上野 秀樹

Corona and breakdown characteristics for a configuration of a sphere with a needle and a plane in N-2 gas are studied. The protrusion was used to simulate a metallic particle attached to a high voltage conductor surface in power apparatus. The corona and breakdown characteristics depend on the vertical distance between the needle tip and the bottom sphere. It was observed that the breakdown path changed from needle-to-plane to sphere-to-plane while increasing the vertical distance of the needle from the plane. Although corona was generated at the needle-tip at first and developed in the direction of the plane, both the needle-plane and the sphere-plane breakdown occurred at some short vertical distances. The sphere-plane breakdown in that distance was triggered by corona from the needle.

Barrier discharge characteristics have been investigated for twin needles-plane electrode configuration in dry air. Characteristics of partial discharge depending on the distance between the tips of twin needles have been focused. In the case of d equal to 1.0mm˜2.0mm (d : distance between the tips of twin needle), the discharge inception voltage value increased compared with that of the single needle-plane electrode configuration. Moreover, for the d equal to 4.0mm, the discharge inception voltage value became almost the same value in the case of the single needle. It is considered that the differences of the discharge inception voltage value have been caused by the influence of tip of needle each other. In addition, discharge images by intensified still camera and CCD camera, power consumption, and ozone concentration were examined.

The creeping flashover voltage-time characteristics for the composite insulating configuration by insertion of a barrier between a needle electrode and a plane electrode in N-2 gas have been investigated. A maximum creeping flashover voltage of around 10 mus has been found in N-2 gas for negative polarity. This anomalous voltage-time characteristic is associated with the low field relaxation effect of the accumulated charges on the barrier for an applied pulse voltage with a highly steep wave front. (C) 2003 Wiley Periodicals, Inc.

This paper describes local corona behavior and creeping discharge on composite electrode systems in N-2. The composite electrode consisted of a needle contacted with a borosilicate glass or a ZnO disk on a needle-plane configuration. The discharge voltages increased when the needle was in contact with the glass with increasing creeping distance (L) from the needle tip to the bottom of the disk. The discharge voltages showed a reversed polarity effect beginning at L = 4 mm. In the case of a needle in contact with ZnO, the discharge voltage increased with distance until L = 2 mm, but decreased beyond L = 2 mm. Observation using an ultrahigh-speed camera showed that the discharge behavior was different for the glass and for the ZnO. Corona photographs taken by a camera with an image intensifier showed that the corona was generated at the triple junction in the case of ZnO. The differences in discharge voltage characteristics and the discharge behavior between the glass and ZnO were associated with the corona properties. (C) 2003 Wiley Periodicals, Inc.

Creeping flashover characteristics under highly nonuniform field for a composite insulating configuration by insertion of a barrier between a needle electrode and a plane electrode in N-2 gas and, N-2/SF6 mixtures have been studied. The creeping flashover voltage in N-2 at higher investigated gas pressure (P = 0.3MPa), especially for the negative needle, has been comparable to that in SF6 gas. In addition, the maximum on voltage - time characteristics of creeping flashover voltage at around 10mus has been found in N-2 for the negative needle. These unique behaviors in N-2 gas should be elucidated to the field relaxation effect by the accumulated charges on the barrier from local corona for an applied pulse voltage with a steep wave front.

This paper describes the discharge characteristics of a needle/dielectric composite electrode in N-2 gas produced by a rectangular pulse voltage. Glass or ZnO was placed in contact with the needle for the needle-plane electrode configuration. In the case of glass in contact with the needle, the discharge voltage increased with increasing L (the distance from the tip of the needle to the dielectric). In the case of ZnO in contact with the needle, the discharge voltage increased with increasing L from 0 mm to 2 mm, but it gradually decreased with increasing L from 2 mm. to 10 mm. It is considered that these differences in the discharge voltage characteristics originate from the Corona extension process and discharge path. (C) 2001 Scripta Technica.

Creeping flashover characteristics for the needle electrode-plane electrode filled with N2/SF6 gas mixtures have been investigated. In the case of the needle-plane configuration, the flashover voltage was enhanced by an admixture of SF6 into N2. On the other hand, by the insertion of the solid dielectric barrier between the needle and the plane, only the negative creeping flashover voltage was reduced drastically by the admixture of SF6 gas into N2 gas, and a highly emissive region at the top of a creeping corona was found in N2/SF6 gas mixture. This behavior is strongly affected by the creeping corona extension process, depending on the creeping distance and the gas pressure.

The effect of a barrier between a needle electrode and a plane one in an (N-2/SF6) gas mixture on creeping flashover was investigated using a microsecond pulse voltage. The SF6 gas content was varied from 0% to 100%, and the gas pressure from 0.1 MPa to 0.3 MPa. The flashover voltage increased with increasing SF6 gas content for a positive needle electrode. For a negative needle electrode, excepting the total pressure of 0.1 MPa, at which similar flashover characteristics were obtained to the positive case, a considerable decrease in flashover voltage was found in the case of a mixture of a few percent SF6 in (N-2/SF6) gas mixture at elevated total pressures. The corona behavior on the barrier in (N-2/SF6) gas mixture was investigated by means of a high-speed digital framing camera. (C) 2000 Scripta Technica.

Creeping discharge characteristics on negative polarity of a composite gas/solid insulating system with N-2/SF6 mixed gas have been studied by inserting a solid insulator between a needle electrode and a plane electrode. In the case of the shorter creeping distance, the flashover voltage on the negative needle increased with increasing SF6 gas content, which was a positive effect of the SF6 gas mixture. When creeping distance was increased, a considerable decrease in the flashover voltage on the negative needle under the gas pressures P of 0.2 MPa and 0.3 MPa was observed by the addition of a small amount of SF6 into N-2. The effect of SF6 gas mixture for the flashover voltage on the negative needle changed from positive to negative at a threshold creeping distance. Furthermore, the threshold creeping distance depended on the gas pressure.

Carbonized materials with flexibility have been prepared by a heat treatment of conducting poly-(1,4-naphtfialene vinylene) films. The electrical and structural properties of the carbonized films have been investigated From the x-ray diffraction pattern for 2400 degrees C-treated film the material consists of the regions with different degree of carbonization. It may originate from a multi-phase graphitization. And the obtained films are highly porous and disordered carbonized materials.

Creeping discharge characteristics of a composite gas/solid insulating system have been studied by inserting a solid insulator between a needle electrode and a plane electrode. Considerable differences have been found in the creeping discharge behaviors of N-2/SF6 and CO2/SF6 systems. With the addition of three-percent of SF6 gas to CO2 gas, the creeping discharge of the CO2/SF6 gas mixture was clearly seen to be strongly affected by the nature of SF6 gas, as revealed by photon emission measurements in a corona and observations using an ultrahigh-speed digital imaging system, On the other hand, the addition of a small amount of SF6 to N-2 caused a significant decrease in the flashover voltage and a peculiar creeping corona extension. The creeping discharge characteristics of N-2/O-2 mixtures are similar to that observed in N-2/SF6 mixtures. Both an electronegative gas (negative ion) and nitrogen play important roles in this behavior.

Electroluminescent (EL) diodes utilizing polysilanes have been fabricated and their optical and EL characteristics have been studied. We have succeeded in demonstrating electroluminescence in the ultraviolet and visible regions using the polysilane EL diodes. We have found that the EL efficiency has been enhanced in polysilane diodes doped with oxadiazole derivative compared with that in undoped polysilane diode.

The doping effects on optical and electrical properties of polysilanes were investigated by in-situ measurement. When polysilanes bearing a p-N,N-dialkylaminophenyl substituent were doped with iodine vapor, drastic spectral changes were observed. The evolved visible absorption up to 700 nm was found to be strong and stable compared to that of iodine-doped polysilanes such as poly(methylphenylsilane). On the basis of the studies concerning iodine doping of the related p-N,N-dimethylaminophenyl-substituted silane and disilane, and also theoretical calculations, this new absorption can be best interpreted by the result of charge transfer consisting of the strong interaction between iodine and dialkylamino substituents in the polysilanes. (C) 1996 John Wiley & Sons, Inc.

Electroluminescent (EL) diodes utilizing polysilanes have been fabricated, and their optical and electroluminescent characteristics have been investigated. We have succeeded in demonstrating electroluminescence from the ultraviolet region to the visible region using the EL diodes with thin polysilane films. The diode characteristics are discussed taking the polymer structure into consideration.

Photoluminescence of polysilanes with aromatic side groups has been found to be strongly quenched upon C-60 doping, in contrast to the case of polysilanes with saturated hydrocarbon side groups in which a clear quenching effect has not been observed. These results have been interpreted by considering the role of the aromatic side group as a mediator for photoinduced electron transfer from electronic states of the main chain polysilanes to the C-60 molecule.

Graphite films and fibers obtained by plasma CVD and subsequent heat treatment at 3000-degrees-C provide an excellent host for intercalation. The conductivities of intercalated graphites were higher than 10(5)S/cm. The ICl-intercalated graphites are thermally stable in air until 300-degrees-C. The air-stability for these is higher than that for CuCl2-intercalated graphites. Graphite films have been synthesized at 1340-degrees-C by plasma CVD using an Fe catalyst without subsequent heat treatment. These graphite films have a conductivity of 10(4)S/cm and high crystallinity, comparable to HOPG. The conductivity is enhanced by intercalation. The highest value was as high as 1.4 x 10(5)S/cm.