Comprehensive comparative analysis of Metal-Oxide nanoadditives impacts on Oil-Filled Finemet and Vitroperm alloy core transformers HST concerning nanofluid thermophysical properties accurate estimation

Abstract

In this paper, a precious analysis is dedicated to thermal properties of three metal oxide-based nanofluid samples as well as their overall effects on a 630 kVA oil natural-air natural three-phase transformer thermal performance. The studied nanofluids comprise a typical mineral oil as the transformer base fluid in which Magnetite, Copper Oxide and Alumina nanoparticles are individually dispersed assuming different solid volume fractions. The suspensions are assessed in terms of density, specific heat capacity, thermal conductivity and viscosity. Furthermore, volume fraction- and temperature-dependent formulas, well-matched with the existing experimental data, are proposed to demonstrate excellent correlation coefficients. Subsequently, the derived formulas are utilized as initial functions for transformer thermal modeling. Actually, to pursue the mentioned approach, performing electromagnetic analyses are indispensable. In this regard, making use of two nanocrystalline alloys, namely, Finemet FT-3 M and Vitroperm 500F as core materials can significantly reduce the transformer resultant losses once compared to the case in which conventional electrical steels are utilized. In this study, to represent the enhancements found in the nanofluid filled transformer perfectly, in addition to analysis of the simulation results against those gained using pure mineral oil, one type of natural ester, Midel 1204, is designated as another option for comparison purposes. It is worth mentioning that by increasing the level of nanoparticles volume concentration, a notable decrease can be observed not only in the oil average temperature, but also in the winding hot spot temperature. The investigations are performed for the transformer under different load rates considering the influence of ambient temperature, and the results accuracy are authenticated through making qualitative comparison against the thermal image of a prototype magnetic nanofluid-immersed transformer. Moreover, the system resultant temperatures are verified to exhibit the finest magnitudes in presence of the studied nanofluids, even lower than that of the ester oil with an extremely high thermal conductivity. Finally, the studied fluids and nanofluids Nusselt numbers versus Rayleigh numbers are attained to demonstrate the results fine agreement with the experimental values, as well as presenting satisfactory enhancement in CuO nanofluid Nusselt number compared to mineral oil-based Alumina/Magnetite/Titania nanofluids results.