Baltic synchronisation: leaving BRELL and joining the European grid

At 6:00 on Saturday 8 February 2025, Lithuania’s operator Litgrid began opening lines. The link to Kaliningrad went at about 6:40, the lines to Belarus at 7:30, Latvia’s line to Russia at 8:00, and at 9:09 Estonia disconnected its last connection to the Russian system. For the first time since the Soviet era, the power grids of Estonia, Latvia and Lithuania were running on their own, with frequency controlled from Tallinn, Riga and Vilnius instead of Moscow.

They stayed that way for about 29 hours. At 14:05 EET on Sunday 9 February, ENTSO-E confirmed that the three systems had been synchronised with the Continental European area, the grid that stretches from Portugal to Poland and serves more than 400 million customers. No consumer lost power at any point.

Why it took until 2025

The Baltic grids grew up inside the Soviet “unified energy system”. After the Soviet collapse in 1992, pulling them out made little sense at first: there were few alternatives, and the Soviet network was reliable. In 2001 the BRELL agreement put the arrangement on a technical footing, and the Baltic states went on buying Russian power, sharing Russian reserves and taking part in dispatch run from Moscow, over 330 kV AC lines to Russia and Belarus.

Joining the EU in 2004 did not change that. The three prime ministers set Continental European synchronisation as a strategic goal in 2007, but the region was close to an electrical island in the west: it had almost no lines to anywhere except Russia and Belarus. Every step afterwards was a new connection. The political deal that fixed the date came at the end of June 2018, when the Baltic states and Poland agreed to synchronise by 2025, the plan announced at the time in Baltic energy systems: synchronisation by 2025.

The motive was never mainly technical. Lithuania, Latvia and Estonia had always treated their dependence on a grid run from Moscow as a security risk, and those concerns grew after the crisis in Ukraine began in 2014. Inside BRELL, frequency for the whole ring was set from Moscow, and in an emergency the Baltic operators leaned on Russian reserves they did not control. Kalle Kilk of Elering put it bluntly on the day of the switch: synchronisation was first of all a security matter. The engineering was the means.

If you compare the 2018 plan with what happened, the striking thing is how little the date moved. The timetable agreed that June named 2025, and the switch came in February of that year, ahead of the end-2025 deadline set for the EU-funded works. For a programme spread across four countries, with some 1,400 km of new or reconstructed high-voltage line and nine new rotating machines, holding a date fixed seven years in advance is a notable record, and it was held through the loss of Estlink 2 in the final weeks.

The links that made it possible

Synchronisation needed two kinds of link. DC cables to the Nordic countries, which carry trade without tying frequencies together, gave the Baltic market access to other supply. An AC connection to Poland was needed for the synchronous joint itself.

Link	Countries	Type	Capacity	In service
Estlink 1	Estonia–Finland	HVDC subsea	350 MW	2006/2007
Estlink 2	Estonia–Finland	HVDC subsea	650 MW	2014
NordBalt	Lithuania–Sweden	HVDC subsea	700 MW	2016
LitPol Link	Lithuania–Poland	400 kV AC overhead	500 MW	2015
Harmony Link	Poland–Lithuania	AC overhead (redesigned)	not yet stated	planned by end of 2030

Estlink 1 was the first break in the isolation. Negotiations started in 1999; the cable across the Gulf of Finland was finished in 2006, after a hard winter gave the project a push. It filled up so quickly that Estlink 2 followed in 2014. NordBalt, from Klaipėda to Nybro in Sweden, added 700 MW in 2016 and runs 450 km, about 400 of them under the Baltic.

LitPol Link did the decisive job. Until 2025 it could only exchange power through a back-to-back DC converter at Alytus, because the grids on either side ran at unsynchronised frequencies. Synchronisation made that converter unnecessary: since 9 February the AC line joins the two grids directly, and the Baltic systems run in step with Poland and everything west of it. Litgrid had spent the previous years reconstructing the Alytus switchyard and the nearby 330 kV and 110 kV lines so that the single AC tie could carry the load.

Harmony Link was meant to be the second joint: a 700 MW subsea HVDC cable of about 330 km from Poland to Lithuania. Its tenders were cancelled in 2023 on cost, and it has been redesigned as a double-circuit 220 kV AC line overland from Ełk to Gižai, to be energised by the end of 2030. Until then the Baltic synchronous connection hangs on one AC corridor, which is the main structural weakness of the arrangement.

Inside the region, Estonia and Latvia also built new lines to each other, among them the Tartu–Valmiera interconnection, and Poland reinforced lines in its own grid, among them Krajnik–Morzyczyn–Dunowo. Elering’s chief executive Kalle Kilk called the programme “the hardest thing we’ve done this century”.

Synchronous condensers: the missing inertia

Leaving the Russian system meant losing more than imports. A large synchronous system gives each part of it inertia (the stored energy of heavy spinning machines that slows any change in frequency), short-circuit current strong enough for protection relays to detect a fault, and a pool of reactive power for voltage control. The Baltic grids had been borrowing all three.

The answer was synchronous condensers, large motors that spin in step with the grid without driving anything, three in each country: at Püssi, Kiisa and Viru in Estonia, at Grobiņa, Ventspils and Līksna in Latvia, and at Telšiai, Alytus and Neris in Lithuania. Six were running at the switch in February 2025 and three more were under construction. Latvia’s operator AST finished the last one, at Līksna, on 29 September 2025, ahead of schedule. Elering’s project notes describe their job as slowing the rate at which frequency changes when supply and demand suddenly fall out of balance; together the nine contribute 2,090 MVA·s of inertia, according to AST’s chairman Rolands Irklis. Each of the Latvian units also provides 100 MVAr of reactive power.

Funding

The total cost for the Baltic states and Poland was about €1.6 billion, according to figures reported by the Estonian broadcaster ERR when the switch was made, with about 75% co-financed by the EU. ENTSO-E and the EU’s climate and infrastructure agency CINEA put support from the Connecting Europe Facility at more than €1.2 billion. The original deadline for completion was the end of 2025; the switch came ten months early.

The Estlink 2 problem

The timing was closer than it looked. On Christmas Day 2024, six weeks before the switch, the anchor of the tanker Eagle S cut Estlink 2 in the Gulf of Finland. The Baltic states went through disconnection and synchronisation with one of their two links to Finland out of service, and the repair was not finished until June 2025. The guide to subsea power cables covers that repair and the anchor-drag incidents around it. Nobody has shown the timing was deliberate, but it made the case for the synchronous condensers and for keeping the switch on schedule at the same time.

What changed after February 2025

Four things changed at once.

Frequency control moved home. Elering, AST and Litgrid now manage frequency and balancing themselves, as part of the Continental European system. On 5 February 2025 they launched a Baltic balancing capacity market to procure the reserves that used to come from Russia; its first auction secured 1,257 MW for each period, made up of 29 MW of frequency containment reserve, 730 MW of upward and 498 MW of downward manual restoration reserve. Automatic frequency restoration reserves were to follow once the European PICASSO platform connection was ready.

Balancing became a local job. Early analyses of the new market found volatile reserve prices in the first months, then a gradual decline as it settled. The region now pays directly for reserves it used to share with a far larger system.

Kaliningrad became an island. With the Lithuanian lines open, the Russian exclave runs on its own, having tested isolated operation in advance.

The next links are all westward or northward. Beyond Harmony Link, Elering and Fingrid are planning Estlink 3, about 700 MW, with the Finnish end not yet fixed and a target around 2035. The Aurora Line between Sweden and Finland, commissioned in November 2025, strengthens the Nordic side of the same market.

The one question still open is resilience. The Baltic grids now depend on a single AC tie to Poland and on subsea cables in one of the busiest and most contested seas in Europe. Harmony Link’s energisation date, the end of 2030, is the one to watch.