The more you know about the blackout in Spain, the less guilty the lack of inertia seems to be renewable

The historic blackout that paralyzed the Iberian Peninsula on April 28 It continues to generate questions waiting for an official report. The narrative that pointed at a low inertia of the system due to the high penetration of renewable energies as guilty of collapse has begun to make waters. The data suggest a concatenation of more complex failures, where inertia, although it played a significant role in its final phase, does not seem to be the trigger for the energy zero.

Context. Until now, experts They placed in the center of the debate The inertia of the electrical system, the capacity of the large rotary machines of the traditional plants to resist sudden frequency changes. The inertia in the European interconnected system is provided by large turbines and synchronous generators that rotate at a speed of 50 cycles per second to maintain the frequency of 50 Hz.

High penetration of renewable energy sources, such as photovoltaic or wind solar, which are coupled to the network by power electronicsthey do not contribute this inertia inherently, which from the beginning was indicated as the root of the problem.

Inertia was correct. However, Vice President Third Sara Aagesen said in the Senate that, in the moments before the blackout, the peninsular electrical system had a level of inertia “according to the recommendations”, according to the data that Red Electrico shared with the government. In statements collected by Europa PressAagesen specified that this level was 2.3 seconds, exceeding the target of two seconds established by the Entso-E European Operators network.

Joan Groizard, Secretary of State for Energy, reinforced this idea pointing out that “many European systems frequently operate with inertia lower than those that had the peninsular electrical system in the moments prior to zero of 28th.” These official statements deflate, in part, the theory that a critical lack of inertia was the root cause of the incident.

A sequence of anomalous events. The investigations point to a series of disturbances that preceded the blackout. Both Aagesen and Groizard talk about the detection of oscillations in the European electrical system hours before the failure. A first “anomalous” oscillation of 0.6 Hz was recorded at 12:03, whose origin, detected in Spain, France and even Germany“It is still known,” according to the minister. A second “usual” oscillation of 0.2 Hz was perceived at 12:19, even in areas as far as Latvia, Groizard said.

Next, the three generation loss events occurred: in just over twenty seconds 2.2 gigawatts were disconnected in the provinces of Granada, Badajoz and Sevilla, between 12:32:57 and 12:33:17. These events coincided with a “situation of overwhelming in the peninsular electrical system, whose cause and consequence are still to be specified.”

A problem of surge. Groizard speaks of voltage peaks as the root of the blackout, clarifying that “the main shooting factor is associated with over -overdraft.” But the government has not been the first to divert the focus of inertia. Luis Badesa, professor at the Polytechnic University of Madrid, pointed in a previous analysis That “two failures are almost very unlikely and point to a common event”, raising as suspicious the “surge in 400 kV lines of the southwest, perhaps linked to the previous oscillations.”

The non -return point came, according to Badesa, at 12:33:20, when “Iberia loses connection with France and becomes an electric island; immediately, the centrals are massively disconnected.” Then, with the electrically isolated Iberian Peninsula, it is when synchronism is lost with the European continent. At that moment, with 59% of electricity from solar and 11% wind, inertia is insufficient.

Then, the lack of inertia did not help. It is at this time, with the disconnected peninsula, when the inertia of the system becomes crucial. According to Badesa: “With little inertia, the frequency began to go down and to change very quickly.” This rapid frequency variation would have caused the shot of the protection relays of numerous centrals, “finishing off the blackout.”

The lack of inertia “aggravated the final problem because he made the Rocof jump, but the origin was in several almost simultaneous generation cuts” previously, Badesa explained, stressing that “no operator designs his network to support three groups out of the service when he is isolated.” In other words, “the low renewable inertia did not cause the initial ruling, but it yesterday accelerated the collapse once Iberia remained alone.”

Waiting for the official report. The available information suggests that the April 28 blackout was not a direct consequence of the low inertia due to renewable penetration, but the result of a complex chain of anomalous oscillations in the European network, followed by multiple almost simultaneous generation losses, possibly linked to overcoming.

The preliminary conclusion is that the stability of a network with increasing weight of renewables does not depend only on inertia, but on the general robustness of the system in the face of multiple contingencies, such as interarene oscillations. For the definitive conclusions, we will have to wait for the official report, the Government hopes to have “in less than three months.”

Image | Diego Delso (CC By-sa 4.0)

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