Compatibility and Interaction Mechanism between EPDM Rubber and a SF₆ Alternative Gas-C₄F₇N/CO₂/O₂

Among the numerous novel eco-friendly insulating gases, C₄F₇N has attracted much attention due to its excellent electrical performance. However, except for the electrical perfomance, the compatibility between the gas medium and the sealing materials is equally important for gas-insulated equipment. At present, studies about the compatibility between C₄F₇N and EPDM, a widely used sealing material in power systems, are available in some previous works, but few focused on the compatibility comparison between C₄F₇N gas mixtures and EPDM with different third monomers. In this paper, we carried out the thermal aging test on ENB-EPDM, DCPD-EPDM, and C₄F₇N gas mixture to perfect the compatibility mechanism between EPDM and C₄F₇N. It was found that both of the EPDM reacted with the gas mixture and led to the property changes in the solid samples and the decomposition of C₄F₇N. On the other hand, by coating silicone grease, the contact between gas and rubber was effectively blocked and the concentration of the decomposition product was significantly reduced. The performance comparison indicates that ENB-EPDM is more suitable for sealing the C₄F₇N gas mixture, which is due to the superior thermal stability of ENB.