Effect of polarity reversal on space charge properties of CB/LDPE composite under DC field

Voltage polarity reversal is a special condition in HVDC transmission system. In this study, low density polyethylene (LDPE) and nano-CB/LDPE composites films were manufactured, and the space charge distribution was measured under DC voltage with and without the polarity reversal respectively by pulsed electro-acoustic (PEA) method to reveal the doping effect of nano-CB on the space charge distribution. 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 test 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. The LDPE with 0.03wt% of CB nanoparticles shows sound performance on inhibiting the space charge accumulation after the voltage polarity reversal.