Preparation And Insulation-Oil-Regeneration Performance Of Polyvinylidene Fluoride Nanofiber Composite Membranes

Under the influence of temperature,electric field,copper iron catalysis and other factors,the insulation oil in long-term operation keeps aging,producing various impurities,causing electrical equipment failure.In order to reduce the waste of resources and avoid environmental pollution caused by oil change,the insulation oil after a period of operation can be purified.Polyvinylidene fluoride（PVDF）is widely used in electrospinning research based on its good thermal stability,chemical stability,and resident polarity.The filtering effect of micron level and below acid and polar impurities needs to be improved.Polyvinylidene fluoride（PVDF）has been widely used in electrospinning research due to its good thermal stability,chemical stability and electret property.However,the filtering effect of micron level and below acid and polar impurities needs to be improved.The filtering effect of PVDF nanofiber membrane for moisture,micron level and smaller acidic and polar impurity particles needs to be improved.In order to obtain better purification performance for insulation oil,PVDF/SiO₂ nanofiber composite membranes with superhydrophobic performance and PVDF/BaTiO₃ nanofiber composite membranes with excellent charge stability were prepared.Due to their poor mechanical property,a micron-grade polypropylene（PP）fiber filter with excellent mechanical property was selected as the substrate to form a three-layer filtration structure where PVDF/SiO₂ or PVDF/BaTiO₃ nanofiber composite membranes were in the middle layer and PP membranes were in the upper and lower layers.Firstly,the micron PP membranes filter out the micron and larger particles of impurities in the insulation oil.Secondly,the moisture,sub-micron and smaller particle impurities that are difficult to be removed are filtered by PVDF/SiO₂ or PVDF/BaTiO₃nanofiber composite membranes.The research of this thesis are as follows.（1）This paper adopted the method of orthogonal design.Combining the visual analysis method and the analysis of variance method,it was determined that the concentration of PVDF spinning solution was a significant factor affecting the dispersion coefficient of nanofibers.Then comparing and analyzing the average pore diameter of membranes,average diameter and dispersion coefficient of the nanofibers.Finally,the optimal spinning parameters of PVDF were determined.Under this condition,PVDF nanofibers with smaller diameter and uniform distribution were obtained.（2）PVDF/SiO₂ nanofiber composite membranes with different doping concentrations were prepared according to the optimal spinning parameters obtained above.The results showed that the hydrophobicity of the PVDF/BaTiO₃ composite membranes were significantly improved and achieved super hydrophobic performance.The optimal hydrophobic angle was 153.86°.In addition,the initial surface potential and charge stability of the doped composite membranes had been improved to varying degrees.In the research on the regeneration performance of insulation oil,moisture content decreased from 40.1 ppm to 13.7 ppm,the acid value decreased from 0.214 mg KOH/g to 0.140 mg KOH/g,the dielectric loss factor tanδdecreased from 1.439%to0.883%,and the breakdown voltage from 23.7 k V rose to 40.9 k V and increased breakdown voltage by 72.6%.（3）PVDF/BaTiO₃ nanofiber composite membranes with different doping concentrations were prepared according to the optimal spinning parameters obtained above.The results showed that the hydrophobicity of the composite membranes with different doping concentrations had been improved to a certain extent,and the maximum hydrophobic angle was 148.68°.In addition,The initial surface potential and the stability of the charge had been significantly improved.The optimal initial surface potential was 1760 V.After the charge decayed for 12 hours,it was 83.2%of the initial value.In the research on the regeneration performance of insulation oil,moisture content decreased from 40.1 ppm to 15.8 ppm,the acid value decreased from 0.214 mg KOH/g to 0.110 mg KOH/g,the dielectric loss factor tanδdecreased from 1.439%to0.958%,and the breakdown voltage from 23.7 k V rose to 38.9 k V and increased breakdown voltage by 64.1%.