Analytical calculation of the thermal impedance of soil under various boundary conditions and configurations to enhance current ratings of buried power transmission and distribution cable systems

Summary

In order to determine the thermal current rating of energy cable systems with the help of analytic expressions, the temperature field within the soil is mostly calculated by using the equivalent configuration of a line source in front of an isothermal boundary representing the soil surface. Although this approximation is valid for a large number of configurations, other boundary constraints may sometimes be taken into consideration. This concerns the boundary condition on the outer jacket of the cable that can also be modelled by a constant heat flux as well as the convective boundary condition on the soil surface. The article presents the analytical solutions of the temperature field, from which the spectrum of the thermal impedance can be derived, under various boundary constraints for steady state, periodic as well as transient problems.

Additional informations

Keywords

ampacity rating, analytical expressions, thermal impedance of soil, Robin boundary condition