Electromagnetic simulations were performed by Simtec to assess the magnetic coupling between parallel connected cables carrying 60Hz AC. These cables connect inverters to transformers in a Photovoltaic Power Station in Brazil. The setup consists of 3 pipes, buried underground, hosting 4 same-phase and parallel connected stranded cables. Moreover, Simtec explored other setups where each pipe hosted cables of different phases. The cables’ current forms a magnetic field and due to the random positioning and distance between them in the same pipe, the magnetic field B is uneven and non–uniform. This scenario leads to uneven ohmic resistance and self and mutual impedance between the cables, resulting to unbalanced current distribution. This phenomenon is undesired because it may lead to unwanted rising of temperature. The cases where each pipe hosted cables of different phases resulted to lower current unbalancing.
The thermal loads were calculated in Ansys Maxwell for the largest possible heat, corresponding to the PV plant working on full electric load for the whole day. The results were imported into Ansys Mechanical for a geometry domain, that included the soil at a depth of 40m. The temperature of a sunny day is constantly imposed at the ground level, while a realistic temperature is set for the soil. These exaggerated conditions are kept for the rest of the simulated scenario, to account for a worst possible scenario for the temperature of the cables. The transient simulation ran for 50 operating years, to find out that an ending temperature had been reached after 5. The resulted temperature is much smaller than the melting point of the cable, demonstrating that there is no melting hazard for the cables.
Ansys tools: Ansys DesignModeler, Ansys Maxwell, Ansys Mechanical