The day Spain and Portugal went dark, told from the control rooms, second by second, and on what it takes to start a dead grid. The narrator is Lily. My cloned voice opens the part for a minute and closes the series. Under the control-room scenes there is a tone that climbs almost too gradually to notice. It is the voltage.
At one minute to eleven on the morning of the twenty-eighth of April last year, an hour and a half before the power went out, a telephone line was open between two control rooms in Spain. At one end was a man at the centre in Seville that runs the local wires for one of the big power companies. At the other was an operator at Red Eléctrica, which runs the national grid. The call was recorded. We do not know their names: in the transcript one is J.A. and the other is P. The man in Seville asked: “What’s going on with the voltages? They’re crazy today.” The operator said it was the usual thing, the solar coming in and going out, and that what they would need was more of the big, steady power stations running. Then the man in Seville said something that would not be heard outside those two rooms for almost a year: “I think we’re going to see a big zero.” Un cero gordo. It is what grid people call a total blackout.
Part two of this series was about the frequency, the one number every machine on the Continent shares. All of it is true, and it is not what happened. The frequency that morning was fine. Klaus Kaschnitz, who jointly led the European investigation, put it plainly: “We have never had a blackout due to over-voltage; this is new to us.”
When I stood at a switchboard in the navy I watched two needles. One was the frequency. The other was the voltage, and I was taught to watch it just as closely, because a ship can lose its lights on either one. This part is about the second needle.
The second balance
Voltage is the height of the fall, from part two, and it behaves differently from frequency. Think of a washing line strung across a yard. How high it hangs outside your own window is the voltage, and it is a local matter. Things that hang on the line pull it down. Take a heavy weight off suddenly and the line springs up. On a grid, some equipment pulls the voltage down and some lets it rise; a wire that is working hard sags and one that is nearly idle climbs. The people in the control room keep that in balance, partly by hand, switching great coils in and out whose only job is to hold the line down. And every piece of equipment on a grid protects itself against too high a voltage the same way. It lets go.
Sweden learned about this balance two days after Christmas in 1983, when a switch arm came loose at a station called Hamra, two of the great lines from the north went out together, and the voltage in the middle of the country sagged and collapsed. The southern half of Sweden went dark. The northern half, with the rivers behind it, never went down, and the main grid was rebuilt in fifty minutes. In Sweden the line sagged to the ground. In Spain it sprang up.
Two rooms
There is a mirror to the Spanish room. In Akron, Ohio, in August 2003, the alarm system in a utility control room stopped delivering alarms, and nothing on any screen said so. On the wall the chart pens drew flat lines. Out in the country, lines sagged into trees that had grown too tall, one after another, and the power they had carried crowded onto the lines that were left. A nuclear operator rang to say: “I don’t know how much longer we’re going to survive.” Just after four o’clock the last big line let go, and in seven minutes fifty million people lost their power. The investigators found it could have been stopped from that room almost to the end. Nobody in the room knew there was anything to stop.
The Spanish room is the opposite case. Its alarms worked, and we can hear the people in it. Some transcripts came out through a court inquiry in the summer of 2025. The rest became public in March of this year, when the power companies gave their copies to a Senate committee and the recordings were played aloud. Those companies are in dispute with Red Eléctrica over who was to blame, and no court has ruled. Red Eléctrica’s head of operations has told Congress the calls are workmates passing a situation on to each other. I think that is fair, and it is what makes them worth hearing.
At three minutes past twelve the grid began to rock, one end of Spain against the other. The operators did what the rule book says. They switched in more lines. They cut exports to France, and set the great direct-current cable under the Pyrenees to send a fixed amount whatever happened, because a steady cable calms a sway. And because the rocking had dragged the voltage low, they switched off some of the coils that hold it down. It worked, it came back, and more coils went out. At nineteen minutes past, the second sway began, the whole peninsula against the rest of Europe. On the phone a shift head at one of the power companies said: “The voltages are swinging in a brutal way.” The operator at the national grid, who was doing everything right, said: “I don’t know. I don’t know.”
At twenty-two minutes past, the sway was cured, and everything they had done to cure it had let the voltage up. Out on the local wires some seven hundred megawatts of small generators, most of them solar panels on roofs and factories, too small to appear on any screen in that room, dropped away. The room asked which gas plants in the south could start. The quickest offer was an hour and a half. A message was relayed from the nuclear plant at Almaraz: if this goes on, the plant will trip. The operator’s reply is on the tape: “Within what we can do, we are carrying out every measure.”
Twenty-seven seconds
At 12:32:57, at a substation near Granada, a transformer that connects a group of power plants read a voltage above its limit and did what it was set to do. It let go, and with it went the weight those plants had put on the line. The voltage stepped up. Nineteen seconds later a second group let go near Badajoz, and one second after that, plants in five provinces. Kaschnitz called that moment the “point of no return”.
Now the first balance failed too. With that much generation gone, the frequency fell and the automatic defences woke up. They were built by careful people, over decades, to save a grid that is short of power, and they do it by shedding load: first the great pumps that lift water into reservoirs, then towns. Every one of those actions took weight off the washing line. The defence built for the first balance wrecked the second. At twenty-four seconds the lines to France opened, to save France. Beside them ran the direct-current cable. Half an hour earlier it had been told to send a fixed amount to France whatever happened. It did, out of a country going dark. Four nuclear reactors tripped. Twenty-seven seconds after Granada the grid of Spain and Portugal collapsed, and three seconds later the instruments read zero.
On the tape the operator swears. Then: “We are disconnecting.” The other end: “We’ve lost everything.” And the operator: “Well. It’s gone.”
Look for the villain in those seconds and there is none. Every device did what it was set to do. Red Eléctrica says some plants were set to let go too early; the owners dispute it; more than thirty cases are open. But look at the kind of thing that went wrong. It was the fit between thousands of settings, each chosen years before, by someone sensible, for one device. The cable is the clearest case, because there the decision was only half an hour old. A setting is a decision frozen in time.
The night
A power station needs power to start. With the whole grid dead there is nothing to plug it into, except for one kind. On the Duero, in a granite gorge on the Portuguese border, stands the hydro station at Aldeadávila. A few minutes after the zero, twenty-two people went to their posts and started the machines from the station’s own batteries, enough to open a gate, and the wat…
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