Impact of Lubricant on Charge Dynamics at Macroscopic Interfaces in HVDC Cable Joints

ABSTRACT Charge dynamics at interfaces in high voltage direct current (HVDC) cable joints consisting of cable, joint insulation and lubricant may have an impact on the overall joint reliability. Although interactions between different lubricants and the joint insulation have been studied in recent years, the effect of lubricant diffusion on the electrical properties and charge dynamics at interfaces remains unclear and is therefore investigated in this paper. Different lubricants were applied at the interface of cross‐linked polyethylene (XLPE) and silicone rubber (SIR) samples, and mass, electrical conductivity, and space charge were measured over a 96 h ageing period. The mass of the samples was found to exhibit nonmonotonic behaviour, indicating complex interactions between the lubricant and material. XLPE experiences a decrease in conductivity while there is an increase in conductivity for SIR, which is linked to the migration of lubricant and therefore changes in trap distribution. Space charge measurements indicate changes in trap characteristics, which depend strongly on the used type of lubricant. The findings highlight that lubricant diffusion affects both the bulk properties and charge accumulation at the interface, and underline the large effect of the type of lubricant. These results are crucial for understanding the long‐term performance of cable joints and insulating materials in HVDC cable systems.