Temperature rise test and analysis of various influencing factors of a MV switchgear

Temperature rise assessment for MV circuit breakers is a critical type test as higher current ratings in MV switchgear influence increased heat losses and elevated temperatures, which, when exceeded permissible limits, result in equipment damage, deterioration of the materials, a shortened service life, and pose a fire hazard. This article explores the challenges of utilizing dry air as an insulating medium instead of SF₆ and investigates the influence of gas pressure on heat convection and conduction through various temperature rise experiments. In addition to typical challenges such as skin and proximity effects, busbar configuration, spacing, enclosure dimensions, and ventilation. Effects of insulation medium on temperature performance and pressure influence on heat transfer is under study. Insulating media such as dry air and SF₆ have significant differences in molecular weight, density, & thermal conductivity. In convection, the lower density of dry air results in a lower heat transfer capacity compared to SF₆ in ambient pressure. Since GIS shows very low gas velocity, the heat capacity of the gas plays major role in convection. Conversely, the higher density of SF₆, while allowing greater heat storage per volume, limits mobility and thereby potentially 2.8 times better convection efficiency under elevated pressure conditions.