Factors affecting the water droplet behavior on mica sheets under the influence of homogeneous electric fields
TL;DR: In this article, the behavior of water droplets on mica sheets under the influence of uniform electric fields was investigated, and various factors affecting the behavior were investigated, including surface discharges.
Abstract: Mica sheets are an important component of electrical machine insulation. Although great attention was given to partial discharges and related aspects of such an insulation, relatively little attention was paid to surface discharges. This paper investigates various factors affecting the behavior of water droplets on mica sheets under the influence of uniform electric fields.
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TL;DR: In this article, the dielectric constants and loss angles of a series of concentrated aqueous ionic solutions have been measured at wave lengths of 10 cm, 3 cm, and 1.25 cm.
Abstract: The dielectric constants and loss angles of a series of concentrated aqueous ionic solutions have been measured at wave‐lengths of 10 cm, 3 cm, and 1.25 cm. From these results the values of the static dielectric constant and relaxation time for these solutions have been calculated on the basis of the Debye formula, which appears to hold accurately. All salts show a lowering of the dielectric constant and a shift in the relaxation time of water. It is found that the dielectric constant e can be represented by a formula e=eω+2δc, where eω is the dielectric constant of water, c is the concentration in moles per liter, and δ has values between −7 and −15 for various salts in concentrations of up to 2 M.In Part I the measurements are described and the results discussed in relation to the structure of ionic solutions. In Part II the validity of the Debye‐Sack saturation theory of the dielectric constant and the effects of the fall of dielectric constant on the electrolytic properties of concentrated solutions ...
617 citations
"Factors affecting the water droplet..." refers background in this paper
...more NaCl in the droplet) implies lower dielectric constant of the water droplet [7-9]....
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TL;DR: In this paper, all reliable sources of data for the static dielectric constant or relative permittivity of water and steam, many of them unpublished or inaccessible, have been collected, evaluated, corrected when required, and converted to the ITS•90 temperature scale.
Abstract: All reliable sources of data for the static dielectric constant or relative permittivity of water and steam, many of them unpublished or inaccessible, have been collected, evaluated, corrected when required, and converted to the ITS‐90 temperature scale. The data extend over a temperature range from 238 to 873 K and over a pressure range from 0.1 MPa up to 1189 MPa. The evaluative part of this work includes a review of the different types of measurement techniques, and the corrections for frequency dependence due to the impedance of circuit components, and to electrode polarization. It also includes a detailed assessment of the uncertainty of each particular data source, as compared to other sources in the same range of pressure and temperature. Both the raw and the corrected data have been tabulated, and are also available on diskette. A comprehensive list of references to the literature is included.
256 citations
"Factors affecting the water droplet..." refers background in this paper
...more NaCl in the droplet) implies lower dielectric constant of the water droplet [7-9]....
[...]
Posted Content•
TL;DR: In this article, the authors studied the dependence of the static dielectric constant of aqueous electrolyte solutions upon the concentration of salt in the solution and temperature, and showed that the formation of ion pairs by a small fraction of disassociated ions can have a significant effect on the static Dielectric constants.
Abstract: We study the dependence of the static dielectric constant of aqueous electrolyte solutions upon the concentration of salt in the solution and temperature. The model takes into account the orientation of the solvent dipoles due to the electric field created by ions, the ionic response to an applied field, and the effect of thermal fluctuations. The analysis suggests that the formation of ion pairs by a small fraction of disassociated ions can have a significant effect on the static dielectric constant. The model predicts the dielectric has the functional dependence $\varepsilon(c)=\varepsilon_w-\beta L(3\alpha c/\beta)$ where $L$ is the Langevin function, $c$ is the salt concentration, $\varepsilon_w$ is the dielectric of the pure water, $\alpha$ is the total excess polarization of the ions and $\beta$ is the relative difference between the water dipole moment and the effective dipole moment of ion pairs as weighted by the density of ion pairs and their structural rigidity. The functional form gives an extremely accurate prediction of the dielectric constant for a variety of salts and a wide range of concentrations by fitting only the parameter $\beta$.
160 citations
08 Jul 1991
TL;DR: In this paper, the surface free energies due to London dispersion and hydrogen bonding forces on the surface of RTV coatings were calculated from the contact angle measurements using both water and methylene iodide.
Abstract: Room temperature vulcanizing (RTV) silicone rubber coatings are applied to electrical insulators to improve their subsequent insulation strength, particularly under wet conditions. Under prolonged wetting the hydrophobicity of the coating is reduced temporarily and the insulator protection is lost. After a dry period, a recovery of the hydrophobicity takes place. To investigate this phenomenon, the surface was subjected to various wetting conditions with and without electrical stress. Measurements of the contact and the sliding angles were used to determine the state of the surface. Using water, the surface free energy of the RTV was calculated from the contact angle measurements as a function of time of exposing the surface to salt-fog. The surface free energies due to London dispersion and hydrogen bonding forces on the surface of RTV coatings were calculated from the contact angle measurements using both water and methylene iodide. Good agreement was obtained with the literature value for a virgin RTV surface. The chemical changes of the surface are shown to be responsible for the loss of hydrophobicity. >
127 citations
TL;DR: In this article, the performance of silicone and EPDM rubber composite insulators was investigated in a long-term outdoor test with high direct and alternating voltages, and the results showed that the difference in performance were related to the differences in the surface structural changes and in the dynamic ability of the surface to compensate the aging.
Abstract: In a long-term outdoor test with high direct and alternating voltages, silicone and ethylene propylene diene monomer (EPDM) rubber composite insulators have, at the beginning, shown a performance superior to that of glass and porcelain insulators. In the long-term test, however, the silicone rubber composite insulator has, in spite of the aging of both insulator types, kept its good performance, while the performance of the EPDM rubber composite insulator was drastically deteriorated. In order to get a better insight into the results obtained, the wettability and the surface structural changes of the insulators were studied by the drop deposition method using a goniometer and by advanced techniques such as scanning electron microscopy, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and secondary ion mass spectrometry. The results show that the differences in performance are related to the differences in the surface structural changes and in the dynamic ability of the surface to compensate the aging. Silicone rubber insulators have higher repellency than the EPDM insulators, especially when aged. The reason seems to be low silicone polymer diffusion from the bulk which covers the insulator surface, embeds the pollutants, and keeps the surface hydrophobic. Porcelain insulators with silicone elastomer coatings show lower water repellency than insulators with massive silicone rubber sheds. When aged, EPDM insulators do not, however, seen to possess the same dynamic recovery of their surface, thus becoming hydrophilic. >
126 citations