Yoshikazu Hoshina

Application of functionally graded material for reducing electric field on electrode and spacer interface

For the size reduction and the enhancing reliability of electric power equipment, the electric field stress around solid insulators should be considered enough. For the relaxation of the field stress, the application of FGM (Functionally Graded Materials) with spatial distribution of dielectric permittivity (¿-FGM) can be an effective solution. In this paper, we investigated the applicability of ¿-FGM for reducing the electric field stress on the electrode surface with contact to the solid dielectrics, which was one of the important factors dominating a long-term reliability of the insulating spacer. Firstly, we carried out numerical simulation of electric field to confirm the reduction of the electric stress by U-shape permittivity distribution. Secondly, we investigated the fabrication feasibility of ¿-FGM with the U-shape distribution. Thirdly, we estimated the longterm electrical insulation performance of the ¿-FGM. Finally, we verified the applicability and the fabrication technique of the ¿-FGM to solid dielectrics for improvement of the electric stress and the long-term insulation performance in electric power equipment.

Permittivity characteristics of epoxy/alumina nanocomposite with high particle dispersibility by combining ultrasonic wave and centrifugal force

This paper proposes a novel technique to fabricate epoxy/alumina nanocomposites with nanoparticle composite process by combination of ultrasonic wave and centrifugal force. The particle dispersion effect of the nanoparticle composite process and its influence on dielectric permittivity were discussed quantitatively. Experimental results clarified that the combination of ultrasonic wave and centrifugal force was effective to increase dispersed nanoparticles and as well as to separate residual agglomerates. We verified that the improvement of particle dispersibility in the nanoparticle composite process by combination of ultrasonic wave and centrifugal force could bring about lower permittivity of the nanocomposites, especially than that of unfilled epoxy material.

Dielectric properties of epoxy/alumina nanocomposite influenced by control of micrometric agglomerates

Introduction of metal oxide nanoparticles to polymer material is known to have unique dielectric behavior and significant advantages in electrical insulation performance in power apparatus. This paper presents an attempt to clarify the influence of dispersibility of nanoparticles, especially focusing on agglomerates, on dielectric properties of a nanocomposite system by changing particle dispersion processes. Experiments were carried out in epoxy/alumina nanocomposites with the particle dispersion techniques by applying ultrasonic wave and centrifugal force. For the dispersibility control of nanoparticles, we changed the duration of ultrasonic wave and centrifugal force. The experimental results clarified the effect of centrifugal force on the separation of agglomerates and the effect of ultrasonic wave on the disruption of agglomerates. Next, we examined the dielectric properties such as relative permittivity and tan δ of the nanocomposites. As the result, we verified that the permittivity of epoxy/alumina nanocomposites became low due to separation and disruption effects of the agglomerates.

Influence of tiny metal particles on charge accumulation phenomena of GIS model spacer in high-pressure SF 6 gas

The charge density distribution of the downsized GIS disc spacer made of epoxy resin was measured in 0.5-MPa (abs.) SF6 gas. A dc voltage was applied to the spacer, and the charge density on the surface was measured using an electrostatic probe. Voltage application and charge measurement were conducted in a sealed chamber without opening it. After the voltage application of 60 kV, radial charge patterns appeared on the spacer. Tiny metal particles whose size is smaller than 0.1 mm were observed on the spacer after the voltage application. Metal particles on the spacer may cause the radial charge accumulation in this experiment: if a metal particle adheres on the spacer, partial discharge may occur near the metal particles and negative charges may progress along the surface of the spacer.

Dielectric properties of SF6/N2 gas mixtures on a full scale model of the gas-insulated busbar

Investigations of the dielectric properties of SF/sub 6/, N/sub 2/ and mixtures have been carried out using a full scale model of a gas-insulated busbar (GIB). The breakdown characteristics under clean conditions are similar to those in a uniform field gas gap. The breakdown voltage is the maximum in SF/sub 6/ and the minimum in N/sub 2/, and shows positive synergism in gas mixtures. The breakdown voltages were proportional to the SF/sub 6/ content raised to the power of 0.12-0.24. In gas mixture at 0.5 MPa, the peculiar breakdown characteristics under particle attached conditions were obtained. The characteristics are dependent on applied voltage waveform. Under power frequency voltage, dielectric strength of gas mixtures in a particular SF/sub 6/ concentration range is higher than that of pure SF/sub 6/. In gas mixtures, the partial discharges behavior should be related to the increase of breakdown voltage. Under negative lightning impulse voltage, an addition of small amounts of SF/sub 6/ to N/sub 2/ results in a decrease of breakdown voltage. The negative ion should play an important role on this behavior.

Dielectric Properties of Epoxy/Alumina Nanocomposite Influenced by Particle Dispersibility

For applications of nanocomposite materials to solid insulator for electric power apparatus, we have to consider various characteristics from mechanical, thermal and electrical points of view. In particular, the agglomerate of nanoparticles would decline the excellent properties of nanocomposite. In this paper, we investigated the influence of dispersibility of nanoparticles on electrical properties. Firstly, we fabricated epoxy/alumina nanocomposites with application of ultrasonic wave and centrifugal force. Secondly, we evaluated the dispersibility of nanoparticles by image analysis of agglomerate diameter from scanning electron microscopy (SEM) and the measurement of filler contents. Then, we examined the dielectric properties such as permittivity and dielectric loss of the nanocomposite. Finally, we verified the influence of the dispersibility of nanoparticles on the dielectric characteristics.

The Surface Flashover Characteristics of Spacer for GIS in SF6 Gas and Mixtures

The SF 6/N 2 gas mixture is probably the most promising dielectric gas among SF 6 substitutes, because nitrogen is cheap and harmless for an environment. Because the boiling point of SF 6/N 2 gas mixture is lower than that of pure SF 6, this mixture will be used in apparatus designed for cold areas.

Dielectric properties in high pressure CO/sub 2/ and N/sub 2/ gas using coaxial cylindrical electrode and on the surface of spacer

CT-SF/sub 6/ gas is widely used in electric power apparatus such as gas insulated switchgears (GIS) and gas circuit breakers (GCB) due to its excellent dielectric and arc-quenching performance. However, SF/sub 6/ gas has been recognized as a greenhouse gas and it was decided to reduce its emissions at COP3 at Kyoto in 1997. Thus, surveys on the amount of emissions and efforts to reduce emissions have been continued all over the world. Simultaneously, studies on alternative gases to SF/sub 6/ gas have increased. In fact, studies on alternative gases, the purpose of which was to find a gas that had better performance than SF/sub 6/ gas, had been carried out previously. However, the purpose of the latest studies is to reduce environmental impact.

Dielectric properties of epoxy/alumina nanocomposite influenced by particle dispersibility and filler content

For the application of nanocomposite materials to solid insulator in electric power apparatus, we investigated the influence of the dispersibility of nanoparticles on dielectric property. Experiments were carried out in epoxy/alumina nanocomposites with the particle dispersion techniques using ultrasonic wave and centrifugal force. As the result, we verified the specific characteristics of dielectric permittivity in nanocomposites with good dispersibility.

Dielectric characteristics of epoxy/alumina nanocomposite with particle dispersion techniques using ultrasonic wave and centrifugal force

In order to derive the specific properties of polymer nanocomposites, we investigated the influence of the dispersibility of nanoparticles on dielectric property. Experiments were carried out for epoxy/alumina nanocomposites with the particle dispersion techniques using ultrasonic wave (USW) and centrifugal force (CF). In this paper, by controlling the application duration of ultrasonic wave, we investigated its influence on particle dispersion and dielectric permittivity. As the result, we verified quantitatively that the extension of the application duration of ultrasonic wave could improve dispersibility of nanoparticles and reduce relative permittivity of nanocomposites.