Investigation on diffusion process of water molecules in sulfur hexafluoride electric equipments based on CFD technique

The humidity of SF₆ gas is an important indicator of the safe operation of gas-insulated electrical equipment. In order to investigate the diffusion process of water molecules in this kind of device, Computational Fluid Dynamics (CFD) technique was firstly used to simulate the diffusion process of water molecules from sampling port to device body under different pressure conditions. It was found that at least 222 hours was needed to achieve complete diffusion equilibrium through molecular thermodynamic movement. Furthermore, it was confirmed that the gas humidity at the sampling port could´t timely reflect the gas humidity inside device body in airtight condition, and the online monitoring device for the moisture content of SF₆ gas should not be installed at sampling ports of electric equipments.