The Calculation of Cable Parameters Using Combined Thermal and Electrical Circuit Models

This paper presents a methodology which can be used to calculate underground cable ampacities and other cable parameters. Capabilities of the methodology include the ability to model both thermally and electrically the presence of conductors, shields, and neutrals in an underground cable system. Unbalanced phase currents associated with conductors connected in parallel and shied and neutral currents along with the effects of ground connections are calculated from the electrical circuit model and are used in the thermal analysis of the cable system. Temperature dependent parameters are determined based on calculated system temperatures. Solutions of both the thermal and electrical circuit models are performed in an iterative procedure until convergence based on conductor temperature occurs. Results from this procedure include not only the calculation of thermal parameters, such as cable ampacities and system temperatures, but also electrical parameters, such as cable voltage drops and open-circuited shield voltages.