Calculation of thermal capacity of underground cables in multicircuit systems

An alternative for the calculation of thermal capacity of underground multicircuit transmission systems is proposed in this paper. The method used for this purpose is based on the calculation of the temperature developed in each component of the cable in the multicircuit system during a certain period of time. The load cycle associated to the cable system is known during this period of time. This method also takes into account the thermal transients suffered by power cables stressed to variable load cycles. The calculation of the temperature is done by means of thermal equivalent models of the phenomenon. In these models, different thermal parameters of the cables and trenches, thermal sources of each cable, and the effect between cables of the same circuit and cables of adjacent circuits located on the same trench are considered. The method mentioned considers the solving of numerical integration of differential equations associated to the thermal circuits and the multiconductor electric circuit, in order to determine the loses due to circular currents. In this manner, it is possible to include different types of cable (e.g. single-pole and three-pole cables. Pipe-Type cables, etc.) and grounding settings metallic shields and armors. The application of the method in a real life case is also exposed; the potential of the developed tool is also demonstrated.