The Baltic states of Lithuania, Latvia and Estonia disconnected their electricity systems from Russia's power grid on Saturday.
They will switch to the European Union's grid on Sunday after operating on their own in the meantime.
"We've reached the goal we for strived for, for so long. We are now in control," Lithuanian Energy Minister Zygimantas Vaiciunas said.
The European Union's top diplomat Kaja Kallas, Estonia's former prime minister, described the the move on X as "a victory for freedom and European unity".
Switch cuts Russia's legacy tie
The grid was the last connection to Russia for the three countries that became independent in the early 1990s after the Soviet Union fell. These countries joined the EU and NATO in 2004.
Talks of decoupling from Russia's power grid have been decades in the making, but the states have faced technological and financial issues. Moscow's invasion of Ukraine made the switch more urgent as they feared being targeted.
While the states had stopped purchasing energy from Russia, Moscow still controlled their power systems.
"We are now removing Russia's ability to use the electricity system as a tool of geopolitical blackmail," Lithuania's Energy Minister Zygimantas Vaiciunas told AFP.
"I like the light better when there are no Russian electrons involved," European Commissioner for Energy, Dan Jorgensen told reporters in Estonian capital Tallinn.
"It's important to underline that this is about security... No European country should be dependent on Russia for anything," he added.
Several undersea power and telecom cables have been severed in the Baltic Sea in recent months. Some politicians have accused Russia of waging a hybrid war but Moscow has denied allegations.
How is the switch being made?
Once physically disconnected from the Russian grid, the Baltic states will operate in isolation mode for roughly 24 hours to test their frequency, stability and power levels.
"We need to carry out some tests to assure Europe that we are a stable energy system," said Rokas Masiulis, head of Litgrid, Lithuania's state-run grid operator.
"We'll switch power stations on and off, observe how the frequency fluctuates and assess our ability to control it."
Once the tests are complete, the states will be integrated to the European power grid through Poland.
What are the risks?
Authorities have warned that the switch could pose security risks.
"Various short-term risks are possible, such as kinetic operations against critical infrastructure, cyber-attacks and disinformation campaigns," Lithuania's state security department told AFP.
Poland's power grid operator, PSE, said it will use drones and helicopters to monitor the connection with Lithuania.
Latvia's President Edgar Rinkevics, in a television interview, said the states were "maximally ready" but could not rule out "provocations."
Meanwhile in Estonia, police and volunteer defense corps will guard critical energy infrastructure till the weekend to thwart any possible sabotage.
