Liquid dielectric

About: Liquid dielectric is a research topic. Over the lifetime, 3702 publications have been published within this topic receiving 45150 citations.

AC breakdown voltage of natural ester mixed with Iron Oxide for oil-immersed power transformer application

Abstract: Nowadays, nanoscale materials are increasingly popular in academic and industrial research. It is expected that the combination of nanoscale materials with other material can contribute more benefits. The use of nanoscale materials often require their dispersion in variety of liquids, to enable them to become part of the liquid product, also known as nanofluids. For example, one of the applications is the nanoparticles dispersed with transformer oil in oil-immersed transformer application. Traditionally, mineral oil is used as dielectric liquid and cooling medium in power transformer. In this paper, dielectric strength of ester oil when mixed with nanoparticles is investigated. For that purpose, AC breakdown voltage test is compliance with ASTM D1816 standard is performed. Statistical analysis and high dimension visualization have been done to analyse and compare the result between fresh ester oil taken from tank and the similar ester oil that mixed with nanoparticles. The results suggest that ester oil mixed with nanoparticles of 0.02 % by volume performs well compared to other samples.

Electrical apparatus having an improved liquid dielectric composition

Abstract: A dielectric liquid composition for use in an electrical apparatus, such as a transformer. The dielectric composition is composed of 10% to 90% by weight of one or more hydrocarbon oils having a molecular weight distribution peak in the range of 460 to 720, and the balance being a polyalphaolefin having a molecular weight distribution peak of 320 to 600. The dielectric liquid composition has a fire point above 300° C., a pour point at least as low as -20° C., and is thermally stable and essentially biodegradable.

Highly Efficient Electrohydrodynamic Pumping: Molecular Isomer Effect of Dielectric Liquids, and Surface States of Electrodes

Abstract: Highly efficient electrohydrodynamic (EHD) pumping was obtained by a combination of a dielectric liquid having a molecular isomer and electrodes with a smooth surface. Four kinds of surface states of Cu electrodes were processed by conventional mechanical polishing, fine diamond paste polishing, chemical etching and Au vapor deposition. A series of hydrofluoroether liquids (HFEs) were used as dielectric liquids: C3F7OCH3 (HFE-7000), C4F9OCH3 (HFE-7100), C4F9OC2H5 (HFE-7200), C6F13OCH3 (HFE-7300), and C5H5F6OC3HF6 (HFE-7600). The coexistence of normal (n-) and isomer (i-) HFEs and their molar fractions were examined by NMR spectroscopy. Among the dielectric liquids, the hybrid n- and i-HFE-7600 showed highly efficient EHD pumping, where the electric current, I, was sufficiently suppressed by the smooth surface of the electrodes. The maximum hydrostatic pressure Δpmax was ∼7500 Pa with 12 kV and I = 19 μA. The smooth surface of the electrodes contributes not only to the formation of a stable electric double layer (EDL) but also to the prevention of charge injection from the electrodes. Polarization pumping derived from the stable EDL enables highly efficient energy transfer without discharging, or damage to the sample and electrodes. The dipole moments of the HFEs were estimated by density functional theory calculations. The hydrostatic pressure was found to be proportional to the difference in the calculated dipole moment between n- and i-HFEs. Numerical simulations were carried out to examine the experimentally obtained electrode gap dependence of the hydrostatic pressure.

Sustainable Machining of Hastelloy in EDM Using Nanoparticle-Infused Biodegradable Dielectric Fluid

Abstract: Electrical discharge machining (EDM) is the unconventional machining technique used extensively for machining difficult-to-machine materials with lower material removal rate and poor surface roughness. To overcome these drawbacks, synthetic dielectric fluid is replaced with nanoparticle-infused biodegradable dielectric fluid in the machining of Hastelloy material. This paper focusses on the machining performances of Hastelloy in EDM using various concentrations of 0.5, 1 and 1.5 wt% of nano-zirconia dispersed in biodegradable canola oil methyl ester as the dielectric medium, and these characteristics were compared with those of the synthetic dielectric medium. Based on the D-optimal design coupled with cuckoo search algorithm, machining was carried out with various dielectric fluids and their influences on the metal removal rate, surface roughness, surface morphology and surface topography in EDM studied. The results proved that the canola oil methyl ester containing 0.5 wt% of nano-zirconia (C-0.5) had provided good surface finish, better surface topography, smooth surface morphology and high metal removal rate in comparison with the other dielectric fluids used in this study.

Pre-breakdown mechanisms in dielectric liquids and predicting models

Abstract: This paper presents a synthetic review of the state of knowledge relative to the pre-breakdown phenomena in dielectric liquids and especially the initiation and propagation of streamer/discharge and their characteristic parameters. The main influencing parameters namely the structure, stopping length, velecity and propagation modes of streamers, current, charge and associated emitted light are developed. These parameters include especially the chemical composition of the liquid (pure or containing specific additives); the applied voltage; the electrode arrangement; the temperature and the hydrostatic pressure. The mechanisms involving in the inception and propagation of streamers are discussed. Recent models enabling to predict the type of streamers that can be initiated and their characteristics when propagating within liquid, are also presented and discussed. It is shown through the experiments and modeling that the pre-breakdown phenomena in dielectric liquids are governed by both electronic and gaseous mechanisms even if one of them is dominant in one case and the second in another.