Study On Space Charge Properties Of Nano-CB/LDPE Composite Under Voltage Polarity Reversal

In recent years,with the application and development of DC power transmission technology,the insulation materials with good electrical performance under various operating conditions of DC cable have broad application prospects and practical value.Electric field distortion caused by the space charge accumulation in the insulation is considered to be one of the obstacles for the operation of high voltage DC cables.In this paper,nano-CB/LDPE composites were fabricated by using the melt blending method.Space charge characteristics and field distortions of nanocomposite films were measured under direct current(DC)field by pulsed electro-acoustic(PEA)method.Dielectric properties and DC breakdown strength were also investigated.Experimental results indicate that,by adding appropriate doping content of CB nanoparticles,the space charge injection threshold of the films was increased,which suppressed homo-polarity space charge injection and ameliorated the field distribution.Breakdown strength of nanocomposite decreased whereas the dielectric permittivity and dielectric loss tangent increased slightly.However,too much CB nanoparticles mixed in LDPE could weaken the suppression effect on charge injection and field distortion.Moreover,According to the experimental results of LDPE,before the polarity reversal,homo-charges are injected and accumulate around the electrodes,and these space charges cannot dissipate completely after the voltage polarity being reversed which resulting in more serious electric field distortion.According to the t est results of CB/LDPE after voltage polarity reversal,the density of shallow trapped charges decreases whereas the density of deep trapped charges increases,and the average charge density is reduced.Based on the comprehensive analysis of the electrical characteristics,filler ratio is initially screened to ensure good comprehensive electrical performance.