Development of Magnetoresistive Current Limiters Based on High-Mobility Indium Antimonide for DC Power Grids

Abstract

Safety mechanisms in power grids are important for protecting the grid and everything in direct electrical contact with it. In this thesis, the magnetoresistive (MR) element of a self-regulating, 2-terminal current-limiting system is studied. The MR element consists of the high-mobility semiconductor indium antimonide (InSb), which shows exceptional resistance variations due to the ordinary magnetoresistive effect.The system can effectively limit fault currents in DC power grids. Stationary FEMsimulations are performed to study the differences between two designs, namely a sandwich design and a planar design, the impact of varying geometric parameters on the performance, and the influence of temperature. Experiments are performed to validate the simulation results.The results show that the geometric design has a big influence on the obtained magnetoresistance. The sandwich model shows better MR performance than the planar model because the entire current path is deflected by the Lorentz force. The planar model has an unavoidable current density component that is independent of the magnetic field. This leads to lower resistance variations but higher geometric flexibility due to the planar design. However, it was observed that the MR performance of the planar model approaches the sandwich model when the thickness t is small compared to the other geometric parameters. Generally, increasing the electrode width w and decreasing the electrode spacing L enhances MR. This effectively increases the deviated current path while simultaneously decreasing the influence of charge accumulation at the model’s geometric boundaries. In the limit of w/L → ∞, no edge effects are present, and the maximum values for MR are reached. In addition togeometric factors, temperature also has a significant impact on performance. Due to resistive heating during the operation, the MR performance significantly decreases.The reason is that the carrier concentration increases with temperature, while the carrier mobility decreases. Because the increase in carrier concentration is greater than the decrease in mobility, resistivity decreases with temperature. This directly leads to less resistance variation. Additionally, a thermal resistance model is discussed that can estimate the properties of potential heat sinks to effectively dissipate unwanted thermal energy.