Numerical calculation of ampacity of cable laying in ventilation tunnel based on coupled fields as well as the analysis on relevant factors

Forced ventilation of cable tunnel is one of the important ways to improve the cable ampacity which is one of important parameters to guarantee safe and reliable operation of underground cable system. According to the theory of fluid dynamics and heat transfer, the 3-D physical and mathematical models of cable tunnel ventilation system for fluid and temperature analysis were established, which were calculated numerically by using finite element method, based on some corresponding assumptions, control equations and boundary conditions. In this process, the fluid field distribution inside axial ventilation tunnel and temperature field distribution were calculated and analyzed, and the strong coupling relationship between fluid field and temperature field was proved. Based on the highest temperature of cable surface calculated above, cable ampacity was computed by using equivalent thermal circuit method and numerical iterative method. Moreover, some influences on cable ampacity were analyzed, and some valuable conclusions were obtained.