Connection codes

The aim of connection codes is to create functional criteria for production plants connected to the transmission and to distribution networks, for consumption and for HVDC equipment.

​Connection codes are:

  • Requirements for Generators, RfG
  • Demand Connection Code, DCC
  • High-voltage Direct Current, HVDC


Requirements for Generators, RfG

The network code for the connection of generators sets requirements for all new synchronous and converter-powered generators connected to the power system. The network code requirements also concern offshore power production. The network code is applicable to existing power production only with regard to revisions. The network code sets no requirements for reserve generators that are not synchronised to the power system.

The network code defines generator size classes from A to D. Size classification starts from 0.8 kW plants (class A), ending in over 30 MW generators or plants connected to a 110 kV grid (class D). The size class of synchronous generators is defined based on those parts, which go inseparably together (e.g. CHP generators).

With regards to converter-connected generators, size class is defined according to the commercial entity built for power production, which is connected behind one connection point.
The compliance of generators must be demonstrated through tests and simulations. In terms of smaller generators, however, a certificate issued by an authorised verification body is usually sufficient. By way of a decision by the authorities, developing technologies may be exempted from the requirements (maximum capacity in Finland 12 MW and 3 MW per technology).

Deviation from network code requirements requires that a party connected to the network carry out a separate cost benefit analysis. A decision on the matter is made by the authorities, after first consulting the transmission system operator (TSO).

Demand Connection Code, DCC

The Demand Connection network code sets requirements for all new network connections. The requirements can also be applied to existing network connections, if significant changes take place in them. The network code requirements are not applicable to storage equipment, with the exception of the power production modules of pump power plants, which have both production and pumping modes.

The network operator of a connection point may not grant a connection permit for a new connection that does not meet the network code requirements.

High-voltage Direct Current, HVDC

The High-Voltage Direct Current network code sets requirements for all new HVDC connections to the interconnected networks. The requirements concern the internal power transmission connections of areas, the connections between them and production connections.