A Study of Transient Electric Field Distribution of XLPE Cable Joint in a VSC-HVDC System

Cross-linked polyethylene (XLPE) cable is one of the key assets in a voltage source converter (VSC) based high-voltage direct current (HVDC) system. Due to the complex geometry and interfaces among different material, cable joints are the most critical part of a cable system. In this paper, two typical transient overvoltages (zero-crossing damped overvoltage, very slow front overvoltage) is obtained in a VSC-HVDC system and their effects on the electric field distribution of the joint insulation is investigated. The results are compared with the standard switching impulse tests. The temperature-dependent and electric field-dependent characteristics of insulation conductivity and the ratio of double-layer material conductivities at the joint interface are discussed. It is found that geometry of the cable joint and the ratio of XLPE and ethylene propylene diene monomer (EPDM) conductivities are the dominant factors on both steady-state DC field and transient electric fields caused by the system overvoltage.