Modelling and analysis of metallic particle contamination in gas insulated substation under pure sf6 and sf6+n2 gas mixtures

Abstract

Compressed Gas Insulated Substations (GIS) and Transmission Lines (CGIT) basically consist of a conductor supported on insulator inside an enclosure, which is filled with SF6 gas. As one is aware of the attractive features of a Gas Insulated Substation (GIS), they also suffer from certain drawbacks. One of them is the outage due to seemingly innocuous conducting particles. Flash over in a GIS is, in general, associated with longer outage times and greater costs than in a conventional air insulated substation. Sulphur hexafluoride (SF6) widely used in Gas insulated substations due to its high dielectric strength and good arc interruption properties. However, SF6 gas has been found to be a green house gas that causes global warming. Among the environmentally benign gases, alternative to SF6 gas, the SF6- N2 gas mixtures is regarded as one of the most attractive gases for the same setup used for SF6, because of the synergetic effect in electrical insulation performance. A study of CIGRE group suggests that 20% of failures in GIS are due to the presence of various conducting contaminants in the form of loose particles which are produced by the abrasions between components during assembly and operation. The presence of metallic contaminant in compressed GIS is a major threat when operated at higher fields. If the effect of these can be reduced, the reliability of GIS can be improved.Therefore, there is an increasing interest in the possible application of mixtures of SF6 and other gases to reduce insulation cost and to minimize the possible hazard of particle-initiated breakdown. Many researchers have studieTherefore, there is an increasing interest in the possible application of mixtures of SF6 and other gases to reduce insulation cost and to minimize the possible hazard of particle-initiated breakdown. Many researchers have studieWhen metallic particles are present in the SF6 gas and the voltage is applied between the electrodes.