Michael Schühle defended his dissertation on “Causes and effects of direct currents in three-phase networks” on October 1, 2024.
The thesis deals with the influences of parasitic DC currents, which can occur in transmission grids and may cause various effects in inductive components. By creating a general simulation model in Matlab Simulink and Simscape, it is possible to simulate the effects of half-wave saturation in ferromagnetic cores. The modeling of the non-linear, hysteresis-prone material properties of the magnetic core is achieved by parameterizing a Jiles-Atherton model. This presents a special challenge within the simulation in order to produce realistic and stable simulations.
When examining inductive current transformers with different cores, the simulation created is used to determine how DC currents affects the respective transmission behavior of the measuring and protection transformers and thus the resulting measurement errors. The rsulting effects on grid operation are considered individually for different current transformers(billing transformers, measuring transformers, protection transformers).
Geomagnetically induced currents represent a particular cause of DC currents. These are caused by charged particles from the sun hiinteracting with the earth's magnetic field. As a result of induction effects, currents arise in the transmission grids with frequencies in the µHz and mHz range, which are called quasi-DC. The thesis develops models for calculating and predicting these GIC currents, using measurement data of the local geomagnetic field, a conductivity model of the ground and the network model of the transmission grid under consideration.