Tomoyuki Fujishima

Relation between leakage impedance and equivalent salt deposit density on an insulator under a saltwater spray

The degree of pollution of an insulator polluted rapidly under a saltwater spray is observed by measurement of the leakage current, which flows between electrodes fixed on the surface of the insulator, under 30 V ac voltage. Long rod insulators were used as samples. The relation between the leakage impedance and the equivalent salt deposit density (ESDD) of the insulators was obtained under several experimental conditions. As a result, the following was found (1) the effect of the wind velocity on the insulator is small, and is especially small when the distance between the electrodes is short, (2) the effect of the distribution of the saltwater drops on the insulator is small, and (3) the leakage impedance does not depend on initial dryness of the insulator surface (and the conductance is low) before the saltwater spray. It is important that the ESDD be above a certain value, and that the distance between the electrodes be short. Furthermore, it was shown that ESDD can be estimated fairly exactly from the leakage impedance.

Propagation velocity and photoemission intensity of a local discharge on an electrolytic surface

An electrolytic solution surface was used to simulate the surface of wet polluted insulators. A local discharge propagates on the solution surface when an impulse voltage is applied to the surface. The intensity of photoemission from the tip of the local discharge, the propagation velocity of the local discharge, and the discharge current were measured simultaneously. It was found that the propagation velocity increases with the photoemission intensity and the resistivity of the solution, and the influence of the air pressure and the applied voltage waveform on the velocity is very small. Furthermore, it was deduced that the ratio of the current through the local discharge tip to the total discharge current is not influenced by the local discharge length and the applied voltage waveform.

Shape of contacting surface between an electrolytic solution and local discharge on it

To develop a propagation model of a local discharge on a wet polluted insulator, the authors have examined the propagation characteristics and the propagation conditions of the local discharge on an electrolytic solution simulating a wet polluted insulator surface. To calculate the relation between the propagation length of,the local discharge and the time required for the propagation, an electric field distribution near the tip of the local discharge must be known. In this paper, the authors have examined a voltage distribution in an electrolytic solution to obtain the electric field. As a result, the shape of the contacting surface between the local discharge and the solution is obtained under impulse voltage. A calculation of the voltage distribution is performed with the shape. A comparison between calculated values and measured values of the distribution is given.

Ozone Generation Properties of Screw electrode Ozonizer by Different Outer Electrodes

AbstractMethyl bromide which is most popular disinfectant of soil has been prohibited from using except for an indispensable use by 2015. Therefore we pay attention to ozone as a substitute of the methyl bromide for soil sterilization, because the ozone is easily generated by dielectric barrier discharges. We have been developing an ozone generation system which is suitable to the soil sterilization and also investigating the soil sterilization with the generated ozone. So we are investigating influences of ozone generation characteristic on the screw electrode ozonizer by changing of outer electrodes, applied voltages, and flow rates of source gases. This time, in order to investigate the influence of the outer electrode form on ozone generation properties, we used two different outer electrodes; the single electrode of 11cm width and 3-divided-electrodes of 1cmx3(electrode spaces of 4cm). As results, maximum values of the ozone concentration, the ozone yield and the ozone generation efficiency were obta...

Effect of divided electrode of screw-type ozonizer for ozone generation and basic study of ozone sterilization effect against bacteria in soil

We have been developing an ozone generation system which is suitable to the soil sterilization and studying ozone generation characteristics. The ozone was generated by using the dielectric barrier discharge with a screw type electrode. From our previous research, we have found that ozone concentration depends on the width of the outer electrode, the flow rate of the source gas and the applied voltage. In this research, we investigated ozone generation characteristics by changing the width of the outer electrode (1cm×1 or 3cm×1) or using divided outer electrodes (1cm×3), under the applied voltage of 0–15.0kV, the source gas of pure oxygen and the flow rate of O2 of 0.5L/min. And we also investigated sterilization ability of the generated ozone by using outer electrode of width of 3cm×1 under the applied voltage of 15.0kV, the source gas of pure oxygen and the flow rate of O2 of 0.5L/min. As a result, we found that supplied electric power is increased with expansion of actual discharge space by using divided outer electrodes. Then high concentration of ozone could be generated in our ozone generation system. Maximum ozone generation efficiency was 228g/kW at ozone concentration of 3.66g/m3 when we used divided outer electrodes of 1cm×3. And, we could verify sterilization effect of ozone.

Improvement of insulation performance of solid/gas composite insulation with embedded electrode

Solid insulated switchgear (SIS) has been developed as a substitution for medium voltage sulfur hexafluoride (SF6) gas insulated switchgears. Its main circuit including a vacuum interrupter is coated with epoxy resin. Therefore, a solid/gas insulation system is composed. For further miniaturization and higher stress design of SIS, improvement of the insulation performance is required. In the solid/gas insulation system, the breakdown strength along the surface is lower than that of solid. Then, the authors investigated the surface insulation performance of the solid/gas insulation system containing an embedded electrode. In the present study, the sizes of the embedded electrode and the solid insulation material were varied and the partial discharge inception voltage and the surface breakdown voltage were measured. As a result, it was found that the surface breakdown voltage varied considerably with the radius of the embedded electrode. From the result, it was deduced that the surface insulation performance could be improved by choosing the size of the embedded electrode appropriately. Moreover, the effects of the thickness of the insulation material and of the surface distance on the surface insulation performance were clarified.

Design of stable wireless sensor network for slope monitoring

This paper presents implementation report for slope monitoring on Wireless Sensor Network (WSN) system by use of IEEE802.15.4 (ZigBee). The purpose of this research is the construction of WSN system which can be sensing and monitoring the deformation of the ground caused by heavy rain in mountain areas with radio communication devices and sensor devices. For the stable data acquisition, some electrical and environmental problems should be solved. In this paper, the techniques for dynamical transition of the communication mode depending on battery capacity, a method of protecting wireless nodes from the lighting, and a optimized design of antenna for WSN are proposed. The experimental results which the proposed system installed at actual test field show that the dynamic wireless network configuration. Moreover, the status of field can be predicted by the obtained data from the improved system.

Ozone generation characteristic by different divided outer electrodes of screw electrode ozonizer

ABSTRACTMethyl bromide is used as the disinfectant of soil and agricultural chemicals. However, methyl bromide has been prohibited from using except for indispensable uses. Therefore, ozone has bee...

Evaluation of rotational and vibrational temperatures of nanosecond pulsed surface discharge on water

This study deals with the plasma temperature of nanosecond pulsed surface discharge on water. The rotational and vibrational temperatures of the discharge were evaluated by emission spectrum of N2 second positive system band. The temperature was obtained by fitting the measured distribution with the simulation results. As a result, the rotational and vibrational temperatures were evaluated approximately 1000 K and 2000 K, respectively. The temperatures were stable irrespective of the applied voltage and current.

Energy consumption characteristics of pulsed arc discharge in high pressure carbon dioxide up to supercritical phase

Energy consumption of pulsed arc discharge E in high pressure CO2 up to supercritical (SC) phase was investigated under positive pulsed voltage that was applied to needle-to-plane electrode by a magnetic pulse compression circuit. The gap distance of approximately several hundred μm was set inside a high pressure chamber. The peak current of pulsed arc discharge was in the range of 400-600 amperes at gas and supercritical phases. The E was calculated by the dumped oscillatory voltage and current under the post-breakdown. In the gas phase, the E increased with medium density up to sub-critical phase. Meanwhile, the E was almost stable irrespective of medium density in the supercritical phase. Spectroscopic measurement was also carried out to confirm the local thermal equilibrium of the arc plasma at SC phase. The spectral distribution was characterized by the black body (Planck) radiation and line spectra of atomic oxygen (777 and 845 nm).