The single European electricity market is growing ever closer together. In this context, 50Hertz is a strong partner at the centre of the European grid. International transmission lines, so-called interconnectors, connect the transmission system of 50Hertz with the transmission systems of other countries. They are part of a sustainable development of the European grid infrastructure. Trusting international cooperation is indispensable to meet the demands of the energy transition in Germany as well as the EU plans to create a single integrated European electricity market while optimising grid development.
An interconnector is a power line connecting the electricity grids of two countries. Interconnectors, i.e. international transmission lines, link the transmission systems of all countries of the EU together, enable international power trade and increase the security of supply. All national transmission systems and their linking cross-border interconnectors together create the European interconnected grid.
The transmission system of 50Hertz is electrically connected to Poland via two international lines, to the Czech Republic via one line and via another with Denmark. A second interconnector with Denmark involving offshore windfarms is currently being constructed. A lot of preparation work is also being performed for the construction of a new interconnector with Sweden across the Baltic Sea and there are plans to create a third interconnection with Poland.
The KONTEK link is a high-voltage direct current (DC) transmission connection (HVDC connection) operated at 400 kV between the transmission grids of 50Hertz and the Danish transmission system operator Energinet.dk (EnDK). With a length of 170 km and a technical transmission capacity of 600 MW both in northbound and southbound direction, the KONTEK line has been in operation between Bentwisch near Rostock and Bjaeverskov in Denmark since 1996.
Another interconnector to Denmark involving German and Danish offshore windfarms is currently under construction and is expected to be operational in Q3 2019. This joint 50Hertz and EnDK project is funded by the European Union: Combined Grid Solution
Germany and Sweden want to link their power grids together via a planned submarine cable connection: the Hansa PowerBridge. This international direct current (DC) line shall be about 300 kilometers long and connect the two electricity transmission grids of Germany and Sweden. The German-Swedish interconnector is expected to contribute to stabilisation of electricity prices in Germany and South Sweden, increase of operational security of transmission grids and the indirect storage of electricity from wind and solar power plants in Scandinavian water pump storages.
For further information on the Hansa PowerBridge interconnector for which intensive preparation is currently taking place, please see here.
Between the transmission grids of 50Hertz and the Czech transmission system operator ČEPS, there is one cross-border alternating current (AC) line between substation Röhrsdorf (Germany) and substation Hradec (Czech Republic) which is in operation since 1959. At the beginning, this line was operated at a nominal voltage of 220 kV. Since an upgrade in 1976, the line is operated at a voltage of 380 kV.
There are currently two cross-border electricity lines (see graph) between the transmission systems of 50Hertz and the Polish transmission system operator PSE. Both lines are alternating current lines (AC). The northern interconnector between the substation Vierraden (Germany) of 50Hertz and the substation Krajnik (Poland) of PSE was commissioned in 1987 with a nominal voltage of 220 kV. After reinforcements of the interconnector and the two substations the nominal voltage level of the interconnector is updated to 380 kV since 2018.A second interconnector with a nominal voltage of 380 kV further to the south, between the substations Hagenwerder (Germany) and Mikułowa (Poland), is in operation since 1999.
A third connection line ("3rd interconnector") between Eisenhüttenstadt (Germany) and Plewiska (Poland) is currently in the planning phase. The project is a European priority project and was declared as an urgently needed project in 2009 by the Bundestag’s Power Grid Expansion Act (ENLAG). In a complementary note to the ten-year grid development plan of the European Network of Transmission System Operators (ENTSO-E), the Polish transmission system operator nevertheless pointed out its altered grid development priorities. Commissioning is therefore only expected as of 2030.
Further information regarding the project
Phase shifting transformers (PSTs) are used to control the electricity flows between transmission systems. If one imagines the transmission grid as a network of water pipelines with many inflows and outflows, the PST functions as an adjustable valve which can increase or decrease the in- and outflow. If the electricity flow on a line is lowered, the electricity flows on the overall interconnected system are redistributed. This makes it possible to avoid overloads on the transmission grid and control the load flow in a targeted manner.
In order to better control cross-border electricity flows, 50Hertz and PSE are installing phase shifting transformers (PSTs) on the two existing interconnectors which are operated in a coordinated manner.
After the successful commissioning of the first four PSTs at the Polish substation in Mikułowa in June 2016, the northern interconnector between Vierraden and Krajnik was temporarily taken out of operation in order to upgrade the two substations to 380 kV. In August 2018 the first two PSTs were commissioned in Vierraden. While the line to Poland is operated at 380 kV, on the German side there is a link to the existing 220 kV lines as construction of the 380 kV Uckermark Line is delayed. In addition to the two PSTs, two 380/220 kV transformers will be used as an intermediate step. With the commissioning of the Uckermark Line (expected after 2020), these two 380/220 kV transformers will be replaced by two more PSTs. After that, the installation of the PSTs in Vierraden will be completed and another important development project can be put into full operation within the European interconnected grid.
PST in the substations Mikułowa, Vierraden, Hradec and Röhrsdorf (on the German-Czech border) are operated by 50Hertz, PSE and ČEPS in a coordinated manner.
Further information regarding the PST projects of 50Hertz and PSE:
Press release: Power flow regulation between Germany and Poland (German)
Press release: Agreement between Polish and German transmission system operators signed (German)
Before commissioning of the first four PSTs in Mikułowa in June 2016, a so-called "virtual Phase Shifting Transformer" (vPST) was operated to control unplanned load flows, ensure system security and foster cross-border electricity trading.In March 2014, 50Hertz and PSE launched the operational phase of the vPST. Beforehand, the partners tested the vPST mechanism during its pilot phase and drew conclusions for the subsequent operational phase. The report prepared jointly by both transmission system operators presents the principles, assignments and most important results of the vPST pilot phase.
Further information regarding the virtual phase shifting transformer of 50Hertz and PSE:
Press release: 50Hertz and PSE Operator cooperate to use phase shifting transporters
Report on vPST pilot phase experience
In order to better control cross-border electricity flows, 50Hertz and ČEPS are installing phase shifting transformers (PSTs) on the interconnector. The first PSTs on the German-Czech interconnector have been commissioned by ČEPS in the Hradec substation in January 2017. On the German side, two PSTs have been commissioned by 50Hertz in the Röhrsdorf substation in late 2017. After some further reconstruction works in substation Röhrsdorf which are expected to take another two years’ time, the PST should also be connected to other lines in the southern region of 50Hertz grid area in order to enable better use of these lines.
Further information regarding the PST projects of 50Hertz and ČEPS: