Objective Submarine cables are an important part of ensuring the stable operation of offshore wind power. As a key area for the land-sea transition of submarine cables, the J-tube section has become a bottleneck restricting the current-carrying capacity of the entire submarine cable system due to its special laying environment and structural characteristics.

Method Taking the J-tube section as the research object, this paper accurately calculated the operating temperature distribution of the submarine cable inside it; Taking the 220 kV, 1000 mm² three-core cross-linked polyethylene insulated AC submarine cable commonly used in engineering as the research carrier, based on the multi-physics field coupling theory, the finite element analysis method was adopted to construct a three-dimensional magneto-thermal-fluid coupling model of the submarine cable J-tube, and systematically analyzed the current-carrying capacity, temperature and loss distribution laws of the air section and seawater section of the J-tube.

Result The study finds that in the seawater section, the high thermal conductivity and good heat dissipation performance of seawater help maintain the stable temperature of the cable, thereby improving its current-carrying capacity; In the air section, due to the low thermal conductivity of air and the influence of natural convection and solar radiation, the cable temperature rises rapidly, which limits the current-carrying capacity and becomes a current-carrying bottleneck section.

Conclusion Comparing the calculation results of the three-dimensional model, two-dimensional model and analytical method, the three-dimensional model has higher calculation accuracy and can more truly reflect the actual working conditions. For the problem of the air bottleneck section of the J-tube, the simulation results show that when the air velocity inside the tube increases from 0.01 m/s to 1 m/s, the conductor temperature decreases and the current-carrying capacity increases significantly. Therefore, changing the air velocity in the air section of the J-tube can improve its current-carrying capacity, providing theoretical support for the optimal design of the J-tube section.