Cross-linked polyethylene (XLPE) and ethylene propylene diene monomer (EPDM) are commonly used materials for high-voltage direct current (DC) cable insulation and enhanced insulation in cable accessories. Dimethyl silicone oil (SG) is commonly employed as a coating material for the cable insulation/enhanced insulation interface. Under prolonged thermal stress

these materials undergo aging. To investigate the effects and mechanisms of coating and aging on the space charge characteristics at the XLPE/EPDM interface

we prepared composite insulation samples with two different interface contact types: one with no coating (XLPE/EPDM) and one coated with dimethyl silicone oil (XLPE/SG/EPDM). A combined aging test was conducted on the double-layer composite insulation samples at 110 ℃

with measurements of electrical conductivity and space charge. Additionally

molecular simulations were used to construct band models for XLPE/EPDM and XLPE/SG/EPDM before and after being aged

and first-principles calculations were employed to determine the electronic structure and interfacial potential barriers. The study reveals that the polarity of the interfacial charges at the XLPE/EPDM interface is related to the Maxwell-Wagner (MW) model

the high interface barrier

and the swelling effect of SG on EPDM. The high interface hole potential barrier (1.52 eV) can result in a charge polarity at the EPDM/XLPE interface that does not conform to the MW model. In contrast

the polarity transformation law of the XLPE/SG/EPDM interfacial charge aligns with the MW model due to the reduced hole potential barrier of the XLPE/SG and EPDM/SG interfaces introduced by the SG. The variations in conductivity of EPDM and XLPE after being aged

along with the reduction in the interface hole potential barrier at the EPDM/XLPE interface

lead to inconsistencies in the charge polarity and magnitude before and after being aged. After being aged

SG can cause swelling in EPDM

resulting in a shift of the charge peak towards the bulk of the EPDM.