongoing debate is not about whether to adopt renewables, but rather about how to effectively adapt the electric grid to high renewable energy penetration scenarios. The IIT report identifies four critical deficiencies:
- Little programmed synchronous generation: Only one group of combined cycle plants was operational in Andalusia , whereas several would usually be running.
- Weak Network: At 9:00 AM, 35% of the 400 kV network was offline in central and southern areas.
- Insufficient Inertia: In Andalusia , the inertia level dropped to 1.3 seconds, which is 35% lower than the 2 seconds recommended by Entso-E.
- Risky Maneuvers: Between 12:00 PM and 12:30 PM, REE connected eleven additional lines to counter oscillations, further reducing the safety margin instead.
The Chronology of a Collapse Announced. The government report previously mentioned a morning characterized by “atypical volatility.” At 12:03 PM, a 0.6 Hz oscillation was observed; at 12:19 PM, another oscillation of 0.2 Hz appeared, but with three times the amplitude. To stabilize the system, REE reduced exports and reconnected lines that had been disconnected. Instead of alleviating the situation, system tension intensified. By 12:26 PM, the operator ordered the start of a combined cycle plant in Andalusia , but the startup time exceeded an hour and a half — there was no capacity for it to take effect. From 12:32 PM onwards, the chain reaction began, culminating in a complete blackout across the peninsula at 12:33:19 PM.
Contradictory Narratives. Discrepancies have emerged in the various reports on this incident. The Government initially cited REE for poor programming and an insufficiency in dynamic tension control capabilities. In response, REE indicated that several power plants failed to meet their obligations to absorb reactive energy, which exacerbated the crisis. Meanwhile, the electrical companies denied any wrongdoing and attributed fault to the government and REE for their lack of transparency .
The new IIT report adds another layer to this ongoing discussion by reinforcing the argument that a lack of scheduled synchronous generation was a critical factor, while also scrutinizing the operational strategies of the system operator. Notably, the analysis has garnered support from prominent international experts like Goran Anderson and Pier Luigi Mancarella .
What Happens Next? The IIT recommends several measures, including a review of synchronous generation programming, enhanced tension control, and improved coordination among all involved parties. In July, the government attempted to pass an “anti-blackout” decree , featuring sanctions and increased public oversight. However, this initiative failed to gain traction in Congress.
Moreover, the Iberian Peninsula remains an “energy island,” with merely 3% interconnection with France, heightening vulnerability to operational errors. Consequently, both Spain and Portugal have urged Paris to expedite interconnection initiatives, expressing frustration over repeated broken promises.
Moving Forward. The European Network of Transmission System Operators (ENTSO-E) plans to release a factual report next Thursday, detailing the chronology and technical data surrounding the blackout. This forthcoming document will be pivotal in guiding discussions between Brussels and Member States regarding accountability and strategic measures moving forward.
The discussion surrounding the April 28 blackout is far from over. The Comillas report has reopened this issue with a critical reminder: the pursuit of a swift energy transition must be matched with adequate strengthening of the energy network and operational rules. The energy sector stands at a crossroads, necessitating immediate action to avert future crises.
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