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OL3 system protection completes Olkiluoto 3 connection to the grid

One of Fingrid’s duties is to connect new, high-capacity power plants to the main grid. The company has made careful preparations for the grid connection of Olkiluoto 3, one of the world’s largest power plant units. The final phase of these preparations includes the implementation of OL3 system protection, which will ensure that the power system functions reliably under all circumstances once the power plant is ready.

Fingrid is ensuring adequate conditions for Teollisuuden Voima TVO, the owner of Olkiluoto 3, to commission the power plant unit with the plant supplier in such a way that it operates safely and reliably under all circumstances.

The OL3 system protection designed and implemented by Fingrid and TVO will fix challenges caused by a trip of power plant unit due to different kind of faults.

“The OL3 system protection will ensure the uninterrupted transmission of electricity in the main grid in the event that there is a fault in Olkiluoto 3 and the power supply to the main grid is interrupted or if Olkiluoto 3 is unable to supply power to the main grid because of a fault in the grid,” says Minna Laasonen, Senior Expert at Fingrid.

A 1,600-megawatt giant

As the reactor at Olkiluoto 3 can produce up to 1,600 megawatts of electricity, a sudden disturbance in such a huge power unit could paralyse Finland’s power system. The OL3 system protection will disconnect electricity consumers in such a way that the change in power to the main grid is no more than 1,300 megawatts in the event of a sudden interruption in the power supply from Olkiluoto 3.

“The OL3 system protection will enable an uninterrupted supply of electricity. This is a technical arrangement that decreases electrical comsumption on eight industrial sites within 0.2 seconds if the power supply from Olkiluoto 3 to the main grid is interrupted. In order to ensure a fast and reliable activation time data communications from Olkiluoto to industrial sites are used, Laasonen says.

She has worked as Project Manager on Fingrid’s project with TVO to ensure that the commissioning of Olkiluoto 3 goes safely and reliably from the perspective of the main grid.

Large factories cut electricity consumption in the event of a fault

The OL3 system protection, which calls for a reduction in electrical loading of approximately 350 megawatts, involves Kemira Chemicals Oy from Äetsä, Metsä Board Corporation’s factories in Joutseno and Kaskinen, Stora Enso Oyj’s factories in Anjalankoski and Imatra, and UPM Paper Ena Oy’s factories in Jämsänkoski, Kaipola and Rauma.

“In terms of the Specifications for the Operational Performance of Power Generating Facility, Olkiluoto 3 is no different from any other power plant, but its enormous output sets it apart. For this reason, OL3 system protection was required to reinforce the reliability of the power grid,” Laasonen says.


Fact box

 Olkiluoto 3 will increase Finland’s self-sufficiency in energy, provide more power on cold winter days and increase the inertia in the Nordic power system.
 With a power output of 1,600 megawatts, Olkiluoto 3 is the largest power plant unit in Finland and the Nordic countries.
 By international comparison, Olkiluoto 3 is the world’s third-largest power plant unit after Taishan 1 and Taishan 2 (1,660 MW) in China.
 Olkiluoto 3 will generate an average of 15 per cent of the electricity consumed in Finland.
 Altogether, the three Olkiluoto power plants will generate one-third of Finland’s electricity.
 Olkiluoto 3 will be connected to the main grid in November 2020, and regular electricity
generation will begin in March 2021.

A unique substation

Olkiluoto 3 will be connected to the main grid via Fingrid’s modernised Olkiluoto substation, which consists of three separate switchgear stations and control buildings. When Olkiluoto 3 is complete, the three nuclear power plants in Olkiluoto will generate one-third of the electricity consumed in Finland.
The substation entity consists of a new 400-kilovolt switchgear station with double circuit breakers built for Olkiluoto 3, two switchgear stations to serve the Olkiluoto 1 and 2 nuclear power plants, and separate control buildings.

Although the power plants are connected to the same station, they can be electrically isolated from each other using switching devices. This makes it possible to ensure that an individual fault could never cause more than one power plant unit to be disconnected from the network. Each switchgear station connects to the main grid via two lines, which increases the reliability of a substation at a critical junction in the main grid and enables maintenance work to take place without interruptions.

“Thanks to the new duplex structure, the Olkiluoto power plants can be isolated from each other more reliably. The switchgear station solution enables an almost unlimited number of different connections to investigate disturbances or interruptions,” says Hannu Heikkinen, Project Manager at Fingrid.

Each switchgear station has two main bus bars. Thanks to the bus bar protection built into the switching stations, a faulty bus bar can be easily disconnected from the network without losing the functionality of the entire station.

“Designing and building dozens of alternative connections was a complex technical process, which required an enormous amount of testing, but we got there in the end,” says Heikkinen.


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