Improved topology helps integrate more energy in the medium-voltage level
In the project NeToVe ('Novel topologies for distribution networks') headed by Siemens, researchers are investigating the topologies of distribution networks in the medium-voltage level. The goal is ensuring the familiar and high reliability of supply but with increased horizontal feed-in from decentralised power generation systems.
As part of the energy transition, the feed-in power of decentralised energy generation systems is to be increased significantly. By 2050, renewable energy will generate 80 percent of the electricity – much of it coming from decentralised systems that feed directly into the distribution network on the low and medium-voltage levels. However, the grids are not designed for these new tasks. This can result in overloads, voltage increases, feeding back of power and increasing harmonic distortions. Therefore, scientists are researching solutions that raise the capacity of the distribution networks, letting them meet future requirements.
Conventional grid expansion would be one option, but it is expensive. Alternative solutions include novel grid topologies with a higher degree of intermeshing. They could offer more flexibility in terms of loads and feed-in due to the fact that several supply areas are coupled. This makes it possible to increase the capacity for horizontal feed-in from decentralised energy generation systems. This is especially true in regions where distribution areas with a high proportion of decentralised energy generation systems are adjacent to areas with a high proportion of loads but little distributed feed-in. The reliability of supply and its quality can be improved through a coordinated increase in the degree of intermeshing in compliance with the permissible operating resource loading by, for example, short-circuit current-limiting measures and load flow controls.
Reducing grid expansion with optimal grids
This type of intervention is only possible with the aid of new operating resources and advanced grid protection technology. The project partners are scientifically determining their requirements, in addition to the fundamental impact of altered grid topologies. The changed grid topology should help to better utilise available operating resources in the existing grid reserves. In doing so, the distribution networks could integrate more renewable energy. This, in turn, lowers the extent of the necessary grid expansion, since the existing infrastructure can be used as far as possible.
The aim of the project is to investigate novel, for example, highly intermeshed grid topologies and tightly coupled supply areas of the medium-voltage distribution networks. On the one hand, the technical feasibility and the limitations of increasing the degree of intermeshing are to be demonstrated, and on the other, how operating conditions changed by altering the degree of intermeshing can be managed. The scientists will research how modified grid topologies could further ensure the currently high supply reliability. They consider it feasible, despite a high level of feed-in into the distribution networks with a simultaneously reduced need for investments and grid expansion effort. They take into account, for example, current-limiting and load-flow-influencing operating resources, methods and new protection concepts.
New approach without restricting user behaviour
These examinations will be conducted in selected exemplary real grids using quasi-stationary grid studies. The project partners are investigating different scenarios in terms of location and output of the generation units and loads. In the next step, they will examine how selected example grids react to an increased intermeshing and expansion of the supply area. Load flow changes, increased short-circuit current and requirements to the newly developed protection technology will be examined along with methods of coordinating protection with the grid. The scientists expect that they will find and develop additional structural measures, beyond increasing the degree of intermeshing, to make distribution networks more efficient.
The investigated approach is fundamentally different from the known approaches with pure production and load control. They are being considered, for example, for smart grid concepts. By increasing intermeshing and expanding the supply area, the transmission and distribution capacity of existing distribution networks is improved. This is achieved with the targeted use of novel operating resources for short-circuit current limitation in the existing infrastructure in conjunction with new protection concepts. End user behaviour is not limited. Large-scale addition of new lines should be avoided, in particular through the use of existing transmission lines. The lines are operated openly, since closed operation is currently not possible for physical and technical reasons.
10/2014 – 09/2017