Haruhisa Fujii

Electrostatic charging and arc discharges on satellite dielectrics simulated by electron beam

This paper describes the electrostatic charging and discharge phenomena of dielectric materials for spacecraft by electron-beam irradiation simulating the hot plasma in space. Thermal control materials were used as the dielectrics tested. Charge accumulation in the dielectric irradiated with the partially penetrating mono-energetic electron beam causes a large potential on the surface. When the large surface potential reaches a critical value, arc discharge occurs. The rate of occurrence of the discharge increases with the electron energy and the electron-beam current density. The characteristics of the discharges, however, depend on the material.

Correlation between two frequency components of various PD pulses in GIS

Detection of partial discharge (PD) signals is one of the most important methods for predictive maintenance of gas insulated switchgears (GIS). Because type of PD source, configuration of a GIS tank and frequency response of a sensor influence a PD spectrum, detected PD pulse has a specified frequency spectrum. Although frequency spectrum is one of valuable information for PD in a GIS, the spectrum measured with spectrum analyzer or FFT processing is generally a result of averaging of many signals so that statistical features of PD are lost. In addition, frequency spectrum is complex and special experience is needed to recognize it. Thus convenient method is required to discriminate various PD pulses. In this paper, we attempt to extract two frequency components from a PD pulse and to process them in order to categorize it easily. Correlation between pulse heights of two frequency components and pulse height distribution resolved with power voltage phase are shown as effective methods to distinguish the type and the location of PD sources.

Resonance characteristics and identification of modes of electromagnetic waves excited by partial discharges in GIS

Electromagnetic waves are used for detection of partial discharges (PD) in GIS (gas-insulated substations). A very wide frequency band up to 1.5 GHz is utilized for detection. There are three categories of electromagnetic wave which can be excited and propagate in coaxial cylindrical structures like GIS, namely, TEM, TE, and TM modes. The characterization and identification of each mode is indispensable to understanding the partial discharge phenomena in GIS. In this paper, peaks in the frequency spectrum excited by PD are identified in each mode and the resonant characteristics of each mode are studied. The following are the major results: (1) The resonance peaks appear at the frequencies defined by the spacer distance. (2) The intensity of each mode depends on the position of discharge source along the radial direction. The lower-order modes including TEM are excited when a discharge source is located near the center conductor. On the other hand, higher-order modes are excited when the discharge source is at the enclosure surface. (3) The experimental profile of each mode excited by PD along the radial direction approximately agrees with the general theory of electromagnetic wave propagation in coaxial cylindrical cavity.

Frequency spectrum of various partial discharges in GIS

Before the breakdown of electrical apparatus partial discharges occur. Measuring partial discharges is very important for predictive maintenance for GIS. In a GIS, several types of defect are probable, such as a metallic particle fixed on conductors, a particle on the spacer and a moving particle. For predictive maintenance it is necessary to understand the characteristics of partial discharges for these defects. We measured frequency spectra and phase distributions for these defects using a practical bus model and made the characteristics of partial discharges clear.

Charging Mechanisms of a Conducting Particle on Dielectric Coated Electrode at AC and DC Electric Fields

The breakdown properties of GIS can be seriously deteriorated by conducting particles which are accidentally mixed at the assembly process. The compact GIS and the gas insulated dc apparatus are expected to be one of the future directions. The particle contamination will be more crucial for both gas insulated apparatus than for the conventional GIS. Special cares against the particle contamination have to be taken for the compact GIS and dc apparatus.

Observation of surface charging on Engineering Test Satellite V of Japan

We developed Potential Monitor (POM) which was installed on geostationary Engineering Test Satellite V (ETS-V) of Japan launched on August 27, 1987. The POM can measure the surface potentials of insulating material samples which get charged in the space environment. Three kinds of thermal control materials were used as the samples. We obtained the following observational results: ( 1 )The charging potentials increased negatively in the shadow of antenna or shunt of solar array paddle. (2)The potentials gradually increased for one year. (3)The potentials changed periodically with the temperature o f the sensing part of the POM.

ELECTRIFICATION OF GLASS SUBSTRATE SURFACE BY PLASMAS

Abstract It is probable that charge-up of a glass substrate during plasma processing, such as ashing and/or etching, deteriorates the production yield of TFT-LCD devices. In order to control the production yield, it is necessary to understand the electrification mechanism of glass surface in plasma and then offer countermeasure to the process. We measured the surface potential of the glass substrate during discharge. We exposed the glass substrate to plasma in a parallel-plate electrode system by introducing Ar, O 2 or SF6 gas into the plasma reactor and exciting with 13.56MHz RF or DC power supply. As a result, we found that the charging of the glass substrate in plasma was considerably affected by gas species and power sources. We discussed the phenomenon from a viewpoint of the ionizatiation and the movement of molecular ions in plasma.

Deterioration of insulating films on silicon wafer due to surface charging during ion implantation

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1 μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35 keV As+ at the beam currents of 1 mA to 10 mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide were influenced by the beam distribution.

Behavior of conductive microparticles under electric field in vacuum and their influence on breakdown characteristics

Impulse breakdown voltage (BDV) for the gap which was injected with copper microparticles with a diameter from 7 to 500 /spl mu/m is measured. Electrode materials are copper, stainless steel, and an alloy of copper and chromium. In the short gap (approximately <5 mm), the BDV does not depend on the particle size or electrode material. However, in the long gap (>5 mm), the BDV varies according to the particle size and electrode material. Compared with the short gap, incrementation of the BDV with an increase in gap length is gradual. For both gap ranges, the BDV under negatively charged particles is lower than the BDV under positive polarity. The effectiveness of electrode surface roughness on the BDV is small compared with the clear gap. Further, AC voltages are applied to a rod-plate gap which was injected in the particles in order to observe their dynamic behavior. The particles begin to move when the upper direction electrostatic force originated by the AC field competes to the gravity force acting on the particles, and are finally removed from the area where the electrostatic force exceeds the gravity force as a result of reflection movements between electrodes.

Improvement of Withstand Voltage at Particle Contamination in DC-GIS Due to Dielectric Coating on Conductor

±500kV DC transmission between Honshu island and Shikoku island in Japan will be operated at the beginning of the next century. High voltage DC-Gas Insulated Switchgear (DC-GIS) equipped in the DC-AC converter station has been developed. One of considerable items for designing the DC-GIS is the effect of the particle contamination to electrical properties more crucial than conventional GIS. the particles floating around the high voltage conductor with negative DC voltage give the most detrimental effect to the insulation properties at application of positive lightning impulse. Therefore it is essential to study and elucidate the phenomena for the realization of compact and highly reliable DC-GIS.