IN Brief:
- Litgrid and PSE have signed a connection point agreement for the 220kV Lithuania–Poland Harmony Link interconnector.
- The physical interface will be approximately 35 metres inside Poland, with PSE acquiring the relevant cable section from Litgrid.
- Construction in Lithuania is planned from the second quarter of 2027, with the link expected to be commissioned by the end of 2030.
Litgrid and Poland’s transmission system operator Polskie Sieci Elektroenergetyczne (PSE) have agreed how they will construct, connect, and test the 220kV Harmony Link electricity interconnector at the Lithuanian–Polish border. Signed in Vilnius on 8 October, their connection point agreement allocates responsibility for the physical interface between the two national sections and for the associated communications infrastructure, allowing the operators and their contractors to proceed with defined technical and contractual obligations.
Harmony Link will connect the planned Gižai substation in Lithuania with Ełk Bis in Poland through a double circuit, 220kV alternating current route incorporating the Norki and Wigry substations. Individual sections will be constructed in separate jurisdictions and may use cables from different manufacturers, although they must ultimately function as a single electrical link. Agreeing the equipment interfaces and ownership boundaries ahead of installation reduces the risk of encountering incompatible components at the point where the two sections meet.
Under the agreed arrangement, the physical connection point will be approximately 35 metres inside Polish territory. PSE will acquire the short cable section between the border and that point from Litgrid for operational reasons. The location establishes the interface at which the companies’ respective construction and maintenance responsibilities meet, including how defects will be addressed during the warranty period. It also avoids treating the national border itself as an automatic boundary between the electrical assets.
Responsibilities extend beyond the short border cable section to preparatory design, fibre optic communications infrastructure, inspections, and the sequence of tests that will follow construction. Operational data and control instructions must be carried reliably between the substations, with communications interfaces coordinated alongside the high voltage equipment. The particular relay and communications architecture will be determined during detailed engineering, while the agreement establishes the operators’ respective roles in checking the integrated installation before energisation.
PSE has identified compatibility between cable systems as a specific consideration, since the equipment on either side may be supplied by different manufacturers. Cable interfaces must be suitable for the insulation systems, operating voltage, and mechanical conditions encountered at the joint or termination. An apparent match in nominal voltage does not automatically establish compatibility between accessories and installed cable designs; these interfaces require manufacturer information, approved installation procedures, and the tests prescribed for the completed connection.
Those cable interfaces form part of a longer route combining underground sections with overhead transmission lines. In Poland, the programme includes refurbishment of the existing 220kV Ostrołęka–Ełk Bis line; on the Lithuanian side, the route passes through Vilkaviškis district, Kalvarija, and Marijampolė towards Gižai. Work on the new connection must be coordinated with existing substation equipment and network operations so that construction and later testing can take place without avoidable disruption to electricity transmission.
Protection design will also have to account for the electrical characteristics of the cables, overhead sections, and connected substations. A fault on one section should be detected and isolated by the appropriate devices without disconnecting unaffected equipment unnecessarily. Because the network spans two transmission systems, relay coordination and switching procedures will have to be established across the interface; the applicable settings cannot be inferred simply from the interconnector’s 220kV voltage rating.
These interfaces arise from Litgrid and PSE’s decision to build an onshore alternating current link in place of the submarine connection originally envisaged, after higher projected costs and pressure on marine cable and converter station manufacturing capacity changed the development case. They signed a revised development cooperation agreement in July 2024 and made an investment decision later that year. The October 2026 border agreement addresses the practical interfaces required to implement that decision.
Following the Baltic states’ synchronisation with Continental Europe’s electricity system in February 2025, further cross-border transfer capability remains a separate engineering objective. Synchronisation brought the systems into a common synchronous area, whereas commercial trading capability depends on the transmission equipment and the constraints under which it can operate. Harmony Link is intended to add another connection between Lithuania and Poland, complementing the existing LitPol Link infrastructure and supporting electricity exchange as generation and demand patterns change.
European Union co-financing through the Connecting Europe Facility supports construction of the interconnector, while planning activity in Lithuania continues around environmental assessment, access to land, and the transmission corridor. These processes sit alongside the engineering work at the national border: cable installation and inspections can only proceed within the applicable approvals, and the two countries’ work programmes must ultimately align with the readiness of their substations and connected transmission sections.
Litgrid expects construction in Lithuania to begin during the second quarter of 2027, with the overall interconnector scheduled for commissioning by the end of 2030. Those dates describe planned milestones rather than completed works, and the individual sections may follow different delivery sequences. The ability to test the assembled connection will ultimately depend on installed cables, substations, communications, and protection equipment being ready together, along with the operational procedures for safely connecting two live transmission networks.
When the sections reach the border, the agreed allocation of ownership and inspection duties will govern how they are connected and how defects are handled. Litgrid and PSE must still complete detailed design, construction, and coordinated testing before electricity can flow through Harmony Link. The connection point agreement removes one contractual uncertainty from that sequence, but it does not alter the operators’ target of completing commissioning by the end of 2030.
