Low Frequency Currents Source Identification

Low frequency neutral point currents have several sources, which can be identified by their frequency spectra, recurring patterns or time of occurrence. The highest currents occur during solar storms which result in geomagnetically induced currents.

The second identified source is the public transport system near neutral point measurement systems. The measured current fluctuations clearly correlates with the operating times of the subway system. In addition, the electric potential difference between the public and the subway earthing systems shows the same pattern. The special timetable, caused by Covid-restrictions further proves this argumentation.

 The analysis shows correlations between changes in voltage levels and transformer neutral point currents. This was done by comparing daily mean trajectories as well as the autocorrelations of neutral point currents and voltages. The voltage changes occur regularly, which can be assigned to the changes on the electricity market. The identified shunt reactor switching operations are a well-known method to regulate the voltage-levels in the transmission grid. Therefore, this effect could also be investigated in other grids and further measurements in neutral points outside of Austria would be of high interest. 

Doi: 10.1109/ICHQP53011.2022.9808423