Modeling and Analysis of Very Fast Transient Over-voltages in 400 kV GIS

Power systems is subjected to various forms of transient phenomena's realized essentially by the sudden variations in the steady state parameters of voltage and current. There is a need for a more reliable operation of system. Gas Insulated Substations have been developed which provide high reliability, consume less space, quick assembly and low maintenance. It is well known that due to switching operations in Gas Insulated Substation (GIS), leads to malfunctioning of substation equipment's. These inappropriate functioning includes misoperation of electronic equipment's, deformation in connected transformer winding and bushing failures. The insulation coordination study thus forms a very important aspect in substation design stage. The dielectric strength of insulation of various connected equipment are effected due to generation very fast transient overvoltage (VFTO), which is caused due to the slow switching operation of disconnector switch in GIS. The objective of this paper is the modeling & analysis of VFTO generation in Gas Insulated Substation and to determine the impact of VFTO on connected equipment. Comparison of different techniques for mitigation of VFTO in GIS are also discussed in the paper. A 400 kV Gas Insulated Substation has been modeled and analyzed using EMTP software.