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The current study addresses the impact of the addition of fullerene and graphene nanoparticles on the AC breakdown voltage (AC BdV) of natural ester (FR3). The nanofluids (NFs) were prepared following the two-step process, and the AC BdV was performed in compliance with IEC 60156 standards. Five different concentrations of NPs were considered (0.1 g/L, 0.2 g/L, 0.3 g/L, 0.4 g/L, and 0.5 g/L). A Student's t-test was performed to compare the base liquid's AC BdV data with different nanofluids. The experimental data were checked to see if they obeyed the Weibull distribution fitting curve, and the AC BdV at 1%, 10%, and 50% risk levels were then calculated. The performed t-test provides evidence that AC BdV data from the base liquid were different from those of different NFs (except 0.2 g/L fullerene, and 0.1 g/L and 0.4 g/L graphene NFs). It is also shown that the Weibull distribution fit the BdV data of all liquids (except 0.5 g/L fullerene NF), and remarkable improvements of AC BdVs at 1%, 10%, and 50% were observed. The best improvement was obtained with 0.4 g/L fullerene and 0.3 g/L graphene NFs. These results show the importance of using nanofluids as substitutes for the existing insulating liquids for current oil-filled power transformers. [ABSTRACT FROM AUTHOR]

This paper is aimed at studying the influence of conducting (Fe3O4), semi-conductive (ZnO), and insulating (ZrO2, SiO2, and Al2O3) nanoparticles (NPs) at various concentrations on the AC dielectric strength of MIDEL 7131 synthetic ester (SE) and partial discharges activity. First, a detailed and improved procedure for preparing nanofluids (NFs) in five concentrations ranging from 0.1 g/L to 0.5 g/L is presented, including high-speed agitation and ultrasonication. Then, the long-term stability is checked based on zeta potential analysis. After preparing and characterizing the NF samples, the following step is to measure their AC breakdown voltage (BDV). Due to the limitation of the high voltage supply (Baur system), the tests are performed according to IEC 60156 standard (2.5 mm gap distance) only with ZnO, ZrO2, and SiO2 NPs, and for comparison, tests are executed for all considered NPs with an electrodes gap of 2 mm. It is shown that the addition of Fe3O4 (20 nm), ZnO (25 nm), ZrO2 (20–30 nm), SiO2 (10–20 nm), Al2O3 (20–30 nm), and Al2O3 (50 nm) NPs improves the dielectric strength of synthetic ester upon an optimal concentration which gives the highest AC BDV. SiO2 (10–20 nm) and Al2O3 (20–30 nm) manifest their best improvement at 0.3 g/L, while for the other NFs, the best improvement is observed at 0.4 g/L. Further, the Anderson–Darling goodness-of-fit test is performed on the experimental data to check their conformity with the Extreme value (EV), normal, and Weibull distributions; the normal and EV fit curves are plotted and used to evaluate the breakdown voltages at probabilities of 1%, 10%, and 50%. It is shown that the AC breakdown voltage outcomes for most investigated nanofluids mostly obey the three EV, normal, and Weibull distributions. Then, the best combinations (nature of NP and optimal concentration), namely Fe3O4 (20 nm, 0.4 g/L), Al2O3 (20–30 nm, 0.3 g/L), and Al2O3 (50 nm, 0.4 g/L) NPs, that highly enhance the AC BDV of SE are chosen for a partial discharge activity investigation and comparison with pure SE. It is shown that the addition of those NPs significantly reduces the activity of partial discharges compared to pure SE. [ABSTRACT FROM AUTHOR]

This paper deals with a comparative study of the electrostatic charging tendency (ECT) of a synthetic oil namely mono/dibenzyltoluene (M/DBT known as Jarylec, a product widely used for impregnating and filling power capacitors; and a mineral oil largely used in high-voltage oil-filled electrical equipment and which is Nynas Nytro Gemini X (NGx). The ECT of insulating oils generated by the charge concentration gradient at the oil-pressboard interface is investigated on a spinning disk system (CIGRE Cell) covered on its both sides with pressboard of different thicknesses versus the rotating speed of the disk and thickness of pressboard. Experimental outcomes show that the ECT of the two investigated liquids is very close at low rotating speeds of the disk that is for 200 and 400 rpm/min. While the ECT of Jarylec is higher than that of mineral oil NGx for higher velocity (600 and 700 rpm/min); the difference increases with the rotating speed of the disk and the thickness of pressboard. However, the observed difference is not so alarming and cannot be exclusive of this synthetic oil for possible use in power transformers provided that it fulfills the other required criteria. [ABSTRACT FROM AUTHOR]

• The date palm mesh fibers have been incorporated into mortar. • The mechanical behavior of the bio-fiber reinforced mortar has been analyzed using 3-point bending tests. • A surface response methodology (SRM) has been developed to optimize the experimental results. • The optimized reinforced mortar provides a 50% increase of the flexural stress compared to the reference configuration. As part of local agricultural date palm waste valorization, this work describes bio-composites made with a cement matrix reinforced with short Mesh date palm fibers for non-structural civil engineering applications. The study focuses in particular on investigating the influence of four parameters on the bending and compression properties of the bio-fiber reinforced mortar: the fiber content, length, NaOH concentration and immersion times of those fibers in the chemical solution. For this purpose, flexural and compression tests have been carried out. An experimental design representing 27 combinations of the above four parameters has been established to minimize the number of experimental trials and build a surface response methodology (SRM) using the design expert software 12 code. The results obtained show that the incorporation of mesh date palm fibers into the mortar improve the mechanical properties of the bio-fiber reinforced mortar. The bending stress of beams with the bio-based reinforcement increases 27.5% compared to the reference configuration; the bending modulus conversely improves by 18.9%. Compression stress and modulus showed increases around 46.6% and 36.3%, respectively. The objective function used to optimize the mechanical properties provides however an increase in bending stress and modulus around 50.0% and 20.0%, respectively, compared to the reference mortar case. The parametric design of the bio-composites that provided the best compression performance was very close to the one identified by the minimum of the objective function. Confirmatory experimental tests results compared to those from the objective function model developed show good agreement, with 3.3% and 3.8% differences for the bending stress and modulus, respectively. [ABSTRACT FROM AUTHOR]