Electromagnetic-Thermal Coupled Simulation and Current-Carrying Capacity Evaluation of Medium-Voltage Cables Laid in Duct

Many distribution cables in urban power grids are laid in ducts nowadays. However, due to complex heat dissipation conditions, simplifications have been made in order to establish an analytical algorithm based on equivalent thermal circuit in IEC 60287-2-1: 2023. Engineering experience indicates that these simplifications generally lead to a conservative value of steady-state current-carrying capacity for cables laid in duct. In the paper, the 8.7/10 kV three-core cross-linked polyethylene (XLPE) cables laid in a typical 3×3 duct were taking as the object, an electromagnetic-thermal field model was developed by finite element method to investigate the influences of various factors on cable's thermal field distribution. On this basis, both simulation method based on thermal field and analytical method based on equivalent thermal circuit were applied to calculate steady-state current-carrying capacity of cables laid in duct with various typical configurations. Results of the two methods were compared, reasons for the deviation were analyzed, and the improved analytical algorithm was proposed. Finally, an experimental set up was constructed to simulate actual installation conditions of cables in duct, and steady-state current-carrying capacity levels were evaluated for both single-core and three-core medium-voltage cables. Based on temperature and current data collected from on-site monitoring, accuracy of the improved analytical algorithm was validated. Results indicated that, the improved analytical algorithm proposed in the paper could output more accurate steady-state current-carrying capacity for the cables laid in duct, with a deviation no higher than 5% from both simulation results and experimental data. The algorithm could provide a reliable theoretical basis for the efficient utilization of cable circuits laid in duct, so it could be of significant value for engineering application.