Thermal Analysis of Power Transformers Under Geomagnetically Induced Current

Temperature distribution in the power transformers is investigated in this study under Geomagnetically Induced Current (GIC) conditions. Thermal stress can significantly reduce the insulation life, and in the case of excessive hot spot temperature (HST), catastrophic failure of transformers is likely, as happened in the past Geomagnetic Disturbance (GMD) events. Although a few reports emphasize the impact of GIC on the local heating within the transformers, especially in the structural parts, the effect of GIC on the thermal condition of transformers has not been investigated profoundly. This article studies the power transformer HST during the GIC. Since finding stray losses under GIC conditions is challenging, a hybrid approach, including a topological transformer model and 3D finite element method (FEM), is implemented. The detailed topological transformer model is utilized in the EMTP time-domain simulations to determine the harmonic currents at different GIC levels. Additionally, FEM is employed to calculate the temperature distribution within the transformer. The simulation results reveal that the structural parts are saturated with low GIC magnitudes, resulting in high stray losses and local hot spot heating in those areas. Furthermore, the tank can reach high temperatures at mid-GIC levels. These results clearly show that the transformer structural parts are highly vulnerable under severe GIC situations.