On February 24 Ukraine’s electric grid operator disconnected the country’s power system from the larger Russian-operated network to which it had always been linked. The long-planned disconnection was meant to be a 72-hour trial proving that Ukraine could operate on its own. The test was a requirement for eventually linking with the European grid, which Ukraine had been working toward since 2017. But four hours after the exercise started, Russia invaded.

Ukraine’s connection to Europe—which was not supposed to occur until 2023—became urgent, and engineers aimed to safely achieve it in just a matter of weeks. On March 16 they reached the key milestone of synchronizing the two systems. It was “a year’s work in two weeks,” according to a statement by Kadri Simson, the European Union commissioner for energy. That is unusual in this field. “For [power grid operators] to move this quickly and with such agility is unprecedented,” says Paul Deane, an energy policy researcher at the University College Cork in Ireland. “No power system has ever synchronized this quickly before.”

Ukraine initiated the process of joining Europe’s grid in 2005 and began working toward that goal in earnest in 2017, as did Moldova. It was part of an ongoing effort to align with Europe and decrease reliance on Russia, which had repeatedly threatened Ukraine’s sovereignty. “Ukraine simply wanted to decouple from Russian dominance in every sense of the word, and the grid is part of that,” says Suriya Jayanti, an Eastern European policy expert and former U.S. diplomat who served as energy chief at the U.S. embassy in Kyiv from 2018 to 2020.

After the late February trial period, Ukrenergo, the Ukrainian grid operator, had intended to temporarily rejoin the system that powers Russia and Belarus. But the Russian invasion made that untenable. “That left Ukraine in isolation mode, which would be incredibly dangerous from a power supply perspective,” Jayanti says. “It means that there’s nowhere for Ukraine to import electricity from. It’s an orphan.” That was a particularly precarious situation given Russian attacks on key energy infrastructure such as the Zaporizhzhia nuclear power plant. (According to Jayanti, Ukraine’s grid was ultimately able to run alone for as long as it did because power demand dropped by about a third as Ukrainians fled the country.)

Three days after the invasion, Ukrenergo sent a letter to the European Network of Transmission System Operators for Electricity (ENTSO-E) requesting authorization to connect to the European grid early. Moldelectrica, the Moldovan operator, made the same request the following day. While European operators wanted to support Ukraine, they had to protect their own grids, so the emergency connection process had to be done carefully. “Utilities and system operators are notoriously risk-averse because the job is to keep the lights on, to keep everyone safe,” says Laura Mehigan, an energy researcher at University College Cork.

An electric grid is a network of power-generating sources and transmission infrastructure that produces electricity and carries it from places such as power plants, wind farms and solar arrays to houses, hospitals and public transit systems. “You can’t just experiment with a power system and hope that it works,” Deane says. Getting power where it is it needed when it is needed is an intricate process, and there is little room for error.

Crucial to this mission is grid interconnection. Linked systems can share electricity across vast areas so that a surplus of energy generated in one location can meet demand in another. “More interconnection means we can move power around more quickly, more efficiently, more cost effectively and take advantage of low-carbon or zero-carbon power sources,” says James Glynn, a senior research scholar at the Center on Global Energy Policy at Columbia University. But connecting these massive networks with many moving parts is no small order.

One of the primary challenges of interconnecting grids is synchronizing them, which is what Ukrenergo, Moldelectrica and ENTSO-E accomplished last week. Synchronization is essential for sharing electricity. The task involves aligning the frequencies of every energy-generation facility in the connecting systems. Frequency is like the heartbeat of the electric grid. Across Europe, energy-generating turbines spin 50 times per second in near-perfect unison. For Ukraine and Moldova to join in, their systems had to be adjusted to match that rhythm. “We can’t stop the power system for an hour and then try to synchronize,” Deane says. “This has to be done while the system is operating.” It is like jumping onto a moving train or a spinning ride at the playground: the train or ride is not stopping, so you had better time the jump perfectly.

Risks persist even now that Ukraine is on board. Interconnected grids do not just allow shared benefits; they also create the potential for shared problems. An issue in one part of the grid, such as a plant failure, could cause a change in frequency to ripple throughout the entire network. In a worst-case scenario, a generator with inadequate power-stabilization capabilities could amplify the change in frequency and send it back to the grid at large. “Once you interconnect two systems, you also have an issue of ensuring that the overall, bigger, interconnected system is as stable and reliable as what was there before,” says Ram Rajagopal, a senior fellow at the Precourt Institute for Energy at Stanford University. A grid that becomes unsynchronized can damage plugged-in appliances such as laptops and microwaves, and it can even damage power plants.

One safeguard against grid instability is inherent to many of Ukraine’s assets: rotational inertia. Once heavy turbines, such as those in the nuclear plants that comprise much of Ukraine’s energy supply, are spinning at a certain frequency, it takes a substantial, sustained change in power to alter their rotation. They are unaffected by minor blips in the power generated to spin them, so their frequency remains stable. This inertia helps power plants dampen slight variations in power instead of transferring them to the rest of the grid. In the case of a major failure, it buys a few precious seconds for response systems to kick in.

Still, ENTSO-E, which represents 35 countries, had numerous concerns about adding Ukraine to its grid. Those concerns related not only to grid stability but also to market, regulatory, cybersecurity and legal issues. Taken together, these factors were a major reason for the project’s original six-year timeline. Some experts thought even six years was an optimistic estimate.

Ukraine planned to address ENTSO-E's remaining concerns throughout 2022. “The only reason that that year can be chopped off is because so much has already been done to confirm all of the technical specifications,” Jayanti says. This month’s emergency authorization to synchronize enables Ukraine to purchase power, but the country cannot yet sell it. To do so, Ukraine is required to install devices called static synchronous compensators, which enhance power stability. It may be many months before Ukraine can obtain them because of supply chain issues and geopolitical obstacles, Jayanti says. In the meantime, to connect Ukraine at all, ENTSO-E adopted additional safeguards to protect the European grid.

Even with the emergency synchronization, it is important to manage expectations, experts say. “This level of interconnection is relatively small,” Deane says. “It’s helpful, but it’s not going to replace all the power in Ukraine if the power plants go down.” For now, electricity in Ukraine is still moving from power stations to the country’s broader distribution network. Should that change, Ukraine can import some electricity from ENTSO-E.

Full integration with the European grid will likely take until the war is over and Ukraine can rebuild. “This is the first step in a long journey. That journey is really about integrating Ukraine into the wider [European] system with a view to integrating more renewables and sharing resources,” Deane says. But those plans “won’t go anywhere until peace returns to the region. It’s just too risky, too dangerous.”

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