A power surge that caused a widespread blackout in Spain and Portugal was the most severe in Europe in the last 20 years, and the first of its kind, a report has found.
Damian Cortinas, president of the association of electricity grid operators Entso-e, said the incident was the first known blackout to be caused by overvoltage, which occurs when there is too much electrical voltage in a network.
This is new territory, Cortinas said, adding the role of Entso-e was not to apportion blame to any party over the cause.
April's outage caused significant disruption for nearly a day when it plunged areas into darkness, cutting internet and telephone connections and halting transport links.
The blackout affected large parts of Spain and Portugal, and briefly impacted southwestern France. The report released on Friday focused on the condition of the power systems on the day of the outage and the sequence of events leading up to it.
A series of cascading overvoltages - an increase in the electrical supply voltage above the established norm - was behind the outage, it concluded. This phenomenon can be caused by surges in networks due to oversupply or lightning strikes, or when protective equipment is insufficient.
According to the report, automatic defence plans were activated but could not prevent the power system from shutting down. It follows several separate investigations and reports by the Spanish government, as well as power and grid companies.
The Spanish government believes the Entso-e report supports its own findings, with Sara Aagesen, minister for ecological transition, asserting it was completely in line with an investigation commissioned that concluded in June that both the national grid provider Red Eléctrica and private electricity companies were at fault.
But both Red Eléctrica and the private firms have insisted they were not to blame. Redeia, owner of Red Eléctrica, has pinpointed the blackout on some coal, gas, and nuclear power plants' failure to help maintain appropriate voltage levels, while Spanish utilities have attributed it to poor planning from grid operators.
The Entso-e report also noted some important data was missing and that collecting complete, high-quality data proved very challenging for this investigation. A final report, planned for the first quarter of next year, will delve deeper into the root causes of the overvoltage and the efforts to control voltage in the system.
The outage has spurred a broader debate about Spain's energy model, with opposition parties suggesting that an increasing reliance on renewable energy could have contributed to the blackout while the government stands firm against these claims.
The loss of power was disruptive enough to force officials at the Madrid Open Tennis tournament to stop games mid-play. When the blackout hit, Spain's nuclear power plants automatically stopped operations, and the oil company Moeve halted operations at its refineries.
As buildings went dark and digital systems failed, emergency services responded to 286 calls for help, freeing people trapped in elevators, and hospitals initiated emergency measures halting routine procedures.
