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 coun Contact online >>
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 lines and to the Czech Republic via one line. There are two interconnectors to Denmark including the Kriegers Flak Combined Grid Solution that has been commissioned in 2020 and which involves German and in future also Danish offshore wind farms. A lot of preparation work is being performed for the construction of a new interconnector with Sweden across the Baltic Sea - the Hansa PowerBridge - 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. 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. More information on the KONTEK interconnector can be found here.
Another interconnector to Denmark involving German and in future also Danish offshore wind farms is in operation since end of 2020. This joint 50Hertz and Energinet project has been funded by the European Union. More information on the Kriegers Flak - Combined Grid Solution can be found here.
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.
Further information on the Hansa PowerBridge interconnector, for which intensive preparation is currently taking place, can be foundhere.
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), isin 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 this project can be found here.
Utilisation of German-Polish interconnectors willfurther increase in consequence of an expected growth of demand for importedenergy as well as higher wholesale prices in Poland. This is one of the conclusionsderived from a study on European power markets commonly carried out by 50Hertzand the Polish TSO PSE S.A. supported by the National Centre for Nuclear Research(NCBJ) in Warsaw. The German and Polish Ministries responsible for energy wereinvolved. The recently finalised investigation was focused on long-term prospects of transmissionsystem operation in the German-Polish region from the perspective of futuremarket outcomes. Different scenarios have beensimulated for the two target years 2025 and 2030.
AnExecutive Summary about the results of the cooperation study is available here.
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.
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 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, since beginning of 2020 the PST canalso 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:
These changes pose significant challenges to the operation of the European transmission grid. First, balancing supply and demand will require additional flexibilities in a system dominated by distributed, intermittent RES-E and new sources of electrical demand. Second, RES-E at a specific point in time will be largely determined by the predominant meteorological conditions with high spatial concentration, increasing average distance between generation and consumption and thus increase the stress on the grid infrastructure. Lastly, market requirements to create a cost-minimal dispatch might contradict those necessary to enable a congestion-free transmission grid.
There are numerous models, which take into account flexibilities and simplified transmission grid constraints. In most cases, these models have been developed to analyse electricity markets, e.g. for investment decision support or operation decision support. In most studies liberalised markets in the United States or Europe are analysed and grid constraints are represented in a linearised way or by import/export constraints between market zones. Hence, most techno-economic models only take these constraints into account.
Few models, which consider flexibilities in a grid context take into account the full AC formulation of transmission grid constraints. Besides the group of studies and models, which consider a linearised form of grid constraints, some models can integrate full AC constraints. However, they are limited to either a very short time horizon or their focus lies on transient technical aspects like fault level detection, transient stability, harmonic analysis, reliability and power flow. Another group of models takes into account many flexibilities and AC restrictions but only on a distribution grid level, thus limiting system size and thereby complexity significantly [8]. A comprehensive overview on modelling approaches and their consideration of the grid can be found in [9].
Another area where transmission constraints are explicitly considered is the co-optimisation of transmission and generation capacities. The complexity of the resulting problem forces modellers to apply linearised transmission grid constraints or reduce the number of modelled flexibilities [10]. Furthermore, such models are often only validated on small scale or test grids, making it difficult to assess their suitability for large real-world power grids [11]. In most cases, the focus lies on investment decisions rather than on utilising operational flexibility in future transmission systems. [12] provide an overview of requirements and approaches to address this problem.
In this paper, we present a modelling framework to investigate the effect of distributed flexibilities on the transmission grid operation and investigate the benefit of utilising distributed flexibilities to reduce grid congestion while taking into account the full AC model of the transmission grid.
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