REN, Portugal's grid operator, has announced that the blackout was caused by a fault in the Spanish electricity grid caused by extreme temperature variations

Portugal's grid operator, REN, explained that the recent blackout was caused by a fault in Spain's electricity grid linked to a rare weather phenomenon. The extreme temperature variations led to abnormal oscillations in high voltage lines, known as 'atmospheric induced variations', causing synchronization failures between power systems and disruptions across the interconnected European grid.