Suppression of fast and very fast transients in GIS

Though lightning surges and switching operation have been reduced to an acceptable level in modern substation insulation coordination, still transformer failures related to lightning and switching are often reported in the gas insulated substation (GIS). There are methods to suppress the stresses created by very fast transient (VFT) from the source side. Ferromagnetic rings and resistor can be mounted on the conductors linked to the disconnector from both sides. Also extra arrester is a method for mitigation of lightning overvoltage. However, these methods are suitable before installing the substation and during the substation design period. This paper covers the estimation of the peak magnitudes of very fast transient overvoltage (VFTO), very fast transient currents (VFTC), and lightning overvoltage at various locations that have been computed in a typical GIS. The aim of this paper is to investigate methods for mitigation of overvoltage magnitude in GIS. The advantages of the proposed methods are their simplicity and low cost for implantation along with producing minimal changes in the installed GIS. Computer simulation has been done using the alternative transients program (ATP).