Electromagnetic and Thermal Analysis of Gas Insulated Substation (GIS)

Abstract

GIS is preferred to AIS now a days because it has many advantages over it viz. small space requirement, better insulation strength etc. Main components of GIS include electrical bus bars, circuit breakers, current transformers, voltage trans- formers, etc. The dielectric medium used in GIS is SF6 which has many advantages over air viz. better insulation strength, chemical stability, non-in ammability, high lifetime etc. The current carrying capacity i.e. Ampacity of any conductor is highly in- uenced by it's maximum operating temperature. Hence, from design point of view, it is important to know what temperatures a particular set of conductors of same dimensions would achieve while supplied with the same amount of electrical current. In this work, the same idea was implemented for single phase and three phase bus bars. A set of four metals viz. Aluminium 6063, Stainless steel, Mild steel, Aluminium AlMgSi were studied as potential choices for making conduct- ors and enclosures of busbar. A particular value of AC steady steate current was allowed to ow through the conductors. The losses occuring in main conductors and in enclosures ( due to induced eddy currents ) were calculated using Maxwell Ansoft software. These loss values were used as inputs for thermal analysis and the subsequent temperature distribution across the cross section of bus bar was obained using Finite Element Method. The best metal of the four was then chosen based on temperature analysis. Secondly, many contaminating particles are generated in GIS due to arcing. Surface of spacers or any other components are also non-uniform. Such non- uniformities or contamination due to particles present in SF6 may lead to increased electric eld and ultimately insulation failure. The e ects of such non-linearity are studied by considering hemi spherical protrusions and depressions on the spacer surface. The e ects of particle presence near the spacer surface are also studied. In both of the cases, the radius and the position of the defects along the spacer surface are varied and subsequent changes in the electric eld intensity magnitude around the spacer surface are observed using Finite Element Method (FEM).