Characteristics of Partial Discharge During Electrical Treeing in XLPE Under DC Voltage

In order to reveal the correlation between tree growth and DC partial discharge (PD) in XLPE DC cable insulation, the DC tree growth and PD experiments were established based on the needle-plate electrode structure, and the effect of temperature on the DC tree growth and PD characteristics was studied through oil bath. Besides, a gas-solid two-phase charge simulation model for PD in tree channel was developed to discuss the effect of space charge and temperature on PD during tree growth and reveal the mechanism of electrical tree growth driven by PD under DC voltage. The results showed that DC tree would "turned" and grew along the horizontal direction near the ground electrode, which was related to the dielectric barrier layer formed near the ground electrode. Meanwhile, the growth of tree along the electric field enlarged the PD amplitude, while the extension of tree along the vertical electric field, that was, in the horizontal direction, stabilized the PD, and there were even discharge fluctuations caused by the generation and self-healing of new and old tree channels. According to the charge simulation, it was found that temperature was a key factor affecting the DC electrical tree growth. For one thing, with the increased temperature, the charge migration and diffusion in the solid insulation was accelerated, and the electric field at the needle tip was strengthened by 45%. For another, the electron impact ionization in the gas tree channel was promoted at high temperatures, and the charge density and discharge current were increased, thereby enhancing the PD intensity and speeding up the DC tree growth. © 2022 Chin. Soc. for Elec. Eng.