Heat and Moisture Coupling for HVAC Tunnel Cable

The ampacity of tunnel cable is heavily dependent on the capacity to diffuse heat into surrounding air. This ability is significantly influenced by wet conditions. Based on the finite element method (FEM), a 3D model of high voltage alternating current (HVAC) tunnel cable is developed, coupling heat and moisture transfer. The thermal properties of air are changing with relative humidity and temperature. Latent heat of evaporation is included. Thermal analysis is conducted by recording the cable maximum temperature as a function of time and relative humidity. Temperature gradient exists not only radially, but also circumferentially and longitudinally.