High-Frequency Model of Magnetic Rings for Simulation of VFTO Damping in Gas-Insulated Switchgear With Full-Scale Validation

Nanocrystalline magnetic rings have been experimentally proven for effective damping of very fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS). The application of any damping solution in a specific GIS setup (rated voltage, GIS arrangement) requires simulation-based design, which, in turn, requires reliable models with proven accuracy in demanding high-frequency and high-current VFTO conditions. This paper presents a new model of a magnetic ring, employing full frequency-dependent characteristics of the ring´s complex impedance, as well as the dedicated approach on modeling the saturation effect of the material magnetization characteristics. The saturation effect is modeled by a bypassing branch, activated at a certain saturation current value calculated according to the specific magnetic material properties and for the VFTO main frequency component. The model was implemented in Electromagnetic Transients Program simulation software and validated experimentally in a full-scale 550-kV GIS test setup. The validation proved the applicability of the model for the assessment of VFTO damping effectiveness with the use of nanocrystalline magnetic rings and, thus, for the design of a particular magnetic-based damping solution in a specific GIS setting.