Quasi-uniform Field Research Articles

임펄스전압에 대한 N2가스의 절연파괴특성

This paper aims to examine the possibility of using an environmentally friendly N₂ as an alternative gas to SF?. For this purpose, we have investigated breakdown characteristics of N₂ under impulse voltages in a quasi-uniform electric field gap. The 1.2/50[㎲] lightning impulse voltage, switching impulse voltages and oscillatory impulse voltages were applied at the test gap. The electric field utilization factor ranges from 0.5 to 0.8. The experimental data of SF6 and N₂ acquired in the same experimental condition are presented in parallel for comparison. As a result, the breakdown voltages in SF? and N₂ are linearly increased with the gas pressure, also the breakdown voltages in N₂ are increased with increasing the gap distance and electric field utilization factor. The positive breakdown voltages are higher than the negative breakdown voltages. The nagative basic lightning impulse withstand level of 150[㎸] in N₂ of about 0.5[㎫] is nearly equal to that in SF? of 0.15[㎫]. It is seen from the results obtained in this work that N₂ can be used as an eco-friendly alternative gas to SF? in distribution power equipment.

Research on identification of nonlinear damping based on time frequency analysis

According to the relationship between damping, strain and time, the piecewise linear wavelet transform and the piecewise linear short time Fourier transform methods are put forward to identify the nonlinear damping of alloy material. The overall nonlinear property of damping is derived from the piecewise local linearisation. The satisfied results obtained from simulations demonstrate that the methods presented are effective. Usually, damping measured in the non-uniform stress field is only a volumetric average. To overcome this deficiency, a trapezoid specimen with quasi-uniform stress field is developed on the basis of the traditional damping experimental equipment. The damping measurement experiment is carried out. The measurement signal is analysed by the two methods presented. The relation curve of damping versus strain has shown that the damping capacity of the alloy Al–33Zn–6Si increases with the increasing strain. The relationship between damping and strain appears obviously nonlinear.

뇌임펄스전압에 대한 SF6와 dry-air의 절연특성

본 논문은 준평등전계에서 뇌임펄스전압에 대한 SF?와 dry-air의 절연파괴 특성에 대하여 기술하였다. 준평등전계로 사용된 구-평판전극계의 전계이용률은 71[%]이다. SF6는 0.1∼0.2[㎫] 범위에서, dry-air는 0.2∼0.6[㎫]에서 SF6와 dry-air의 절연파괴전압을 임펄스전압의 극성과 가스압력에 따라 측정?분석하였다. 그 결과 뇌임펄스전압에 대한 두 가스의 절연파괴전압은 정극성이 부극성보다 높았으며, SF?의 절연파괴전압이 dry-air의 절연파괴전압보다 약 2.67배정도 높았다. 본 연구결과는 뇌서지에 대하여 우수한 성능을 가지는 배전기기에서 SF?의 대체가스 성능 평가에 유용한 정보가 될 것이다.

준평등전계에서 임펄스전압에 대한 N2가스의 절연파괴특성

This paper presents dielectric characteristics of gas under impulse voltages in a quasi-uniform electric field gap. The experiments were carried out at the test gap applied by the 1.2/50[] lightning impulse voltage, 180/2500[] switching impulse voltage, 500[ns]/1[MHz] very fast transient overvoltage(VFTO). The gap separation of sphere-to-plane electrodes was 14[mm] and the electric field utilization factor was about 71.2[%]. The gas pressure ranges from 0.2 to 0.6[MPa]. As a result, the electrical breakdowns are occurred by streamer discharge. Breakdown voltages are linearly increased with the gas pressure and the highest breakdown voltage is appeared under the VFTOs having fast rising time. Breakdown voltages under the positive impulse voltages were higher than those under the negative ones, and also the time to breakdown in the positive polarity is longer than that in the negative polarity.

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-standard Lightning Impulse Waveforms - Breakdown Characteristics for Double-frequency Oscillations under Non-uniform Electric Field

An effective means of rationalization of insulation design for gas insulated switchgear (GIS) is the evaluation of insulation characteristics under actual surge waveforms in the field called non-standard lightning impulse waveforms (non-standard-LIWs). The preceding researches examined quasi-uniform electric field SF6 gas gaps and partly the cone-shaped insulating spacers that represent an insulation element of GIS in order to obtain the insulation characteristics under various non-standard-LIWs. As a result, the breakdown voltages under non-standard-LIWs are higher than those under standard-LIWs, allowing the authors to identify a road map for rationalizing GIS insulation designs. In applying this rationalization technique, experimental study was conducted on single-frequency oscillations to identify the influence of the non-uniform electric field. As a result, the breakdown characteristics were found to be different from those in a quasi-uniform electric field. This paper describes the insulation characteristics under double-frequency oscillations as typical examples of nonstandard-LIWs while varying the applied voltage polarities, frequencies, and damping factors in order to study the influences of non-uniform electric field in further detail. The experimental results show that positive-polarity waveforms pose more demanding insulation requirements and that it is appropriate to conduct experiments using positive-polarity in order to consider dielectric strengths. Moreover, it was confirmed that changing the waveform parameters under positive-polarity did not cause major changes in the breakdown voltages, which remained constantly higher than those under standard-LIWs, and gave little influence to the application of the rationalization techniques.

A Study of Parameters Influencing Streamer Inception in Silicone Gel

This paper presents an experimental study of streamer inception in a silicone gel. Many parameters are able to influence the inception of discharges in a gel: voltage wave shape, electrode geometry, temperature, etc. In this work, streamer inception is studied in various conditions of electrode shapes (from sharp points up to quasi-uniform field), voltage (ac, dc, impulse voltage) and temperature. Streamer inception is detected by the measurement of breakdown voltages in selected conditions. The results obtained show that streamer inception field varies when the electrode shape is changed, in a similar way as in liquids: the inception field decreases when the electrode surface increases. On the other hand, temperature and voltage wave shape have almost no influence on the inception field. Results are discussed in comparison with data already obtained in liquids in similar conditions.

ガス絶縁開閉装置の非標準雷インパルス波形に対する不平等電界下での絶縁破壊特性

To improve insulation specification of a gas insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF6 gas under actual surge (called non-standard lightning impulse waveform) occurring in the field substation. The authors had observed the insulation characteristics of SF6 gas gap under various types of non-standard lightning impulse waveforms and compared them with under standard lightning impulse waveform quantitatively. From the investigation of the experimental results, the evaluation method for real surges is shown and the method is applied to typical surges for various UHV and 500kV systems. In the proceeding study, therefore, only for the quasi-uniform electric field (with a typical range of the field utilization factors in the bus of a GIS) was investigated. In this paper, the insulation characteristics of SF6 gas gap for non-uniform electric field were observed experimentally and investigated about the evaluation method of converting non-standard lightning impulse waveforms equivalently to the standard lightning impulse waveform.

Tunable narrowband terahertz emission from mastered laser–electron beam interaction

A tunable source of coherent narrowband terahertz radiation is realized by using a laser to modulate the emission characteristics of a relativistic electron beam. In the quest for sources of optical radiation in the terahertz domain, promising candidates are nonlinear optical processes occurring when an intense laser beam interacts with a material medium1,2,3,4,5. Besides conventional media (such as crystals), relativistic electrons also show striking nonlinear collective behaviours, which can lead to powerful laser-induced coherent emission6,7, revealing huge potentials of these devices as terahertz sources8. However, up to now only broadband emissions were reported, and experimental control of their radiation properties, such as their spectra9,10, remained an important challenge. Here, we demonstrate the possibility of mastering the coherent emission experimentally by producing tunable narrowband terahertz radiation. The interaction is made to occur between an electron beam and laser pulses possessing a longitudinal quasi-sinusoidal modulation, and the narrowband emission occurs in a region of quasi-uniform magnetic field. The process therefore strongly differs from classical synchrotron radiation experiments, where narrowband emission occurs inside a periodic magnetic field.

Effect of electrode surface roughness and dielectric coating on breakdown characteristics of high pressure CO2 and N2 in a quasi-uniform electric field

SF6 gas has excellent dielectric strength and interrupting capability and is used in various applications such as gas insulated switchgear (GIS) in substations. However, since SF6 has a high global warming potential (GWP), it is imperative to reduce its use and develop recovery technology for its reuse. This paper examined the potential of alternative insulating gases for GIS, determining experimentally the ac and lightning impulse breakdown characteristics of CO2 and N2 gases, which have little environmental impact, in a quasi-uniform electric field. The effect of electrode surface roughness is greater in N2 than in CO2. The impulse ratio in a quasi-uniform electric field was smaller in N2 than in CO2 at low pressure, but this reversed when the pressure reached 1.2 MPa. The dielectric strength of an electrode with a dielectric coating was approximately equal to that of a specular-finish bare electrode in either CO2 or N2 when an ac voltage was applied. When lightning impulse voltage was applied, a significant improvement of dielectric strength was observed if a dielectric coating was applied to the electrode considered to be the initial electron source.

Deactivating Metal Particle by Optimizing Insulation Configuration in Spark Gap Switch

As a new method to protect the spark gap from metal particle contamination, the effect of the metal inserted insulator on the controlling behavior of metal particles was investigated in a quasi-uniform electric field. Considering that the inserted metal electrodes can decrease the electric field around the insulator and divert the electrostatic force away from the insulator, the method can be used to prevent the particles from moving toward the insulator so as to reduce the possibility of a breakdown. The inserted metal electrodes can reverse the direction of the particles' horizontal motion. A study on the insulator shape indicates that the inserted metal electrodes can repulse the particle and improve the particle lifting voltage significantly near the vertical surface of the insulator or ribbed insulator. For the insulator with a tilting surface the inserted metal electrodes have little influence on the particle motion. In addition, the size of the inserted electrodes shows a significant effect on the control of particle motion.

Three-Dimensional Magnetic Motion Capture Using Four Square Coils

A new magnetic method of motion capture is proposed. To produce reference magnetic fields, this method uses a simple coil system which consists of two pairs of square coils, which are placed along the sides of two sets of opposite surfaces of a cubic frame where one pair of the coils is rotated through 90 degrees from the other. Two quasi-uniform magnetic fields and one gradient magnetic field are successively generated by these coils and are measured by a triaxial magnetic sensor attached to the moving object. The coordinates of the object are calculated by the Gauss-Newton method from several scalar functions defined by scalar products of the measured magnetic field vectors. The effective area where motion capture can be stably performed was numerically estimated to be a little larger than a cubic area with an edge length of 60 percent of that of the cubic frame.

Energy Spectra Stemming from Interactions of Alfvén Waves and Turbulent Eddies

We present a numerical analysis of an incompressible decaying magnetohydrodynamic turbulence run on a grid of 1536{3} points. The Taylor Reynolds number at the maximum of dissipation is approximately 1100, and the initial condition is a superposition of large-scale Arn'old-Beltrami-Childress flows and random noise at small scales, with no uniform magnetic field. The initial kinetic and magnetic energies are equal, with negligible correlation. The resulting energy spectrum is a combination of two components, each moderately resolved. Isotropy obtains in the large scales, with a spectral law compatible with the Iroshnikov-Kraichnan theory stemming from the weakening of nonlinear interactions due to Alfvén waves; scaling of structure functions confirms the non-Kolmogorovian nature of the flow in this range. At small scales, weak turbulence emerges with a k{perpendicular}{-2} spectrum, the perpendicular direction referring to the local quasiuniform magnetic field.

Breakdown Characteristics of N2O Gas Mixtures for Quasiuniform Electric Field under Lightning Impulse Voltage

From the viewpoint of mitigating global warming by SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, this paper discusses breakdown (BD) characteristics of different electronegative gas mixtures with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O gas as SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas substitutes for quasi-uniform electric field under lightning impulse voltage applications. Experimental results revealed the positive synergism in breakdown strength of binary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O / CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and ternary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O / CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures, respectively. Furthermore, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas as a retardant gas was also mixed with the electronegative gas mixtures in order to reduce the electron energy into the effective levels of electron attachment ability by the electronegative gas mixtures. As the result, ternary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O / CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and quaternary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O / CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures could exhibit the significant synergistic effect in breakdown strength. The optimum mixture rate of quaternary N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O / CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> / N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures was consistent with that estimated by assuming the independent contribution of component gases to the improvement of impulse BD characteristics.

New Methods for Nonlinear Damping Identification of Damping Alloy

This paper presents two methods for the identification of nonlinear internal damping of alloy. One is the moving autoregressive model (MARM) method, and the other is the time-varying autoregressive model (TVARM) method. These procedures have been successfully implemented on two numerical examples. Comparison between simulation results demonstrates that the computation accuracy of the TVARM method is higher than that of the MARM method. In the experiments, the internal damping properties of the alloy Al-33Zn-6Si are researched, employing the rectangle beam with a nonuniform stress field and the trapezoid beam with a quasi-uniform stress field, respectively. Experimental results show that the internal damping of the alloy increases with the increasing strain and appears a nonlinear behavior. Moreover, the damping values of the trapezoid beam are relatively higher than those of the rectangle beam. Compared to the MARM method, the TVARM method can give a better description of nonlinear damping because the relation curve of loss factor versus strain obtained by the TVARM method is smoother than that obtained by the MARM method.

Nucleation of Protein Crystals under the Influence of Solution Shear Flow

Several recent theories and simulations have predicted that shear flow could enhance, or, conversely, suppress the nucleation of crystals from solution. Such modulations would offer a pathway for nucleation control and provide a novel explanation for numerous mysteries in nucleation research. For experimental tests of the effects of shear flow on protein crystal nucleation, we found that if a protein solution droplet of approximately 5 microL (2-3 mm diameter at base) is held on a hydrophobic substrate in an enclosed environment and in a quasi-uniform constant electric field of 2 to 6 kV cm(-1), a rotational flow with a maximum rate at the droplet top of approximately 10 microm s(-1) is induced. The shear rate varies from 10(-3) to 10(-1) s(-1). The likely mechanism of the rotational flow involves adsorption of the protein and amphiphylic buffer molecules on the air-water interface and their redistribution in the electric field, leading to nonuniform surface tension of the droplet and surface tension-driven flow. Observations of the number of nucleated crystals in 24- and 72-h experiments with the proteins ferritin, apoferritin, and lysozyme revealed that the crystals are typically nucleated at a certain radius of the droplet, that is, at a preferred shear rate. Variations of the rotational flow velocity resulted in suppression or enhancement of the total number of nucleated crystals of ferritin and apoferritin, while all solution flow rates were found to enhance lysozyme crystal nucleation. These observations show that shear flow may strongly affect nucleation, and that for some systems, an optimal flow velocity, leading to fastest nucleation, exists. Comparison with the predictions of theories and simulations suggest that the formation of ordered nuclei in a "normal" protein solution cannot be affected by such low shear rates. We conclude that the flow acts by helping or suppressing the formation of ordered nuclei within mesoscopic metastable dense liquid clusters. Such clusters were recently shown to exist in protein solutions and to constitute the first step in the nucleation mechanism of many protein and nonproteinsystems.

High-Gain Active Composite Right/Left-Handed Leaky-Wave Antenna

A novel high-gain active composite right/left-handed (CRLH) metamaterial leaky-wave antenna (LWA) is presented. This antenna, which is designed to operate at broadside, is constituted by passive CRLH leaky-wave sections interconnected by amplifiers, which regenerate the power progressively leaked out of the structure in the radiation process in order to increase the effective aperture of the antenna and thereby its gain. The gain is further enhanced by a matching regeneration effect induced by the quasi-unilateral nature of the amplifiers. Both the cases of quasi-uniform and binomial field distributions, corresponding to maximum directivity and minimum side-lobe level, respectively, have been described. An active LWA prototype is demonstrated in transmission mode with a gain enhancement of 8.9 dB compared to its passive counterpart. The proposed antenna can attain an arbitrarily high gain by simple increase of the length of the structure, without penalty in terms of return loss and without requiring a complicated feeding network like conventional array antennas

Growth and profile modification of carbon nanotubes designed for field emission applications by hydrogen plasma pretreatment

In chemical vapor deposition (CVD) of carbon nanotubes (CNTs), formation and density control of nano-sized catalysts is critical in obtaining vertically aligned nanotubes. Two commonly adopted methods of achieving catalytic nanoparticles are heat-treatment and plasma pretreatment of a catalytic thin film. In this study, the CNTs were grown inside silicon trench arrays utilizing microwave plasma CVD. The effects of hydrogen plasma pretreatment of the nickel catalysts on the growth of CNTs and their subsequent field emission characteristics were investigated. Without plasma pretreatment, randomly oriented, short CNTs with low tube density grew. With plasma pretreatment, vertically aligned and highly dense CNTs were observed to grow but longer pretreatment resulted in shorter CNTs. The plasma pretreatment technique was successfully employed to achieve gated CNT microcathodes with a convex-shape surface profile, having quasi-uniform electric field distribution on the CNT tips. CNT sample with 1-min pretreatment exhibited the lowest turn-on field of ∼5 V/μm and achieved a current density of 1.0 mA/cm 2 at a threshold field of 8.0 V/μm. Overall, the hydrogen plasma pretreatment has been demonstrated to be a useful technique for the synthesis of vertically aligned CNTs and surface profile tweaking in gated structures.

The ground state of two-dimensional electrons in a nonuniform magnetic field

An exact solution to the Schrodinger equation for the ground state of two-dimensional Pauli electrons in a nonuniform transverse magnetic field H is presented for two cases. In the first case, the field H depends on a single variable, H = H(y), while in the second case, the field is axially symmetric, H = H(ρ), ρ2=x2+y2. The electron density distributions n = n(y) and n = n(ρ) that correspond to a completely filled lower level are found. For quasiuniform fields of fixed sign, the functions n(y) and n(ρ) are locally related to the magnetic field: n(y) = H(y)/ϕ0 and n(ρ) = H(ρ)/ϕ0, where ϕ0 = hc/|e| is a magnetic flux quantum. Magnetic fields are considered that are periodic, singular, and bounded in the plane xy. Finite electron objects in a nonuniform magnetic field are analyzed.

Fabrication of aligned convex CNT field emission triode by MPCVD

In this work, vertically aligned carbon nanotubes (CNTs) were used to form a gated microcathode with a convex surface profile, being selectively synthesized from Microwave Plasma Chemical Vapor Deposition (MPCVD) with nickel (Ni) as a catalyst. A single-mask microfabrication process achieved an array of 10 μm × 10 μm CNT microtriodes with self-aligned gate. The convex profile is important in preventing cathode-gate leakage without resorting to more complicated fabrication processes or utilizing a gate over-etching approach. The main mechanism for the formation of the convex-shaped CNT microcathodes was investigated and is proposed to be the result of plasma etching of CNTs near the gate opening region due to higher plasma density during the growth process, leading to slower growth rate or shorter CNTs at the circumferential area. Additionally, previous simulation work has predicted that this type of surface profile is beneficial for more quasi-uniform electric field distribution on CNT tips. Field emission characteristics of the triode device were investigated, whereby a gate turn-on voltage as low as 25 V was achieved. The low turn-on of the device is mainly due to the smaller gate aperture made possible by the convex-shaped CNT microcathodes.

高気圧SF&lt;sub&gt;6&lt;/sub&gt;の雷サージ領域V&amp;mdash;t特性の定量的評価

Since gas-insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore the sparkover voltage and time (V-t) characteristics of SF6 in a very short time range of less than 1μs are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V-t characteristics of SF6 at a gas pressure of 0.5MPa using a steep-front square impulse voltage under a quasi-uniform field gap and presents a quantitative evaluation of the V-t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V-t characteristics of positive polarity were observed to be almost flat over a long time range from 80ns to 10μs, and rose steeply over a short time range from 80ns down to 20ns. For negative polarity, the V-t characteristics exhibit a gentle rise from 200ns down to 40ns. In the estimation of V-t characteristics, the equal-area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lightning impulse, we found that the application of equal area criterion with these parameters for the non-oscillating impulse and oscillating impulse of up to 5.3MHz as a model of lightning surge and disconnector switching surge is possible.