Study On Insulation Characteristics Of Environmental Friendly Insulating Gas HFO-1234ze (E) And Its Decomposition Characteristics With Micro Water

SF₆ has been widely used in gas-insulated power transmission and distribution equipment due to its excellent insulation performance and arc extinguishing ability.However,SF6 has a strong greenhouse effect and does great harm to the environment.Therefore,it is urgent to find a gas to replace SF₆.In recent years,trans-1,3,3,3-tetrafluropropylene（HFO-1234ze（E））has attracted attention due to its excellent environmental protection and insulation properties.In order to fully grasp the insulation performance and decomposition characteristics of HFO-1234ze（E）gas,this paper explores the DC and power frequency breakdown characteristics of HFO-1234ze（E）/N₂ and HFO-1234ze（E）/CO₂ mixture.The microdecomposition characteristics of HFO-1234ze（E）with trace water in power equipment were studied theoretically.Firstly,the DC breakdown tests of HFO-1234ze（E）/N₂ and HFO-1234ze（E）/CO₂mixtures were carried out in different electric fields.The experimental results show that HFO-1234ze（E）/CO₂ mixture gas with a higher proportion of HFO-1234ze（E）/CO₂mixture gas has a higher positive and negative DC breakdown voltage in slightly uneven electric field.The positive and negative DC breakdown voltages of 30%HFO-1234ze（E）/70%CO₂ mixture at 0.3 MPa are 1.26 times and 1.15 times of30%SF6/70%N₂ mixture at 0.15 MPa,respectively.In the heterogeneous electric field,the positive DC breakdown voltage of HFO-1234ze（E）/CO₂ mixture is higher,and the positive DC breakdown voltage of 20%HFO-1234ze（E）/80%CO₂ mixture is 1.81 times that of 30%SF₆/70%N₂ mixture at 0.15 MPa.The negative DC breakdown voltage of HFO-1234ze（E）/N₂ mixture is higher,and the negative DC breakdown voltage of30%HFO-1234ze（E）/70%N₂mixture is 1.80 times of that of 30%SF₆/70%N₂ mixture under 0.15 MPa.In the extremely heterogeneous electric field,the positive DC breakdown voltage of HFO-1234ze（E）/CO₂ mixture appears serious saturation phenomenon and even slightly downward trend with the increase of air pressure and proportion of HFO-1234ze（E）.The experimental results show that the breakdown voltage of HFO-1234ze（E）/CO₂ mixture is higher than that of HFO-1234ze（E）/N₂mixture in slightly uneven electric field or very heterogeneous electric field.The breakdown voltage of 30%HFO-1234ze（E）/70%CO₂ mixture at 0.3 MPa is 1.10 times and 1.77 times of 30%SF₆/70%N₂ mixture at 0.15 MPa,respectively.Secondly,the breakdown characteristics of HFO-1234ze（E）/N₂ and HFO-1234ze（E）/CO₂ mixtures were investigated.The experimental results show that the breakdown voltage of HFO-1234ze（E）/CO₂ mixture is higher than that of HFO-1234ze（E）/N₂ mixture in slightly uneven electric field or very heterogeneous electric field.The breakdown voltage of 30%HFO-1234ze（E）/70%CO₂ mixture at 0.3 MPa is1.10 times and 1.77 times of 30%SF₆/70%N₂ mixture at 0.15 MPa,respectively.By comparing the breakdown voltage data of 30%HFO-1234ze（E）/70%N₂ mixture gas and 30%SF₆/70%N₂ mixture gas at 0.15 MPa.It can be found that the sensitivity of 30%HFO-1234ze（E）/70%N₂ mixture gas to electric field inhomogeneity is less than30%SF₆/70%N₂ mixture gas at 0.15 MPa.Overall,the HFO-1234ze（E）/CO₂ mixture has higher insulation strength and produces fewer solid products after breakdown.Considering solid product precipitation,insulation strength and economy,30%HFO-1234ze（E）/70%CO₂ mixture at 0.25 MPa-0.3 MPa has the potential to replace30%SF₆/70%N₂ mixture at 0.15 MPa.Finally,the decomposition characteristics of HFO-1234ze（E）in power equipment containing a small amount of water are explored from the micro level.The reaction enthalpy and reaction energy barrier of the possible reaction path of HFO-1234ze（E）/H₂O were calculated by using Gaussian 09W software,and the main decomposition products were predicted according to the energy magnitude.By calculating the ionization energy,electron affinity energy and molecular orbital energy gap of the main decomposition products,it is found that the insulation strength of the main decomposition products of HFO-1234ze（E）/H₂O is poor,and some of the products are toxic,flammable and have strong greenhouse effect through literature review.