Dynamic Thermal Model for Different Size Trefoil Power Cables with Various Loads in Non-Forced-Ventilated Tunnels

This paper presents a dynamic thermal model for trefoil cables of different sizes (and/or loads) installed in non-forced-ventilated tunnels. This is a step forward from the available calculations that only treat identical and equally loaded cables in steady-state. The circuit model includes heat transfer into all tunnel wall surfaces. Results demonstrate that conductor temperature is independent of tunnel size beyond three cable diameters for engineering purposes. This paper also demonstrates that for non-forced-ventilated tunnels, different from cables installed in free air, the induced heating from cables installed below other cables is negligible for all practical purposes. A dynamic equivalent thermal circuit is proposed. The model is validated with numerous finite element transient simulations. All results are within small percent differences. Transient ratings for general cable arrangements installed in non-forced-ventilated tunnels can be computed with the methods proposed in this paper.