The Determination of the Diffusion Rate of SF6 into Nitrogen

Although gaseous mixtures of SF6 and N2 show particular dielectric characteristics, the diffusion process of SF6 into N2 has not been investigated in detail. This paper describes such an investigation using the variation in the sparkover voltage between spark gaps to determine the diffusion rate of SF6 into N2. It was found that the local sparkover voltage increases gradually with time when SF6 diffuses into N2 and this increase corresponds to an increase of the local SF6 content measured with a gas chromatograph. This diffusion process was also calculated using the binary gas-phase diffusion coefficient proposed by Fuller. This diffusion coefficient uses the hard sphere model. It was found that changes in the calculated local SF6 content is nearly equal to the measured local SF6 gas content for low SF6 concentrations.