Interim ruling by the Supreme Administrative Court on the transmission system protection for Olkiluoto 3

The Court decided to prohibit the enforcement of the Market Court’s decisions issued in autumn 2025 in both the responsibility and cost matters. According to the ruling, the earlier decisions of the Energy Authority must be complied with during the appeal process until the Supreme Administrative Court issues its final decision or orders otherwise.

The case concerns two Market Court decisions from 2025. In September 2025, the Market Court ruled on the implementation responsibility of the transmission system protection largely in line with the position of the transmission system operator, Fingrid. In November 2025, the Market Court annulled the Energy Authority’s decision on the principles for determining the system protection charges and referred the matter back to the authority for reconsideration.

The Energy Authority had originally issued decisions on the matter in January 2024 (responsibility) and December 2024 (cost allocation). Under these decisions, Fingrid is responsible for implementing the system protection and is entitled to charge the majority of the related costs to Teollisuuden Voima Oyj (TVO).

The Energy Authority, Fingrid and TVO appealed the Market Court’s decisions to the Supreme Administrative Court. Requests to suspend enforcement were submitted by the Energy Authority and TVO in the responsibility matter, and by the Energy Authority and Fingrid in the cost matter. The Supreme Administrative Court approved all requests.

In its interim ruling, the Court emphasized the importance of ensuring that the arrangements related to the transmission system protection are clearly and unambiguously organized during the legal proceedings, taking into account the continuity of operations. On this basis, it considered the suspension of enforcement justified.

The Supreme Administrative Court will issue its final ruling in due course concerning Fingrid’s system responsibility and the principles for determining the system protection costs.

Transmission system protection and OL3 generation

According to Fingrid, the current electricity system is not, as such, equipped to accommodate the full output of the Olkiluoto 3 plant, which is approximately 1600 MW. When OL3 generation exceeds 1300 MW, a dedicated protection system is required to ensure the operability of the transmission grid also in disturbance situations.

In practice, the protection is implemented, for example, by controlling industrial electricity consumption and using battery storage systems. If the protection system is not fully available, OL3 output has had to be temporarily reduced at Fingrid’s request. This may occur, for example, when industrial facilities participating in the protection system are undergoing maintenance outages.