Survey of Harmonic Grid Impedance Measurements on the Medium Voltage Level up to 100 kHz

The harmonic grid impedance is a crucial system property utilized in various applications. However, traditional simulation-based methods are often limited by the lack of access to essential information, such as equipment characteristics, load behaviors, and grid topologies. In response, measurement-based black-box techniques have been developed, with initial commercial solutions available for low-voltage applications. Unfortunately, for the medium-voltage level, only a limited number of prototypes exist. Unlike other techniques, which require large, immobile setups, the measurement system described in measurement system is the first of its kind to be successfully applied in several research projects at various grid connection points. This paper presents, for the first time, real-world grid impedance measurements collected from multiple sites over extended time periods on the medium-voltage level. In addition to the measurement data, this paper provides comprehensive metadata for each measurement site, which is presented in measurement sites and metadata and the appendix, significantly enhancing the usability of these results for further research. The measurement results have been thoroughly analyzed, providing valuable insights into medium-voltage grid behavior. The evaluation of the measurement data in presentation and evaluation of the measurement data includes general observations comparing grid impedances at various connection points, as well as graphical and statistical evaluations of the time-dependent behavior of grid impedance. Special attention is given to resonance points, and the influence of renewable energy installations on grid impedance. Finally, the results are summarized and discussed in conclusion of the measurement results.