GIS disconnector switching operation — VFTO study

Very Fast Transient overvoltages (VFTO) in power systems are result of switching operations such as disconnector opening and closing inside GIS substation. The VFTO causes great threat to the insulation of the high-voltage equipment (e.g. bushings or windings of transformers). These transients are associated with very short rise times in the nanoseconds range, and are normally followed by oscillations having the frequency spectrum well above several MHz. In the present paper simulation results of the VFT overvoltages at the transformer terminals, resulting from a disconnector switching operations in a typical GIS substation are presented. In a common approach used for insulation coordination study, typically a single re- or prestrike in the disconnector is analyzed. In the presented paper an advanced model of the GIS disconnector is involved. The new model enables the analysis of multiple re- or prestrikes generated during the operation of the device. This in turn allows one to analyze the impact of the repetitive phenomenon on the HV equipment. The simulation results with use of high-frequency power network components were performed using the ATP/EMTP program.