This paper is aimed at the variation of AC and lightning impulse (LI) breakdown voltages of samples enriched with fullerene (C 60 ) nanoparticles (NPs) of natural ester, which stand out as an ...alternative to mineral oils. C 60 nanofluids with long-term stability and good dielectric properties are examined in this study on five samples for concentrations of NPs ranging 0.05 to 0.4 g/L concentrations. The AC and LI breakdown voltage measurements of each sample are repeated thirty times and the conformity of these measurements of the normal distribution is tested with the Shapiro-Wilk test. Conformity of all samples to normal distribution is accepted by this test and withstand voltages are calculated at 1%, 10% and 50% breakdown probabilities. The AC breakdown voltage performances of 0.3 and 0.4 g/L C 60 nanofluids are increased compared to natural ester. This increase rate is 5.1% and 7.8%, respectively. The withstand voltages at 1% and 10% breakdown probabilities increase by 20.2% and 13.2% compared to natural ester at 0.4 g/L C 60 nanofluid. 0.1 g/L C 60 nanofluid has 8.2% better performance than natural ester at LI breakdown voltages. Withstand voltages of 1% and 10% probability of this nanofluid are 6.5% and 7.7% higher than natural ester, respectively. These measurement results show that C 60 doped nanofluids can meet performance requirements in power system equipment with high power demands.
In this letter, we report on demonstrating a high performance vertical β-Ga 2 O 3 Schottky barrier diode (SBD) based on a self-aligned beveled fluorine plasma treatment (BFPT) edge termination ...structure. Owing to the strong electronegativity of fluorine ions, the fixed negative charges introduced by F ions during self-aligned BFPT process alleviate the electric field crowding, reduce the reverse leakage current and improve the breakdown voltage up to 1 050V even with a low differential on resistance of 2.5 mΩ·cm 2 , combining with a high Ion/Ioff of 109, a Schottky barrier height of 1.03 eV and a low ideality factor of 1.07-1.11.Without implantation and post annealing, the self-aligned BFPT can serve as a simple, effective and viable edge termination technique to fabricate high performance β-Ga 2 O 3 rectifiers.
In this study, three different insulating liquids, natural ester, mineral oil which is currently used by the Public Power Corporation of Greece and a nanofluid of surface coated Fe3O4 nanoparticles ...into a natural ester matrix, were subjected to AC voltage stress and their statistical breakdown voltage was measured and compared. Three different electrode configurations were used during the measurements in order to study the effect of non-uniform fields on the breakdown voltage distribution. Four different statistical distributions were used for the statistical processing of the experimental results. The two of them were the frequently used normal and Weibull distributions; in addition, Gumbel and generalised extreme value (GEV) function distributions were studied. It was shown that, in most cases, the experimental data followed GEV and Weibull functions rather than normal or Gumbel. Therefore, GEV statistics fits indiscriminately better to the experimental results concerning breakdown voltage, for the three different electrodes configuration and the three understudied insulating oils. The experimental results indicated that nanofluid has better performance, in terms of dielectric breakdown voltage, compared with natural ester oil and mineral oil, hence nanofluid is considered as a potential substitute of the conventional dielectric liquids, with enhanced properties and prospects.
The electrocaloric (EC) effect in ferroelectric materials has been studied extensively to develop materials for solid-state cooling applications. The Na0.5Bi0.5TiO3-based ferroelectric material is ...selected for this particular application. The Ti4+ of the lead-free Na0.5Bi0.5TiO3 is completely replaced by (Mg1/3Nb2/3)4+ to enhance the dielectric breakdown strength and to observe the EC effect. The lead-free Na0.5Bi0.5(Mg1/3Nb2/3)O3 is synthesized via the columbite route with optimized processing conditions. The material shows a frequency-independent high ferroelectric–paraelectric transition temperature (460 °C) with a slim polarization vs electric field loop. The adiabatic temperature change (ΔT) of the compound is evaluated from the temperature-dependent polarization behavior, and calculated ΔT is ≈ 0.135 K at room temperature. The room-temperature EC strength and leakage current of the material are examined to check its suitability for solid-state refrigeration.
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•Na0.5Bi0.5(Mg1/3Nb2/3)O3 shows enhanced breakdown voltage and reduced leakage current.•Polarization property of Na0.5Bi0.5TiO3 and Na0.5Bi0.5(Mg1/3Nb2/3)O3 differs significantly.•This Pb-free ceramic is suitable for solid-state cooling.
The continuous development of electrical systems and high voltage transformers builds the need for looking for new insulating media or to improve the insulating properties of commercially available ...transformer oils (TO) by various modification techniques. One of these techniques is the modification of existing mineral oils by the addition of different types of nanoparticles in various concentrations. These types of materials, suspensions of nanoparticles called nanofluids, have found numerous applications in the energy industry, especially in heat exchanger systems and solar cells. Much research has been done on attempts to replace mineral oils (MO), which are harmful for the environment, with natural ester oils (NE), but to make this possible, it is necessary to improve the insulating properties of these oils, for example by adding nanoparticles. This paper presents an extensive overview of the insulating properties; including for AC, DC and the lightning impulse breakdown voltage; for both mineral and natural ester oils containing various type of nanoparticles (NP). It is presented that the use of nanofluids could improve the efficiency of existing high voltage infrastructures with a low financial cost.
High-voltage vertical Ga 2 O 3 MISFETs are developed employing halide vapor phase epitaxial (HVPE) layers on bulk Ga 2 O 3 (001) substrates. The low charge concentration of ~10 16 cm -3 in the ...n-drift region allows three terminal breakdown voltages to reach up to 1057 V without field plates. The devices operate in the enhancement mode (E-mode) with a threshold voltage of ~1.2-2.2 V, a current ON/OFF ratio of ~10 8 , an ON resistance of ~13-18 mΩ·cm 2 , and an output current of >300 A/cm 2 . This is the first report of high-voltage vertical Ga 2 O 3 transistors with E-mode operation, a significant milestone toward realizing Ga 2 O 3 based power electronics.
A novel superjunction (SJ) lateral double-diffused MOSFET ( >950 V) with a thin layer SOI combining the advantage of low specific on-resistance R on,sp of the SJ and the high breakdown voltage VB of ...the thin SOI is proposed and experimentally demonstrated in this letter. Based on our previously developed equivalent substrate model, the optimized SJ endows the device with a respectably reduced R on,sp without sacrificing V B . Meanwhile, the thin layer SOI is designed with the enhanced dielectric layer field principle to carry out a high V B . The experimental results exhibit a R on,sp of 145 mg·cm 2 with a V B of 977 V. This represents a reduction in R on,sp by 18.1% when compared with the theoretical R on,sp ∝ V B 2.5 "silicon limit".
Introducing nanoparticles to enhance the performance of mineral transformer oil has been considered in many studies recently. Typically, researchers focused on the use of widespread types of ...nanoparticles like aluminum oxide, silicon dioxide, titanium dioxide, etc. However, there is no consensus on which type, or concentration is suitable for this application. In this paper, the authors studied different types of nanoparticles to investigate their effects on the electrical performance of mineral transformer oil with and without the use of surfactants. Design-of-experiments (DOE) approach was adopted to systematically produce oil-based nanoparticles, referred as nanofluids, under different concentrations of nanoparticles and surfactants. With three concentration levels of three nanoparticles, namely zinc iron oxide (ZnFe 2 O 4 ), titanium carbide (TiC), and molybdenum dioxide (MoO 3 ), the nanofluids were produced with three types of surfactants, which were oleic acid (OA), cetyl trimethyl ammonium bromide (CTAB), and polyvinyl alcohol (PA) under three different concentrations. Fifty successive AC breakdown voltage tests were carried out for each sample using mushroom-mushroom cell according to IEC 60156. The results showed the dominance of TiC for two samples with and without surfactants. Additionally, the DOE results showed the importance of concentration of nanoparticles and their types to enhance mineral oil's performance.
•During the operation of high-voltage switches, mechanical and thermal stress occurs.•Conductive/metal particles emerge within the inter-electrode gap.•Influence of the conductive particles on ...dielectric strength were examined.•The results are empirically verified in controlled laboratory conditions.
The aim of this paper is to determine how the shape, number, position and dimensions of the conductive particles produced during switching operations influence the dielectric strength of the gas-filled switches insulated under pressure which are in the state of open contacts. To this end we have developed a numerical program that makes it possible to calculate dc values of the breakdown voltage of bi-electrode gas-filled system in which conductive particles of defined shape and dimensions are present in inter-electrode gap. The calculation results are empirically tested (and verified) in controlled laboratory conditions. Based on the obtained results suggestions are made as to how to extend the life span of gas-insulated circuit breakers using SF6 and N2 mixture instead of pure SF6.
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