Steady-State Thermal Circuit Modeling of HVDC Cable Joints Considering Axial Heat Transfer Effect and Its Application

The internal temperature rise of a high-voltage direct-current (HVDC) cable joint is an essential indicator to reflect its operation status. Based on the thermal characteristic of the cable line and the structural features of the joint, this paper proposes a steady-state thermal circuit model for HVDC cable joints, which takes the heat transfer effect along the axial direction into consideration. The model-based thermal equilibrium equations can be accordingly established, and the detailed solution process is introduced. A 160 kV DC cable joint is taken as a case study to demonstrate the solution and analysis of the steady-state thermal field. It is shown that when the result of this thermal circuit model is compared with the solution of a finite element method (FEM) model, the temperature deviation on each node of the conductor is less than 1 ℃, which testifies the accuracy of the model. The axial temperature distribution characteristic along the central conductor is calculated to show that the temperature is high in the middle of the joint and lowers down to the end, indicating the existence of heat transfer from the joint to the cables on both sides. With the higher load current and ambient temperature, the range of axial heat transfer from the joint becomes wider, and the adiabatic boundary distance is recommended to be 5 m. In addition, a method is proposed on how to deduce the conductor temperature from the surface temperature of the joint. Based on it, the temperature data measured on the joint surface can be effectively utilized to determine the temperature distribution of the central conductor, which is helpful for the evaluation of the joint status and the conductor connector resistance.