Damping of VFTO in Gas-Insulated Switchgear by a New Coating Material

Several methods of attenuation of very-fast transient overvoltages (VFTOs) in gas-insulated switchgear (GIS) are under development. An approach that is currently gaining high attention among researchers is based on the application of magnetic cores dissipating the energy associated with VFTO due to eddy current losses and magnetic hysteresis losses. This paper presents an advancement in this approach by introducing a new material type (denoted in this paper as “nanoflakes”). This new material comprises macro pieces of nanocrystalline ribbons (with the size ranging in square millimeters), acquired from crumbled nanocrystalline cores of a standard design. The material is characterized by relatively high magnetic permeability, poor electrical conductivity, and high saturation flux level. The material is suitable for application as a coating layer applied to the surfaces of an inner and/or an outer GIS conductor, as a fill-in material in the GIS shielding elements, or as a standard shaped core. This paper presents the material major features, outlines its development process, and reports on validation of the material effectiveness in real VFTO conditions. The validation is based on the measurement of VFTO attenuation in a full-scale 550 kV GIS test setup.