Very Fast Transient Overvoltages generated by Gas Insulated Substations

Very fast transient overvoltages (VFTO) are caused by disconnector switching operations within a gas insulated substation (GIS). The very fast transient overvoltages contains very high frequency components in the order of several 10psilas of MHz and may cause high frequency oscillations in the transformer windings, leading to possible overstressing of the transformer insulation. By modelling a gas insulated substation as very short transmission lines with an electromagnetic transient programme it is possible to predict the magnitude of these fast transients and their high frequency components. In this paper, PSCAD/EMTDC was used to model the switching operation of disconnectors in a GIS installation.