Showing papers on "Liquid dielectric published in 1970"

Electrohydrodynamic Stability of Space‐Charge‐Limited Currents in Dielectric Liquids. I. Theoretical Study

Abstract: Liquid motion is often observed when an electric field is applied to a dielectric liquid. An analysis of the steady cellular convection which results when charge is injected uniformly into the free surface of a film of an insulating liquid is discussed. The initial, steady‐state current is space‐charge‐limited. The method of exchange of stabilities is assumed to be valid; velocity and potential perturbations on the initial steady state lead to a characteristic equation which determines the conditions for onset of instability. This characteristic equation is of the seventh order and has nonconstant coefficients. A numerical integration has been performed on the equation and the resulting solutions show that a critical potential exists above which convection will occur. The condition for instability is R = 99 = eV0/μη., where η is the dynamic coefficient of viscosity, μ is the charge carrier mobility, and e is the permittivity. The dimensionless number R is analogous to the Rayleigh number in hydrodynamics....

Sealed electrical connector

Abstract: A reusable electrical connector for making an electrical connection in adverse environments in which the electrical connection is made by passing a contact through a self-sealing, precut opening into a sealed chamber filled with dielectric fluid to electrically contact a contact position in the fluid and which chamber has means for instantaneously adjusting in volume to changes in the ambient pressure or with the insertion or removal of the electrical contact to maintain interior portions in equilibrium with the pressure of the environment and to prevent the loss of fluid from the sealed chamber

Dielectric Loss and Voltage Breakdown in Liquid Nitrogen and Hydrogen

Abstract: Cryogenic liquids have unusual physical properties. At low-voltage stress the dielectric loss in the cryogenic liquid is so small that it can not be accurately measured. As the voltage stress is increased, the dissipation factor increases to the order of 0.002, which is higher than for many conventional dielectric liquids. Both the voltage and the time of application influence the dielectric loss. Voltage breakdown is relatively high in both liquid hydrogen and liquid nitrogen. When pressure is increased somewhat at constant temperature to eliminate boiling, the electric strength is increased significantly. When the pressure is increased still further, the electric strength of the cryogenic liquid shows little or no additional increase. Cryogenic liquids have potential use as dielectrics in cable and other types of electrical apparatus. Studies of their dielectric prop-properties may improve the basic understanding of dielectric performance also.

Microwave phase shifter with liquid dielectric having metallic particles in suspension

Abstract: Microwave phase shifters and electronic beam steering antennas are described which use an electrically controllable anisotropy dielectric medium in the microwave beam path.

Dielectric Characteristics of Compressed Gas Insulated Cables

Abstract: This paper describes the dielectric characteristics of compressed gas insulated cables, particularly the dielectric performances of sulphur hexafluoride (SF6) gas and also of the insulating spacers.

Electrical discharge machining process and dielectric fluid useful therein

Abstract: An electrical discharge machining process using as a dielectric fluid a composition comprising a base oil and a minor amount of a conductivity additive containing a chromium salt of an alkyl salicylic acid and an alkaline earth metal salt of a dialkyl sulfosuccinate.

Insulation Systems for Cryogenic Cable

Abstract: The measured dissipation factor and breakdown strength of certain dielectric materials impregnated with cryogenic liquids suitable for cryogenic cable application are presented. The separate and combined influence of different factors which affect dielectric loss and breakdown strength are discussed.

Electrical inductive apparatus having liquid and solid dielectric means

Abstract: Electrical inductive apparatus of the type which includes an insulating structure comprising liquid dielectric means in series with solid insulating means. The solid insulating means is formed of a first organic resin and a filler which includes a second organic resin. The first organic resin is selected to provide the required chemical resistance and mechanical properties and the second organic resin is selected to have a dielectric constant which is lower than the first organic resin, to provide solid insulating means having a composite dielectric constant which more closely matches that of the liquid dielectric means than that of the first organic resin alone.

Thermal Diffusion Effects on the Electrohydrodynamic Rayleigh‐Taylor Bulk Instability

Abstract: A dielectric liquid heated from above becomes unstable when a vertical alternating electric field of sufficient magnitude is applied. The effects of thermal diffusion on that instability are explored. The voltage for incipient instability is compared with experimental results.

Apparent charge mobility from breakdown times in a dielectric liquid

Abstract: It is shown that LeBlanc's hopping electron model, despite being originally based on faulty data, still gives good agreement with apparent charge mobilities derived from nanosecond breakdown formative time-lags. Thus this model has not been proved invalid, as has been assumed, although direct supporting evidence is still required.

The mobility of charge-carriers in dielectric liquids

Abstract: This thesis describes work carried out in the Department of Applied Physics, Durham University, from October 1964 to September 1967. The work was a continuation of investigations, under the supervision of Dr. M.J. Mo rant, into the electrical properties of dielectric liquids. The work of Sletten in 1959 and that of Morant and Kahan in 1964 has shown that dissolved oxygen has a marked effect on the breakdown strength and the conductivity of a typical dielectric liquid, n-hexane. The present investigation shows that the reduced breakdown strength and increased conductivity observed on de-gassing hexane may not be explained in terms of an increase in carrier mobility. The mobility of photo-injected carriers in highly de-gassed hexane is found to be no greater than the mobility of the same carriers in air-saturated liquid. Further, no increase of mobility with applied field is observed in the de-gassed liquid for fields up to 140 KV/cm; nor is there any indication, under these conditions, of the existence of an additional 'fast' carrier. The variation of the injected current with both the applied field and the degree of oxidation of the cathode, however, indicates that the 'oxygen effect' referred to above is an electrode, surface phenomenon and not a property of the liquid itself. The current transients from which the mobility determinations were made are not exactly of the form predicted by simple theory. This and other anomalous observations indicate a strong interaction between the charge-carriers and the neutral liquid molecules. Such an interaction is consistent with self-trapping of the injected carriers by polarization of the surrounding medium. Suggestions for further work on the identification of the charge-carriers in dielectric liquids and on the factors affecting breakdown and conductivity are made in the text.

Electrohydrodynamic Bulk instability of a Slightly Conducting Fluid between Two Coaxial Cylinders with a Small Temperature Gradient

Abstract: This study deals theoretically with the bulk instability of a viscous, incompressible, slightly conducting, dielectric fluid contained between two coaxial cylinders with a radial temperature gradient and under a radial electric field. A gradient in electrical conductivity resulting from the temperature gradient causes free charges to accumulate in the fluid when the electric field is applied. In the case considered, the gradient in dielectric constant can be neglected with the significant electric force being that due to the free charges. It is found that the stability criteria depend on the magnitude of the imposed potential, temperature gradient, fluid properties and geometrical configuration. In solving the stability problem by the linear perturbation theory it is assumed that the motion due to instability is two-dimensional and stationary. The limiting cases when the electrical conductivity goes to infinity or zero are discussed.

Current pulses due to discharges in a gaseous cavity in solid dielectric

Abstract: Experiments using a technique incorporating a microstrip transmission line have shown that the rise time of the initial current pulses due to discharges in a gaseous cavity of depth 0.05 mm in solid dielectric is approximately 250 ps.