Towards a Baltic Sea Region Strategy in Critical ... - Helsinki.fi

CRITICAL INFRASTRUCTURE PROTECTION IN THE BALTIC SEA REGION
In the north, the Finnish and Swedish transmission grids are connected via an
aerial cable. In the south, the Fennoskan marine cable connects Finland and
Sweden. In the near future, a new Fennoskan 2 marine cable will be ready for use.
The Estlink marine cable links the Finnish and Estonian together. The main
connection between the Finnish and Russian transmission networks is 400 kV
double lines. Also, there are minor connections near Imatra in South-East Finland
and Inari in Lapland. In Utsjoki, Lappland, there is a connection line between
Finland and Norway. The most of the electricity used in Åland island between
Finland and Sweden comes from Sweden via a marine cable.
The transmission grid (voltage level 400-220 kV) is an interconnected
(meshed) network with multiple routes available for the power to reach a certain
destination. It carries high electric power over long distances. The sub
transmission grid, or regional grid (voltage level 130 – 40 kV), is a radial or
locally meshed network connected to the national transmission grid via infeed
points.
The high voltage network (over 70 kV) is built using aerial cables, usually
with either 400 kV lines and steel towers, or 110 kV lines and wooden poles. Both
lines are ensured from fallen trees with a wide right-of-way.
The distribution grid carries electric power from the transmission grid or the
sub transmission network to the final consumers. The primary distribution network
voltage level is 20 kV or 10 kV. The voltage level for domestic consumers in the
low voltage network is 400/230 V.
The medium voltage network (70 kV – 0.5 kV) in rural areas is built using
aerial cables with wooden poles, but in cities and built-in areas also underground
cables are commonly used. The right-of-way in the medium voltage network is
considerably narrower compared to the high voltage network and is therefore more
vulnerable to falling trees.
The low voltage network (400/230 V) is a radial network with aerial lines in
rural areas and underground cables in cities. Even if the medium voltage and low
voltage networks are built as a meshed network, they are normally used as a radial
network, which is more economic. However, in case of disturbances, the meshed
network can be reconnected and the consequences reduced by ensuring electricity
supply from an alternative direction.
The use of different voltage levels in different networks is based on
economic optimization and improvement of safety. Different networks are
connected to each other via transformer stations where the higher voltage level is
transformed to the lower level.
A variety of measuring devices, both at generation plants and spread across
the transmission grid, are connected to control centres where they allow operators
to monitor the state of the system. By sending electronic commands via
telecommunication networks back out, operators can control the settings of the
generator plants, reconfigure the grid, and - at least in limited ways - affect its
electrical properties. Electricity power system monitoring and grid control are not
completely dependent on telecommunications: electricity production, transmission
and distribution are working even when telecommunication services are not
available. However, monitoring information would not be in real time, which
would complicate the control of the power systems.
62 NORDREGIO REPORT 2007:5