Investigation of surface charge distribution on different polymer materials under AC voltage

In this paper, a measurement system of dynamic surface charge distribution based on Pockels effect was designed. Different polymer materials such as LDPE, PP, OPP, PET and PTFE were employed in the test. The surface charge distributions on dielectrics under needle-plate electrode have been measured within two cycles of sinusoidal voltage (50Hz, peak value 4kV). By analyzing the pattern and maximum charge density of charge distribution, the surface charge characteristics under different permittivity were compared and discussed. Results show that under positive voltage initiation, the positive streamer channels in the second positive half cycle were curved, which is affected by the residual charges in the first negative half cycle. The radius of charge distribution, charge density at the channel tip and the number of the positive channels increase with the increase of permittivity. Under negative voltage initiation, the maximum charge density at the negative peak voltage has negative correlation with distribution radius of surface charge. It was found that the bigger permittivity is, the bigger maximum charge density and the smaller distribution radius will be. The density of low-level traps in dielectrics is the dominant factor affecting the surface charge distribution.