Showing papers on "Liquid dielectric published in 1971"

A Statistical Approach to the Discussion of the Dielectric Strength in Electric Cables

Abstract: The application of statistical methods to the field of cable dielectric strength is discussed on the basis of experimental results.

Dielectric Recovery and Shield-Currents in Vacuum-Arc Interrupters

Abstract: Dielectric recovery data is presented following forced current interruption of 930 A dc copper vapor arcs in a vacuum interrupter. At given free recovery periods during the first 6 to 25 , us following interruption, the instantaneous dielectric strength is determined by the application of high voltage step function pulses. This instantaneous dielectric strength is defined as the maximum voltage which can be consistently reapplied without causing reignition. The influence of electrode spacing (0.6 or 1.3 cm), shield potential and the polarity of the reapplied voltage on the recovery of dielectric strength have been determined. The more rapid rate of recovery initially observed at long spacings is attributed to the lower mean inter-electrode vapor density immediately following interruption. Recovery is also more rapid for "reverse" rather than "same" polarity reapplication indicating surface effects, in particular the roughening of the cathode surface during arcing. Post arc currents lead to an initial reduction of dielectric strength for "reverse" reapplication with the vapor shield tied to the "arcing-anode". The mechanism of these post arc currents has been investigated by observations of the high ion currents which flow to a negatively biased shield during and immediately following arcing.

Oil-immersed transformer gas analysis

Abstract: A sampling and testing device for diagnosing a condition of a dielectric fluid in an electrical apparatus, eg, an oilimmersed transformer, by sampling dielectric liquid from the apparatus and extracting dissolved gases from the sampled dielectric fluid and subjecting the extracted gases to analysis for composition so as to infer the condition of the dielectric liquid therefrom The device employs a cylinder disposed as part of the electrical apparatus, said cylinder having an inlet valve to draw dielectric liquid samples by vacuum Gases that may have been generated and dissolved in the sampled dielectric liquid because of local heating or electrical arcs and faults within the electrical apparatus, are liberated by creating partial vacuum in the cylinder, in a closed condition thereof Gases so extracted are conveyed through a controllable gas outlet valve on the cylinder into a gas analyzer for analysis of gas-composition so as to infer the condition of the liquid dielectric therefrom Dielectric liquid sampled from the electrical apparatus is returned thereto in a closed circuit Said cylinder comprises a piston including a flange portion which is expediently provided with a plurality of apertures connecting opposite sidefaces of the flange portion, whereby, during an outward stroke of the piston, dielectric liquid is ejected out of the apertures forcibly thereby facilitating degasification of the dielectric sample within the cylinder

Liquid cooled ozone generator

Abstract: An ozone generator module of the electirc discharge field type is provided having at least one cell comprising an assembly of three concentric tubular members, the inner and outer tubular members being electrodes separated by a tubular dielectric member spaced from one of the electrodes a distance sufficient to define a high density electric discharge zone between them, the cell or cells being disposed within a liquid container. Substantially optimum conditions for the production of ozone are provided by making the cross sectional dimension of the field uniform throughout to within a very small range of tolerance and by controlling the temperature of the electrodes by cooling them with liquid coolants one of which is a dielectric liquid, and limiting the density of the field by regulating the voltage across the field and the frequency employed.

Fluidic phase shifter

Abstract: Apparatus including an expandable dielectric container and dielectric fluid therein disposed in a waveguide for propagating electromagnetic waves to change the phase thereof. The fluid may be introduced slowly or rapidly into the waveguide or may be continuously circulated through the waveguide to provide cooling.

Cooling system for foam insulated bus

Abstract: In isolated phase bus systems comprising spaced substantially parallel aligned inner and outer tubular conductors, the interior space thereof being filled with a dielectric foam insulation made up of a predetermined percentage of open cells to enable free migration of vapors. A liquid dielectric having an appropriately selected and relatively low boiling point is inserted into the bus until it reaches a level whereby it substantially covers the inner conductor which is supported by the foam insulation. Conduction of current raises the bus temperature. If the magnitude of the current is such as to raise the temperature above a predetermined level, the liquid dielectric boils and vaporizes. The vaporized dielectric tends to move to a cooler zone within the structure and become condensed whereby the liquid dielectric continuously recirculates through the system to prevent the bus from exceeding a predetermined operating temperature. The controlled amount of the open cells provided in the foam and the positioning of the inner conductor below the longitudinal axis of the outer conductor substantially reduces the amount of liquid dielectric required with no reduction in dielectric withstand. The liquid dielectric may for example be taken from the group comprised of freons, ucons, or other liquids having predetermined relatively low boiling points and having the characteristics that they are non-reactive with the dielectric foam insulation.

Space-charge-influenced current in a dielectric liquid

Abstract: In a dielectric liquid with high applied voltages, the current-voltage relationship is known only in two extreme cases: emission-limited injection and space-charge-limited injection. In an actual case, such as in the electrofluiddynamic generator, neither situation is true. In this paper, a more generalized theory of which the extreme cases lead to the above limiting cases is developed. Comparison with the experimental results of Tobazeon showed good agreement.

Measurement of dielectric liquid motion under electrostatic stress by a laser-Doppler method

Abstract: Measurements on ion-induced liquid motion, which are necessary for the accurate determination of true ion mobilities, have been made using a laser-Doppler method. This method enables one to measure localized flow velocity with little effect on the system. It has been found that the bulk motion is influenced by the electrode geometry, the voltage polarity and the strength of the applied field.

Effect of a non-uniform alternating electric field on the thermal boundary layer near a heated vertical plate

Abstract: A thermal boundary layer is established by heating a vertical plate in a dielectric liquid. An alternating voltage is applied between the heated plate and another plate which is not parallel to the heated plate. This voltage produces a non-uni- form electric field which in turn produces electrical forces acting on the gradients in dielectric permittivity which result from the temperature gradients. These electrical forces alter the boundary layer. In this paper approximate equations are developed which allow one to calculate the boundary-layer,thickness, velocity, and Nusselt numbers for the boundary layer in the presence of the non-uniform electric field. Numerical calculations show that the heat-transfer coefficient can be either increased or decreased by the non-uniform field, depending on whether the field is strongest at the top or bottom of the plates and also on the field strength. Experiments were performed which demonstrate the change in heat transfer caused by the non-uniform field.

Electrical Conduction and Dielectric Losses

Abstract: Electrical conduction in dielectrics is the ordered motion of weakly bound charged particles under the influence of an electric field. The available information on electrical conduction in solid dielectrics refers mainly to polycrystalline and amorphous materials; electrical conduction in single-crystal dielectrics has not yet been investigated sufficiently thoroughly.

Dependence of the statistical breakdown time-lag of a liquid dielectric on electrode geometry

Abstract: It is shown experimentally that the mean statistical time-lag for electric breakdown in n-hexane is inversely proportional to the area of a planar electrode system and independent of the electrode spacing. This is consistent with the conjecture that for given materials the rate of initiation of breakdowns per unit area is a unique function of stress.

High voltage capacitor

Abstract: A high energy density, high voltage capacitor. The capacitor comprises a plurality of stacked capacitor winding sections having tab connectors extending completely through the windings and folded back adjacent opposed sides of the windings. The winding sections with the tab connectors are stacked and compressed to series connect the sections. The sections are impregnated with a scavenger-type dielectric fluid and are encapsulated in a solid organopolymeric body.

Controllable liquid artificial dielectrics

Abstract: A novel approach to microwave phase control, utilizing liquid artificial dielectrics, is described. These media have been fabricated with permittivities which vary in magnitude and anisotropy according to the strength of an applied electric control field. Continuously controlled permittivity increases of at least 20 percent in the electric field direction are realizable in liquid suspensions having low loss and very high dielectric strength. A simple waveguide liquid dielectric phase shifter has been built at Ku band and its operating characteristics measured. This approach can be applied to the design of electrically variable microwave lenses, power dividers, and resonant cavities as well as phase shifters.

High voltage energy storage capacitor

Abstract: A capacitor comprising an electrode and dielectric assembly, a polyurethane body encapsulating the assembly, and terminal means for providing electrical connection with the assembly through the polyurethane body. The electrode and dielectric assembly comprises metal electrodes which are separated by an absorbent dielectric material impregnated with a liquid dielectric fluid. The capacitor may be made by impregnating the electrode and dielectric assembly with castor oil liquid dielectric, and subsequently encapsulating the impregnated assembly with polyurethane plastic.

The mobility of charges photo-injected into a liquid dielectric

Abstract: A method has been developed for measuring the transit times of charges injected into a dielectric while maintaining a stationary average current. This has enabled estimates of the mobility of photo-injected charges in n-hexane to be made over a range of nearly three decades of power input. Absence of any dependence of apparent mobility upon power suggests that liquid motion is not a significant factor in the transport of charges at the level of injection normally associated with this technique. The value of mobility obtained is (75 ± 10) × 10−4 cm2 V−1 S−1, close to that obtained by Swan who used a similar injection technique.

Voltage Vector Analysis for Corona Location in Transformers

Abstract: Location of corona or "partial discharges" in transformers can be an extremely difficult, costly and time-consuming process, especially if disassembly is required. The present state-of-the-art is such that a variety of sonic and electrical corona location techniques are employed, none of which is completely adequate, but with experience and patience, corona sources can be found.

Coaxial Cell for Liquid Dielectric Measurements from 300 to 9000 MHz

Abstract: The dielectric constant and loss of a liquid dielectric are determined from measurements of the input impedance of a coaxial cell terminated with a short circuit. The location of the short circuit is continuously variable over a range of 2.5 cm to allow selection of the optimum sample length. Dielectric constants from 1 to 100 with high or low loss have been measured in the frequency range 300–9000 MHz using the General Radio type 900LB slotted line.

Method of making an impregnated plastic dielectric capacitor

Abstract: An all film capacitor includes a sheet of plastic material in film form wound with the capacitor electrode foil, the film being capable of impregnation by a dielectric liquid medium and having been wetted by the dielectric liquid prior to impregnation. The plastic film and dielectric liquid form the dielectric system of the capacitor. In processing, a dielectric liquid medium is applied to the film to provide a wet film and the wet film is wound with the foil into a capacitor pack. The pack, or packs, are subjected to an elevated temperature and vacuum to draw off volatile material such as water vapor, i.e., the pack is dried. Subsequent to drying, the pack, or packs, are positioned in a capacitor tank for soaking in the dielectric liquid, again at an elevated temperature and under a vacuum. Complete impregnation of the film by the liquid dielectric occurs during soaking. If desired, the same film material can be wound on the outside of the capacitor packs to insulate the packs from the capacitor tank.

Statistical effects of environmental factors on liquid-breakdown measurements

Abstract: The breakdown of a dielectric liquid in a practical environment is described by a hybrid statistical distribution based on the `weak-link? principle. By forming a convolution of two random processes with distinct distributions, it has been possible to relate certain parameters, of a breakdown test to the statistical behaviour of the dielectric. The application of this concept to the prediction of electric strength for large volumes of liquid is indicated.

Lightning Impulse and Switching Surge Breakdown of Liquid Nitrogen-Impregnated Wrapped Dielectrics for Cryogenic Cables

Abstract: In this paper experimental results are presented which indicate that flexible resistive cryogenic EHV cables employing a liquid nitrogen-impregnated dielectric wrap will withstand values of electric stress under lightning impulse and switching surge conditions comparable to those achievable in EHV oil/paper cables. To simulate the geometry of a cable, each test specimen consisted of a tape-wrapped insulation layer between concentric cylindrical electrodes (with stress cones added at the ends of the sample). The samples included fifteen wrapped with spunbonded olefin fiber tapes, three wrapped with high-density cellulose EHV cable paper, and for comparison purposes, a liquid cell with concentric cylindrical electrodes. The data are consistent with observations on similar insulation systems at 60 Hz since the wrapped dielectrics impregnated with liquid nitrogen withstood a substantially higher electric stress under these conditions than the liquid nitrogen alone.

Electrical capacitors with amide impregnants

Abstract: Mono-N-substituted and di-N-substituted amides are advantageously used for dielectric oil applications. The appropriate substitution provides the amides with the required physical and electrical characteristics necessary for use as a dielectric liquid in AC and energy storage capacitors.

The Research in Discharge Suppression of High Voltage Crosslinked Polyethylene Insulated Power Cable

Abstract: The main reason why high voltage plastic power cables lead to the dielectric breakdown is considered the insulation deterioration which is brought about by partial discharges within voids and other anomalies. We have taken various measures in order to suppress these partial discharges. Then we got an idea that when some semi-conductive organic material is blended in the insulation material, the surface resistivity of voids in the insulation and between the insulation and semi-conductive layer is reduced. Our study based on this idea produced effectual results. This paper describes the theoretical analysis, fundamental experiments and application experiments to cables and cable joints.

Electrical capacitor having improved provision for heat removal

Abstract: 1,240,859. Capacitors. GENERAL ELECTRIC CO. 8 Oct., 1968 [24 Nov., 1967], No. 47690/68. Heading H1M. End walls 2c, 2d of a capacitor casing shown in cross-section are flexible to respond to thermal expansion and contraction of dielectric fluid filling the casing and impregnating capacitor rolls 4, while side walls 2a, 2b are in heattransfer contact with at least the middle rolls to remove heat therefrom. As shown side walls 2a, 2b are bowed to maintain contact with the rolls which have an insulating wrapping 10 of e.g. kraft paper, but they may be flat and rendered rigid by being sufficiently thick (Fig. 3, not shown) or provided with ribs (Fig. 4, not shown). To improve heat-conduction, additional members of good thermal conductivity may be interposed between the rolls and the casing in direct contact with the side and end walls (Fig. 5, not shown). The dielectric fluid may be liquid, e.g. chlorinated diphenyl or mineral oil, or gaseous e.g. sulphur hexafluoride.

Electrohydromagnetic instability of superposed fluids

Abstract: The problem of stability of superposed viscous liquids subject simultaneously to electric and magnetic fields is investigated using the normal mode analysis. A configuration of an electrically conducting liquid topped by a dielectric liquid is envisaged in a downward gravity field. The electric field is assumed along the gravity field, while the magnetic field is taken to be either along or normal to the electric field. Criteria of instability are derived in both cases. It is found that a vertical electric field has a destabilizing influence and renders an otherwise stable configuration (bottom heavy arrangement) unstable for small wavelengths, while the effect of the magnetic field is stabilizing.

High voltage electric circuit breaker with rapid response tripping means

Abstract: A high voltage electric circuit breaker comprising a high potential tank mounted atop an insulating column. Opening of the circuit breaker is initiated by an operator located atop the insulating column in a housing filled with high dielectric strength fluid. The operator is maintained at ground potential by electroconductive structure extending vertically through the column between the operator and the base of the column. The operator is connected to control means within the high potential tank by a short operating rod of insulating material that extends through said dielectric fluid.

Breakdown in a Dielectric Liquid

Abstract: WHEN a dielectric liquid is suddenly subjected to a high electric stress, it retains its insulating properties for a certain length of time and then instantaneously (that is, within a nanosecond) becomes a very good conductor when the discharge path is established. In order to observe this phenomenon it is necessary to use a test cell which is an integral part of a carefully matched coaxial system1, otherwise spurious oscillatory phenomena appear. (Indeed, photographs have been published in the literature in which the true step function response is almost completely masked by such oscillations.)