An abrupt loss of power generation at a substation in Granada, followed by failures seconds later in Badajoz and Seville, triggered an unprecedented blackout across Spain and Portugal last month, Spain's energy minister has said.
Sara Aagesen told politicians that the three initial incidents, whose cause has yet to be determined, led to a generation loss of 2.2 gigawatts of electricity, which triggered a series of grid disconnections.
Several investigations are looking into the 28 April power outage, but it is the first time Spanish authorities have pointed to a specific origin.
Establishing the cause of the outage will take time and there will likely be no simple answers to what appears to be a complex issue, Ms Aagesen said.
"We are analysing millions of pieces of data. We also continue to make progress in identifying where these generation losses occurred and we already know that they started in Granada, Badajoz and Seville," Ms Aagesen added.
A spokesperson for grid operator REE said Spain's main transmission grid had no incidents on 28 April before the blackout and the power loss "occurred due to causes outside" the grid, possibly at generation plants themselves or in smaller grids not managed by REE.
The Spanish government's investigation is also looking at reports by operators of volatility in the days before the blackout and is examining excessive voltage as one possible cause for the loss of generation, according to Ms Aagesen.
Investigators, Ms Aagesen said, had ruled out any cyberattack on REE's grid, an imbalance in supply and demand or insufficient grid capacity.
She also denied suggestions by some opposition politicians that the government had received and ignored warnings from experts that a major blackout could occur, adding that it would be premature to attribute responsibilities until it is known what happened that day.
"There was no alert, no warning," she said.
Spain's use of renewable energy as an increasing part of its electricity generation has come under scrutiny since the blackout, as has its plan to phase out nuclear energy by 2035.
Critics have claimed that one possible contributor to the outage may have been a lack of so-called "grid inertia" because of the relatively small share of nuclear and fossil fuel generation in Spain's power mix.
Ms Aagesen defended the government's energy policy, saying that renewables have lowered bills for households and businesses and will allow Spain to attract more investment while providing more energy autonomy at a time of geopolitical instability.
Spain's electricity system continues to use the same level of renewables as it did before and during the outage, she said.
"A mix with more renewables reduces external risks. It enables us to anticipate, adapt to, and respond quickly to any eventuality."
Ms Aagesen signalled openness to extending the life of nuclear plants, but only if operators could guarantee their security and acceptable prices for consumers, and if this could be shown to contribute to security of supply.
