Effect Of Temperature On Space Charge Characteristics Of CB/LDPE Nanocomposites

In recent years,DC cable transmission has developed rapidly.The development of cable insulation materials with space charge suppression capability through nano filling has received a lot of attention from scholars.Carbon black(CB)/low density polyethylene(LDPE)nanocomposite insulation materials have the potential for further research and development.Due to the heating of cable core,the insulation part of DC cable will withstand the high temperature in the range of normal temperature?70?.Therefore,it is of great significance to explore the space charge suppression characteristics and mechanism of CB/LDPE Composite at different temperatures for the development of new DC cable materials.In this paper,pure Low Density Polyethylene(LDPE)samples and carbon black(CB)/LDPE nanocomposite samples with CB doping concentration of 0.01wt%,0.03wt%,0.05wt%and 0.07wt%were fabricated by melt blending method.Two types of nano CB particles,CB1 and CB2,were selected.The space charge accumulation characteristics of the samples at different temperatures and electric field forms were obtained by pulsed electro-acoustic(PEA)method,and the mean magnitude of the volume density of the charge,the apparent mobility and trap parameters of space charge are calculated.The conductivity,dielectric properties and FTIR spectra of the samples were analyzed.The results show the space charge accumulation characteristics of CB/LDPE composites at different temperatures were significantly improved compared with LDPE.When the temperature increases from 30? to 50?,the space charge accumulation in pure LDPE and CB1?CB2/LDPE increases significantly,which is mainly due to the increase of the charge injected by the electrode with the increase of temperature.When the temperature increases from 50? to 70?,the space charge accumulation in the CB1/LDPE sample decreases.This is mainly because the high temperature intensifies the charge injection,but also the charge migration,which makes more charge migrate out of the sample through the electrode,leading to the decrease of the space charge in the sample.However,for CB2/LDPE samples,the space charge accumulation in the samples is further increased,which is mainly due to the deeper energy level trap introduced by nano CB2 particles in the samples,which inhibits the charge transfer process and weakens the effect of high temperature promoting carrier migration.In the process of polarity reversal,there was no significant electric field enhancement at the interface of pure LDPE and CB/LDPE composite samples with different concentrations.This is mainly due to the accumulation of heteropolar charges in the samples under the DC electric field.In the process of polarity reversal,the heteropolar charges that originally remained near the electrode turned into homopolar charges,which weakened the electric field at the interface between the sample and the electrode.The comprehensive analysis shows that the CB1/LDPE sample with 0.03wt%nano filling concentration has the best space charge inhibition effect,which shows good space charge inhibition ability under different temperature and different electric field forms,and the dielectric properties and chemical structure of the material have not changed significantly.The research results have guiding significance for the development of new insulation materials for DC cables.