Values Of Electric Strength Research Articles

Influence of nano-oil preparation conditions on its electrical strength

This study presents the results of experiments aimed at determining the breakdown voltage of liquids containing carbon nanotubes and other microinclusions; which were dispersed in mineral insulating oil used in electrical transformers. The liquid was obtained by various methods with the mandatory use of ultrasonic dispersant. The electrical strength of the carbon nanotube-based nano-oil was found to be significantly less than the electrical strength of the zinc and titanium nano-oxide-based nano-oil. At low concentrations the values of electrical strength approximately correspond to the values of electrical strength of pure liquid; but with increasing concentration the electrical strength of all nanofluids decreases. It is shown that the nanofluid preparation technology has a strong influence on its breakdown voltage.

Electrical Strength of Natural Esters Doped by Iron Nanopowder in a Hydrophobic Carbon Shell.

The paper presents the results of measurements of electrical strength of Midel 1204 natural ester doped with iron nanopowder in a hydrophobic carbon shell. The research was conducted for different concentrations of the dopant. The samples were prepared in the High Voltage Technique Laboratory. After mixing, they were tightly closed, and the first measurements were taken after 5 weeks of dissolution of the dopant in liquid. The tests were repeated after another 2 weeks and 3 weeks of dissolution of nanoparticles. An increase in both mean and maximum breakdown voltage was shown for the tested liquid mixtures. The concentration for which the value of electrical strength begins to decrease was indicated. It was also shown that a longer time of dissolution of nanoparticles causes an increase in the electric strength value for the tested samples.

Production of Ti, La, Pb, Cd, Mn, Zr, and Y oxide thin films on complex surfaces of etched aluminum foils for electrolytic capacitors by the pyrolysis method of salts of organic acids

Experimental results of depositions of thin Ti, La, Pb, Cd, Mn, Zr, and Y oxide films on the surface of a 50-μm-thick aluminum foil, used for manufacturing electrolytic capacitors by the pyrolysis method of salts of carboxylic acids, are presented. The obtained samples are characterized by capacitance values of 40 to 240 μF/cm2 and electric strength values in an interval of 0.5 to 2 V, except for Ti oxides, whose samples have an electric strength of 2 to 8 V. The obtained capacitance and electric strength values are close to the values possessed by commercially produced aluminum foils with thicknesses of 70–107 μm having an aluminum oxide dielectric on the surface.

Breakdown strength of solid dielectrics in liquid nitrogen

The objective of this research was to determine if a relationship could be found between dielectric strength and other properties of electrical insulating materials in the medium of liquid nitrogen on an empirical basis by using variables predicted by basic theory. A simple equation of the form E=A+Blog (rhov/xir tandelta) to predict the dielectric strength of a solid insulating material in liquid nitrogen medium has been proposed. The equation requires the values of volume resistivity (rhov), relative permittivity (xir) and loss tangent (tandelta) in the medium of liquid nitrogen, which may be obtained easily by low voltage non-destructive measurements. The values of electric strength calculated using this equation for Crepe paper, Kraft paper, varnished paper, pressboard, presspahn, mica, bakelite and asbestos are quite in agreement with the experimentally measured values. It is expected that the equations obtained will help the designers as a handy tool for quick estimation of breakdown strength of solid dielectrics dipped in liquid nitrogen.

High voltage breakdown studies of sol–gel MgO–ZrO 2 insulation coatings under various pressures at 298 K and 77 K

High voltage breakdown (HV bd) tests were performed to investigate electrical properties of high temperature MgO–ZrO 2 insulation coatings on long-length stainless steel (SS) tapes under various pressures at room temperature (298 K) and liquid nitrogen temperature (77 K) for applications of HTS/LTS coils and magnets. After solutions were prepared from Mg and Zr based precursors, solvent and chelating agent, the coating were fabricated on SS substrates using reel-to-reel sol–gel technique. Coating thicknesses for 4, 8, and 9 dippings were about 7, 12, and 13 μm, respectively, and thickness of epoxy-impregnated samples (stycast 2850 FT/24 LV) were measured to be 32 μm. The pressure from 0 GPa to 0.54 GPa was applied on to test couples, the stycast thicknesses between the layers were varied 32–20 μm. Thickness of the coatings and epoxy-impregnated using stycast were determined by using environmental scanning electron microscopy (ESEM). The resistance, capacitance, and HV bd of the samples were measured by using standard machines HP 439 a high resistance meter, 161 analog digital capacitance meter and model 200–02R high voltage power supply, respectively. Electric strength and dielectric constant were calculated at 298 and 77 K under various pressures. The high HV bd, and electric strength values of the samples were 2.84 kV and 45.91 kV/mm, respectively. ESEM observation revealed that arcing spots in the insulation coatings become larger and deeper for higher HV bd’s.

Sputtered yttrium oxide thin films appropriate for electrochemical sensors

This work deals with Y 2O 3 thin films prepared by r.f. diode sputtering for application in electrochemical sensors. The influence of annealing on selected electrical and mechanical properties of Y 2O 3 thin films has been studied. With increasing annealing temperature the values of electrical strength and electrical resistivity increase, whereas, the values of relative permittivity and Young's modulus decrease. Yttrium oxide films have a polycrystalline structure without cubic structural change caused by annealing. The change from compressive to tensile stresses takes place in Y 2O 3 films with increasing temperature. The properties of Y 2O 3 thin films are comparable with the published data. The Y 2O 3 film was used as an insulation layer in vertically arranged electrodes in a microelectrochemical cell. The redox recycling phenomenon was demonstrated with the redox couple [Fe(CN) 6] 3−/4−.

Dielectric properties of polymers containing dispersed TCNQ salts

AbstractTetracyanoquinodimethane salts have been incorporated into insulating polymers to raise their dielectric constants. Cast films prepared from mixtures of insulating polymers and tetracyanoquinodimethane salts in a solvent show a high dielectric constant (>20). The dielectric constant of the films varies with the tetracyanoquinodimethane salts. High values were attained with the films containing high‐conducting tetracyanoquinodimethane salts. These values remain constant over a range of frequencies (102–104 Hz). Dissipation factors and electric strength values of the films are also reported.

Sample-shape effects in electric-strength measurements on porcelain at power frequency

Various shapes of test sample have been recommended for determining the electric strength of ceramics. The form described by the British Standards Institution (BS 1598: 1949) for a proof test for electric strength would normally be chosen, but this type always fails by surface flashover rather than by puncture through the material. It was therefore decided to compare the electric-strength values obtained from five sample shapes (including a thinner version of the BS sample), all prepared from one batch of h.v. porcelain, produced by the same forming process and fired together. The thickness of the porcelain, the surface finish and the electrode material were varied, but other factors influencing the results were standardised. All samples were inspected for faults visually, by a fluorescent-penetrant method under ultraviolet light, and in some cases by X radiography. The fluorescent-penetrant method was very quick and easily applied, and more successful in detecting flaws than X ray inspection.On the bases of the electric-strength results, their consistencies of determined values, and the ease of manufacture and test procedure, an 80mm-diameter disc with a spherical depression in one face, using fired-on silver electrodes on a ground surface, was found to be most satisfactory.

Influence of the Ambient Medium on the Breakdown Voltage of Sheet Insulating Materials

IT is common experience to find that the values of electric strength of sheet insulating materials are lower when the measurement is made with the material immersed in oil than when the specimen is tested in air. This is usually explained by stating that the voltage for inception of discharge is higher in the liquid because of the higher electric strength of the liquid, so that when discharges do occur in this medium they are more intense and hence more damaging because of the higher voltage-drop across the discharge channel.

The impulse breakdown strength of pyrex glass

Synopsis The electric strengt of Pyrex glass has been measured at temperatures between −50°C and +100°C, using approximately linearly rising impulse voltages of durations between 30 secs and 1 × 10−5 sec. The values of electric strength obtained from successive comparable measurements were within ± 2½% of each other, which is within the limits of the known random error. The high degree of reproducibility obtained in the present investigation is attributed to the technique used for cleaning the surface of the glass before applying electrodes. At the lowest temperature (−50°C) the electric strength was independent of impulse duration between 1 × 10−5 sec and 1.0 sec and amounted to 9.2 MV/cm. With the shortest impulse (1 × 10−5 sec) the electric strength was independent of temperature between −50°C and +100°C and its value was also 9.2 MV/cm. Above −50°C and with impulses of duration greater than 1 × 10−5 sec the electric strength was less than the above value and decreased with both increasing temperature and increasing impulse duration. The constant value of 9.2 MV/cm is very probably the intrinsic electirc strength of Pyrex glass. This value was not influenced by the choice of various electrode materials. The lower values obtained in the present investigation are attributed to space charge distortion of the electric field, caused by the accumulation of ions near to the electrodes. Since the ionic conductivity of Pyrex glass increases with rise in temperature, this effect may be expected to become more and more important as the temperature is raised, or as the impulse duration is increased.

Variation of the Electric Strength of KCl and NaCl Crystals with Temperature

The paper describes measurements of the electric strength of crystals of KCl and NaCl which were made using both d c. and standard 1/50 μsec unidirectional impulse voltages at temperatures between - 74° c and + 140° c. In this range of temperature, which included for both KCl and NaCl a transition from a region in which the electric strength increased with rise in temperature to one in which it decreased, no significant difference was found between values of electric strength obtained using d.c. and corresponding values obtained with impulses. This result contrasts with that of Suita for KCl. It supports qualitatively Frohlich's theory of breakdown.

ELECTRIC STRENGTH OF SOLID DIELECTRICS

IN a paper, by W. G. Standring, of the National Physical Laboratory, which is published in the Power Engineering Section of the Journal of the Institution of Electrical Engineers, of August, a discussion is given of the behaviour of a number of insulating materials under disruptive voltages. Experiments were carried out with the object of filling large gaps in our knowledge in a field which has only been partially explored. At the present time, a knowledge of electric strength is of twofold interest. It is of fundamental importance to the engineer, and values of electric strength should provide guidance to the mathematical physicist in developing theories to explain the mechanism of electric breakdown.

The electric strength of mica and its variation with temperature

The electric strength of mica in air, and the intrinsic electric strength and d.c. conductivity of mica, have been measured over extensive ranges of temperature. The effects of thickness and pre-conditioning on electric strength have also been investigated. The experimental conditions necessary for the determination of intrinsic electric strength are considered and two methods suitable for mica are described. The intrinsic electric-strength values thereby obtained are shown to compare satisfactorily with the predictions of Frohlich's theory of electric breakdown in polar crystals. The relevance of the results to industrial applications of mica is discussed.