Analysis of the Three-Dimensional Temperature Distribution and Ampacity of Forced Ventilation Multi-loop Cable Tunnel by Finite Element Method

Abstract

Cable tunnel in a multi-loop laying arrangement can improve the underground space utilization. Forced ventilation is an effective measure to increase the ampacity of the cables in such application, ensuring the safe and reliable operation of the cable. However, the commonly used IEC-60287 standard for ampacity computation is an analytical method based on ideal models and simplified conditions without considering the three-dimensional distribution of a physical field. In this respect, this paper establishes a three-dimensional coupled multi-physics field model, and solves the distributions of the temperature field and fluid field in the long-distance cable tunnel based on the finite element method. Also, the paper studies the variation law of the cable temperature field under the forced ventilation and its influence on the ampacity. The results show that in the forced ventilation, the air velocity and temperature are the key factors affecting the ampacity. Higher air velocity is conducive to heat dissipation in the tunnel, effectively increasing the ampacity. The higher the air temperature is, the less heat is dissipated in the tunnel, and the more decreased corresponding ampacity.