Mechanism of space charge accumulation in crosslinked polyethylene under temperature gradient

Space charge will accumulate within polyethylene when stressed under DC high voltage, and a temperature gradient will form throughout the insulation when a HVDC cable is in service. Previous research has revealed that temperature gradient can enhance hetero charge accumulation at the low temperature end, but the high temperature only helps a small quantity of homo charge accumulate, and the mechanism was explained for hetero charge formation due to ionization of impurities within the insulation and blocked extraction of injected carriers. However there is no direct evidence to distinguish whether the hetero charge is injected carriers or the ions. This paper intends to investigate and explain the influence of temperature gradient onto hetero charge formation. It was concluded that temperature gradient across the sample thickness could affect the space charge through its influence to the mobility of carriers, and the temperature difference between two electrodes could also influence the entire space charge distribution through its influence to the charge injection and extraction. The space charge distribution in cross-linked polyethylene (XLPE) samples with different thickness under different temperature differences and temperature gradient was investigated. The results show that both the temperature difference between the electrodes and the temperature gradient across the thickness can enhance the hetero charge accumulation.