Portugese power bosses blamed the widepread power outages on "anomalous oscillations" in very high-voltage lines. The effect is known as "induced atmospheric variation" and it could take up to a week for the network to fully normalise again. 

Portugal's grid operator, REN (Rede Eletrica Nacional) has claimed interruptions to its own power supply were the result of a "fault in the Spanish electricity grid". Spain has not yet responded to the claim. Earlier, it was claimed by the head of Spain's electricity network restoring power could take between six and 10 hours.

REN added that "due to extreme temperature variations in the interior or Spain, there were anomalous oscillations in the very high voltage lines (400 KV), a phenomenon known as 'induced atmospheric vibration'".

"These oscillations caused synchronisation failures between the electrical systems, leading to successive disturbances across the interconnected European network."

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