Estimation of soil thermal parameters from surface temperature of underground cables and prediction of cable rating

Distributed temperature sensing (DTS) systems have been installed by power utilities on underground cables to monitor in real time the cable surface temperature for reliable and cost-effective operation of cables. However, full use of advanced DTS depends on the solution of two problems. One is to determine the conductor temperature from the measured surface temperature, and the other is to predict the maximum allowable carrying currents under emergency overloading conditions. A technique for solving these two problems is developed, the basic principle of which is based on estimation of the soil thermal parameters by matching the computed thermal field to that obtained from measurements. The technique developed makes use of two basic methods -the finite-element method and a gradient-based optimisation method. Laboratory tests were carried out to verify this technique.