Programming mistakes from Spain's transmission system operator (TSO) and "improper" disconnection of generating units by utilities contributed to Spain's 28 April blackout, according to Spain's vice-president and ecological transition minister, Sara Aagesen.
Aagesen addressed the public following a meeting with the council of ministers, in which she presented a report on the government's findings from its investigation into the blackout that affected the Iberian peninsula on 28 April.
Poor planning for voltage controls may have contributed to the blackout on 28 April. The day before the Iberian outage, Spanish TSO Red Electrica requested that 10 thermal plants be available in case of voltage issues on 28 April, Aagesen said.
Market mechanisms meant the plants were not expected to be part of the 28 April generation mix, but the TSO often selects thermal units spread across Spain for back-up in case of an extraordinary event, in exchange for financial compensation. At 20:00 local time (18:00 GMT) on the night before the blackout, one of the thermal plants informed the TSO that it would not be able to operate the next day, and the TSO decided not to select another plant to take its place.
The TSO "decided to reprogramme [for the next day], but not replace the need for a thermal plant", which meant the TSO went into the day of the blackout with "resources for voltage control that were inferior to what they had calculated the previous morning for the middle hours [of 28 April]".
Some of the generation that disconnected from the grid in the initial stages of the blackout happened in an "improper manner". While some units automatically disconnected to protect themselves from voltage fluctuations, it was suggested that some generation units should not have done so. This created a wider "wave of over-voltage", amplifying the effects.
And generation loss was detected not only in the Badajoz, Granada and Sevilla provinces as previously believed, but also in Caceres, Huelva and Segovia. This phase of the blackout took place within the space of 21 seconds.
There is still no indication that a cyber attack took place on 28 April. The minister reiterated the government's stance on the matter, ruling out external influences on the events during the blackout.
The full report covering the government's investigation into the blackout, approved by the council of ministers, will be published this evening. Aagesen will hold a meeting with her Portuguese counterpart, Maria da Graca Carvalho, in Portugal this evening at 20:00 local time (20:00 BST).
