Thermal analysis of mineral oil-based nanofluids of distribution transformers exposed to simultaneous current and voltage harmonics

The exact thermal evaluation of distribution transformers (DTs), which are critical and costly pieces of equipment for the power grids, may contribute to preventing the respective failures. Therefore, the present study non-uniformly investigated DT for correct anticipation of hotspot temperature (HST). Optical fibre sensors (OFSs) were applied for assessing our newly developed non-uniform 3D computational fluid dynamic (CFD)-based modelling while performing the temperature rise test (TRT). It should be noted that this new 3D CFD-based thermal analysis showed an error percentage of 0.11% (0.1°C) in comparison to the OFS measurement, reflecting the ideal efficiency and accuracy of the model. Moreover, thermography for both top-oil temperature (TOT) and bottom-oil temperature (BOT) was employed to validate the results from non-uniform 3D (three-dimensional) CFD-based thermal evaluations. The results indicated an acceptable level of relationship between thermography and thermal analysis of 3D CFD at the specified two spots, with an error percentage of <0.65%, demonstrating the acceptable accuracy of the new non-uniform 3D CFD-based model. In the following, yet importantly, the new non-uniform 3D model was subjected to the total harmonic distortions (THD) for the current and voltage of 5%, 10%, and 15%, which raised the HST more than the original model without harmonics by 3.3°C, 7.1°C, and 10.3°C, respectively. Ultimately, different mineral oil-based nanofluids’, such as multi-walled carbon nanotubes (MWCNTs) and diamond nanoparticles, influence on the HST decrement of DT in simultaneous current and voltage harmonics was investigated.