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Power transformers are inconsiderable group of the electrical appliances with two components insulation system. One of the components - liquid insulating medium plays two roles- insulating and cooling. It can be mineral as well as synthetic based liquid. Second component is an organic based solid insulation usually of cellulose character. Organic materials of this structure are sensitive to an operational...
During the fermentation of an alcoholic beverage, the water/alcohol ratio changes with time, and it is expected that the process can be monitored by the dielectric measurement. We have developed a complex permittivity measurement system of a liquid or gel specimen of 1 mm3 order volume by using a waveguide and a capillary and observed complex permittivity of a Japanese alcoholic beverage sake specimens...
Streamer inception as a function of temperature was studied in pure cyclohexane in needle-plane geometry under impulse voltage with a positive needle electrode. The temperature of the sample volume was regulated to 0, 20, 40 and 60degC, where 0degC is below the freezing point of cyclohexane (6degC). A sensitive differential charge measurement, with sensitivity down to 0.1 pC, and a photomultiplier...
The paper presents the concept of modifying dielectric properties of hydrocarbons by the addition of C60 fullerenes. Streaming electrification current of pure and C60-doped toluene was examined using rotating electrometer constructed by authors of this work. The influence of C60 addition on electrification current was determined.
Analyzing of ionic mediums conductivity to explain an appearing of charge density was made by previous authors. Other papers give according methods, programs and results. There is a large difference between dielectric liquids (with low conductivity), quasi-neutral plasma and other mediums with strong ionic conductivity. Charge density in dielectric liquids has an important role for a conductivity...
Relative dielectric constant and dissipation factor (tandelta) values as a function of frequency have been measured for a variety of water types. The effect of water absorption on the permittivity properties of crystalline powders or nanopowders when exposed to various humidity levels is also examined. Powdered materials were characterized by XRD and were calcite (CaCO3), anatase, rutile (TiO2), gamma...
This paper deals with two-dimensional EHD flow occurring between a blade and a plate electrode a distance H apart. This type of EHD flow, known as electro-hydrodynamic plumes, arises when sharp metallic contours submerged in non conducting liquids support high electrostatic potential resulting in charge injection. The aim of this paper is to analyze, from a numerical point of view, the evolution of...
Pulsed positive streamers in water were investigated in the needle-to-plate electrode configuration with an electrode gap of 20 mm. The characteristics of streamer and its propagation in water were observed with the use of an ICCD camera. The ICCD camera images showed clearly streamers with a few streamer branches having their channel diameters of ~250 mum. The images also showed that the streamers...
The paper deals with the electrophysical principles of the method of electrogas- and electro-hydrodynamic conversion of electric signals to pneumatic (hydraulic) signals and vice versa using corona discharge for the control of gas and liquid volumes, flows and jets of working media in electropneumohydraulic systems, including problems of formulating requirements for the working media and electric...
This paper continues the description commenced of generalized results of the research work [1-9] of the method of electrogas- and electro-hydrodynamic conversion of electric signals to pneumatic (hydraulic) signals and vice versa using corona discharge for the control of gas and liquid drops, volumes and flows of working media in electropneumohydraulic systems. Obtained is a formula for the initial...
As a part of a research program at EDF, University of Poitiers has developed a prototype of a sensor dedicated to the monitoring of oil flow electrification through transformer pressboard-made channels. This phenomenon can be responsible for destructive breakdowns when the resulting charge accumulation leads to high electrical fields. In order to identify transformers running electrostatic hazards,...
Electrohydrodynamic effects on bubble motion in dielectric fluids has found positive application for enhanced boiling heat transfer, for example in refrigerators. However the motion of bubbles in columns of dielectric fluid is also of interest where the presence of bubbles may adversely affect the breakdown performance of the liquid dielectric when employed as an electrical insulation. This is the...
A wall jet is a flow which is particularly interesting from both practical and theoretical points of view. Most of the times it is used to inject turbulence and shear stress into a flow directed along a wall. In the most frequent engineering applications (cooling or heating surfaces, atomization of fluids, etc ...) the turbulence structure in the vicinity of the surface of the wall is a "key...
A detailed review of progress-to-date in the field of electrohydrodynamic (EHD) conduction pumping is presented. Analytical, numerical, and experimental research studies that have been published in this field are summarized and a detailed scientific overview of the conduction pumping model is provided. Applications are also presented in which conduction pumping has been investigated successfully to...
The purpose of this work is to evaluate the chemical stability of a bio-degradable insulating oil composed by a mixture of esters based on rape-seed oil. The measurements are done in comparison with a commercial mineral oil. Both oils are subjected to accelerated ageing conditions at 120degC under air (open beaker method). Dielectric properties (dissipation factor, permittivity, conductivity, AC breakdown...
In recent years, the use of vegetable-based oils for electrical insulation has been considered, in particular to replace mineral oil in medium voltage system. Up to now, little attention has been paid to the properties of these liquids under high voltage at large gaps, that should be important for their application in very high voltage systems. This paper reports an investigation about discharge propagation...
The problem of a high-voltage applied to a wedge-shaped oil gap in power transformers is considered as far as induced distortions and tangential electric stresses are concerned. Near-tip distortions and electric stress concentration occur due to the essentially difference in the relative permittivity between the insulating oil and the pressboard. When the magnitude of tangential electric stress intensity...
The combination of a solid and a liquid insulation is the most frequently used insulating system in high voltage apparatus, where components have to be insulated and loss heat has to be dissipated. The requirements on the liquid part of the insulating system are not only the electric and dielectric performance but also the performance regarding environmental requirements and dehydration capability...
This paper presents an experimental study of pre-breakdown discharges in water (usually called ldquostreamersrdquo) and transient breakdown arcs (called ldquosparksrdquo) generated by high voltage pulses, in relation with their potential application to degrade organic molecules for depollution purposes. An experimental set-up is described using semiconductor high voltage switches to produce high voltage...
The initial stage of prebreakdown cathode processes was studied with the help of Schlieren method and electrooptical Kerr effect, with laser light exposure of ap 3 nanosecond. Experiments were performed by using triangular voltage pulses with time rise of ap 1 mus, time decay of ap 0.1 mus and total width of ap 2 mus. Interelectrode gap was 3 - 5 mm with electrode diameter of 50 mm. Field intensity...
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