Hybrid Model for Air Core Reactors in EMC Simulations of High Voltage Converter Stations

Recently, accurate EMC simulation methodologies for high voltage converter stations have been developed and presented. These methodologies can model complete substations, and cover conducted and radiated emissions. The simulations rely on numerical full-wave methods coupled to circuit solvers. Main subject of this study are the air core reactors used in such high voltage converter stations. They have complex geometries and are therefore typically included in system models as impedance netlists only. As a consequence, electromagnetic coupling and radiation effects of the reactors are neglected, what can negatively impact the accuracy in cases where they are installed outdoors or near other components. In this paper, we present a hybrid approach for efficient modeling of air core reactors as part of large, system-level models of medium and high voltage converter stations. The model consists of a simplified 3D single-turn coil, coupled to a circuit model at schematic level. The correct magnitude of the magnetic field is obtained by multiplying the winding current by the number of reactor turns and injecting them into the 3D single-turn coil using an ideal transformer. Implementation is done in CST Microwave Studio. The results are compared to measurements, to equivalent lumped circuit models and to full wave simulations.