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We investigate the deformation and coalescence of two closely spaced drops of conducting liquid suspended in an insulating fluid under the action of an electric field. The equations governing droplets deformation are derived in the case of drops subjected to a potential difference. The critical conditions for existence of a stationary solution are determined for drops anchored on capillary tubes in...
The effect of a dc uniform electric field on the behaviour of bubbles in liquid nitrogen such as their growth, deformation and departure frequency has been experimentally investigated. The experiment was performed using a stainless steel mesh-plate electrode. The experimental results show that (1) prolate spherical bubbles are formed in the direction of electric field and bubble deformation increases...
The problem of instability of a horizontal interface between water and an insulating fluid, electrically influenced by a metallic sphere located just above it, is considered here with its relevance to the basic electrocoalescence phenomenon of close water droplets suspended in an insulating medium. Results are presented of preliminary experiments performed using visualisation and shadowscopy techniques...
For superconducting high voltage devices liquid nitrogen can not only be used as cooling liquid but also for electrical insulation purposes. Under the programme of a 110 kV fault current limiter project the breakdown and withstand voltages of liquid nitrogen are examined in a new cryogenic high voltage test facility named "Fatelini". Target withstand voltages for this new facility itself...
We analyze the AC electro-osmotic motion of a 1:1 aqueous solution, taking into account the difference in mobilities and diffusion coefficients between positive and negative ions. This model serves to understand the behavior of common systems as a solution of NaCl in water. We pay special attention to two cases. First, the case of slightly different mobilities, that can model a KCl solution. Second,...
One of the key component of electrical power distribution networks is transformers, interconnecting between transmission and distribution voltage level or between different networks. Cooling affords a liquid immersed insulation for high power use, thus the insulation of these devices usually consists of mineral oil and cellulose based porous material immersed therewith. Synthetic ester fluids as well...
This paper focuses on the comparative analysis of two different methods for water content estimation in power transformers. The first method under study is the Karl-Fisher coulometric method that measures the water content in oil and correlates it to the water content in paper. Use of four well known correlation curves is compared and discussed in the paper.
This paper presents the development of an electrohydrodynamic conduction micropump using Printed circuit board/liquid crystal polymer MEMS technology. One of the most important parameter for designing this kind of pump is the level of applied voltage. In the last investigations, the distance between high voltage electrode and ground electrode was fixed in few millimeters. In this work, the distance...
Corrosion of copper conductors due to Sulphur in transformer oil is a serious problem affecting both Power and converter transformers. The reactive and corrosive sulphur components are of very low order in fresh transformer oils but during service, some sulphur components are converted to reactive and corrosive forms which react with copper forming copper sulphide. Copper sulphide migrates from conductor...
Breakdown mechanism in water are not well understood. In the present study, we focus both on the ignition and propagation of the plasma in a bubble/water bi-phasic medium, as well as on the sustaining of DC plasmas in a gas bubble. Two geometries are studied : either the bubble is localized in a water filled capillary, or it is surrounded by water. Electrical study, fast CCD imaging, and time resolved...
Electrohydrodynamic (EHD) conduction phenomenon involves the interaction of electric field and flow field in a dielectric fluid medium via the process of dissociation and recombination of free charges. This paper numerically studies the effect of electric conduction phenomenon on the heat transfer characteristics of a Poiseuille flow. The numerical domain consists of six electrode pairs positioned...
Electrorheological (ER) fluids are suspensions of fine particles dispersed in a dielectric liquid. Upon application of an electric field, the solid phase (particles) fibrillates along the field lines between the electrodes. Thus, the rheological properties of the suspension are drastically modified (strongly dependence of the viscosity of the suspension on the applied field strength). To understand...
From viewpoints of low environment impact, palm fatty acid ester oil (PFAE) is potent insulating liquid for power transformers because of its high biodegradation performance. Moreover, PFAE has high permittivity, low viscosity, high thermal and chemical stability and high productivity. These characteristics well satisfy the requirement of electric insulation performance in power transformers. In this...
In this contribution, the different states of water in insulating fluids are presented. It is proposed to separate ldquosolubility limitrdquo and ldquosaturation limitrdquo concepts. It is shown, that confusion of these concepts, results in erroneous interpretation and analysis of the data and, accordingly, in the diagnostic conclusions. The differentiation of water states and consequent analysis...
The inactivation of E.coli and total coli bacteria during pulsed corona discharge in the river water was investigated. The bacterial suspension of volume 157 ml was polluted with E.coli and total coli with concentration of 230 cfu/100 cm3 and 1500 cfu/100 cm3, respectively. The processing was conducted in a tube reactor with hollow needle-to-rod electrode system. The 2 min. of treatment caused decrease...
The corona discharge has been realized close to point electrode under both negative and positive high voltage in normal liquid helium (LHe) at 4.2 K. The experiments have been carried out at constant temperature and for different pressures in a wide range. An intensity of the visible light emitted from the zone closed to tip was enough for its spectroscopic analysis. The shift and width of the spectra...
The supersonic streamer propagation in liquid can be explained by the ionization process in the liquid before the streamer. The strong electric field is required for this process and it is realized due to charge separation in the streamer head. The electric field strength decreases abruptly behind the streamer heard. It leads to electron density decreasing in both the electronegative gases and the...
We have compared three different methods for calculating the ionization potential and electron affinities for typical molecules used in streamer propagation studies. The calculation of the ionization potential is straightforward. The electron affinities are more difficult to calculate and we discuss the reason for these problems.
The preparation of colloidal suspension through a simple method, injection of a small amount of toluene solution of target materials into non-solvent acetonitrile, has been successfully demonstrated for various conjugated polymers such as poly(3-octadecylthiophene), PAT-18. a poly(9,9-dioctylfluorenyl-2,7-yleneethynylene), POFE and poly(2-methoxy-5-(2psila-ethylhexyloxy)- 1,4-phenylene vinylene),...
The complex experimental studies of the discharge mechanism in transformer oil under negative polarity (NP) of the lightning impulse were carried out using alternative diagnostic methods. Novel data concerning propagation mechanism and parameters of the predischarge channels were obtained. The results indicate that oil breakdown both under negative and positive polarity similar in a number of properties...
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