The dissipation of heat was studied for the underground cables of a Photovoltaic Power Station for BIOSAR SA in Oakey, Australia. These cables connect the Photovoltaic (PV) solar panels with the inverter and are subjected to thermal loads caused by ohmic losses and the solar radiation. The cables are arranged in parallel routes inside trenches filled with sand, that has higher thermal conductivity than the soil. To examine the risk of melting, an Electrical and the associated Thermal Analysis were performed for these cables. The study employed the special coupled finite element technology of Ansys Mechanical, to account for both the mechanical and electrical forces.
The geometry of the cables was created from scratch in Ansys DesignModeler and the exact stratification of soils, the concrete base of the inverter and the protective plastic pipes were transferred in the model. The sheath, insulation and conductors of each cable were simplified into a solid conductor and these assumptions were validated to ensure that both electric and thermal fields are properly solved. The heat transfer by thermal conduction, convection and radiation were simulated for a soil depth up to 11m. Finally, the solar radiation loads were averaged for the whole day, while the ohmic loads are kept constant and corresponding to uninterrupted plant production. Although this was the worst-case scenario (and also unachievable), the design was confirmed to protect the cables from melting.
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