Gas mixture candidates for SF6 replacement in medium voltage switchgear: Analysis and modeling of the filling episodes

A more environmentally friendly replacement for SF6 must be found for medium voltage switchgear, as a change in European regulations will come into force soon. The mixing process of alternative binary and ternary gas mixtures is studied, which are made up of the hydrofluoroolefin HFO-1336mzz(E) (C4F6H2) and the heptafluoroisopropil trifluoromethyl ketone (C5F10O), using dry air or N2 as carrier gases. The mixture's monitoring, meaning the evolution of the concentration concerning time and position, is carried out by UV-VIS spectroscopy technology in a gas chamber that has been designed to be analogous to a medium voltage cell. The mixing process is described using a mathematical model that considers molecular diffusion, Fick’s Law, and natural convection, the effect of gravity. This work aims to configure a tool for predicting the dynamics of gas mixtures of different components, estimating the diffusivities of the mixture's components, and analyzing the behaviors derived from the use of different concentrations.