A government investigation found that efforts by Red Eléctrica de España, Spain's grid operator, to address a small instability in the system actually led to more severe issues, causing a self-reinforcing cascade where high voltages caused power plants to drop off the grid.

MADRID (Reuters) -Spanish grid operator Redeia will release its own report on the causes of the massive blackout that hit the Iberian peninsula on April 28, its chair, Beatriz Corredor, told a news briefing on Wednesday.

Spanish authorities say the massive power outage in April across Spain and Portugal was due to technical and planning errors that led to a cascade of failures in the grid.