Harmonics impact on hotspot temperature increment of distribution transformers: Nonuniform magnetic-thermal approach

Since insulation condition and hotspot temperature (HST) are strongly correlated, accurate thermal evaluation of distribution transformers, an expensive and critical piece of equipment for the power grid, can help to avoid failure. In this research, distribution transformer is nonuniformly studied for accurate HST prediction. The distribution transformer has been treated as the 2D axial symmetry with nonuniform losses for the magnetic analysis. The distribution transformer is accurately represented in 3D for the thermal analysis. Optical fiber sensors (OFSs) are used to assess the suggested nonuniform 3D CFD-based modelling throughout the temperature rise test (TRT). Thus, the suggested 3D CFD-based thermal analysis has an error percentage of 0.11 % (0.1 °C) when comparing to OFSs measurements, demonstrating the model's excellent accuracy and efficiency. The nonuniform 3D CFD-based thermal assessments’ findings are validated using thermography for both top-oil temperature (TOT) and bottom-oil temperature (BOT). Thus, the obtained findings show that there is good agreement between thermography and 3D CFD-based thermal analysis at the stated 2 spots. As a result, the error percentage is less than 0.65 %, showing that suggested nonuniform 3D CFD-based model suggested is accurate. Last but not least, the proposed nonuniform 3D model is exposed to total harmonic distortions (THD) for the current of 5 %, 10 %, 15 %, 18.3 %, and 51.9 %, respectively, raising the HST above the original model without harmonics by 2.8 °C, 6.1 °C, 8.9 °C, 12.9 °C, and 46.4 °C.