Electrical and physical evaluation on heterogeneous interfaces between two kinds of XLPE

Two XLPE cables (A, B) and two crosslinkable polyethylene (PE) tapes (A, B) were prepared. By combining XLPE and PE tapes, four different case interfaces were obtained. AA and BB represent the homogeneous interfaces and AB and BA represent the heterogeneous interfaces. The objective of this study was to define characteristics of the interfaces of two kinds of dielectric materials as a cable joint in solid dielectric cable system. AC and impulse voltage were applied in the prepared specimens with termination. The electrical strength of the heterogeneous interfaces was approximately 15% lower than that of homogeneous interfaces. Physical properties (tensile strength, degree of crosslinking and variation of crystallinity) were investigated for these four interfaces. All specimens containing the interface show lower values of about 25% in tensile strength, about 10% in degree of crosslinking compared with bulk parts that represent pure cable insulation or crosslinked polyethylene tape. The homogeneous interface has about 10% higher strength compared to the heterogeneous interface. The difference in electrical performance is presumably caused by the difference of physical properties from different level of chemical bonding with two kinds of XLPE. In addition, crystalline morphology affected the electrical performance.