A comparison between 2-D isothermal region matrix and finite element analysis cable rating methods for water cooled circuits

Electrical power transmission networks may be constructed using many different cable types and each cable route is unique comprising multiple sections, each operating in a different thermal environment. In order to manage the cable assets of this transmission system effectively it is desirable to be able to rate the load capacity of these cables precisely. In order to operate the network, cable ratings are determined using expedient cable rating calculations, typically analytical or one-dimensional finite difference methods. The case for forced cooling is more complex requiring the use of two-dimensional (2-D) isothermal region matrices or finite element analysis (FEA) methods. To attribute confidence limits to cable ratings attained using these methods; ratings for a single-core cable arrangement including the effect of forced cooling are solved by two methods and results are compared. In addition to the typical assumption of an isothermal ground surface boundary, a heat-flux boundary using a model of forced air convection has been investigated using a 2-D FEA model. This shows the isothermal boundary assumption to be optimistic