Influence of the Temperature- and Field-Dependent Conductivity of EPDM Insulation on the Electrical Field Distribution in HVDC Prefabricated Joints for XLPE Cables

Under HVDC operation, the nonlinear temperature- and field-dependent conductivity behaviors of insulation materials will significantly affect the electrical field distribution in cable joints, potentially leading to localized field enhancement and reliability concerns. This study conducts an electro-thermal coupled simulation to investigate a DC 160 kV prefabricated joint with XLPE as the cable insulation and EPDM as the joint insulation. By adjusting the nonlinear conductivity parameters of EPDM material, the effects of its activation energy and electrical field-dependent coefficient on the DC electrical field distribution of the joint under different load scenarios were analyzed. Results show that the steady-state DC field strength at the XLPE-EPDM insulation interface is strongly influenced by these two parameters of EPDM conductivity, particularly at the root of the stress cone, where the maximum field distortion commonly occurs. Notably, as the conductivity activation energy decreases or the field-dependent coefficient increases, the field distortion at the root of stress cone diminishes. When the EPDM-to-XLPE activation energy ratio falls below 0.92 or the field-dependent coefficient ratio exceeds 0.75, under full-load conditions, the maximum electrical field strength shifts from the root of stress cone to the insulation outer surface of cables connected on both sides. This may enhance the system reliability, as the joint interfaces are normally more vulnerable than cable main body. This study provides a theoretical basis for material selection and performance matching for HVDC prefabricated cable joints.