Temperature field and ampacity calculation of cable buried in local conduit using 3D finite element method

There is an air layer between external diameter of power cables and inner diameter of conduit, and heat transfer of air is a coupling process of air natural convection, air conduction, and radiation. Consequently, heat transfer of power cables and soil can be described by heat conduction equations. The heat transfer of air in conduit can be described by momentum conservation equation, energy equation and continuity equation, and the heat transfer between fluid and solid can be solved by iteration method. Thereby, the 3D finite element method (FEM) and vorticity-stream function are used to solve the coupling equations of fluid structure interaction, moreover, the temperature distribution of underground power cables in local segment of conduit can be calculated. Thus, the hottest point of power cables is found, and the ampacity of power cables is obtained by iteration method. The result shows that the ampacity of underground power cables in local segments of conduit is lower than power cables all directly buried in underground.