Investigation On Charge Transport And Trap Characteristics Of LDPE/AlN Nanocomposite Dielectrics

With the rapid development of the flexible HVDC transmission in recent years,the application of HVDC cable is becoming more and more widespread.The problem of space charge in polyethylene insulation material under DC high field is the key factor that restricts the development of HVDC cable.Nanocomposite technology is an important way to improve the space charge behavior of polyethylene.At present,it is generally believed that traps in the interface of nanocomposite dielectric play a vital role in the suppression of space charge.However,there is a lack of in-depth understanding of the essence and mechanism of traps.The electron paramagnetic resonance technology is helpful for the study of the charge trap physical and chemical properties of LDPE/A1N nanocomposites.Based on this background,this paper focuses on the study of charge transport and trap characteristics of LDPE/AlN nanocomposites.Polyethylene based AIN nanocomposites with different doping contents were prepared by melt blending,and their physical and chemical structures were studied.SEM was used to characterize the morphology of the nano composite section and found that AIN nanoparticles in polyethylene matrix is approximately uniform distribution and good dispersibility.On the type of functional groups and vibration sample by Fourier transform infrared spectroscopy,nano doping does not introduce new functionality,nevertheless,some functional groups of vibration intensity changes.The dielectric properties of LDPE/AlN nanocomposites were studied.The breakdown characteristics of nanocomposites show that the breakdown field strength first increases and then decreases with the increase of AlN nanoparticles.When doping content is 0.5%,the breakdown field strength gets its maximum 120.7kV/mm,which is 16%higher than that of pure LDPE.The dielectric constant and dielectric loss of LDPE/AlN nanocomposites increase with the increase of temperature and electric field strength.And with the increase of AIN doping content,they both decrease first and then increase.Studying on the electrical conductivity of nano composite material with different doping content at different temperatures and electric fields is found,with the increase of temperature and electric field,conduction current increases,the resistivity decreases;the conduction current of LDPE/AlN nanocomposites is smaller than LDPE,the resistivity is higher than that of pure LDPE,when the doping content is 3%,the conduction current of LDPE/AlN composite is the lowest and the resistivity is the largest.The charge transport and trap characteristics of LDPE/AlN nanocomposites were investigated.The space charge measurement results show that a large amount of space charge accumulated in pure LDPE under high field strength;The doping of AIN nanoparticles have inhibitory effect on space charge,the space charge accumulated less and more nearly the electrode surface;When the doping content is 3%,the effect of space charge suppression is the best.The study of nano composite trap energy density distribution by using isothermal discharge current method found that trap density in the nanocomposites with 0.5%and 3%doped is obviously higher than that of the pure LDPE,which shows an agreement with the experimental results that the space charge accumulation and conduction current in the nanocomposites with 0.5%and 3%are less than pure polyethylene.It indicates that a large number introduction of traps in nano composite materials plays an important role in regulation for charge transport.The electron paramagnetic resonance(EPR)technique was used to study the physical and chemical properties of charge traps in LDPE/AIN nanocomposites.The results show that the signal of the EPR spectrum enhances with the increase of space charge in the material;when the charge is not injected,the signal intensity of the EPR spectrum of the nanocomposite is 3?5 times than that in pure LDPE.The EPR signal intensity of the nanocomposite is similar to that of pure LDPE after the injection of charge.The LDPE/AlN composes of 0.5%and 3%appeare hyperfine structure at 50kV/mm.Based on the analysis of the structure characterization,dielectric properties,conductivity and space charge measurement,we can infer that traps are related to carbonyl and hydroxyl groups in materials.