Takeshi Takashima

High Frequency Characteristics of Impedances to Ground And Field Distributions of Ground Electrodes

High frequency characteristics of impedances to ground and field distributions of ground electrodes are calculated by the current simulation method together with the method of images. Numerical calculations concerning some typical electrodes are shown. An expression for approximating impedances to ground from corresponding dc resistances is proposed and errors are estimated.

Calculation of Complex Fields in Conducting Media

A method for calculating complex fields between lec electrods in conducting media is proposed. It is shown that there exist dual relationships between a complex field due to an alternating current source in a conducting medium and an electrostatic field due to a charge in a dielectric medium. If a solution to the problem of an electrostatic field is known, then the solution to the corresponding problem of a complex field is easily bobtained on the basis of the above dual relationships. Numerical calculations and experiments were carried out to verify the proposed method.

I-V characteristics and liquid motion in needle-to-plane and razor blade-to-plane configurations in transformer oil and liquid nitrogen

Current-voltage (I-V) characteristics are measured in a negative needle-to-plane configuration and a negative razor blade-to-plane configuration in transformer oil and liquid nitrogen. Linear pots of V vs. I/sup 1/2/ in the former configuration of V vs. I/sup 1/3/ in the latter configuration are obtained respectively in the space-charge limitation (SCL). The liquid motions in the above two configurations in SCL are computed respectively from both the Navier-Stokes equation and the continuity equation by the finite-difference method. From the experimental and computational results of the liquid motions, the relations between V and I in two configurations are derived, respectively. >

Effects of plasma diameter and operating frequency on dynamic behaviour of induction thermal plasma

A numerical approach is presented for the analysis of the dynamic behaviour of the induction thermal plasma under step-like change of the sustaining magnetic field. The time-dependent energy conservation equation which includes thermal conduction, radiation and convection loss terms was solved numerically in conjunction with the continuity equation and Maxwells electromagnetic field equations. A one-dimensional model with radial direction is adopted for the first approximation to analyse the transient aspects of the radial distributions of the temperature, the penetrating electromagnetic fields and the input and losses. Calculations were carried out for an Ar-induction thermal plasma with a diameter from 2 to 7 cm, operated at a frequency of 3 MHz and a pressure of 760 Torr. Special attention was given to the time constant which is a measure of the time necessary for the plasma to converge to a new steady state. The response time of the induction thermal plasma was a few milliseconds and had a strong dependence upon the diameter of the plasma across which the mass and energy diffusions take place under the off-balancing condition between the input and the loss. The transient aspect of a high-power induction plasma operated with a low frequency of 300 kHz is also discussed.

Transport and thermodynamic properties of SF/sub 6/ gas contaminated by PTFE reinforced with Al/sub 2/O/sub 3/ and BN particles

The computational approach in which time-dependent balance equations of mass, momentum, and energy are solved numerically is becoming an important technique for analyzing electric arcs in a gas circuit breaker (GCB) or gas-insulated switchgear (GIS). In this paper, the transport and thermodynamic properties of SF/sub 6/ gas necessary for this approach as basic data are calculated under multimixed condition by PTFE(-C/sub 2/F/sub 4/-) reinforced with alumina (-Al/sub 2/ O/sub 3/-) or BN particles. Calculations are carried out for a wide range of temperatures from 1500 to 30000 K, of pressures from 0.1 to 0.4 MPa, and of concentration ratios from 0 to 50%. The results show that the change of electron density is significant for alumina-reinforced PTFE, but insignificant for BN-reinforced PTFE contamination. Henceforth, the electrical conductivity varies only for alumina-reinforced PTFE contamination. The thermal conductivity, however, changes distinctly by mixing alumina-reinforced PTFE as well as by mixing BN-reinforced PTFE. Up to three characteristic peaks (T<3600 K), the thermal conductivity decreases, but above this temperature, augmented thermal conductivity is noticed until 7000 K for alumina and until 12000 K for BN. All thermodynamic properties and viscosity vary only at a higher level of contamination, at or above 10% admixture ratio.

The dynamic behaviour of wall-stabilized arcs contaminated by Cu and PTFE vapours

The transport and thermodynamic properties of gas under contaminated conditions with Cu and PTFE vapours have been determined taking into account the new introduction of molecular particles, produced by chemical interactions between gas and impurities like CuF, , and , making in total 25 species. The main concern of this work is to predict, from the obtained material properties data, the transient behaviour of gas wall-stabilized arcs with these types of contamination that inevitably happen in gas circuit breakers during arc interruption. The results indicate that the electron density and the electrical conductivity increase with Cu vapour contamination, especially below 9000 K, due to the lower ionization potential of Cu atoms, but are almost invariant with PTFE contamination. The thermal conductivity changes only at higher admixture ratios above around 10% for both impurities. Typical increases in due to molecular dissociation have been found at temperatures around 4000 K for Cu vapour and at 3000 - 8000 K for PTFE vapour contamination. The transient behaviours of contaminated gas arcs have been analysed for step-current modulation in the wall-stabilized arcs under the condition of no gas flow. The greater value of arc conductance with Cu vapour contamination broadens the arc current channel, exposing possible disturbance of the current interruption function in gas circuit breakers. PTFE vapour contamination does not affect the arc decay process in wall-stabilized arcs significantly.

Electric Fields in Dielectric Multi-Layers Calculated by Digital Computer

The electric field of a point charge or a spherical conductor in three or more dielectric layers on a plane conductor is calculated ated by digital computer. That of a point charge is calculated by the method of images, and that of a spherical conductor by the charge simulation method in combination with the method of images. Numerical examples show that the potential, the field strength, and the flux density, all satisfy the boundary conditions with good accuracy. The method can be applied to fields of a line charge, a pillar conductor, and an electrode of body of revolution in the same circumstance.

Copper vapor effect on RF inductively coupled SF/sub 6/ plasmas

Considering inductively coupled plasma (ICP) as an alternative way to study the copper (Cu) vapor effect in SF/sub 6/ circuit breaker arcs, a two-dimensional, axisymmetric model was solved, for a torch of 82-mm inner diameter, to predict the change of plasma properties: temperature, velocity, electric and magnetic fields, joule heating, and Lorentz force. For the four considered sets of thermophysical properties with 0%, 0.1%, 1%, and 10% Cu concentration (molar) ratio in SF/sub 6/, plasma properties were calculated for 130-slpm gas flow: 80-slpm SF/sub 6/ in the sheath channel and 50-slpm argon in the intermediate channel at pressure 100 and 200 torr. The radial temperature distribution as well as the Lorentz force and the joule heating broadened along the torch diameter by Cu vapor admixture. This predicted elongation of plasma for Cu vapor inclusion was confirmed experimentally determining the radial temperature distribution.

Generation of 50-kHz large area induction thermal plasma for high rate, uniform processing

Numerical and experimental approaches were made to produce a large area induction thermal plasma as a basic technology for high rate, uniform processing of materials. A high-power 50-kHz magnetic field was applied to a small dc plasma as a source of charged particles and a transient expansion of it was initiated in the radial direction. The time necessary to reach a new steady state plasma with a larger diameter of 100 mm was found to be around 20 and 2 ms, and the minimum sustaining power for the plasma to be 65 and 25 kW under the plasma pressure of 100 and 10 kPa, respectively. Experiments were performed to produce a 100-mm diameter plasma under a soft vacuum condition of 10 kPa. At a plate power level of 60 kW, the 50-kHz magnetic field was coupled with a small source plasma and expanded it successfully to a wide plasma of 100 mm in diameter. The temperature of the induction plasma was uniformly distributed and estimated as around 10000 K by spectroscopic analysis.

Electric Fields Due to a Point or a Line Charge in Two Dielectric Layers on a Conducting Plane

Electric fields due to a point charge located in two dielectric layers on a conducting plane are sought. By an extensive application of the theory of images, the fields are expressed accurately in the form of infinite series of image charges. The series are convergent and the fields may be calculated. In the case of a line charge, the same expressions as in point one are presented.