Experimental and Theoretical Study of the Interaction Between SF₆/N₂ and EPDM: A Comparative Study With SF₆

Mixing nitrogen (N2) into sulfur hexafluoride (SF6) is considered a beneficial measure to reduce the consumption of SF6. Minimal interaction and airtightness are key factors in maintaining the long-term stable operation of the equipment. To provide theoretical support for the application of ethylene propylene diene monomer (EPDM) in SF6/N2 insulated equipment, the interaction mechanism and permeability of SF6/N2 with EPDM at different temperatures are investigated. The experimental results are comparatively analyzed using Fourier transform infrared (FTIR) and tensile properties tests. In the meantime, the bond length distribution and diffusion coefficient of gas molecules in EPDM are analyzed using molecular dynamics (MDs). The adsorption performance [adsorption energy, transfer charge, and density of states (DOS)] of EPDM on gas molecules is also analyzed by density-functional theory (DFT). The results show that the infrared spectra of the experimental groups almost overlapped before and after experiments with little gas products. The mechanical properties are slightly worse than SF6/N2. The averages of SF6 and N2 bond lengths at 383 K increase by 5.97% and 0.57% compared to those at 298 K, respectively. The permeation coefficient of N2 is 5.28 times higher than that of SF6 in the SF6/N2 gas mixture at room temperature. The adsorption energy and transfer charge of EPDM on the SF6 (-0.902 eV, 0.0456 e) are higher than those of the N2 (-0.214 eV, 0.0204 e) indicating that EPDM has stronger adsorption effect on SF6. The analysis of the DOS further confirms it. The interaction between EPDM and SF6 as well as N2 is mainly van der Waals force and a small amount of hydrogen bonding, and the force strength of SF6 is stronger than that of N2. Overall, the interaction of EPDM with both SF6 and N2 is minimal. However, it is necessary to take appropriate measures to prevent SF6 and N2 leakage.