Ampacity Analysis of EHVDC Cable Accessories Based on Electro-Thermal-Fluid Field Coupling

Extra-high-voltage direct current (EHVDC) transmission is a key technology for future power system. Cable accessories, including joints and terminations, significantly impact system ampacity and long-term stability. Although air and liquid are contained in accessories, existing studies focus mainly on electro-thermal field coupling, with limited analysis of fluid dynamics, particularly at 525 kV voltage level, where electro-thermal-fluid interactions remain underexplored. This study conducts a Multiphysics simulation of 525 kV DC cable accessories, analyzing the electric, thermal, and fluid field distributions. Results show that the support rod of the stress cone in outdoor terminations obstructs convection, creating localized hot spots which limit the current ampacity and increase the insulation failure risk. In contrast to it, the modular prefabricated joint will not be the thermal bottleneck of the cable system, with the conductor temperature at the joint center lower than that of the adjacent cable sections. Therefore, it is essential to optimize the structure design and material selection of the outdoor terminations so as to enhance heat dissipation and mitigate thermal stress for increasing ampacity and ensuring reliable operation of EHVDC cable systems.