Study On The Decomposition Characteristics Of C₄F₇N/N₂ Mixed Gas Under Partial Overheat Fault

Perfluoroisobutyronitrile(C4F7N)gas has excellent insulation properties,and its GWP value is lower than that of currently used SF6 gas,but there is a problem of excessively high liquefaction temperature.As an insulating gas with various properties,it has great potential to completely replace SF6 gas.At present,the domestic decomposition of C4F7N and its mixed gas,especially the decomposition mechanism when overheating occurs,is still in its infancy.In this thesis,N2 is selected as the buffer gas of C4F7N for research.In this thesis,the various molecules of the mixed gas are firstly modeled in Gaussian 16 software,and the C4F7N/N2 mixed gas system is comprehensively calculated at the micro level using density functional theory combined with the 6-311G(d,p)basis set.Explains The evolution steps and mechanism of the hybrid system in detail.Obtain the energy barriers involved in the reaction path and the vibration frequency and geometric parameters of the particles And the transition state structure information of the reaction system is determined by frequency analysis method and intrinsic reaction coordinate method.The reaction system involves 35 reactions,including an optimized reaction of 10 particles combining with N atoms and 25 particle scanning decomposition reactions.Then the scanning decomposition reaction includes 7 reactions with obvious transition state structure and 18 reactions without obvious transition state structure.This thesis simulates the reaction rate based on the transition state theory and the variational transition state theory,and obtains the reaction rate of all reactions in the temperature range of 300K-3500K(26.85℃-3226.85℃).After that,the equilibrium constant of the reaction system was calculated,and the state of the forward and reverse development direction of each reaction was analyzed.Finally,by carrying out experiments under different working conditions,the influence of temperature and mixed gas mixture ratio on the main decomposition products in the local overheating fault is analyzed.The C4F7N/N2 mixed gas was subjected to overheating failure decomposition experiments and gas chromatography-mass spectrometer was used to diagnose the characteristic gas components of the resulting gas.The C3F6 and C2F3N(CNCF3)gases as important decomposition components were determined and analyzed.The research in this article provides an important theoretical basis and engineering guidance for fault state monitoring and diagnosis of insulation equipment using this mixed gas.