A Novel Dynamic Ampacity Assessment Method for Direct Burial Cables Based on an Electro-Thermal-Fluid Multiphysics Coupling Model

Traditional ampacity evaluation methods for direct burial cables, like the correction factor method and the IEC 60287 analytical method, suffer from large calculation errors when dealing with complex installation environments. This paper investigated the influence of multiple environmental factors and proximity effects on the ampacity of 35 kV YJLV22-26/35 3 × 400 mm² direct burial cables using an electro-thermal-fluid coupling FEM model. The results indicate that when accounting for surface temperature and burial depth, the correction factor method may overestimate ampacity by up to 7%, while the analytical method may underestimate it by up to 24%. When soil thermal resistance variations are considered, the correction factor method could overestimate ampacity by 14%, whereas the analytical method may underestimate it by 10%. Due to neglecting solar radiation and air convection effects, these two methods can introduce calculation errors of 23% and 34%, respectively. The ampacity of multi-circuit parallel configurations increases with greater circuit spacing. Based on FEM simulation results, a new dynamic ampacity evaluation method has been proposed that comprehensively considers multiple environmental variables including ambient temperature, burial depth, soil thermal resistivity, solar radiation intensity, wind speed, the number of parallel circuits, and circuit spacing. This method can be directly applied to guide engineering design.