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She said the partly state-owned grid operator, Red Eléctrica, had miscalculated the power capacity needs for that day, explaining that the "system did not have enough dynamic voltage capacity".

That extra force could be pressure, voltage, magnets or mechanical stress.

The report stated that one of three supergrid transformers - which enable voltage to be stepped up or down so electricity can be efficiently distributed - became disconnected and caught fire.

Two basic technologies are used to interconnect parts of a grid or countries - a standard transmission line that carries alternating currents, and increasingly, high voltage direct current lines.

Transmission towers must be grounded — or carefully connected to the earth — to safely dissipate energy from lightning strikes and voltage surges.