Reduction of AC flashover strength by the attachment of insulating strings on the insulator surfaces

AC flashover voltage in air (ACFOV) decreases when nylon string is attached on the PMMA insulator surface which has a backside electrode. The decrease in ACFOV by the attachment is explained by the generation and the propagation of the negative surface leader along the string. When the contact angle between the HV electrode and the insulator surface is in a range from 90° to 120°, some of the negative surface leaders generated proceed along the string to the grounded counterelectrode. The magnitude of the negative leader along the string is stronger than that of the leader on the insulator without a string. In the range of the contact angle from 120° to 180°, the negative surface leader which does not appear on the insulator without a string is generated along the string by the attachment. In both ranges of the contact angle, the negative leader along the string promotes the flashover.     

Dynamics of RC helicopter and control

It is hard to fly an RC helicopter desirably because of its dynamical instability and the fast responce of motion, so that some stabilizing control system has to be developed. The first step of design is the derivation of the mathematical model. Dynamics of a helicopter is much complicated due to the rotating blades and its validity is difficult to be evaluated. In this paper, the mathematical model of a hovering RC helicopter is derived and its validity is confirmed experimentally by designing the stabilizing control system of the gimbal equipment which has three degrees of freedom, rolling, pitching and yawing. At the same time, two kinds of small sensors are investigated and used to control the above equipment.     

Expression, purification and characterization of recombinant crambin

Crambin, a small hydrophobic protein (4.7 kDa and 46 residues),has been successfully expressed in Escherichia coli from anartificial, synthetic gene. Several expression systems wereinvestigated. Ultimately, crambin was successfully expressedas a fusion protein with the maltose binding protein, whichwas purified by affinity chromatography. Crambin expressed asa C-terminal domain was then cleaved from the fusion proteinwith Factor Xa protease and purified. Circular dichroism spectroscopyand amino acid analysis suggested that the purified materialwas identical to crambin isolated from seed. For positive identificationthe protein was crystallized from an ethanol–water solution,by a novel method involving the inclusion of phospholipids inthe crystallization buffer, and then subjected to crystallographicanalysis, Diffraction data were collected at the Brookhavensynchrotron (beamline-X12C) to a resolution of 1.32 Åat 150 K. The structure, refined to an R value of 9.6%, confirmedthat the cloned protein was crambin. The availability of clonedcrambin will allow site-specific mutagenesis studies to be performedon the protein known to the highest resolution.     

Impulse Withstand Voltage between Foil Conductors on Printed Wiring Board

The impulse flashover voltage (FOV) in air across a short gap between foil conductors on a printed wiring board was studied to obtain fundamental and remarkable characteristics that will be useful in the design of wiring on the board. Two types of conductor configuration on the test boards were studied. The studied gap distance (d) ranged from 20 mum to 1200 mum. The board thicknesses (t) and the foil thickness (s) were changed from 60 mum to 800 mum and from 6 mum to 18 mum, respectively. The following results were obtained in the two types of the conductor configuration. FOVs for the boards in the studied range are independent of the foil thickness. FOV is almost un-influenced by the board thickness in the gap distance range shorter than 30 mum or 50 mum. In the gap distance longer than this range, FOV characteristics strictly depend on the board thickness; FOV for t=60 mum steeply increases with an increase in the gap distance, and FOV for t=800 mum gradually increases with an increase in the gap distance. These experimental results were discussed basing upon the calculation results of electric field around the HV foil conductor edge.     

Charging characteristics on dielectric surface by differentcharging processes in vacuum

This paper describes charging characteristics on a dielectric surface in vacuum by electron irradiation and field emission by a triple junction under negative and positive DC HV applications. The authors measured the 2-D distribution of electrostatic charging on a dielectric surface in situ. Experimental results revealed that the negative charge distribution caused by the electron beam had a conical shape over the whole surface. On the other hand, for a triple junction, it was an acute distribution around the triple junction. Moreover, they quantitatively investigated the difference of the 2-D charging distribution, using certain shape parameters, between the two charging processes mentioned above. In addition, they examined the time decay characteristics of the surface potential on the dielectric in vacuum     

Charging characteristics and electric field distribution on alumina as affected by triple junctions in vacuum

This paper describes the dependence of the charging characteristics on the electric field distribution on the alumina (Al/sub 2/O/sub 3/) surface as affected by the triple junction in vacuum. For HV electrical insulation design of vacuum interrupter, surface flashover in vacuum is very important problem to be solved. Attention should be paid to the fact that the insulation characteristics on the dielectric surface are strongly influenced by field emission of electrons from the triple junction and the accumulated charges on the dielectric surface. In order to clarify the charging mechanism, we measured the charging characteristics for various types of triple junctions. In particular, we focused on the influence of the electric field distribution along the solid dielectrics and near the cathode triple junction (CTJ) on the charging characteristics. The results confirmed that the electric field distribution strongly affected the 2-dimensional (2D) distribution of the surface charge on the dielectric sample. Consequently, it was found that positive charging was generated on alumina, when the incident angle of the electric line of force on the alumina surface became >60/spl deg/.     

真空中不同温度下典型脉冲功率领域用有机绝缘材料介电特性的研究

针对脉冲功率领域最常采用的环氧树脂、交联聚苯乙烯和聚乙烯3种典型绝缘材料,设计了一套适用于真空中且可以控温的标准三电极系统。在真空中对不同温度和频率下的介电参数(介电常数、介质损耗、表面电阻率和体积电阻率)进行了测试,并研究了烘烤对其介电性能的影响。结果表明:在不同的温度和频率下,3种材料中聚乙烯的εr和tanδ最小,环氧树脂最大;交联聚苯乙烯的体积电阻率和表面电阻率最大,环氧树脂和聚乙烯次之。烘烤可在一定程度上降低绝缘材料的介电常数和电阻率。综合比较3种材料的电性能和耐热性能,其中交联聚苯乙烯的性能最好,适用于真空脉冲功率领域绝缘。