Numerical Simulation Of Space Charge Transport In Polymer For High Voltage Direct Current Cable

Space charge accumulation affects electric field distribution and causes the local field distortion in the insulation when HVDC cable operates,which likely leads to electrical trees and even results in insulation breakdown.In order to study the transport characteristic of space charge in HVDC polymer cable and analyze the mechanism of nanofiller content on space charge transport in nanocomposites,the dynamic characteristics of space charges in polymer under DC electric fields were numerically investigated.The results can provide a reference for both the insulation design and the dynamic simulation of space charges in HVDC cables,as well as the regulation and control of polymeric materials.Firstly,the bipolar charge transport model was solved by finite element software,and the reliability of the software implementation was verified.The finite element software was utilized to solve the mathematical model based on the bipolar charge transport process,and then the contributions of micro particles and space charge behaviors in the charge transport process were analyzed.The simulation results agree well with the experimental phenomena,which verify the reliability of the software solution.The simulation results also show that trapped charges decide space charge and electric field distributions,and the trapping process is dominant in the processes of charge transport.Secondly,a parametric analysis was made to reveal the mechanism of the polarity effect on space charge distributions under DC electric fields.The effects of mobility,trapping coefficient,detrapping barrier height and injection barrier height on the asymmetric distribution of space charge and electric field were analyzed.The results show that the mobility of mobile charges significantly affects the asymmetric distributions of both space charges and electric field,while the trapping coefficient depends on its order of magnitude.Both the detrapping barrier height and the injection barrier height have contributions to the polarity effect.Thirdly,the effects of the applied voltage polarity,electrode structure and the ionization of the neutral particles on the charge transport were studied.The transient distributions of space charge and electric field under several polarity reversals were investigated.Next,the one-dimensional axial symmetry bipolar charge transport model was established in polar coordinates,and the effect of the plate electrode and the axial symmetry electrode on the charge transport was compared.What's more,ionization equations were introduced to simulate the ionization and transmission of impurities and other neutral particles.The results show that the behaviors of electric field under polarity reversal are with the polarity effect.The effect of electrode structure on charge transport is more significant under the polarity reversal.The ionization of neutral particles not only forms hetero-charge distributions but also changes the transport of electrons and holes in the base materials.Finally,the mechanism of nanofiller content on space charge transport in polypropylene nanocomposites was analyzed.The physical parameters were changed regularly with the increase of nanofiller content to keep the simulated space charge distributions fitting with experiments.The volume conductivities in PP nanocomposites prove that the assumptions about parameters in this paper are reasonable.The weakened space charge and the increased uniformity of electric field caused by nanoparticles are due to the reduction of mobility,trapping coefficient,ionization rate and the increase of deep trap density,detrapping barrier height and injection barrier.In a certain range,the higher content of nanofiller,the greater influence on charge transport.In addition,the non-uniform distribution of nanoparticles was discussed.