Statistical Property of Breakdown between Electrode and Shield in High-Voltage Vacuum Interrupter

Statistical property of the breakdown between stainless or copper electrode and stainless arc shield is studied by applying (250 × 2000)-?s switching impulses to model vacuum interrupters. Higher breakdown voltages are obtained in negative polarity than in positive polarity. The effective area of breakdown which takes the electric-field distribution on the anode surface into account is introduced to explain the polarity effect of breakdown voltage using Weibull statistics.     

Technological progress of axial magnetic field vacuum interrupters

New methods have been developed for investigating vacuum arcs applied to the improvements of vacuum interrupter electrodes. Electrode surface temperature measurements reveal the anode surface melting condition at the current interruption and its influence on interruption capability, and a digital image processing technology gives us a clear understanding of the arcing phenomenon. Measurements and test results have shown the advantages of axial magnetic field electrodes in increasing the interruption capability of vacuum interrupters. It is confirmed that axial magnetic field electrodes are superior to other types of electrodes, and we believe that these new investigation methods promote the optimization of the electrode structure and the realization of higher voltage and current rating vacuum interrupters     

Experimental characterization of arc instabilities and their effecton current chopping in low-surge vacuum interrupters

In low-current vacuum arcs, short (<500-ns) peaks in arc voltage (instabilities), with a height of up to ten times the normal arc voltage, are abundantly present. The instabilities are thought to be caused by ion starvation near the anode. A number of parameters of these instabilities, occurring in vacuum interrupters with AgWC (low-surge) and CuCr (conventional) contact material, have been analyzed statistically in a practical AC circuit. A striking difference in median rate of rise and height is found. It is found plausible that these parameters reflect important switching characteristics such as recovery (peak rate of rise) and current chopping level (peak height). Also, the dependence of the parameters on momentary arc current and contact distance is studied and explained qualitatively     

Use of Axial Magnetic Fields to Improve High-Current Vacuum Interrupters

When an axial magnetic field is applied to a vacuum arc, the arc tends to be stabilized in its diffuse mode. A minimum arc voltage is found for a certain magnetic field. In this condition, interrupting current is significantly increased, and it is nearly proportional to the diameter of electrodes. About ten years ago, a practical axial magnetic field electrode was developed for vacuum circuit breakers. Since then, through various improvements in its structure, this electrode has been refined for practical application in vacuum circuit breaker interrupters. The application has successfully covered not only medium-voltage circuit breakers, but also high-voltage (84 kV), dc high-voltage, and high-current circuit breakers. In this paper, ten years experience in this area is described.     

Characteristics of a vacuum switching contact based on bipolaraxial magnetic field

Axial magnetic field (AMF) contacts can increase the interruption capability of vacuum interrupters. Depending on the design, the principles of the local axial field arrangement are different. For unipolar arrangements the direction of the axial magnetic field is the same within the whole contact area. For bipolar arrangements, the polarity of the field changes once. In this paper investigations have been carried out to characterize a bipolar AMF contact system and to test its interruption performance. The influence of the bipolar AMF on the arc development and the thermal stress is described by high speed camera and contact surface pictures. In addition, three-dimensional AMF simulations have been performed by means of a finite-element program to estimate the influence of slots within the contact plates on the AMF performance. The high interruption capability of the bipolar AMF contact system has been verified in different test laboratories up to 12 kV/80 kA_RMS (symmetrical) and 36 kV/40 kA_RMS (including 40% DC) by three and single phase tests. The investigations are completed by measuring the post-arc current and the shield-potential during recovery period, both describing the switching behavior of the contact system     

Vacuum interrupter design based on arc magnetic field interactionfor horseshoe electrode

Computational methods for evaluating the complex magnetic field structure in axial magnetic field type vacuum interrupters based on horseshoe electrode geometry are demonstrated. Arcing behavior can only be understood by incorporating an arcing model. An essentially low-current arcing model is capable of predicting the high-current arcing behavior and can be used to optimize the contact structure     

Physical and theoretical aspects of a new vacuum arc controltechnology-self arc diffusion by electrode: SADE

Our new vacuum arc control technology SADE doubles the high current interruption capability of our conventional axial magnetic field technology. First, we describe the vacuum arc motion behavior recorded by a high speed charge-coupled device video camera. This arc behavior is closely related to axial magnetic field intensity. In particular, it depends on the profile of the externally generated axial magnetic field. The anode spot is likely to move to the highest magnetic field intensity. Second, we describe analytical results for concentration of vacuum arc at the anode side contact surface. This analysis implies the possibility of an ideal magnetic field profile and intensity for vacuum arc control. Finally, we describe experimental results for vacuum arc control compared with the physical and theoretical results mentioned above, and we show a practical electrode configuration for vacuum interrupters and its application in a high current interruption experiment     

The Investigation of Copper-Chromium Contacts in Vacuum Interrpters Subjected to an Axial Magnetic Field

The characteristics of a vacuum arc between CuCr contacts under an axial magnetic field have been investigated. Test samples were made of CuCr contacts, and the arcing voltage was measured. The arcing voltage of the CuCr contacts under an axial magnetic field is lower than that of pure copper contacts by 10-20 V. From the measurement of the post-arc current and interruption test results, it was found that the arc concentrates and a part of the electrode melts at a rather low current, but that the electrode melting does not affect the interrupting capability. Also, the insulation characteristics were measured. With respect to voltage conditioning, high-current conditioning improved the breakdown voltage by 50 percent for a 20-mm gap and by 100 percent for a 3-mm gap. These test results show that CuCr contacts, used with axial magnetic fields, are promising for use in high-voltage and high-power vacuum interrupters.     

Theoretical basis of the design of magnetic field generator for DCvacuum circuit breakers

The magnetic field generator (MFG) for producing the transverse magnetic field switching off the direct current in the vacuum chamber is presented. The method of calculating generator coils inductance for different geometrical dimensions and various systems of coils connections, assuming the maximization of the magnetic flux density value in the contact gap and the maximization of the vacuum chamber switching ability, is presented. The possibilities of MAG program for designing magnetic field generators is described     

The behavior of vacuum arcs between spiral contacts with small gaps

The application of small gaps in high-current vacuum interrupters highlights the interdependence of the contact design, the contact gap, and the arc behavior. In this investigation, a framing camera was used to record the appearance and motion of drawn vacuum arcs between spiral-petal contacts with final gaps of 2 to 3 mm. After the rupture of the molten metal bridge, a high-pressure arc column formed and expanded across the width of the spiral arm. With a single arc column for the duration of the half-cycle, an intense anode spot formed if the peak current exceeded ~15 kA. Compared to results previously obtained at larger gaps, the arc motion was greatly reduced, and severe contact damage was observed at lower currents     

Cold-field switching in PVDF-TrFE ferroelectric polymer nanomesas

Polarization reversal in ferroelectric nanomesas of polyvinylidene fluoride with trifluoroethylene has been probed by ultrahigh vacuum piezoresponse force microscopy in a wide temperature range from 89 to 326 K. In dramatic contrast to the macroscopic data, the piezoresponse force microscopy local switching was nonthermally activated and, at the same time, occurring at electric fields significantly lower than the intrinsic switching threshold. A "cold-field" defect-mediated extrinsic switching is shown to be an adequate scenario describing this peculiar switching behavior. The extrinsic character of the observed polarization reversal suggests that there is no fundamental bar for lowering the coercive field in ferroelectric polymer nanostructures, which is of importance for their applications in functional electronics.     

A high current electron switch with deep volume charge compensation

The current switching by means of a gas-filled electron switch has been studied experimentally and theoretically. The switch showed complete controllability under deep volume charge compensation conditions. The switched current density was an order of magnitude higher than the current density of a similar vacuum switch     

Sculpting the vacuum in a photonic band gap micro-chip

We describe the engineering of the electromagnetic vacuum in a 2D–3D photonic bandgap (PBG) hetero-structure. This facilitates the development of novel active devices and the observation of novel quantum electrodynamic phenomena. We consider a specific architecture suitable as an all-optical micro-transistor capable of novel ultra-fast response with low switching power requirements. This relies on a unique collective atomic switching and population inversion achieved by coherent resonant pumping in a suitably engineered vacuum. Specific waveguide architectures within the 3D PBG micro-chip provide local density-of-states (LDOS) peaks near their cutoff frequency. These provide “building blocks” for electromagnetic vacuum engineering without recourse to conventional high Q-factor micro-cavities. For the all-optical micro-transistor, a fork shape LDOS within the micro-chip is desirable, using trimodal waveguide architecture. We delineate the functional robustness of these architectures to disorder caused by manufacturing errors within the PBG micro-chip.     

Twenty-five years of progress in vacuum arc research andutilization

Progress in understanding and applying vacuum arcs is reviewed. Laser diagnostics have demonstrated the existence of micron-sized regions in the cathode spot plasma having electron densities exceeding 10²⁶ m^-3. The expanding plasma produces a highly ionized jet whose ions typically have charge states of 1-3 and energies of 50-150 eV. Gas dynamic and explosive emission models have been formulated to explain cathode spot operation. In cases where the arc is constricted at the anode, forming an anode spot, or the anode is thermally isolated, forming a hot anode vacuum arc, material emitted from the anode may dominate the interelectrode plasma. Evaporation from liquid droplets may also provide a substantial component of the plasma, and the presence of these droplets can have deleterious consequences in applications. The vacuum arc has been extensively utilized as a plasma source, particularly for the deposition of protective coatings and thin films, and as a switching medium in electrical distribution circuit breakers     

Switching phenomena in CdIn2S4 thin films

Summary Two kinds of switching phenomena in CdIn₂S₄ polycrystalline and amorphous thin films which were prepared by the vacuum evaporation method and the d.c. sputtering method, respectively, were studied. One is the so-called memory switching phenomenon arising from the low resistive filament path. Another is a characteristic switching phenomenon in which the resistivity abruptly changes whenever the ambient temperature reaches a critical value. The switching time is fast and about 100 ns. This switching phenomenon is related to the native defects in the CdIn₂S₄ lattice, because they can be observed in the polycrystalline as well as in the amorphous thin films. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

太赫兹源场致发射电子源

通过粒子模拟(PIC)软件模拟计算了在ps级别下二极与三极结构碳纳米管场致发射的电流密度与电子注聚焦性能。阳极电压在2 kV时,二极结构下电流密度达到1.85 A/cm2;三极结构下,栅压700 V时发射电流密度达到2.3 A/cm2,且在一定的三极结构参数与电极电压下,可以获得较好的电子注聚束效果。通过碳纳米管二极管发射实验,获得了6.6 A/cm2的发射电流密度,总发射电流达到52.1 mA,可以为太赫兹器件提供连续发射的电子注。     

Bistable behaviour in squeezed vacua: I. Stationary analysis

A time-independent theoretical and numerical analysis of an optical bistable model of two-level atoms in a ring cavity, driven by a coherent field and in contact with a squeezed vacuum field is presented in the two cases of absorptive and dispersive optical bistability (OB). In the former case, a suitable choice of the phase of the squeezed vacuum field reduces the threshold for OB to occur compared with the normal vacuum case. In the latter case, regions of OB are identified as one or two disconnected simple closed curves depending on the cooperation parameter [0pt] : is the maximum possible value of the critical value of C at fixed values of the squeezed vacuum field parameters. Phase switching effects between different (output) states of the system is investigated in detail. In the absorptive case, one- or two-way optical switching is possible depending on [0pt] . We also present results which demonstrate more complicated switching behaviour in the dispersive case. Received 12 March 1999 and Received in final form 20 August 1999     

Upon the influence of the post-arc current on the low voltageswitching process in vacuum

The paper presents one stage of the scientific research, performed for the investigation of the post-arc (p.a.) current within low voltage switching process in vacuum, when interrupting short-circuit currents of high values. A large power equipment, supplied by the mains and providing an accurate reproduction of the processes, concerning the short circuit phenomenon (U=1.5 kV; I=100 kA) was used. An experimental model, which can reproduce the switching conditions of the power circuit-breaker in vacuum, was available as well. The influence of an axial magnetic field on the p.a. current and the switching process was also explored     

Mechanism analysis of switching direction transformation in an Er2O3 based RRAM device

The resistive random access memory (RRAM) based on resistive switching effect has considered to be the most advanced next generation memory, in which the switching direction determines the order of reading-writing. In this work, the rare-earth metal Er₂O₃ was used as functional layer, and Ag and indium-tin-oxide (ITO) are selected as top and bottom electrode to fabricate resistive switching device. Further, it is observed that the switching direction and memory window of resistive switching device can be regulated by exchanging top and bottom electrode. Moreover, the complementary switching memory behavior in Ag/Er₂O₃/ITO/Er₂O₃/Ag structure was also observed. Through mechanism analysis, it is expected that the barrier changes and metal-ions oxidation-reduction should be responsible for the conversion of switching direction and regulation of memory window. This work opens up a way to the development of next generation new concept memory.