Finland currently depends on electricity imports in times of peak demand. Electricity is transferred to Finland through high-voltage direct current (HVDC) connections, especially from Sweden. Alternating current (AC) is converted to direct current in HVDC stations for transfer through undersea cables, and then converted back to alternating current.
"If there is an interruption in the import connection, the missing transfer capacity has to be replaced with more expensive electricity produced in Finland using power plants that generate balancing power or in Fingrid's back-up plants", says Harri Nurminen from the Finnish national grid operator, Fingrid. He is responsible for HVDC Care agreements at Fingrid.
Nurminen works as a senior specialist in a unit to which Fingrid focused its HVDC expertise at the beginning of 2016. It also reorganized the condition management of HVDC connections and shared responsibilities with its partners. ABB is responsible for the maintenance of the Finnish Fenno-Skan 1 and two HVDC stations, which join the main grids of Finland and Sweden, and those of Estlink 1, which joins the main grids of Finland and Estonia. The aim of the reform was to invest more in improving the availability and reliability of HVDC connections.
"The number of interruptions in Fingrid's HVDC connections dropped almost by a half during the first year, and their average duration has decreased even more. During 2017, we did not have a single interruption in the Fenno-Skan connections between Finland and Sweden. Many factors can cause interruptions. In any case, it is evident that investing in the condition management of HVDC connections has been effective and that the maintenance activities in general have reached an entirely new level", Nurminen says.
Interruptions solved quickly
If there is an interruption in the HVDC systems, Fingrid contacts ABB's on-call expert who comes to the station to find out what has happened and what must be done to recover the connection. Remote connections are also utilized in troubleshooting, in order to create a preliminary assessment of the situation based on the alarms and event notifications generated by the HVDC system and to determine the measures necessary to repair the fault and recover the HVDC connection.
"It is important to first promptly draw up a reliable assessment about how long the connection will be out of use," Nurminen says. After the assessment, ABB's experts will start the repair work. Another aim is to find out the root cause of the incident in order to avoid corresponding interruptions in the future.
Reliable electricity supplies are thus increasingly dependent on the effectiveness of HVDC maintenance. There is a lot of pressure on the work of the HVDC experts, considering that the faults can be severe and the HVDC system is a challenging technical system. Knowledge of direct current technology helps a lot if a component in the HVDC station's circuit is damaged. However, the fault could equally well be in the automation system's circuit board or in the cooling system, for example. "In addition to general knowledge, every team member has special expertise that others can utilize," says Ari-Pekka Laakkonen, project manager of ABB's HVDC services in Finland. According to Laakkonen, close cooperation is pursued between ABB and Fingrid's experts in dealing with the rarest faults and finding out their root causes. "It is also important for us to adhere to the processes agreed upon with the customer and continuously develop our operations."
HVDC system - an increasingly important part of the power system in Finland
The main grid managed by Fingrid is part of the pan-Nordic electricity system and the common electricity market. High-voltage direct current connections (HVDC) between Finland and Sweden, and between Finland and Estonia make up more than 40% of the border transfer capacity of Finland's main grid. A 100 MW HVDC connection between Naantali and the Åland Islands was taken into use in 2015, delivered by ABB. The operating features of the system are secured using ABB's HVDC services. ABB is a pioneer in HVDC technology and has delivered more than half of the world's HVDC systems.
ABB's HVDC connections in Finland
- Rauma - Dannebo, Sweden
- since 1989
- 500 MW
- Rauma - Finnböle, Sweden
- since 2011
- 800 MW
- Naantali - Ytterby, Åland Islands
- since 2015
- 100 MW
ABB's HVDC Care solution 2016-2020
- 24/7 on-call HVDC expert service, troubleshooting and fault repair
- Preventive maintenance, e.g. annual maintenance
- Station and system checks
- Developing maintenance together with the customer