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As authorities in Argentina try to figure out why electricity surged on a transmission line and touched off a massive blackout covering three nations, experts say power companies should have spotted the problem and taken action to limit the outage.

While government officials say it could have happened anywhere, U.S. industry experts say safeguards put in place after the giant Northeast blackout in 2003 would likely stop a recurrence.

Here are answers to some questions about what happened and how it could be prevented:

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WHAT COULD HAVE CAUSED THIS?

Argentina's energy secretary said that somewhere along the transmission line between two hydroelectric powerplants, the line was damaged or couldn't handle the electric load. The plants kept generating power, and there was too much of it on that part of the grid. That caused an overload, which tripped circuits that protect the generators, shutting them down. That left the system short of electricity to meet demand, and even though it was a Sunday when electric use was low, other generators didn't have enough capacity to pick up the slack, tripping protection circuits on the rest of the power plants and bringing down the entire grid. That blacked out Argentina, Uruguay and parts of Paraguay. Experts say a tree limb bringing down a power line or a lightning strike damaging equipment could have been causes. "Everything has to be in balance," said Susan Tierney, an expert on energy policy at the U.S.-based Analysis Group consulting firm. "One big thing happens and everything goes haywire."

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COULD SOMETHING HAVE BEEN DONE TO LIMIT THE OUTAGE?

Yes. Power grids can be programmed to sense surges and reroute power to other lines to stop from tripping circuits that protect generators. If the circuits are tripped and generators are shut down, utilities would black out smaller areas to deal with a shortage and stop the problem from spreading. When a fault occurs on a line "you try to isolate the fault and not let it spread to three times the size of Texas," said Alan Mantooth, director of the National Center for Reliable Electric Power Transmission and a University of Arkansas electrical engineering professor. Most systems have sensors to detect power surges or shortages and software that can take generators offline or reroute electricity. But Argentina's system apparently didn't react fast enough. "If the automatic system had worked correctly, we would not be talking about this," said former Argentine Energy Secretary Daniel Montamat said.

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COULD THIS HAVE BEEN A CYBER ATTACK?

Argentine government energy officials have not ruled it out, but it's unlikely. Power plants or sensors designed to shut off parts of the system when there are surges or power shortages could be hacked, but such an attack would have to cause a lot of simultaneous problems. Hackers would have to know how the system operates, which would be difficult, said Raúl Bertero, president of the Center for the Study of Energy Regulatory Activity in Argentina.

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WHY DO OUTAGES HAPPEN?

Outages can be caused by weather as it happened with a devastating hurricane in Puerto Rico, cyberattacks like ones that hit Ukraine or equipment outages like in the Eastern U.S., Tierney said. They can also be sparked by attacks on critical equipment.

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WHERE ELSE IN THE WORLD HAVE THERE BEEN MASSIVE OUTAGES?

Brazil was spared this time, but a similar outage in the region's largest country left more than 60 million in the dark in 2009. Three months ago, crisis-torn Venezuela suffered its worst power outage.

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IS THE ARGENTINA OUTAGE SIMILAR TO THE 2003 BLACKOUT THAT AFFECTED 50 MILLION PEOPLE IN THE U.S. AND PARTS OF CANADA?

Yes. A similar cascade of failures happened after a tree limb brought down a transmission line near Cleveland, Ohio.

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COULD ANOTHER BIG BLACKOUT LIKE THIS HAPPEN IN THE U.S.?

Never say never, experts say, but after the 2003 blackout Congress passed a law setting reliability standards. Now, sensors are in place and powerplant and transmission companies constantly watch demand and supply to keep them in balance, said Tierney. Michigan-based ITC Holdings Corp., the largest U.S. independent transmission company, constantly monitors its system and the weather, trying to anticipate what might happen, said Jon Jipping, chief operating officer. For instance, the company generates wind power in Iowa, and if high winds are forecast, generators are taken off line to prevent a surge, or maintenance on lines would be stopped so they can handle added electricity, he said. "There's never a time when we're in a situation where we don't know what's going to happen absent something that's so catastrophic that we can't even predict," Jipping said. Tierney said power systems in Europe take similar precautions.

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WHAT DOES ARGENTINA NEED TO DO TO STOP THIS FROM HAPPENING AGAIN?

Better coordination between electric utilities to spot problems and isolate them. Train plant operators and update software and sensors. Take immediate action. And just having a catastrophe should help. "There may never have been something so instructive that happened to these grid operators," said Tierney.

Argentine energy officials defend the power system as "robust."

It had been known for being in a state of disrepair for years. But since President Mauricio Macri came into power in 2015, he has cut energy subsidies and price freezes by the previous administration that he said left the energy industry unprofitable and weakened the grid. He also has reinvested in the grid, and outages have become less common. But he has faced large protests against a spike in utility costs.

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Associated Press writer Tom Krisher reported this story from Detroit and AP writer Luis Andres Henao reported in Buenos Aires, Argentina. AP writer Almudena Calatrava in Buenos Aires contributed to this report.