Iberia blackout caused by domino effect of failings in milliseconds

The European Network of Transmission System Operators for Electricity has today published its first findings into the catastrophic blackout in April that knocked out power across Spain and Portugal.

"This was the most severe blackout incident on the European power system in over 20 years, and the first ever of its kind," the association said.

In its initial report, ENTSO-E - which represents European transmission system operators - states that "the exceptional character of this incident highlights the need to improve the resilience the power system".

ENTSO-E adds that at the very least, several key technical areas need "to be further investigated and analysed".

Podcast: Applying grid resilience lessons from Spain’s blackout
Video: How can the energy sector beat the blackouts?

These areas are: voltage management instruments available; assessment of grid users’ behaviour in voltage control and disconnections; performance of the system defence plan and possible improvement; analysis of the various steps of the restoration phase; and data exchange with stakeholders to enhance relevance and accuracy of system operation.

Click here to access the full ENTSO-E report

The report presents a detailed breakdown of events on April 28, leading up to 12.32, which ENTSO-E regards as "the starting point of incident".

At that point within 57 seconds there were "several important generation trips", including "a loss of 208MW identified distributed wind and solar generators in northern and southern Spain".

The reasons for these events, the report says, are not known.

Then in just over a further minute, "major disconnection events occurred in the regions of Granada, Badajoz, Sevilla, Segovia, Huelva, and Cáceres, which resulted in an additional loss of generation of at least 2GW".

ENSO-E states that the various phases of the numerous disconnections were happening within milliseconds.

At 12:33, the report found that "the voltage of the south area of Spain sharply increased, and consequently also in Portugal. The over-voltage triggered a cascade of generation losses that caused the frequency of the Spanish and Portuguese power system to decline".

Then milliseconds later, "the power systems of Spain and Portugal started losing synchronism with the rest of the European System".

Between 12:33:19 and 12:33:22, the automatic load shedding and system defence plans of Spain and Portugal kicked in, “but unable to prevent the collapse of the Iberian power system”.

At 12:33:20, the AC interconnection to Morocco tripped and a millisecond later, the AC overhead lines between France and Spain were disconnected by protection devices against a loss of synchronism.

Finally, says the report, at 12:33:23, “the electrical separation of the Iberian system was completed by the tripping of the HVDC lines that transmitted power from Spain to France due to constant power mode at this time, and all system parameters of the Spanish and Portuguese electricity systems collapsed”.

However, in terms of pinpointing exactly what caused the lights to go out, the report stresses that "the investigation to determine the root causes of the incident is still ongoing, and their analysis will be presented in a final report. Understanding events of this scale and complexity requires time and a rigorous technical and scientific approach."

In the days after the blackout on April 28, ENTSO-E set up, in accordance with EU regulations, an expert panel to investigate the incident.

Read:
Five seconds to failure: why Iberia’s blackout is a red warning for Europe
Portugal to invest €137m in grid upgrades following April blackout
Spain’s TSO defends itself against blackout blame game

The 45-person panel was led by Klaus Kaschnitz of APG in Austria and Richard Balog from MAVIR in Hungary, experts from TSOs not directly affected by the incident.

Also included were panelists from both affected and non-affected TSOs, including Red Electrica from Spain, Portugal's REN and RTE from France.

The panel held seven meetings over five months and have now published what it calls its 'factual findings'.

It will now begin work on its final report, which is due in early 2026.

ENTSO-E said the final report will analyse in detail the events of 28 April, notably "the root causes of the incident, evaluate the actions undertaken to control the voltage and to mitigate the oscillations, assess the performance of generators in regard to protection settings and contribution to voltage control, assess the performance of the system defence plan and analyse the various steps of the restoration phase".

The final report will also consider the incident in a broader context by "examining the behaviour of the Iberian power system on the days preceding the blackout".

The discussion continues at Enlit Europe in Bilbao. Don’t miss it