Meyer, Marc Florian

The rising proportion of nonlinear electrical consumers causes the harmonic load of electrical distribution systems to increase. Depending on the acting grid impedance this leads to either complied permissible limit values of harmonic load or a danger to safe grid operation. Exemplary Hamburg’s sewage treatment plant is chosen to record harmonic load by means of a developed measurement concept during regular energy supply by the distribution system operator. The acquired measurement data are integrated into a simulation model to infer the harmonic load when operated in island mode, where grid impedance is greater as if connected to public grid. A measure to comply with the limit values is presented and demonstrates the effectiveness of passive filters.

In this work, a frequency-dependent transformer model is derived with the help of a measurement device that determines the frequency response of the grid impedance at an arbitrary point of connection to the power grid. In this case, the measurement device was connected to a 20 kV medium voltage grid of a wind farm. The disconnection and reconnection of the wind turbine’s transformers revealed the impact the open circuit input impedance of the transformers has on the positive sequence component of the grid impedance. First deriving a positive sequence grid model from the measurement without the transformers, later analyzing the impact the transformers have on the grid impedance, allowed the calculation of the positive sequence component of a frequency-dependent open circuit transformer model, which results in the same impact on the overall grid impedance as observed in the measurements.