Preparation And Insulating Oil Purification Performance Of Polyvinylidene Fluoride Nanofiber Membrane

Insulating oil is an important insulating medium in oil-filled electrical equipment such as transformers.Under the long-term action of electric field,thermal field and other factors,aging products such as moisture and organic acids will be produced.Moisture and organic acids will cooperate to accelerate the deterioration of electrical performance of insulating oil,which seriously threatens the safe and stable operation of electrical equipment.Purification of insulating oil can effectively reduce the failure probability of transformer,operation cost and environmental pollution.The current methods of insulating oil purification have the problems of complicated treatment process and low purification efficiency.In order to solve this problem,the hydrophobicity and electropolarity of PVDF nanofiber membrane were improved by adding polytetrafluoroethylene(PTFE)nanoparticles to PVDF.The insulating oil containing different organic acids and moisture was prepared.The purification performance of PVDF/PTFE nano-composite fiber membrane for organic acids and moisture in insulating oil was studied.The main research contents are as follows:?The appropriate PVDF concentration was determined by pre-spinning experiment.The influence of spinning parameters on the diameter distribution and physico-chemical properties of nanofiber membrane was studied by orthogonal experiment,and the optimized spinning parameters were obtained.The results show that the spinning solution has good spinnability when the concentration of PVDF in the spinning solution is 12 wt.%,and the prepared fiber membrane is smooth without bead string.Intuitive analysis and ANOVA found that the spinning voltage and N,N-dimethylformamide(DMF)/acetone mass ratio were significant factors affecting the fiber diameter dispersion coefficient and the average fiber diameter,respectively,and the optimized spinning parameters were determined to be 9:1 DMF/acetone mass ratio,20 k V spinning voltage,and 0.75 m L/h feed flow rate in combination with the hydrophobicity of the fiber membrane.?The PVDF/PTFE composite fiber membrane was prepared with optimized spinning parameters to study the effect of PTFE content and particle size on the physicochemical properties of the composite fiber membrane.The addition of PTFE reduces the surface energy of the composite fiber membrane while increasing the roughness.During the spinning process,the local amorphous region of PVDF is transformed into?-phase,thereby effectively improving the hydrophobicity and electret polarity of the composite fiber membrane.When the average particle size of PTFE is100 nm,the pure water contact angle of the composite fiber membrane reaches the maximum value,the oil contact angle is approximately zero,the?-phase content is significantly increased,and the composite fiber membrane with the best comprehensive physicochemical performance is obtained.?The filtration performance of the composite fiber membrane for different contaminants in oil was investigated by testing the acid value,moisture content,power frequency breakdown voltage and broadband dielectric spectrum of the oil samples before and after filtration.The results show that among organic acids,the composite fiber membrane has the best filtration effect on acetic acid,with a one-time filtration rate of up to 69.4%,and the power frequency breakdown voltage increased from 43.9 k V to 64.4 k V.The dielectric loss factor and relative dielectric constant of the oil samples were significantly reduced at low frequencies and were close to the level of new oil,indicating that the organic acids in the oil were effectively filtered.The one-time filtration efficiency of the composite fiber membrane for moisture in the oil reached 76%,and the moisture content of the filtered oil sample was reduced to 7.2mg/L.The power frequency breakdown voltage was increased from 21.8 k V to 65.2 k V.The PVDF/PTFE composite fiber membrane has better filtration effect for trace moisture and acid products in the oil,which can effectively restore the electrical properties of the insulating oil.?The working life of the composite fiber membrane was preliminarily evaluated based on the moisture and organic acid in the oil.The test results showed that the PVDF/PTFE composite fiber membrane has good chemical stability,its hydrophobicity is not easily destroyed under the impact of oil flow,and has a higher working life when purifying moisture in oil,after filtering 5200 m L of insulating oil with moisture content of 28.8 mg/L using a composite fiber membrane with an area of 1.25×10^-3m²,the water filtering performance of the composite fiber began to deteriorate.The polarity and acidity of formic acid in organic acids are stronger than that of acetic acid,and the working life of the composite fiber membrane in filtering acetic acid in oil is longer than that of formic acid.The addition of PTFE particles effectively improves the hydrophobicity and electret performance of the PVDF fiber membrane,improves the purification effect of the composite fiber membrane on the moisture and organic acid in the oil,and effectively restores the electrical performance of the insulating oil.PVDF/PTFE composite fiber membrane used for insulating oil purification can simplify the subsequent treatment process and improve the purification efficiency,which has a promising application prospect.