Estonia, Latvia and Lithuania disconnected from the IPS/UPS joint network and, subject to last-minute tests, they will synchronise with the EU's grid on Sunday after operating on their own in the meantime.
European Commission President Ursula von der Leyen will speak at a ceremony on Sunday to mark the switch to the EU system, her office said on Friday.
"We've reached the goal we strived for, for so long. We are now in control," Lithuanian Energy Minister Zygimantas Vaiciunas told a press conference.
The operators successfully undertook frequency management trials on Saturday, testing the Baltic grid's stability during interruptions, such as sudden shutdowns of power plants, Lithuanian grid operator Litgrid said on Saturday evening.
Further trials on Sunday will test the Baltic grid's ability to manage current.
Immediately after disconnecting, Latvian workers used a crane to reach the high-voltage wires in Vilaka, 100 metres from the Russian border, and cut them. They handed out chopped wire as keepsakes to cheering observers.
"We will never use it again. We are moving on," Latvia's Energy Minister Kaspars Melnis told Reuters in Vilaka.
Plans for the Baltics to decouple from the grid of their former Soviet imperial overlord, debated for decades, gained momentum following Moscow's annexation of Crimea in 2014.
The grid was the final remaining link to Russia for the three countries, which re-emerged as independent nations in the early 1990s at the fall of the Soviet Union. They joined the European Union and NATO in 2004.
The three staunch supporters of Kyiv stopped purchases of power from Russia following Moscow's invasion of Ukraine in 2022, but have relied on the Russian grid to control frequencies and stabilise networks to avoid outages.
"By ending the energy dependence of the Baltic states on Russia, we are leaving the aggressor without the option of using energy as a weapon against us," Estonian Foreign Minister Margus Tsahkna said.
An army truck was seen at the Rezekne power substation near the Latvia-Russia border, and officers with guns were patrolling the vicinity and in the nearby town, indicative of Baltic worries of attempted sabotage to disrupt the switch.
The Baltic Sea region is on high alert after power cable, telecom links and gas pipeline outages between the Baltics and Sweden or Finland.
All were believed to have been caused by ships dragging anchors along the seabed following Russia's invasion of Ukraine.
Russia has denied any involvement.
"The system is stable, the process is happening smoothly, no one is noticing that something changed," Melnis said.
Maintaining a constant power supply requires a stable grid frequency, which can more easily be obtained over time in a large synchronised area such as Russia or continental Europe, compared to what the Baltics can do on their own, analysts say.
Lithuania's energy ministry told Reuters it has drawn up contingency plans whereby some heavy energy users, such as factories, could be temporarily disconnected from the grid in the event of power shortages, to maintain essential supplies during the switch.
For Russia, the decoupling means its Kaliningrad exclave, located between Lithuania, Poland and the Baltic Sea, is cut off from Russia's main grid, leaving it to maintain its power system alone.
