Grid connection solution

​The electricity system security and usability are always affected by a grid connection solution. When planning a grid connection for our customer we evaluate system security, transmission capacity and electricity safety of the main grid to promote a good quality solution. Equally important we consider environmental issues as well as the impact on the total cost of the planned solution. The grid connection solution is planned and agreed with our customer on a case-by-case basis.

A new connection may not unreasonably weaken the main grid's usability and that of other customers’ connections. The protection of the connecting network is done by our customer in accordance with the connection solution principles. 

The parties pay for the costs of the planning of their own network and for the costs of subsequent construction, operation and maintenance of the connection.

Connection to a substation (switchyard connection)

A switchyard connection means a connection to a 400 kV, 220 kV or 110 kV switchyard of the main grid network. If planned connections locate close to a switchyard, these will be directly connected to a switchyard instead of a power transmission line.

Table: Grid connection to a substation

Connection solution​​Connecting power
400 kV switchyard​ 250 MW or more
​110 kV or 220 kV switchyard ​Less than 250 MW

Based on our company project time window we estimate the planning and construction of a new switchyard to take 24 months.

Connection to a 110 kV power transmission line

Due to the geographical distances in Finland, the lines for the power transmission are long and the substation are far apart. Consequently, connection solutions to 110 kV power lines are also possible when transmission capacity of the main grid and other technical terms and conditions are first taken into account. A power line connection means a branch line or a substation connection with a fixed or a switching device solution connecting to a 110 kV power line of the main grid.

The maximum permitted rated current of a transformer without mechanical
ventilation (ONAN) is 25 MVA. By equipping the transformer in question with
mechanical ventilation (ONAF), the loading of the transformer up to 30 MW is
permitted. A maximum of two transformers can be switched to a single connection point provided that the lower-voltage networks between the two transformers are not joined in parallel.

In general, power plant shall be connected to Fingrid’s switchyard circuit breaker
bay. If the transmission capacity so permits, small synchronous generators of less than 5 MW or converter connected power plants of up to 30 MW may be connected to the Fingrid’s 110 kV transmission line, as long as their short-circuit current fed to the main grid is no more than 1.2 times the rated current of the power plant.

Table: Grid connection to a 110 kV power transmission line

Connection solution​​Maximum power of transformer​Maximum power of generator
​110 kV power line connection
25 MVA
5 MW (30 MW*)​

* Only if the short-circuit current fed by the power plant is a maximum of 1.2 times the rated current of the power plant.

The power line transmission capacity and the regional system security of the main grid must always be verified with Fingrid. Fingrid makes the necessary grid analyses together with the customer.