Compatibility of Molecular Sieves with C4F7N/CO2 Insulating Gas Mixture

Abstract

As a promising SF6 alternative, C4F7N/CO2 gas mixture shows comparable insulating performance to SF6 with a much lower global warming potential (GWP). However, the compatibility of materials used in gas-insulated apparatus with this gas mixture has raised more concerns due to the lower inertness of the gas mixture. Among those materials, molecular sieves with a huge specific surface area require extra attention since the rate of a chemical reaction can be greatly raised by increasing the surface area of a solid reactant. In this study, two kinds of molecular sieves, one made of zeolite, the other made of an organic compound, are selected for long-term thermal aging with the C4F7N/CO2 gas mixture. The aging process lasts for up to 9 months. The gas mixtures and products after aging are analyzed by gas chromatography-mass spectrometer (GC-MS), and dielectric strength tests. The results show that the zeolite molecular sieves exhibit incompatibility with the gas mixture. The catalytic effect brought up by the zeolite molecular sieves during aging is considered accountable for the incompatibility observed. For the organic molecular sieves, although they do not show incompatibility with the gas mixture, they may decompose during the long-term thermal aging.