Transverse Magnetic Field Contacts Research Articles

Study on the vacuum arc characteristics between novel straight slot transverse magnetic contacts with auxiliary slots on the back

The motion stability of the vacuum arc between TMF contacts significantly affects the breaking capacity of vacuum switches. The vacuum arc movement can be effectively controlled by slots on the TMF contacts to provide the necessary driving force. However, the necessary cross-slot movement of the arc affects its stability. In this paper, a novel straight-slot transverse magnetic field (SSTMF) contact structure with additional auxiliary slots on the back is proposed to improve current distribution and avoid stagnation at the contact center. The simulation analysis was conducted on the force acting on the arc at different positions and the magnetic field distribution between the contacts. Additionally, the arcing experiments were performed in a demountable vacuum chamber for both novel and traditional SSTMF contacts. The SEM analyses were carried out for the contacts after the experiments. Combined with simulation and comparative experimental results, it is verified that the auxiliary slots can improve the control and driving effect on the arc. This can provide ideas and references for future contact design and improve the breaking performance of vacuum circuit breakers.

Experimental study of the vacuum arc motion-diffuse transition in cup-shaped transverse magnetic field contacts

The arc in transverse magnetic field (TMF) contacts transitions to diffusion mode before current zero, affecting arc morphology and motion. TMF-generated force competes with local overheating's stagnation effect, impacting contact surface ablation. Cup-shaped TMF contacts exhibit slow, fast, and unstable transitions. Arc voltage declines gently, rapidly, or in repeated steps. Peak current, contact diameter, contact piece structure, and iron core influence transition characteristics. Transition energy increases linearly with peak current. Larger contact diameter and iron cores make transition constant earlier and transition current higher. Compared to circular contacts, annular contacts delay transition constant and widen transition current range. Scanning electron microscope (SEM) images showed that the ablation cathode surfaces exhibited five morphologies: melting pit, periphery, lamellar, particle, and pore. Energy dispersive spectrum (EDS) analyses show that the periphery has a higher Cu content than the interior, suggesting less Cu loss during fracture and less droplet splashing. The peripheral Cu content is comparable between the two contacts, 62.94 % vs. 62.37 %. However, the interior Cu content of contact NO.4 is higher than NO.6 at 60.54 % vs. 56.26 %. This indicates that the difference in the effect of fast and slow transitions on the cathode surface activity is mainly in the interior region.

Investigation of the influence of opening speed on vacuum arc under transverse magnetic field

The objective of this paper is to investigate the vacuum arc characteristics on transverse magnetic field (TMF) contacts at different opening speeds. Experiments are carried out at different opening speeds. The experimental current ranges from 7 to 16 kA (peak current) at approximately 50 Hz. The contact material is CuCr30. The results show that increasing the opening speed increases the expansion speed of the arc after ignition. A higher opening speed increases the gap distance at which an anode spot occurs and reduces the duration of the instability stage, and it also reduces the duration of the motion stage. The arc motion can be optimized by adjusting the opening speed. The moment of contacts separation has no obvious influence on the gap distance at the transition of the arc mode. When the arc ignites between the arms, it expands slowly. This phenomenon is analyzed by a finite element method. The simulation results show that the ignition position influences the current direction, which influences electromagnetic force of the arc. The radial electromagnetic force is smaller when the arc ignites between the arms, causing a stagnation of the arc.

Experimental investigation on “glow flow” phenomenon during current-zero period between transverse magnetic contacts

The inter-electrode state of the transverse magnetic field contact during the current-zero period is determined by the evolution of the arcing process. It has an important effect on whether the vacuum switch can be successfully broken. In this paper, a series of contacts were subjected to arcing and fixed gap distance experiments. The results show that a special inter-electrode phenomenon (glow flow) appears during the current-zero period when the current exceeds the threshold for the transition from diffused to constricted state of the vacuum arc. The mechanism behind the formation of this phenomenon was elucidated through an analysis of multiple sets of experimental results. It is found that the inter-electrode phenomenon arises from the disruption of the equilibrium process between the pressure from the arc column plasma and the anode vapor flux on the near-anode side at the current-zero. The copper vapor falls and is ionized by collisions with heat-emitting electrons. The experimental results and theoretical analysis also show that this phenomenon has a time interval with the reignition phenomenon. When this phenomenon is intense to a certain degree, the reignition will occur with high probability. The observation and theoretical analysis results of this paper are relatively consistent with the research results of other scholars, which can help to improve the vacuum arc characteristics and interrupting mechanism. This can provide a basis for improving the arc extinction performance of the vacuum switch.

Simulation Analysis and Experimental Investigation of the Iron-Core Cup-Shaped Transverse Magnetic Field Contact

The transverse magnetic field (TMF) contact uses self-generated TMF to drive the arc movement and has been widely used in the field of vacuum breaking. An iron-core cup-shaped TMF contact was designed by adding an iron core and changing the parameters of the cup wall based on the structure of the traditional cup-shaped TMF contact to optimize the gap magnetic field distribution of the cup-shaped TMF contact and improve the force characteristics of the vacuum arc. From the aspects of simulation and experiment, the gap magnetic field characteristics, arc force, and vacuum arc characteristics of the iron-core cup-shaped TMF contact were studied. The simulation analysis model of the iron-core cup-shaped TMF contact was established by COMSOL Multiphysics software, and the gap magnetic field characteristics and arc force were analyzed. Compared with the traditional cup-shaped TMF contact, the tangential electromagnetic force on the arc is increased by 30%, and the radial electromagnetic force is reduced by 36%. The arcing processes of the iron-core cup-shaped TMF contact and the traditional cup-shaped TMF contact were analyzed through experiments. The results show that the iron-core cup-shaped TMF contact has a faster arc movement speed, longer movement duration, and less metal droplet splashing.

Vacuum arc characteristics of an AMF–TMF composite contact with fixed AMF contacts under different opening velocities

The objective of this paper is to determine the vacuum arc characteristics of a novel axial magnetic field (AMF)–transverse magnetic field (TMF) composite contact under different opening velocities. The AMF–TMF composite contact consists of a pair of outer fixed AMF contacts and a pair of inner movable TMF contacts. Drawn arc experiments were carried out in an L–C discharging circuit with this composite contact system to observe the differences in the arc development process under different opening velocities. The opening velocity of the inner movable contact was set to 1.3, 1.8, and 2.3 m/s. The arc current was up to 20 kA rms. In the experiments, the arc behavior was recorded using a high-speed camera. The arc current of each contact and the arc voltage were measured. Then the arc characteristics, including the arc current transfer characteristics, diffused arc duration, and mental droplet distribution before zero current, were quantitatively analyzed. Furthermore, magnetic field calculation was carried out to explain why the arc characteristics are different under different opening velocities. Experimental results show that with an increase in the opening velocity from 1.3 to 2.3 m/s, the diffused arc duration before zero current increases from 1.05 to 1.75 ms when the cathode is on the fixed side and increases from 1.30 to 1.90 ms when the anode is on the fixed side. In addition, the quantity of mental droplets between contacts before zero current is less with high opening velocity. It indicates stronger short-current breaking capacity under higher opening velocity. From the simulation results, it can be seen that during the arcing period, more current transfers to the fixed AMF contact under higher opening velocity and generates a stronger AMF. It could explain the earlier diffusion of the vacuum arc column under higher opening velocity.

Investigation of Vacuum Arc and Erosion Characteristics of Spiral TMF Contacts With Different Materials

The transverse magnetic field (TMF) can drive the arc to rotate, to reduce the erosion of contact. In this article, TMF contacts of six commonly used materials (CuCr10, CuCr30, CuCr50, WCu10, WCu30, and CuW-WC) are investigated by experiments at the current of 5, 10, and 15 kA. Experimental results show that the contact material has a significant impact on the arc, the arc on CuCr materials rotates, and shows noisy voltage, while the arc on WCu hardly rotates and exhibits a stable arc voltage because of staying in the diffuse mode. Though the erosion of CuCr contacts is more severe than WCu contacts, the results of breaking operations also indicate that CuCr contacts outperform WCu contacts, where CuCr10 contact has a lower breaking capacity than CuCr30 and CuCr50. Moreover, the steel support disk of the interrupter contacts plays a role in the reignition of the arc after a half-cycle of current which is obvious from the erosion of the disk and from records of the arc appearance.

The influence of weak transverse magnetic field on plasma dissipation process in the post-arc phase in a vacuum interrupter

Transverse magnetic field (TMF) contacts and applying external TMF are often adopted for reducing the ablation of the contact surface, but TMF will also affect the breaking performance of the vacuum interrupters. In this work, we investigated the influence of weak TMF on the expansion of the plasma in the post-arc phase with one-dimensional implicit particle-in-cell/Monte Carlo collision model, and we added an external circuit to the model to ensure the correctness of the calculation results. We simulated multiple magnetic field strengths (<30 mT), compared the plasma expansion process with the TMF strengths of 0 mT and 10 mT, and discussed the influence of metal vapor density on the insulation performance recovery of the vacuum interrupter. From the results, applying TMF with strength below 5 mT has little effect on the expansion of the plasma, and the TMF can increase the plasma density which improve the flow capacity of vacuum circuit breakers when the magnetic field above 10 mT, which is because the particles become more difficult to leave the discharge area under the force of the magnetic field. In general, we find that weak external TMF may adversely affect the breaking performance of the vacuum circuit breakers.

Investigation on the arc root characteristics of vacuum arc between the iron-core cup-shaped transverse magnetic field contacts

The severity of the contact surface ablation determines the breaking capacity of the vacuum circuit breaker, and the interaction between the arc root and the electrode is the main cause of the contact surface ablation. The characteristics of the arc root determine the magnitude of the electromagnetic force received by the arc during the movement stage as well as the shape and speed of the arc movement. It will eventually affect the temperature of the contact surface and the ablation situation. This paper studied the arc root characteristics of high-current constricted vacuum arcs between the iron-core cup-shaped transverse magnetic field contacts and put forward the idea of using the ratio of cathode and anode arc root areas to quantitatively analyze the concentration of vacuum arc. The research on the arc root characteristics of the vacuum arc can help to improve the arc characteristics and arcing mechanism, and the proposition of the ratio can provide a new method for the study of constricted arc. This can provide a basis for improving the arc extinction performance of the switch, reducing the ablation of the contact material, and improving the contact life.

Capacitive making of double‐break vacuum circuit breaker: Transverse magnetic field contacts are superior to axial magnetic field contacts

Previous studies mainly focused on the behaviours of single-break vacuum circuit breakers (VCBs) in switching capacitor banks. The prestrike characteristics of double-break VCBs subjected to axial magnetic fields (AMFs) and transverse magnetic fields (TMFs) in capacitive making operations, to find a proper structure of double-break VCBs for capacitive switching are experimentally investigated here. Special attention is given to the prestrike gap, inrush current interruption, prestrike voltage, prestrike electric field strength and erosion on contact surfaces of double-break VCBs. The results show that the 50% prestrike gap d50 and the scatter in prestrike gaps are significantly reduced by nearly 50% by the TMF double-break VCB compared with the AMF double-break VCB. The 50% prestrike arcing time ta50 of the TMF double-break VCB can be reduced by 37.0% compared with the AMF double-break VCB. The voltage distribution ratio between two vacuum interrupters (VIs) is more balanced in the TMF double-break VCB (6:4) than in the AMF double-break VCB (7:3) when prestrike occurs. The TMF double-break VCB can reduce the erosion caused by inrush currents on contact surfaces compared with the AMF double-break VCB. In switching capacitor banks, the TMF double-break VCB is superior to the AMF double-break VCB.

An improved deep learning-based algorithm for 3D reconstruction of vacuum arcs.

Extensive attempts have been made to enable the application of deep learning to 3D plasma reconstruction. However, due to the limitation on the number of available training samples, deep learning-based methods have insufficient generalization ability compared to the traditional iterative methods. This paper proposes an improved algorithm named convolutional neural network-maximum likelihood expectation maximization-split-Bergman (CNN-MLEM-SB) based on the combination of the deep learning CNN and an iterative algorithm known as MLEM-SB. This method uses the prediction result of a CNN as the initial value and then corrects it using the MLEM-SB to obtain the final results. The proposed method is verified experimentally by reconstructing two types of vacuum arcs with and without transverse magnetic field (TMF) control. In addition, the CNN and the proposed algorithm are compared with respect to accuracy and generalization ability. The results show that the CNN can effectively reconstruct the arcs between a pair of disk contacts, which has specific distribution patterns: its structural similarity indexmeasurement (SSIM) can reach 0.952. However, the SSIM decreases to 0.868 for the arc between a pair of TMF contacts, which is controlled by the TMF and has complex distribution patterns. Compared with the CNN reconstruction method, the proposed algorithm can achieve a higher reconstruction accuracy for any arc shape. Compared with the iterative algorithm, the proposed algorithm's reconstruction efficiency is higher by 38.24% and 35.36% for the vacuum arc between the disk and the TMF contacts, respectively.

Numerical simulation of vacuum arc movement between transverse magnetic field contacts

The contact system of the vacuum switch is a crucial factor affecting the breaking performance of the vacuum switch. The study of the arc characteristics has significant impacts in improving the breaking ability of the vacuum switch. It is difficult to fully grasp the characteristics of the vacuum arc by experimental methods. The vacuum arc simulation model can obtain the internal parameters spatial distribution and motion characteristics more effectively. A high-current vacuum arc magnetohydrodynamic model was established, which considered the influence of ion and electron viscosity and the combined effect of the transverse magnetic field (TMF) and the axial magnetic field (AMF). The simulation obtained the plasma parameters of the arc column region as well as the temperature distribution characteristics of the cathode and anode surfaces. In addition, the changes in plasma parameters during arc movement under the action of different TMF and AMF components between TMF contacts were discussed. The simulation results are relatively consistent with the experimental results and the existing research results, which provide theoretical support for the research on the mechanism of vacuum arc motion characteristics.

Numerical Simulation of Multispecies Vacuum Arc Subjected to Actual Spatial Magnetic Fields

A three-dimensional (3-D) model for multispecies vacuum arc considering ionization and recombination process has been built in this article. With the model, the arc behaviors and species characteristics subjected to actual spatial magnetic fields of cup-shaped axial magnetic field (AMF) contact and transverse magnetic field-axial magnetic field (TMF-AMF) contact are investigated and compared. Furthermore, the validity of the model is verified by comparing with the experiments. Simulation results show that contact structures affect the species distributions of the arc by changing magnetic field and current density distributions. More triple charged ions are generated through ionization under higher electron temperature so that the triple charged ions gather where current constricts. The heat flux density is large in the current contraction region, where the contribution from triple charged ions is large as well. Spatial magnetic field distribution affects the Lorentz force acting on ion components. The force distribution is relatively uniform and the species are subject to inward force on the arc edge under cup-shaped AMF contact. For TMF-AMF contact, the double charged ions are subject to the force pointing to the TMF contact arms, whereas the triple charged ions are subject to the force pointing to the arc center. In addition, the consideration of arc species can improve the accuracy of the simulation results of the heat flux distribution, leading to a good agreement of the erosion condition between experiments and simulation.

Investigation on arc characteristics in cup‐shaped contacts with different structure for transverse magnetic field vacuum circuit breaker

AbstractThe cup‐shaped transverse magnetic field (TMF) contacts contain radial components and tangential components in the TMF generated when the current is interrupted. The tangential force generated by the radial magnetic field component drives the vacuum arc to rotate, and the tangential magnetic field component generates a radial force that causes the vacuum arc to move radially outward. In this paper, in order to study the influence of the arc force direction on the arc characteristics, the influence of the contact structure parameters such as the inclination of the inner wall on the arc force direction is simulated, and the breaking tests of different levels of current are carried out on the contact with different structure parameters. It is found that the direction of the Lorentz force has a significant effect on the breaking characteristics of the current, and the tangential and radial force components have varying degrees of influence on the motion characteristics of the arc during the start process and the metal droplet splashing.

Study of Vacuum Arc Rotation Characteristics of Different Transverse Magnetic Field Contacts

As a special phenomenon under transverse magnetic field (TMF) contacts, vacuum arc rotation deserves more attention. In this article, rotation characteristics of three typical TMF contacts, i.e., swastika-type, cup-shaped, and double-TMF contacts, are systematically studied. According to arc images, recorded by a high-speed camera, physical terms related to arc rotation such as rotation duration and rotation speed are clearly defined. The magnetic field and Lorentz force are calculated and the force balance of the moving arc is analyzed. On this basis, the effects of arc ignition mode, peak current, and contact type on arc rotation are investigated. Arc voltage noise as well as arc splashing outside caused by rotation is also discussed. The results show that the duration from ignition to rotation in two-point arc ignition (TPAI) mode is usually the shortest because of the rapidest constructed column formation. As the peak current increases, arc rotation becomes easier. Due to stronger TMF, the arc under double-TMF contacts has the longest rotation duration and the highest rotation speed.

3D reconstruction of dynamic behaviors of vacuum arcs under transverse magnetic fields via computer tomography.

The transverse magnetic field (TMF) contacts make the vacuum arcs deviate from the axisymmetric structure, so complete spatiotemporal evolution information of the plasma cannot be obtained by adopting one- or two-dimensional (2D) diagnostic methods. To address the issues, computer tomography was introduced in this paper. First, a multi-angle diagnostic imaging system based on split fiber bundles was proposed, which used a high-speed camera to simultaneously acquire eight angles of the arc image over time. In addition, a tomography algorithm called the maximum likelihood expectation maximum with Split Bregman denoising was proposed to reconstruct the dynamic spatiotemporal characteristics of the arc under complex conditions. Then, the three-dimensional (3D) distribution of Cu i and Cr i particles inside the contact gap was obtained by adopting optical filters. The 3D distribution of the vacuum arc had shown an obvious asymmetrical pattern under the TMF contacts, and there was a ring-like aggregation zone inside the arc, which can cause severe ablation on the anode contacts. According to the reconstructed 3D distribution of Cu i and Cr i, it is found that the metal vapor was mainly concentrated near the electrode surface and showed a clear distribution of non-uniform aggregates, while the concentration of particles in the gap was low. Moreover, on the cathode surface, the cathode spots moved in the form of groups driven by the TMF, while the anode surface was ablated by the electric arc, and the metal vapor existed in the form of bands.

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 of vacuum arc cathode spot movement between transverse magnetic field contacts

Vacuum switches have been extensively used in the field of medium voltage. Carrying out relevant research on vacuum arc is particularly important for improving the performance and reliability of vacuum switches. The vacuum arc cathode spots provide metal vapor and electrons, which determine the breaking capacity of the vacuum switches to some extent. Therefore, based on the simulation model of the cathode spots between the transverse magnetic field (TMF) contacts, the motion phenomenon and distribution of the cathode spot were simulated and the characteristics of the initial diffusion stage of cathode spots between TMF contacts were studied. The simulation results showed that the probability of generating a cathode spot in the direction of retrograde motion increased with the increase in the TMF component and the direction of motion varied with the angle between the magnetic field and the contact. The diffusion process of cathode spots under wan-shaped contacts, cup-shaped contacts, and spiral-shaped contacts was simulated. The ring-shaped distribution of the cathode spots between cup-shaped contacts with a large current in the initial diffusion stage was formed by the self-generated magnetic field of cathode spots, while the axial magnetic field component and the clustered cathode spots destroyed the ring-shaped distribution. Taking the distribution of cathode spots and current from experiments as initial conditions, the simulation results of cathode spot distribution in the initial diffusion stage and the arc root radius were consistent with the experimental results.

Effect of TMF and AMF Components on Expansion Process in Different Ignition Modes of Vacuum Arc Between Spiral-Type TMF Contacts

The drawn vacuum arc begins with a bridge column formed from the explosion of a liquid metal bridge after separating the contacts. The expansion process of the initial arc has an effect on arc motion or diffusion. In order to deeply study the influence of transverse magnetic field (TMF) and axial magnetic field (AMF) on the drawn arc characteristics in the initial expansion stage, in this article, arc ignition mode and appearance under two groups of contacts with different AMF and TMF components were experimentally studied. It was found that simultaneously reducing TMF and AMF components would end the expansion stage earlier, and the fluctuation of the arc column pressure during the expansion was larger. When TMF and AMF components were further reduced, the arc needs to take a longer time to extend across the slot gap due to insufficient Ampere force. When TMF was basically unchanged and AMF was reduced, the arc burned more intense, the diameter of the arc column was smaller, and the arc would merge earlier in multipoint ignition mode. The characteristics of arc voltage, pressure, and duration of expansion stage were analyzed, founding that the arc with a moderate TMF and AMF components had a smaller rising slope of arc voltage, a faster reducing speed of arc pressure, and a smaller range of the duration of expansion stage. In addition, the variation of magnetic field strength in different ignition modes and contact structures during the arc expansion stage was simulated to explain the mechanism of arc behavior.

Two-Dimensional Observation of Copper Atoms After Forced Extinction of Vacuum Arcs by Laser-Induced Fluorescence

The distribution and dissipation of neutral atoms are crucial for understanding the dielectric recovery process after interrupting direct current (DC) vacuum arcs. This article aims to investigate the dissipation of copper atoms after a forced extinction of the vacuum arc experimentally, adopting the plane laser-induced fluorescence method. The change in the 2-D distribution of copper atoms with time is presented. The results show that the magnetic fields, the axial magnetic field (AMF), and the transverse magnetic field (TMF) have a limited effect on the initial density of copper atoms. For both the AMF and the TMF, the copper atom densities at current zero (CZ) vary in the range (6– $8) \times 10^{17}\,\,\text{m}^{-3}$ when 3-kA vacuum arcs are forced to 0 in 0.2 ms. Contrary to the TMF case, in the AMF case, the evaporation on the anode after the CZ results in long-existing atoms near it. Consequently, the atom density of the TMF decays faster than that of the AMF, which indicates that a vacuum interrupter with the TMF contacts has a better performance when interrupting a DC load. The difference between the two magnetic fields originates from the arc control patterns. Namely, the AMF tends to keep vacuum arcs in a stable mode, which is unfavorable for a DC interruption; on the contrary, the TMF drives the vacuum arcs to move at high velocities resulting in faster dissipation of copper atoms after the CZ. In addition, the composition proportion of CuCr contacts has a limited effect on the diffusion of copper atoms when a low-vacuum arc is interrupted.