Investigation of Impedance-Based Protection Mechanisms for Dry-Type Iron Core Reactors Under Core Saturation Conditions

This paper discusses the potential core saturation issue in dry-type iron core reactors caused by power system harmonics and proposes a protection strategy based on variations in third harmonic impedance characteristics. First, an equivalent model of the dry-type iron core reactor is established by integrating its electromagnetic characteristics. Electromagnetic simulations using the COMSOL software are then conducted to analyse the dynamic trend of the reactor's equivalent inductance during core saturation. Subsequently, a power system model containing a high-voltage capacitor device was built based on Simulink. Simulations show that when the 3rd harmonic content reaches 6%, the reactor core enters a saturated state; whereas the 5th and 7th harmonics need to reach 11% and 24% content, respectively, to trigger saturation. Further analysis reveals that, compared with the fundamental wave and the 5th/7th harmonics, the 3rd harmonic impedance ratio curve exhibits unique identifiability in both single- and multifrequency harmonic scenarios: in weak and strong grid conditions, the corresponding inductance loss rate α can be accurately identified within specific ranges; in complex multifrequency harmonic environments, this identification range narrows further, with significantly improved precision. This characteristic provides a reliable basis for real-time monitoring of the saturation state of dry-type iron core reactors, confirms the effectiveness and stability of the protection method based on the 3rd harmonic impedance characteristics in complex grid environments and offers key theoretical support for the design of related protection logic.