A Technique for Assessment of Thermal Condition and Current Rating of Underground Power Cables Installed in Duct Banks

For reliable operation of underground power cables, it has been a common practice that power utilities mount thermal sensors on cable surface to directly monitor their thermal condition. This method could not be applied readily to those cables installed in duct banks due to the inconvenience in mounting sensors on cable surface. Alternatively, sensors have to be mounted outside the duct banks. In this paper, a technique is developed to assess the cable insulation thermal condition through estimation of soil thermal parameters, which is performed by matching the computed temperature to that measured with sensors. The matching process involves two methods: the finite element method (FEM) and a gradient-based optimization method. With the estimated soil parameters, the cable temperature could be computed by the FEM such that the assessment of thermal condition could be achieved indirectly from the temperature recorded with sensors mounted some distance away from the cables. Network application proves its effectiveness in accurate assessment of thermal condition of three underground cable circuits installed in three duct banks entering a 230kV substation.