What caused the blackout in Spain and Portugal?

Spain, Portugal and some of south-west France suffered a massive power cut on Monday with major cities including Madrid, Barcelona and Lisbon among those affected.

- by Isabella Boneham

Houses, offices, trains, traffic lights and even the Madrid open tennis tournament were all hit. The Spanish and Portuguese governments as well as network operators scrambled to understand the problem and raced to fix it.

Red Eléctrica de España (REE), Spain's electric network, said Spain and Portugal were hit by “el cero” - the zero. Its Portuguese counterpart, Redes Energéticas Nacionais (REN), said the outage started at 11:33am Western European summer time.

By mid-afternoon the Spanish operator, which is partly state-owned, said that it had started to recover voltage in the north, south and west of the Iberian peninsula.

The recovery process could only be carried out gradually, to avoid overloading parts of the grid as each generator connects.