Vacuum Interrupters Research Articles

Research on the current-zero period of vacuum arc interruption and equivalent model of post-arc gap

In this paper, the current breaking experiments of vacuum interrupter are conducted and the waveforms of voltage and current are obtained. The results show that there is current instability phenomenon when the value of is low and the value of instability-initiation current decreases as the value of increases. The number of voltage spikes will also decrease and irregular oscillation will weaken. According to the experimental results and theoretical analysis, the ‘memory characteristic’ of plasma is proposed and a new mathematical model of post-arc initial plasma density is estabilished which will provides a new method for the calculation of the sheath growth. The equivalent circuit model of post-arc gap is established to analyze the transient recovery voltage. The equivalent parameters in the circuit are obtained by the calculation of sheath growth and plasma density and verified by comparison with measurements. Through the comparison of experimental results between the axial magnetic field (AMF) contact and the butt contact, the effects of AMF on post-arc plasma density and sheath growth are analyzed. The results show that AMF can make the post-arc plasma density higher and the sheath growth slower.

Study on Arc Evolution Behaviour of Breaking Short Circuit Current for a Fast Vacuum Circuit Breaker

Abstract A fast vacuum circuit breaker (FVCB), driven by an electromagnetic repulsion mechanism, has an extremely short opening time, and in coordination with the controlled switching technology contributes to breaking a short circuit current with the minimum arcing time. The objective of the paper is to determine the arc evolution behaviour of fast vacuum circuit breakers with a minimum arcing time. A 40.5 kV vacuum interrupter (VI) was used, which was equipped with a pair of CuCr50 (Cr 50 wt%) axial magnetic field (AMF) contacts. The diameters of the contact were Φ50mm, Φ58 mm and Φ65 mm respectively. The arc evolution behaviour in the drawn arc experiment was photographed by a high-speed camera through a glass envelope of the VI. The experiment results showed that an initial intense arc tended to evolve into a diffuse arc when the arcing time is larger than a critical arc diffusion time under a certain opening velocity. The critical arc diffusion time for the vacuum arc is defined as arc evolving from the instant of contact separation to an appearance of separated cathode spots. For a Φ50 mm cup-type AMF contact, the critical arc diffusion time decreases from 0.7 ms to 0.46 ms, with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. What’s more, for a Φ58 mm cup-type AMF contact, the critical arc diffusion time decreases from 1.0 ms to 0.58 ms with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. For a Φ65 mm cup-type AMF contact, the critical arc diffusion time decreases from 1.30 ms to 0.64 ms with the increase of the opening velocity from 2.52 m/s to 4.65 m/s. The critical arc diffusion time increases with the increase of the diameter of the contact under the same opening velocity.

Prestrike inrush current arc behavior in AMF vacuum interrupters subjected to contact plate slots

Inrush current prestrike arcs can cause local surface melting of contacts in vacuum interrupters (VIs) and cause strong contact welding during capacitive load operations. The contact welding rupture would seriously damage the appearance of the contact surface and lead to a high restrike possibility during the next opening operation. The slots on the contact plate can remarkably influence the inrush current prestrike arc behavior. The objective of this paper is to research the influence of contact plate slots on prestrike inrush current arc behavior during the capacitive-making processes of VIs. The experimental results showed that the no-plate-slot VIs had better performance than the VIs with plate slots during the prestrike arcing process. In addition, according to the simulation results, the AMF flux density in the arc region is lower in the VIs with plate slots than in the VIs without plate slots at the peak of 20-kA amplitude inrush current, which together with the effect of the slots contributes to the stationary intense arcs in the VIs with plate slots.

Impact Phenomena of Metallic Microparticles under Breakdown Voltages in Vacuum Interrupters

This paper studies the impact phenomena of the metallic microparticles with the vacuum gap in the range of 10–50 mm under different breakdown voltages in vacuum interrupters. The results show that for the vacuum gap 10–40 mm, the average impact velocities of the microparticles increase linearly with the increase of the vacuum gap, and the impact could damage the cathode surface, which would cause irregularities and give high local field enhancement, finally it may lead to vacuum breakdown. For the vacuum gap 40–50 mm, the average impact velocities of the microparticles are thought to enter the saturation region and remain nearly constant. The impact could cause more metal vapor, which may lead to developing gradually into the vacuum breakdown. Furthermore, the materials with the higher yield stress will cause more obvious fractures and broken phenomena on the edge of the craters, which would have an influence on the vacuum breakdown.

Study on the Effect of Helium on the Dielectric Strength of Medium-Voltage Vacuum Interrupters

This paper presents the results of a comparative analysis of the dielectric strength of disconnecting vacuum interrupters operating on air and helium. The breakdown voltage Ud was measured in the pressure range from 8.0 × 10−4 Pa to 3.0 × 101 Pa for air and from 8.0 × 10−4 Pa to 7.0 × 102 Pa for helium, while varying the interelectrode distance from 1.0 to 5.0 mm. Dedicated laboratory workstations were used to determine the actual pressure values in the vacuum interrupters tested and to precisely measure and record the dielectric strength results of the test object. It was found that the helium-filled vacuum interrupter maintains its full dielectric strength in significantly larger pressure ranges, while the air-filled vacuum interrupter loses its insulating properties. Thus, it is possible to make vacuum interrupters based on the working medium associated with pure helium, with larger working pressure ratings. Under such conditions, it is easier to maintain the tightness of the device and to limit cut-off currents and overvoltages associated with vacuum switchgear.

Effect of Cr@RGO structure on microstructure and properties of RGO/CuCr25 composite

CuCr alloy with high Cr content (20–50 wt.%) is the main contact material for medium voltage and high current vacuum interrupters. However, the influence of network distribution of Cr particles affect the conductivity of CuCr alloy, and its properties strongly depend on the size of Cr particles. In this paper, Cr@RGO (Cr powder coated with reduced GO) was prepared by BSA (bovine serum protein) electrostatic assembly method, and then RGO/CuCr composites with different graphene content were prepared by vacuum hot pressing sintering process. The results show that the size of Cr particles decreases with the increase of graphene content and the network of Cr particles became fractured. When the content of RGO is 3.0 wt.%, the size of Cr phase is 19.9 μm, which is 23.8% less than that of CuCr25 of 26.1 μm. The Brinell hardness and electrical conductivity of 3.0 wt.% RGO/CuCr composite are 102.5 HB and 52.9% IACS, which is increased by 8% and 6% in contrast with that of CuCr25. And the Preparation of RGO/CuCr is simple, feasible, replicable and easy to achieve the goal of the industrial preparation.

Thomson-Coil Actuator System for Enhanced Active Resonant DC Circuit Breakers

Enhanced active resonant (EAR) dc circuit breakers (DCCBs) are a promising set of recently proposed DCCB concepts. As other DCCBs, EAR DCCBs still require a fast mechanical switch. The requirements on the actuator of the mechanical switch depend on the DCCB concept and the dc grid and are derived here for an EAR DCCB. Thomson-coil actuators (TCAs) can open and close mechanical switches sufficiently fast to satisfy the requirements. This work studies experimentally a TCA system with active damping for an off-the-shelf industrial vacuum interrupter used as mechanical switch in an EAR DCCB. The prototype is explained in detail, and extensive measurement results are presented, showing that active damping must be perfectly timed to be effective. A novel Thomson-coil (TC) driver is proposed and studied experimentally, which operates the TCA more efficiently by recycling energy during the actuation. Moreover, the novel TC driver reduces the capacitive storage by 50% and allows for faster recharging with lower charging current. Finally, the autoreclosing and proactive commutation operation of the TCA system and the interruption capability of the prototype EAR DCCB are demonstrated experimentally.

Novel Design of 3-D Microstructure Contact Material Generating Autoexcitation Magnetic Field

The development of vacuum circuit breaker (VCB) toward large current and high voltage is extremely limited with contact material. Herein, a new type of VCB contact model including microstructure is proposed. Emerging contact material achieves the breakthrough from external applying to self-excited magnetic field, besides strong magnetic strength and low temperature rise. Three-dimensional finite-element simulations, which contain microcoil, unit groups, and coupled contacts, were implemented. And the influence factors involve eddy current losses, iron core diameter, units’ spacing, and copper–chromium layer thickness. Simulation results indicate that the magnetic field is the most efficient when the distance between the coupled coils is 1.65 mm and the thickness of the Cu–Cr layer is 3 mm. Moreover, the relative practical models and measures were carried out to verify the distribution of magnetic field, and the results were in good agreement with theoretical predictions. Therefore, the theoretical data can guide the design of practical contact models and support the optimization of structural parameters, applied to vacuum interrupter.

Measurement of contamination amount and direct simulation Monte Carlo simulation of contamination process in a model vacuum interrupter

The contamination process of a model vacuum interrupter was investigated by measuring the amount of contamination and conducting direct simulation Monte Carlo (DSMC) evaluations. The numerical simulations revealed suitable results, and the simulation model could be used to predict the contamination profile. In addition, appropriate results for designing arc shields were obtained from a parametric study of the DSMC assessments. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Study on Preparatory Stage of Sheath During the Interruption of Vacuum Interrupters

During the breaking process of a vacuum interrupter, there is a time interval between current zero and generation of recovery voltage. This time interval is variable and matters to the calculation of continuous transition model, but always simplified as a constant. In this article, we put forward the concept of preparatory stage of sheath, analyze the production mechanism and influence on breaking ability, and give the computation method for the duration of this stage. In order to verify the rationality of the theoretical analysis and calculation method proposed in this article, experimental measurement is conducted. The experimental results are in good agreement with the values of duration calculated by the theoretical formula in this article in terms of magnitude and variation law.

Comparative Study of the Properties of Cu-Cr-Mo System Electrical Contact Material by Sintering and Infiltration Methods

Contact materials in high-voltage vacuum interrupters require properties such as high conductivity, density and hardness to minimize arc heat damage. In this study, Cu–Cr–Mo alloy contact materials were examined for their usage as high-voltage contact materials. Ball milling was performed after analyzing the raw materials of the Cu, Cr and Mo powders. A green compact was produced using high pressure with a mixed powder. Subsequently, the composite was produced by sintering via the temperature and infiltration method according to the Cu content in the green compact. The composite sintering method produced a density of 8.55 g/cm3 (relative density 93%), a hardness of 217 HV and an electrical conductivity of 40.7% IACS at 1200 °C. The composite of 10 wt.% Cu produced by the Cu infiltration method exhibited a density of 8.7 g/cm3 (relative density 94%), hardness of 274 HV and electrical conductivity of 39 IACS% at 1300 °C. The measurements of the physical properties of our newly established method demonstrated a new possibility of using the Cu–Cr–Mo alloy as a contact material for high-voltage vacuum interrupters.

진공 인터럽터의 내부 결함에 대한 부분방전 특성

본 논문에서는 진공차단기(VCB)의 핵심 부품이자, 개폐 시 발생된 아크를 소호하는 진공 인터럽터 (VI)에 내부 결함이 생길 경우에 발생되는 부분방전(PD)의 특성에 대해 다루었다. PD를 발생시키기 위한 결함 모의에는 상용 VI와 그 접점으로 만든 전극계를 사용하였다. 내부 결함의 종류는 VI의 일반적 고장원인인 진공누설 결함, 불완전한 개방결함으로 선정하였다. 방전개시전압(DIV), 겉보기전하량, 펄스 수, 극성비, PRPD의 측면에서 결함 별 PD 특성을 정상조건과 비교했다. 각 결함에서의 DIV는 정상 상태에서 보다 2kV 씩 감소되었으며 복합 결함의 DIV는 19kV이었다. 그리고 최대 인가전압에서 진공누설 결함에서의 겉보기 전하량은 불완전한 개방 결함에서 보다 8.3% 높았다. 또한, DIV에서 검출된 각 결함 별 부극성 펄스의 비율은 정상상태에서 보다 3~5% 높게 검출되었으며 복합결함에서의 부극성비율은 54%였다. 그러므로 본 논문의 결과는 진공 인터럽터의 온라인 절연 진단에 활용할 수 있을 것으로 사료된다.

Melting Pattern of Vacuum Interrupter Contacts Subjected to High Inrush Currents at High Frequencies

One important aspect in capacitor switching concerns the high inrush current during the energizing of the capacitor. For vacuum interrupters, it is assumed that the modification of the contact surface due to high inrush currents has the highest impact on the current breaking performance. One peculiarity of capacitor switching is the high rate of switching operations easily achieving 1000 operations in a couple of years. Two vacuum breakers were therefore operated up to 1000 times in a simple test circuit simulating the making of high inrush currents. According to standards, peak and frequency of inrush currents are 20 kA and 4250 Hz for back-to-back capacitor switching, or around 5 kA and 400 Hz for single bank switching. The range of inrush currents was extended here to peak currents up to 60 kA and frequencies up to 24 kHz. Peak current and frequency have an important impact on radius and current density of the inrush current arc, and thus on the energy deposited under the arc roots. Under the conditions prevailing here, the whole surface of the contacts exhibits a uniform melting pattern with the depth of the solidified melt being less than 1 mm after 1000 operations. It is assumed that the arc moves on the contact surface driven by the radial magnetic forces generated by this kind of contact and distributes the arc energy all over the contact surface. The inrush current integral ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ICI</i> ) might be a measure of the available energy for contact melting or erosion. However, since the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ICI</i> has no relation to the arc current density, it is only representative for a particular melting pattern of the contact surface if frequency and peak inrush currents are varied in a limited range.

The Influence of TMF and AMF Components on Arc Movement Characteristics in Spiral-Slot Contacts

Spiral-slot contacts produce an axial magnetic field (AMF) and the transverse magnetic field (TMF). The magnetic field between TMF contacts will affect the breaking performance of vacuum interrupters. In order to study the effect of TMF and AMF on arcing process and movement characteristics, five contacts with different TMF and AMF, but the same ratio of TMF to AMF, were designed and experimentally investigated in a demountable vacuum chamber. The arc movement phenomenon under different TMF and AMF was obtained. It was found that increasing TMF and AMF could reduce the arc jets to the outer electrode, and arc stagnation was more likely to occur in the later stage of the movement. The influence of TMF and AMF on arc movement characteristics and the utilization of contact surfaces was investigated. With the increase in TMF and AMF, the number of arc rotations increased, and the range of arc movement and the utilization of contact surface increased first and then decreased. Simulations were performed to analyze that the influence mechanism of TMF and AMF on arc movement characteristics was investigated. With the increase in TMF and AMF, the tangential force of the concentrated arc was increased, and the radial force was reduced.

Simulation and verification of thermal conductivity of CuCr30 contact material based on morphological changes of Cr particles

In order to improve the thermal deposition of CuCr contact material for vacuum interrupter, CuCr30 contact material was treated with large deformation treatment to change the morphology and distribution of Cr particles, and the effect of the morphology change of Cr particle on the thermal conductivity of CuCr30 contact material was studied. At the same time, the finite element simulation of the thermal transfer behavior of the extruded and cast CuCr30 contact materials was carried out by using ANSYS software. The studies show that the large deformation treatment (deformation ratio 16:1) changes the morphology and distribution of Cr particles in CuCr30 contact material, making it change from dendritic to longitudinally arranged quasi-fibrous. Influenced by the morphology and distribution of Cr particles, the thermal conductivity of CuCr30 contact material is anisotropic, and the effective thermal conductivity varies significantly with the direction. Indeed along the deformation direction, the thermal conductivity of the extruded state is obviously higher than that of the cast state, increasing by 5.8 %. However, perpendicular to the extrusion direction, the thermal conductivity has little changes, and obvious deposition phenomenon appears in the process of thermal conduction. The finite element simulation results of the effective thermal conductivity of CuCr30 material by ANSYS are in good agreement with the measured results, and the error range is 0.7 %∼1%.

Anodic Glow and Conductive Channel Formation in Single and Double Long Vacuum Gaps

The evolution processes of vacuum breakdowns in single- and double-break vacuum interrupters are reported in this paper, in order to reveal the formation mechanisms for the conductive channels in vacuum arcs. Breakdown experiments in two vacuum interrupters containing 10-30 mm gaps with single-break and double-break are studied. The light emission during breakdowns is observed by an intensified charge coupled device camera, with the current and voltage waveforms being recorded simultaneously. According to the results, there is no difference between the evolution processes of breakdowns in small gaps and large gaps. The establishment of the conductive channel and sustaining of the vacuum arc can be achieved by the effect of the cathode without any contribution from the anodic glow. In the double-break interrupter, the transition from insulation to conduction for the two serial connected gaps starts simultaneously but evolves independently.

Test stand for testing and diagnostics of medium voltage vacuum interrupters

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Increasing the breaking capacity of the 10 kV VAC in comparison with its own axial and radial magnetic fields

The research work considers vacuum arc-extinguishing chambers with axial and radial magnetic fields. The object of research is vacuum arc suppression chambers with an axial magnetic field of 10 kV, 20 kA and with a radial magnetic field of 10 kV, 40 kA as well as ways to increase the breaking capacity by changing the configuration for each type of chambers. The research work uses the method of mathematical modeling of physical processes in the Comsol Multiphysics software package, graphical modeling of chambers is performed in Compass v18. 0. The results showed that changing the geometric parameters of vacuum arc-extinguishing chambers can increase the breaking capacity. Based on the results obtained, it can be concluded that to increase the maximum cut-off current, it is sufficient to change the geometry of the vacuum arc-extinguishing chamber. In combination with other ways to increase the breaking capacity, it is possible to expand the area of application of vacuum interrupters - the most reliable, safe and environmentally friendly switching devices.

Charging potential measurement of floating electrode modeled on the arc shield of vacuum interrupter under AC voltage application

AbstractA charging potential of a floating electrode modeled on vacuum interrupter was measured under unipolar AC voltage application using a surface potential meter. As a result, when a lower voltage was applied to the samples, only an induced potential depending on the electrostatic capacities of the sample and surrounding objects around the sample was measured from the floating electrode. However, in the case of high voltage application, not only induced voltage but also a positive charging potential was observed from the floating electrode which was enough to change the potential of the floating electrode. This is due to the field electron emission from the floating electrode itself.

Comparison of Conventional and Flash Spark Plasma Sintering of Cu–Cr Pseudo-Alloys: Kinetics, Structure, Properties

Spark plasma sintering (SPS) is widely used for the consolidation of different materials. Copper-based pseudo alloys have found a variety of applications including as electrodes in vacuum interrupters of high-voltage electric circuits. How does the kinetics of SPS consolidation for such alloys depend on the heating rate? Do SPS kinetics depend on the microstructure of the media to be sintered? These questions were addressed by the investigation of SPS kinetics in the heating rate range of 0.1 to 50 K/s. The latter conditions were achieved through flash spark plasma sintering (FSPS). We also compared the sintering kinetics for the conventional copper–chromium mixture and for the mechanically induced copper/chromium nanostructured particles. It was shown that, under FSPS conditions, the observed maximum consolidation rates were 20–30 times higher than that for conventional SPS with a heating rate of 100 K/min. Under the investigated conditions, the sintering rate for mechanically induced composite Cu/Cr particles was 2–4 times higher compared to the conventional Cu + Cr mixtures. The apparent sintering activation energy for the Cu/Cr powder was twice less than that for Cu–Cr mixture. It was concluded that the FSPS of nanostructured powders is an efficient approach for the fabrication of pseudo-alloys.