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

Internal temperature rise of high voltage direct current (HVDC) cable joint is essential indicator to reflect its operation status. Based on thermal characteristic of cable line and structural features of joints, steady-state thermal circuit mode of HVDC cable joints considering axial heat transfer effect was proposed. Model-based thermal equilibrium equations were established, and detailed solution process was introduced. ±160 kV DC cable joint was taken as a case to demonstrate the solution and analysis of steady-state thermal field. Results showed that the deviation between calculation data of thermal circuit model and solution of finite element method (FEM) model was small, temperature deviation on each conductor node was less than 1 ℃, which testified the sufficient accuracy of thermal circuit model. Axial temperature distribution characteristic along the central conductor was calculated to show that temperature was higher in the middle of joint and lowers down to the end, indicating the existence of heat transfer from joint to cables on both sides. With the higher load current and ambient temperature, the range of axial heat transfer from the joint becomed wider, and the adiabatic boundary distance was recommended to be 5 m. In addition, a method was proposed on how to deduce conductor temperature from surface temperature of the joint. Based on it, temperature data measured on the joint surface could be effectively utilized to determine temperature distribution of the central conductor, which was helpful for the evaluation of joint status and conductor connector resistance.