Comparison of Transportation Carriers in the Insulating Materials for HVDC Cable Joint

As an interface between the different insulating polymers exists in the joints of High Voltage Direct Current (HVDC) cables, the differences in the field-and-temperature dependence of the conductivities of the materials is regarded as a problem leading to interface charge accumulation and field distortion. In this report, using blocking materials to prevent charge injection from one or both sides of the electrodes, the contributions of charge injection and ionization in low-density polyethylene (LDPE), cross-linked polyethylene with nanoparticles (nano-XLPE) and ethylene propylene diene monomer (EPDM) are distinguished and evaluated based on the results from pulsed electro-acoustic (PEA) method. It is found that the contributions of charge injection and ionization behave differently in different materials. The mechanism behind the field-and-temperature dependences of the conductivities of the three materials is explained successfully. This study helps to clarify the charge transfer mechanism, and thus supports the quantitative calculation of the space charge and electric field distribution in cable joints.