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.

Spain's power grid operator and the country's electricity companies traded blame on Wednesday over the April blackout that crippled the Iberian Peninsula, a day after a long-awaited government report highlighted their responsibility.

The outage began shortly after noon on April 28 in Spain and lasted through nightfall, disrupting businesses, transit systems, cellular networks, internet connectivity and other critical infrastructure.