Damping of VFTO by RF resonator and nanocrystalline materials

Very fast transient overvoltages (VFTO) are a well known phenomena in gas insulated switchgears (GIS). The main reasons for VFTO are switching operations of disconnectors. Thereby, several pre- or restrikes between the switching contacts occur and initiate steep voltage rises propagating inside the GIS. As VFTO cause several problems, especially in ultra high voltage (UHV) GIS a reliable method for damping these transient voltages is in demand. Two new approaches are presented in this paper. A matched radio frequency resonator formed by shielding inside the GIS was investigated inside a high voltage experimental test setup. Also, thin tapes of a nanocrystalline alloy wounded up to rings were tested. Addicted to the properties of the damping methods, the test setup and the damping method itself the first VFTO-amplitude was damped up to 20 percent. Even a higher damping is possible. Besides high voltage tests and their results, this paper illustrates the theoretical background of both damping methods.