28.11.2019 13:32
Power System

Fingrid’s substation connecting the Olkiluoto nuclear power plants to the main grid completed – special attention paid to operational reliability

Fingrid’s Olkiluoto substation, which is one of the most important substations in the main grid, has been fully completed. The solutions used at the substation are unique in Finland. Once Olkiluoto 3 is ready, the partially renovated and partially newly built substation will be connected to the three nuclear power plants in Olkiluoto producing one third of the electricity consumed in Finland. The project, which is valued at approximately EUR 14 million, was already mainly introduced in the summer of 2019, after which some finishing touches have continued to be carried out at the substation.

The Fingrid substation located in Olkiluoto, Eurajoki consists of three separate switching stations and control centre buildings. During the renovation work, the old, ageing switching station, originally built in the late 1970s, was dismantled and replaced by a new 400-kilovolt double circuit breaker switching station. In conjunction with this, major transmission line arrangements were carried out between the power plant and the substation.

Duplication as a guarantee for reliability

In addition to the new switching station built to connect the Olkiluoto 3 nuclear power plant to be commissioned in 2020, the unit is supplemented by two switching stations serving the Olkiluoto 1 and 2 nuclear power plants and separate control centre buildings. The new substation improves operational reliability and also enables versatile connections in the event of various disturbances and maintenance outages.

“As a whole, the 400-kilovolt substation in Olkiluoto is the only one of its kind in Finland. The substation connects a significant portion of Finland’s electricity production to the Finnish main grid. With new solutions and backups, we also ensure operational reliability in the event of any disturbances”, promises Timo Kiiveri, Senior Vice President responsible for asset management at Fingrid.

The risk of an electricity shortage was just a scare

A fire that occurred at Fingrid’s Olkiluoto substation in the summer of 2018 was a practical test for Fingrid’s preparedness to act in a real situation involving the threat of an electricity shortage.

“Fortunately, the substation’s renovation work was already well underway in the summer of 2018. The fault repair process was quick thanks to the ongoing construction work. The newly renovated structures enable the Olkiluoto power plants to be separated from each other more reliably than before. Various disturbance and outage situations can be dealt with effectively”, says Timo Kiiveri.

Special arrangements to connect Olkiluoto 3 to the main grid

Fingrid and Teollisuuden Voima (TVO) are preparing for the connection of Olkiluoto 3 in Eurajoki to the main grid next year. The connection requires special arrangements as, once completed, Olkiluoto 3 will be considerably larger than the earlier electricity production units.

Olkiluoto 3 will have a net power output of 1,600 megawatts. The electricity system of Finland can withstand a fault in a power plant with a maximum size of 1,300 megawatts. Fingrid and TVO have agreed on a unique special arrangement to connect the large plant unit to the electricity system. In technical terms, the arrangement means that if Olkiluoto 3 is disconnected from the grid, industrial consumption will be limited in nearly real time so that the sudden deviation in production and consumption in the electricity system remains within the allowed 1,300 megawatt limit. Fingrid and TVO have agreed on the practical implementation of this kind of system protection for Olkiluoto 3. In addition, the authorities have ensured that the implementation of the system protection will not have an impact on Fingrid’s handling of system responsibility.

“We have improved the reliability of the grid connections at the Olkiluoto nuclear power plants and are fully prepared to receive the electricity generated by the third reactor in Olkiluoto to the main grid”, says Timo Kiiveri.


Timo Kiiveri, Senior Vice President, Asset Management
tel. +358 40 543 3039


Info box:

  • The ageing 400-kilovolt switching station A in Olkiluoto was replaced by two separate switching stations.
  • The changes improve the reliability of the grid connection of the Olkiluoto nuclear power plant units and ensure that the nuclear power plant units are able to supply electricity to the main grid without disturbances.
  • The new switching stations C and D were commissioned in June 2019.
  • The old switching station A was completely dismantled.
  • The value of the investment is approximately EUR 14 million.