Takahiko Yamashita

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.

The characteristics of the surface discharge on the covered conductor for distribution systems

In relation to the prevention of outages due to the contact of animals, plants, etc. in distribution systems, the authors studied on the characteristics of the surface discharge on the covered conductor when a grounded bird nest was in contact with the covered conductor and a lightning surge appeared. Experiments were conducted in the laboratory with a test line consisted of a covered conductor, an insulator and a tie wire. The tie wire was grounded and a lightning impulse voltage was applied to the conductor. The surface flashover voltage was measured with a damaged conductor. A knife trace passed through the conductor jacket was impressed artificially to simulate the actual condition. The surface flashover voltage was measured for the position of a knife trace. Experiments were conducted under dry or wet conditions. As a result, the polarity effect was observed. Then, the characteristics of the surface discharge propagation were observed. The propagation length of the surface discharge was measured with a nondamaged conductor. Furthermore, to clarify the behaviour of the surface discharge, streak photographs were taken by an image-converter camera.<<ETX>>

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.

Water Absorption Characteristics and Property Change of EPR for Electrical Insulation

Tree was observed in ethylene-propylene rubber (EPR) used for electrical insulation. From the inspection, it was found that the tree has water and ions. Then, it is guessed that these are in relation to the tree generation. From this inspection result, the authors investigated the water absorption characteristics of several kinds of EPR. These EPRs have different cross-linking materials. Further, we investigated the property change of EPRs after water absorption. As a result, the water absorption characteristics were clarified and it was found that the characteristics vary depending on the kind of EPR. The dissolved elements and ions in water, the property changes of hardness and crosslink density and etc. were clarified. From the measurement of water absorption characteristics, it was found that EPR has two kinds of water. One is the water that can be easily removed from EPRs and the other one is the water that is considered to be strongly connected with the materials. The considerable property changes can not be observed, however, some kinds of ions were detected in the water

Basic study on surface insulation design of solid/gas composite insulation system with embedded electrode

Solid insulated switchgear (SIS) has been developed as a substitution for medium voltage SF6 gas insulated switchgear. Its main circuits including a vacuum interrupter are coated with epoxy resin and a solid/gas insulation system is formed. For further miniaturization and higher stress design, the authors investigated the surface insulation performance of the solid/gas insulation system containing an embedded electrode. In the previous study, the authors investigated the surface breakdown characteristics. The authors also investigated the surface discharge propagation characteristics and proposed an estimation method of the surface breakdown voltage. In the present study, the authors investigated the surface breakdown characteristics numerically. The calculation was done based on the estimation method proposed previously. The divided voltage ratio, the radius of the embedded electrode, the enhancement factor of the surface insulation strength and the peak value of the surface breakdown voltage are examined. As a result, the characteristics of the parameters and the criteria for the optimum insulation design were clarified.

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.