Insulation recovery characteristics after current interruption by various vacuum interrupter electrodes

Insulation recovery characteristics after current interruption for a vacuum interrupter were investigated. We used spiral and axial magnetic field electrodes for comparison of the electrode structure, while CuBi and CuCr were also used for comparison of the contact material. This paper describes how the axial magnetic field electrode and CuCr (50%) performed best in our experimental data. In addition, we discussed reasons for the variation in characteristics between electrodes.     

Dielectric strength of a vacuum interrupter contact gap after making current operations

Experimental results concerning the breakdown voltage and prebreakdown current of a vacuum interrupter contact gap, after making current operations, are presented. The dielectric strength of the contact gap is lowest for a switching sequence during which a making of high current is followed by a no-load contact opening. The breakdown voltage is much lower than after making operation, followed by interruption of a sufficiently high current. The basic process of breakdown initiation appears to be field electron emission from a specific structure on the contact surface, created by weld rupture.     

The irreversibility of dielectric strength of vacuum interruptersafter short-circuit current interruption

The irreversibility of dielectric strength of commercial vacuum interrupters after a large number of consecutive short-circuit current interruptions is investigated in order to find out how dielectric performance of a vacuum interrupter degrades during its service life. Breakdown voltage data were measured in appropriate experiments in which the types of tested interrupters and arcing conditions were varied. It was found that for interrupters with poor contact material the dielectric strength can deteriorate severely, falling below limits required by standards. It is concluded that the most important for the irreversible decrease in the dielectric strength is the contact material, i.e. its erosion properties. It appears that contacts with axial magnetic field are less susceptible to irreversible changes in dielectric strength after short-circuit current interruption than contacts with transverse magnetic field     

Optical studies of surface discharge under dc voltage in vacuum

Utilizing a high-sensitivity photomultiplier tube (PMT) and an intensified charge coupled device (ICCD) camera, the light emission from the surface of polytetrafluoroethylene (PTFE) and alumina ceramic samples was investigated in vacuum under a stepped dc voltage in order to study the initiation and development of surface discharge. Different from the classical electrode contact by butting electrodes on a sample directly, to achieve a fine contact between electrodes and the surface of a sample, the metalized electrodes were employed by sputtering two additional gold contacts on each sample in advance. The two types of materials showed quite different optical characteristics. It was suggested that there were several processes possibly related to the initiation mechanism of the surface discharge. Besides the field electron emission from the cathode triple junction (CTJ) for the classical electrode contact, there were charge injection and transport in the surface states of dielectrics, and charge trapping and detrapping phenomena. Electroluminescence (EL) emission was emitted due to the radiative recombination of electrons and holes injected. These processes were strongly dependent on the electrode contact manner and the surface states of insulating materials.     

Theoretical studies on nanosecond surface discharge phenomena observed using Lichtenberg figure method

Contents The nanosecond surface discharge phenomena on the insulation plate have been studied using a Lichtenberg figure method. In the experimental setup voltages of +7 to 22kV, pressures of 150–760 Torr and pulse widths of 3–11 nsec were applied. The developing length of the positive corona streamer has been precisely measured against the applied voltage as a function of the pressure at a given pulse width.It was found that with increasing pressure there was an increase of inception voltage, while the time lag of corona streamer inception decreased. The developing velocity of charged particles on the insulation plate is discussed from a view point of a modified drift theory of charged particles. Finally, it is concluded that the detardation factor due to the photoelectric emission from the insulation plate plays a more important role in the corona streamer development than the electron collision ionization or the gas photoionization.

---

Theoretische Untersuchung von Gleitentladungen im Nano-Sekunden-Zeitbereich mit der Methode der Lichtenbergschen Figuren

Übersicht Es wurden Gleitentladungen auf Isolierstoffoberflächen im Nano-Sekunden-Zeitbereich mit der Methode der Lichtenbergschen Figuren untersucht. Experimentell wurden Spannungen von +7 bis 22 kV, Impulsbreiten von 3 bis 11 ns und Gasdrücke über dem Isolator von 150 bis 760 Torr angewendet. Die Elektrodenanordnung bestand aus einer Nadel und einer ebenen Elektrode, die mit der Isolierstoffplatte bedeckt war. Die Ausbreitungslänge der positiven Koronaentladung wurde als Funktion der Spannung bei verschiedenen Drücken und konstanter Impulsbreite gemessen.Es zeigt sich, daß sich bei zunehmendem Druck die Einsatzspannung der Koronaentladung erhöht, während sich die Verzögerungszeit vermindert. Die Ausbreitungsgeschwindigkeit der Koronaentladung auf der Isolierstoffoberfläche wird unter dem Gesichtspunkt einer modifizierten Theorie der Ladungsträgerbeweglichkeit auf der Oberfläche diskutiert. Bezüglich der Ausbreitung der Koronaentladung auf der Isolierstoffoberfläche zeigt ich, daß offensichtlich die Photoelektronenemission von der Oberfläche einen größeren Einfluß hat als Elektronenstöße und Photoionisation im Gasraum über dem Isolierstoff.

     

放电电流密度对DMFC交流阻抗的影响

测试了膜电极组件(MEA)在不同工作电流密度(J)下的交流阻抗谱,并用等效电路L1R1 (CR2)[ QR3(L2R4)]进行拟合.内阻变化最平缓,先减小,后略微增大,变化幅度小于初始值的10％;阴极法拉第阻抗随着电流密度的增大而减小,当J＞ 1.00 A/cm2时,产生的水膜导致三相界面减少后,该阻抗又增大;阳极反应...     

The influence of the contact surface shape on vacuum arc chute performance

The performances of vacuum arc chutes (VAC) that contain contact systems (CS) with axial magnetic fields in which the first contact surface is convex and the second contact surface enveloping the first one is concave are analyzed. The new CS allows for the VAC diameter and mass to be reduced; the additional contact pressure necessary to compensate for the electrodynamic force of contact throwing, which appears due to a short circuit in the current, to be decreased; and for the life span of the VAC to be increased greatly. The improvements to VAC performance is connected with the self-shielding phenomenon that takes place in the new CS.     

Equivalent circuit modeling of discharge current injected in contact with an ESD‐gun

The transient electromagnetic (EM) fields caused by an electrostatic discharge (ESD) have broadband frequency spectra, which cause serious failure to high‐tech information equipment. From this perspective, ESD testing for the EM immunity of the equipment is specified by IEC 61000‐4‐2, in which the detailed waveform of the discharge current injected onto the IEC recommended Pellegrini target in contact with an ESD‐gun is prescribed for calibration. However, the factors for determining the current waveform remain unclear, and thus the IEC prescribed current waveform is unlikely to be injected into actual equipment. In this study, based on the structure of an ESD‐gun, an equivalent circuit modeling is proposed for analyzing the discharge current injected onto a 50‐Ω SMA connector instead of the IEC target that has frequency‐dependent transmission characteristics. Its validity is confirmed by comparing the calculated current waveform with the measured result. The proposed circuit modeling is also validated from measurement of the discharge current injected onto a transmission line by the ESD‐gun. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 8–14, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10367     

Effect of surface current on photoelectron emission from mica

The relationship between photoelectron emission and the conduction mechanism on the surface of cleaved muscovite mica film was investigated; that is, under atmospheric conditions and subjected to UV irradiation, a low‐energy photoelectron counter measured the photothreshold energy of photoelectron emission from a surface treated by fast atom bombardment (FAB). Such emission was found to have a close relationship to the surface structure and surface conduction characteristics in that the photothreshold of the FAB‐treated mica surface varied from 5.0 to 5.8 eV, whereas no variation occurred in the untreated surface; the difference being attributed to different carriers of surface current. Results indicate that the surface states of mica play an important role in the electronic conduction of the surface, as well as the photoelectron emission from it. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 1–10, 2000     

短间隙磁控放电离子电流特性及影响因素研究

传统Penning磁控放电理论测量真空间隙要求真空间距大于10mm,无法测量现有短间距1~7mm触发真空开关内部真空度。因此,本文实验研究了在短间隙1~7mm条件下,磁控管放电离子电流特性及其影响因素。实验结果表明,Penning磁控放电下随着气压由10-4Pa向10-1Pa增加时,离子电流波形由三角波逐渐向方波转变,并非呈一方波不变。在电场和磁场满足Penning磁控放电着火条件下,离子电流峰值只受电场影响,与磁场无关;离子电流脉冲宽度只受磁场的影响,与电场无关。离子电流峰值与电荷随气压的变化呈幂函数变化。     

Determination of gas pressure in vacuum interrupter based on partial discharge

Partial discharge characteristics in air under a low vacuum region were studied to develop a diagnosis technique to determine the gas pressure in a vacuum interrupter. The pressures were set at from 1.3 Pa to 2.6 kPa in order to simulate the leakage of gas into the vacuum interrupter. The structure of the vacuum interrupter, the measurement and the circuit construction for the experimental setup were described. The measurement of partial discharge occurring inside the vacuum interrupter was performed with a current transformer, intensified charge coupled device (1CCD) camera and photomultiplier tube. The measurement of partial discharge light intensity with a photomultiplier tube was more sensitive compared with that measured with a current transformer. From this result, an attempt has been made to distinguish the pressure below and above 260 Pa on the basis of the rise time and peak intensity of discharge light pulses. A relatively longer rise time (2 mus) with a smaller magnitude (less than 0.5 mA) was attributed to a Townsend-like discharge at pressures below 260 Pa, while a sharper rise time ~(10-100 ns) with a larger magnitude (greater than 1 mA) was characterized as a streamer-like discharge above 260 Pa. In addition, the estimation of gas pressure in a vacuum interrupter was made based on phase-resolved discharge characteristics utilizing an artificial neural network.     

Effect of electrode surface roughness on breakdown conditioning under non-uniform electric field in vacuum

Breakdown (BD) characteristics in vacuum are strongly dependent on the electrode surface conditions, such as surface roughness. However, there is little known concerning the details of the relationship between the surface roughness and BD conditioning effect. In practical application, it is important to clarify how the surface roughness affects the breakdown conditioning characteristics, especially for the non-uniform field configuration. This paper discusses the effect of surface roughness on breakdown conditioning characteristics under non-uniform electric field in vacuum under applications of negative standard lightning impulse voltage. For this purpose, we examined the BD conditioning of a rod-to-plane electrode made of SUS304 and Cu-Cr. The surface roughness of R_a is controlled from 0.3 to 2.5 mum. Experimental results revealed that the enhancement of surface roughness of electrodes increases the number of BD to complete the conditioning effect. We explained the results from the observed results of the electrode surface. Consequently, we could clarify the effect of surface roughness on the conditioning effect under non-uniform electric field in vacuum quantitatively.     

Calculation of an interruption arc current and time of arc quenching in low-voltage current breakers

For the analytical calculation of an arc current in the process of arc quenching, an average statistical curve of a change of an interruption arc voltage is constructed and mathematically described. This curve is based on experimental data obtained during short-circuit current interruption by nonspeed and selective circuit breakers of different design, in particular, with different volumes of arc chutes. Features of short-circuit current interruption in a three-phase system are considered.     

真空断路器触头弹跳性能分析

触头的弹跳性能是真空断路器稳定工作的重要指标之一，通过对VS1—12型真空断路器（配用永磁操动机构）的分合闸弹跳性能进行理论和试验分析，得出了其产生弹跳的原因及处理的基本方法。     

Changes of Cu electrode surface conditions and prebreakdown current characteristics caused by repetitive breakdowns in a vacuum

To clarify factors influencing the conditioning effect produced by repetitive breakdowns of a vacuum gap, changes of electrode surface conditions before and after 500 breakdowns caused by impulse voltage application were investigated. Changes of prebreakdown current characteristics were also investigated. The electrode material was copper. The electrode surfaces were analyzed by X‐ray photoelectron spectroscopy (XPS). XPS analysis revealed that the electrode surfaces were completely cleaned by repetitive breakdowns. Prebreakdown characteristics were classified into three patterns: (1) displacement current alone, (2) field emission current as well as displacement current, (3) explosive current increase. Patterns (1) and (4) were observed mainly in the early stage of repetitive breakdowns, while pattern (2) was found in the later stage. It has been concluded that the breakdown mechanism changes during conditioning by repetitive breakdowns. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 11‐18, 2000     

Electrical contact between a local discharge on an electrolyticsolution and the solution surface [wet polluted insulators]

An electrolytic solution surface was used to simulate the surface of wet polluted insulators. A local discharge propagates on the solution surface when a voltage is applied to the surface. The electrical contact between the local discharge on the electrolytic solution and the solution surface was examined. The distribution of the current from the local discharge to the solution is estimated from the potential distribution measured with probes placed in the solution. The resistivity of the solution is varied from ~80 to 370 Ω cm. Impulse voltages of 2/80 μs, 10/800 μs and 100/2500 μs are used as the applied voltage. The peak value of the applied voltage was 1.05 to 1.4× the 50% flashover voltage V₅₀ under each set of experimental conditions. As a result, it is found that most of the discharge current flows from the tip part of the local discharge, and the current from the local discharge column is considerably lower. Furthermore, the distribution of the current from the local discharge to the solution is found to be barely influenced by the resistivity of the solution, the peak value of the applied voltage, or the applied voltage waveform     

涡流脉冲热像对钢轨滚动接触疲劳裂纹表面长度的量化评估研究

涡流脉冲热像技术作为一种新型的无损检测技术,兼具有感应加热非接触、高效和红外热像快速直观等优点,已应用于不同领域关键部件的缺陷检测与评估.针对钢轨踏面存在的滚动接触疲劳裂纹,利用涡流脉冲热像开展裂纹表面长度量化研究分析.针对滚动接触疲劳裂纹形貌分布复杂这一特点,设计了一套结合裂纹响应提取和裂纹识别的流程.并通过线性拟合...     

Study of propagation phenomena of partial discharge pulses in gasinsulated substation

This paper describes the results of tests and discussions carried out to develop a system for monitoring partial discharges generated in gas-insulated substations (GIS). They include the propagation characteristics and the mechanisms of partial discharge pulses in the GIS, the results of computer simulation, and the results of comparisons with previous tests to verify the partial discharge locating method