Selection of Optimal Mitigation Technique to Suppress the VFTOS in 765KV UHV GIS Substations

Abstract

Suppression of VFTOs by using four different devices in 765KV UHV GIS substation is presented in this paper.  Restrike and prestrike occurs repeatedly while operating a disconnector switch into ON state or into OFF state. In GIS, travelling waves propagate through switchgear, due to the rapid time for the voltage breakdown.  Dielectric strength of components of substation reduces with this high-frequency transients. As a result of the interface between transient over voltages and enclosures, transient ground potential rise or transient enclosure voltages appear for a very short duration. This creates flashovers to nearby grounded items. It is necessary to reduce VFTOs in GIS based EHV substation. Four techniques are presented to suppress VFTOs in a 765KV UHV substation and results are compared in terms of peak value, rise time and settling time of oscillations. Simulation is performed on 765KV substation using MATLAB/SIMULINK.