Hisao Matsuo

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.

Electrical contact between a local discharge on an electrolytic solution and the solution surface [wet polluted insulators]

An electrolytic solution surface was used to simulate the surface of wet polluted insulators. A local discharge propagates on the solution surface when a voltage is applied to the surface. The electrical contact between the local discharge on the electrolytic solution and the solution surface was examined. The distribution of the current from the local discharge to the solution is estimated from the potential distribution measured with probes placed in the solution. The resistivity of the solution is varied from /spl sim/80 to 370 /spl Omega/ cm. Impulse voltages of 2/80 /spl mu/s, 10/800 /spl mu/s and 100/2500 /spl mu/s are used as the applied voltage. The peak value of the applied voltage was 1.05 to 1.4/spl times/ the 50% flashover voltage V/sub 50/ under each set of experimental conditions. As a result, it is found that most of the discharge current flows from the tip part of the local discharge, and the current from the local discharge column is considerably lower. Furthermore, the distribution of the current from the local discharge to the solution is found to be barely influenced by the resistivity of the solution, the peak value of the applied voltage, or the applied voltage waveform.

Characteristics of Microwave Plasma and Preparation of a-Si Thin Film

The characteristics of a plasma produced by launching 2.45 GHz microwave beams through a glass of pure argon gas have been studied. A direct observation of the microwave electric field with a loop antenna placed in the tube revealed that a plasma is produced at the microwave inlet. The threshold condition for a microwave discharge was experimentally obtained under a wide range of argon gas pressures and magnetic fields. The threshold gas pressure strongly decreases as the magnetic field approaches the electron cyclotron resonance (ECR) condition. By mixing SiH4 gas (20%) with argon gas, an amorphous silicon thin film can be prepared in the microwave plasma. The impurity content and the morphology of the film depend on the substrate location.

Relationship between Photo-Emission and Propagation Velocity of Local Discharge on Electrolytic Surfaces

This paper presents experimental studies of local discharge propagation along an electrolytic surface under the application of impulse voltage. Experiments were performed using a water channel with point/plane electrodes. The resistivity of the electrolyte (aqueous solution of potassium chloride) was varied from 350 to 3000 ¿cm. Local discharges propagate on the electrolytic surface and emit light which is more intense at thetip of a local discharge. The discharge velocity and the intensity of the photo-emission from the tip of the local discharge were measured simultaneously. It is found that the velocity of the local discharge is determined by the intensity of the photo-emission and is independent of the length of the water channel and the applied voltage when the resistance per unit length of water channel is the same. The local discharge propagation mechanism is also discussed.

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>>

Current density at the local discharge tip on an electrolytic surface

Experimental results are presented on the current density at the local discharge tip on electrolytic surfaces, which simulate the surfaces of wet polluted insulators. A rod-plane electrode system with the electrolyte layer on the plane electrode was used inside a Pyrex glass chamber. The air pressure in the chamber was changed from approximately 6.67 to 101 kPa. The resistivity of the aqueous solution of potassium chloride was changed from approximately A 10 to 880 Omega -cm. The current density at the interface between the local discharge tip and the electrolytic surface was measured by two methods (one with the probes set in an electrolyte, the other using a camera to photograph the local discharge tip). As a result, it was found that the current density was constant, regardless of the discharge current and that it increased with air pressure and decreased with an increase of the resistivity of the electrolytic solution. >

Gas Temperatures in Impulse Discharge Channels at Low-Pressure Air

Two types of glow-to-arc transition processes, following constricted and transitional glows, in a nonuniform field gap between a point anode and a protrusion on a plane cathode in low-pressure air under impulse voltage are investigated, observing the spatiotemporal variation of emission intensity of the discharges by means of an image converter camera. At the same time, the distribution of gas temperature along the gap axis is measured spectroscopically with high resolution in time. The results show that the gas temperature is raised to a considerably high, though not extreme level. Along the positive column, the gas temperature rise is higher in the constricted region, especially at two parts near the respective tips of the point anode and the cathode protrusion. The transition mechanisms from the glow to the arc are discussed.

Observation of Potential Relaxation Instability in a Bounded Discharge Plasma

A potential relaxation instability (PRI), which causes a periodic motion of a potential jump and plasma expansion accompanying a high-density fluctuation level (¿60 percent), is observed in a bounded discharge plasma. The instability is found to create a high electron drift velocity and a spatial growth of density and potential fluctuations, and to accelerate a test wave. An additional supplement of a plasma into the boundary suppresses the instability. At the same time, the fluctuation decreases (<5 percent) and the frequency difference of the wave spectrum between nth and (n - 1) th (n is an integer) higher harmonics decreases as the frequency increases. However, when the potential relaxation instability is excited, this frequency difference keeps constant.