Realistic distribution grid models for harmonic studies across different network levels

Inhalt:
The transition towards renewable energy sources and the increasing amount of power electronics introduced at all voltage levels have an influence on harmonic levels, both in transmission and distribution grids. This has to be taken into account when analysing harmonic propagation, especially across the border between distribution and transmission grids. Therefore, models of typical distribution grids have been developed in order to be embedded into an existing transmission grid model for harmonic studies. The models are created in a network calculation software and include three high voltage (HV) grids and two medium voltage (MV) grids. The distribution grid models feature different types of lines, multiple aggregated downstream network models as well as conventional and inverter based generation units. The three different HVgrids represent a typical urban area, a typical rural area and a typical suburban area, while the MV-grids represent an urban and a rural area. This paper describes the models of the five distribution grids in detail, which have been developed based on a survey amongst seven German distribution system operators (DSO). This includes the network topology, the impedance models of the generation units, the aggregated network models as well as the transformer and lines. Next, the harmonic nodal impedance is discussed for the different distribution grid configurations. The results show that the impedance in rural areas is different from the impedance in urban areas. Furthermore, a sensitivity analysis shows the influence of the type of aggregated load model on the harmonic node impedance.