Abstract
Mineral oil has been chosen as an insulating liquid in power transformers due to its superior characteristics, such as being an effective insulation medium and a great cooling agent. Meanwhile, the performance of mineral oil as an insulation liquid can be further enhanced by dispersing nanoparticles into the mineral oil, and this composition is called nanofluids. However, the incorporation of nanoparticles into the mineral oil conventionally causes the nanoparticles to agglomerate and settle as sediment in the base fluid, thereby limiting the improvement of the insulation properties. In addition, limited studies have been reported for the transformer oil as a base fluid using Aluminum Oxide (Al2O3) as nanoparticles. Hence, this paper reported an experimental study to investigate the significant role of cold plasma treatment in modifying and treating the surface of nano-alumina to obtain a better interaction between the nano-alumina and the base fluid, consequently improving the insulation characteristics such as breakdown voltage, partial discharge characteristics, thermal conductivity, and viscosity of the nanofluids. The plasma treatment process was conducted on the surface of nano-alumina under atmospheric pressure plasma by using the dielectric barrier discharge concept. The breakdown strength and partial discharge characteristics of the nanofluids were measured according to IEC 60156 and IEC 60270 standards, respectively. In contrast, the viscosity and thermal conductivity of the nanofluids were determined using Brookfield DV-II + Pro Automated viscometer and Decagon KD2-Pro conductivity meter, respectively. The results indicate that the 0.1 wt% of plasma-treated alumina nanofluids has shown the most comprehensive improvements in electrical properties, dispersion stability, and thermal properties. Therefore, the plasma treatment has improved the nanoparticles dispersion and stability in nanofluids by providing stronger interactions between the mineral oil and the nanoparticles.
Highlights
Since 1892, mineral oil has been used as an insulation medium due to its excellent insulating properties and has effectively served as a dielectric coolant [1]
The electrical insulation properties such as partial discharge and breakdown strength were enhanced by incorporating the nanoparticles into the base fluids. This has been proven by numerous studies conducted, such as Jin et al [11] that investigated the properties of mineral oil-based silica nanofluids, and the results showed that the addition of SiO2 nanoparticles had improved the alternating current (AC) breakdown voltage of the mineral oil
Samples, the untreated and plasma-treated nanofluids show an average partial discharge (PD) magnitude of about 177 pC and 176 pC, respectively. These results demonstrate that the addition of alumina nanoparticles into the mineral oil would certainly enhance its PD characteristics, as revealed by Muangpratoom et al [37], Mohamad et al [38], and Jacob et al [39]
Summary
Since 1892, mineral oil has been used as an insulation medium due to its excellent insulating properties and has effectively served as a dielectric coolant [1]. One of the reasons that mineral oils have been chosen as a transformer oil is the ability to transfer heat more effectively than solid-based insulating materials, where solid insulations typically have issues, such as containing void impurities and poor thermal conductivity. Mineral oil has improved self-healing after failure, making it suitable for power transformer insulation [2]. Ahmadi et al [4] conducted a comprehensive study to compare various machine learning approaches in modeling the dynamic viscosity of nanofluid. The new approach of enhanced artificial neural network (EANN) was developed by Bagherzadeh et al [5] to predict the thermal conductivity of hybrid nanofluids. Peng et al [6] highlighted that the artificial neural network might estimate the nanofluid thermal conductivity with high accuracy
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