Contact Arc Research Articles

Molecular dynamics simulation of cathode crater formation in the cathode spot of vacuum arcs

A three-dimensional model based on molecular dynamics has been developed to describe the formation of a single cathode spot in vacuum arcs. The formation of the cathode spot is assumed to be controlled by the plasma ions, the effect of which is simulated in LAMMPS through the process of ion bombardment. The cathode is represented by structured copper atoms, while the ions are continuously injected into the domain with a certain velocity towards the cathode surface. Ion bombardment leads to the appearance of a crater, which is caused by the accumulation of pressure effect against the relaxation of substrate temperature. The size of the crater is found to be determined by the spatial distribution of the injected ions. The formation of the cathode spot is also scrutinised by electron emission from the cathode surface with variable surface temperature during the cathode spot development process. In addition, the evaporated atoms forming the metal vapour are observed. This study provides a description of the formation of the cathode spot at microscale, which shall be helpful to further studies of the arc rooting and arc contact (electrode) erosion in vacuum environment.

Capsule Dynamics, Implantation, and Explantation of the Smaller Incision, New-Generation Implantable Miniature Telescope: a Miyake-Apple Study.

The smaller incision, new-generation implantable miniature telescope is a novel implant to optimize vision in retinal patients with central vision loss. Using Miyake-Apple techniques we visualized the device implantation, repositioning, and explantation, while noting capsular bag dynamics. Using the Miyake-Apple technique, we assessed capsular bag deformation after successful implantation of the device in human autopsy eyes. We assessed rescue strategies for converting a sulcus implantation to a capsular implantation and explantation strategies. We noted the occurrence of posterior capsule striae, zonular stress, and the haptics' arc of contact with the capsular bag after implantation. Acceptable zonular stress was observed during the successful implantation of the SING IMT. When it was implanted in the sulcus, one could reposition the haptics into the bag with two spatulas using counter-pressure in an effective strategy despite inducing tolerable, medium zonular stress. A similar technique, in reverse, allows safe explantation without damaging the rhexis or the bag, while inducing similar medium, tolerable zonular stress. In all eyes we examined, the implant considerably stretches the bag, inducing a capsular bag deformation and posterior capsule striae. The SING IMT can be safely implanted without significant zonular stress. In sulcus implantation and explantation, repositioning of the haptic is achievable without perturbing zonular stress using the presented approaches. It stretches average-sized capsular bags to support its weight. This is achieved by an increased arc of contact of the haptics with the capsular equator.

Radial–axial feeding process design for large-scale flat ring by quantitative estimation of ring roundness error

Due to the large size and thin wall characteristics, the large-scale ring is prone to plastic instability, resulting in loss of ring roundness. An analytical calculation model of roundness error is proposed to design the feeding process. This model is established by analytically deriving the relationships between feeding process, ring geometry, contact arc length, rolling force, ring vibration angle, ring bending angle, contact arc length increment and ring roundness error at different rolling stages. Compared with numerical calculation and production trial, the analytical model can predict the roundness error with reasonable accuracy and high efficiency and guide feeding process design.

Design improvement of the conversion mechanism from balloon inflation to bending motion for inflatable film actuators

Various soft actuators have been investigated to overcome the drawbacks of conventional solid machines and explore the applications of soft robotics. In particular, and because they are expected to be applicable in minimally invasive medicine because of their safety, soft inflatable microactuators using an actuation conversion mechanism from balloon inflation to bending motion have been proposed for high-output bending motion. These microactuators could be applied to create an operation space by safely moving organs and tissues; however, the conversion efficiency could be further improved. This study aimed to improve conversion efficiency by investigating the design of the conversion mechanism. The contact conditions between the inflated balloon and conversion film were examined to improve the contact area for force transmission, with the contact area dependent on the length of the contact arc between the balloon and force conversion mechanism and on the amount of balloon deformation. In addition, surface contact friction between the balloon and film, which affects actuator performance, was also investigated. The generated force of the improved device is 1.21 N at 80 kPa when it bends 10 mm, which is 2.2 times the generated force of the previous design. This improved soft inflatable microactuator is expected to assist in performing operations in a limited space, such as in endoscopic or laparoscopic operations.

Analysis of SF6 contact based on QPSO-SVR

In the condition evaluation of the high-voltage SF6 circuit breaker, contact resistance and mass loss have a significant impact on the arc contact. To that end, this paper proposes a method based on quantum particle swarm optimization and support vector regression (QPSO-SVR), the implementation of which can effectively predict the contact resistance increment and mass loss of the circuit breaker arc contacts under different arc current conditions, and the best support vector regression (SVR) algorithm training parameters are obtained through experimental data. To validate the proposed method’s accuracy, it is compared to other prediction methods, and the results show that the QPSO-SVR method has good predictive ability for experimental data under different discharge parameters. The relative error of prediction for contact resistance increment is 3.023%, and the relative error of prediction for mass loss is 4.61%, indicating good accuracy and robustness. It can serve as a reference for the maintenance of high-voltage SF6 circuit breakers, which is useful. It is of great significance to the maintenance of SF6 circuit breaker.

Numerical simulation of cold longitudinal asymmetric rolling process

The modeling of the asymmetric cold rolling process of steel strip is carried out using the Deform program. During the study, the diameter of the barrel of the upper work roll is varied from 570 to 600 mm, the diameter of the barrel of the lower work roll was left unchanged at 600 mm, and changes in the structural parameters of the deformation zone, as well as the required rolling torques and forces, are recorded. The results are obtained for the conditions of rolling strips made of low-carbon steels with a thickness of 2 mm or more, as well as 0.35...0.5 mm. It is found that the discrepancy in power between the drives of the upper and lower rolls during asymmetric rolling can reach 25 % of the power required to conduct the process on rolls with the same barrel diameter. It is also shown that the changing of the contact arc with the indicated changes in power and a decrease in the diameter of the working roll barrel from 600 to 570 mm ranges from 3 to 5 % of the length of the arc of contact in the absence of a difference in the diameters of the barrels of the rolls. Fluctuation in moments when taking into account the factor of asymmetric rolling reaches 20 % of the corresponding values typical for the technological process on rolls with the same barrel diameter. An increase in the asymmetry of the rolling process leads to a slope of the neutral section in the deformation zone with an increase in the proportion of the advance zone in the arc of contact of the upper work roll with a smaller diameter of the barrel and the strip. An assumption is made, which requires further research, about the possibility of creating only one advance section along the entire length of the interaction of the roll with a smaller diameter of the barrel and the strip. Such a structure of the contact zone is theoretically able to reduce the required power of the main drive.

Research on Electrical Contact Characteristics of Brush-Rail Device With Transient Large Current

An excellent electrical contact state is necessary to ensure safe and stable operation of the system. Therein, contact resistance and arc ablation are essential indexes for estimating the contact state. In view of the characteristics of brush-rail device with transient large current for AC electromagnetic propulsion, a contact resistance model and the concept of arc ablative trigger boundary are proposed in this paper. Firstly, an equivalent circuit model is developed based on structural properties of brush-rail device. Then, the corresponding contact resistance model is established considering the contact pressure, amplitude and frequency of current, sliding velocity and consecutive run times. In addition, the main affecting factors of arc ablation are analyzed and the p-v parameters of arc ablation boundary are determined. Finally, the contact resistance and arc ablative trigger boundary of the brush-rail device are tested on a rotating transient large current experimental platform, which proves the correctness of the proposed method.

Development of contact arc carburization process

The possibility of using the developed technology of contact arc carburization for various parts of agricultural equipment is investigated. The composition of the electrode for contact arc carburization has been developed, which provides a high-intensity transfer of carbon atoms from the surface of the electrode to the surface layer of the metal of the part. It is shown that the quality of the surface of the parts hardened by contact arc carburization is not inferior to the quality of the surface of the parts treated with a laser beam.

Electroplastic rolling of refractory metal strips: mathematical modelling of the process

In order to analyze the electroplastic deformation process, the authors developed a mathematical model that simulates strip rolling with high-density electric current going through the deformation zone. The model consists of two main parts: a model for determining the strip temperature beyond the deformation zone; and a model of the deformation zone. The paper describes temperature fields calculated for a tungsten strip rolled out of a 200 μm thick and 200 μm wide workpiece at the electric current power W equal to 0.2 and 0.4 kW and rolling speeds V equal to 8.5, 28 and 50 mm/s. It was established that the maximum temperature of the strip Tmax is reached inside the deformation zone, the length of which is taken equal to the length of the contact arc ld. In the section located at a distance of more than 3·l d before the rolling stand, the temperature of the strip is equal to 25 оC, which corresponds to the ambient temperature. After the rolling stand, the strip cools down due to heat dissipation. How quickly the strip will cool down is dictated by the cooling conditions, rolling speed and strip size. Obviously, a thinner strip transfers heat more intensely. A drastic temperature increase was observed in the deformation zone of the rolling stand. After exiting from the deformation zone, the strip, heated to the deformation temperature, gradually cools down as a result of heat dissipation. The intensity of the lengthwise temperature decrease rises as the rolling speed and the heat transfer coefficient go down. The results obtained with the help of the mathematical model were used to revise the technical data of the electroplastic rolling mill (the spacing between its key components, roll design, rolling speed, electric current density, etc.) and to elaborate recommended thermomechanical rolling regimes for micron thin molybdenum and tungsten strips.

SIMULATION MODELING OF ASYMMETRIC SHEET ROLLING STABILITY

Asymmetric rolling using work rolls of different diameters is one of the ways to reduce production costs and optimize the roll stock. It is shown that the use of technology of asymmetric continuous sheet rolling in rolls with different diameters requires the solution of new technological problems associated with the treatment of steel sheets by pressure in conditions of different contact arc lengths in the deformation center. One of the risks of this rolling method is the occurrence of slippage of work rolls relative to the strip, which may lead to the emergence of negative self-oscillation effects. The paper presents the results of simulation of strip gripping stability at different grades in order to eliminate slippage during asymmetric rolling in rolls with different diameters and the same circumferential speed at constant rolling speed. Ways of identifying technological modes, inclined to appearance of rolling process instability in the form of rolls slipping relative to the strip, are offered. Recommendations on the optimum value of roughness of working rolls during asymmetrical rolling on various sections are given

Analysis of force and deformation parameters in corrugated clad rolling

Corrugated clad rolling is an emerging and promising technology to produce composite plates with a three-dimensional corrugated interface and excellent performance. A new analytical model is proposed to predict and analyze force and deformation parameters in corrugated clad rolling using the slab method, which solves the problem that there is no suitable analytical model to improve the precision of automatic production control. The analytical model is proposed by selecting a differential element perpendicular to the rolling direction, analyzing the corresponding differential equilibrium equations and calculating the integral constants according to the yield and boundary conditions. Dynamic rolling forces under different contact states between the composite plate and rolls are presented creatively considering the special features of the new corrugated clad rolling that there are multiple complex shapes and stress states in the deformation zone and that there are various outlet conditions of the corrugated composite plate. The accuracy of the proposed analytical model is verified by the comparisons of the calculated values from the model, the FEM results, and the experimental measurements. The error of the proposed model is within 7.36%. The specific rolling pressure distributions along the projected contact arc, the specific horizontal stress distributions along the projected contact arc, the dynamic rolling forces, and the positions of the lower neutral point can be conveniently and accurately calculated by the proposed model, which can help to analyze the mechanism of the corrugated rolling with the variation of the rolling reduction rate, the shear yield stress ratio and the friction factor ratio. The proposed analytical model of dynamic rolling force and deformation parameters is especially suitable for the analysis of the new corrugated clad rolling and can provide technical support for the control precision of automatic production.

Analysis of Visual Characteristics of Short-circuited Arc Sites

Identifying the cause of fire at a fire site is an important fire prevention measure to prevent recurrence. In particular, information about molten marks of the copper wire is essential to check whether electric power is being supplied at the fire site. This study aims to analyse the visual characteristics of arc sites formed by a short circuit to identify the molten marks at the fire site. When a short circuit occurs, electromagnetic force is generated by the short circuit current, and the arc repulsion force is generated by the contact arc. In this study, the effects of the forces, which act on the short-circuited melted area, on the formation of copper molten marks were investigated. Copper molten marks formed by a short circuit were experimentally fabricated, and the visual characteristics based on the force that was applied to the melted area were identified and classified based on features. The results showed that the melted area was affected by both the arc repulsion and electromagnetic forces, resulting in the visual differences between the short-circuited arc sites and flame-melted ones, which are affected by gravity and molecular force. These results provide a theoretical basis for discriminating between arc sites formed by a short circuit and flame-melted marks at the fire site. The validity of this study was verified via a comparative analysis using shape and cross-sectional microstructure of molten marks collected at the fire site.

An Experimental Study of Short-Circuit Current Making Operation of Air Medium-Voltage Load Break Switches

Replacing SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , the most potent greenhouse gas, with an alternative gas is a challenge faced by medium-voltage load break switches (MV-LBS). Air is a possible alternative, but there are some challenges regarding low dielectric strength leading to high arcing time and dissipated energy. Therefore, understanding the switching processes for both interruption and making operations in air MV-LBS is crucial to designing efficient compact switchgear. This work focuses on making operations in air MV-LBS. A synthetic test circuit and a model switch are designed based on the standards to simulate making operations under fault conditions similar to a real test. The test condition is set to achieve high pre-strike arcing time and energy. The results show that the most destructive impact of the making short-circuit current occurs in the first half-cycle of the load current when the pre-strike arc is formed. For an average short-circuit current with a peak of 22 kA and a breakdown voltage of 20 kV, the switch failed to re-open due to the arcing contacts welding after four successive making operations without main contacts and seven successive operations with main contacts. It has been shown that the total arcing contact mass loss occurs mainly during the pre-arcing time.Increasing the closing speed could be a possible solution to minimize the impact of arcing.

Modeling for prediction of sawing force based on the maximum undeformed chip distribution in the granite sawing

Sawing by circular saw blades is predominant in the mechanized treatment of natural stone. The predictive sawing force is crucial for optimizing, controlling, and monitoring the sawing process. In this work, a novel model for predicting sawing force, which is based on the distribution of the undeformed chip thickness at the sawing contact arc, was proposed. Based on the analysis of the undeformed chip geometry of the circular saw blade, the segment surface was divided into the front end and rear end according to the contact pattern between the segments and granite, and the models of the maximum undeformed chip thickness of diamond particles on the front end and rear end were established. Results showed that the new proposed force model fully considered the distribution of undeformed chips compared with the current model. The novel model has higher prediction accuracy, the mean maximum absolute error is within 3.77%, and the maximum absolute error is within 7.83%. Through theoretical analysis, the ratio of the maximum undeformed chip thickness of the front segment to the rear segment is 1.67, which can fully explain the wear non-uniformity of the segment. The proposed model is of great significance to the optimization of the saw blade structure and process parameters.

Assessment of pantograph-catenary interaction in a railway overlap section via a novel optical-based method

• Pantograph-catenary interactions at an existing overlap span are investigated. • A novel optical-based method is proposed and implemented at the overlap span. • Single- and double-pantograph train passages are obtained and studied. • Dynamic effects rendering high contact forces, contact loss and arcing are studied. • Peak contact force, transition distance and train speed show a strong correlation. Smooth pantograph-catenary contact is essential for regular train operation. However, catenary section overlaps are locations where peak contact forces occur, which significantly affects current collection quality. This work studies pantograph-catenary interaction and transition at an existing overlap span by using a novel optical-based measuring method. Image sequences of eleven single- and two double-pantograph train passages were processed to obtain wire displacement responses. The unsynchronised vibration of two contact wires was found, and the first contact wire exhibits different modal responses. The spatial motion paths of contact wires were obtained to estimate the pantograph-catenary interaction. Dynamic effects rendering high contact forces, contact loss and arcing were investigated. The results show that pantographs with a long transition distance and a high intersection gradient cause a serve impulse with the second contact wire, resulting in contact loss and arcing. Finally, this study successfully estimated the transition distance and found it has a strong positive correlation with peak contact forces and train speeds. The transition distance exhibits an increasing tendency with increasing train speed. The longer transition distance results in a higher peak contact force.

An Experimental Laboratory Study Using the Miyake-Apple Posterior View Technique to Investigate the Dynamics Between Capsular Bags and Different IOL Models.

To evaluate the dynamics between capsular bags and different intraocular lens (IOL) models in human cadaver eyes using the Miyake-Apple posterior view technique. In an in vitro laboratory study, human cadaver eyes were prepared according to the Miyake-Apple posterior view technique. Five IOLs from each of the six groups (Avansee 1P [Simonvision], Avansee 3P [Simonvision], CT Lucia [Carl Zeiss Meditec], Acrysof [Alcon Laboratories, Inc], RayOne [Rayner], and CT Asphina [Carl Zeiss Meditec]) were implanted into capsular bags with different diameters. The empty capsular bag diameter and capsular bag diameter with an IOL in it were evaluated based on the Miyake-Apple view pictures. Posterior capsule striae were observed and compared between groups. The arc of contact between IOLs and the capsular equator was noted. Correlations between the empty capsular bag diameter and the capsular bag diameter with IOL, as well as between the empty capsular bag diameter and the arc of contact, were examined. With the Avansee 3P as a reference, the area deviation of the haptics of IOL models with looped haptics was compared. The capsular bag diameter with IOL inside and the arc of contact were proportional to the empty capsular bag diameter. The RayOne, Avansee 3P, and CT Lucia showed a longer arc of contact. Posterior capsule striae were observed in the Avansee 1P (1, 20%), Avansee 3P (5, 100%), Acrysof (1, 20%), and RayOne (2, 40%). Areas of deviation were 0.38 mm2 (Avansee 1P), 0.24 mm2 (CT Lucia), 0.34 mm2 (Acrysof), and 0.31 mm2 (RayOne), respectively. Different IOL models showed varied characteristics in terms of capsular bag fitting and arc of contact. Understanding these dynamics is critical to optimizing postoperative outcomes. [J Refract Surg. 2022;38(10):654-660.].

Simulation research on the pre-strike characteristics of SF6 circuit breaker

The pre-strike duration of SF6 circuit breaker closing is one of the indicators to measure the ablative state of contacts, obtaining the pre-strike characteristics of SF6 circuit breaker closing is very important to evaluate the electrical life state of circuit breakers. In this paper, the simulation model of the electrical and fluid coupling simulation of the 110kv SF6 circuit breaker is established, and the pre-strike characteristics of the closing process are studied. The results show that the maximum point of the synchronous midfield is always on the surface of the static arc contact. The density of SF6 on the arc-extinguishing chamber is almost constant; the pressure output of the pressure chamber has little effect on the pre-strike voltage curve. Under the phase voltage of 110kv voltage, the duration of the circuit breaker pre-strike duration is 0.9054ms, which is close to the measured value. Results can provide the basis for the actual life circuit life evaluation.

Seismic Performance of Building with Novel Steel Roller Isolation Bearing: Experimental and Numerical Studies

ABSTRACT This study proposed a novel steel roller isolation bearing (SRIB). Compared with the traditional rolling bearing, the symmetrical hyperboloid and the contact arc in the middle of the rolling surface made SRIB have stable working performance. The actual mechanical properties of SRIB were obtained by theoretical analysis, experiment and numerical studies. Particular attention was the damping of SRIB that was very small, so the magneto-rheological damper was used as an additional damping device to work with SRIB. The results shown that SRIB had stable and good seismic isolation performance and had better control effect combined with additional damping device.

Research on a coupler with arc surface contact and its effect on a train collision

Based on the multi-body dynamics a three-dimensional train collision model including a coupler-buffer substructure is established in this paper. During the train collision, the dynamic responses of coupler-buffer substructure are comprehensively analysed. Some key parameters, such as the coupler initial deflection angle, max-angle, friction force at the arc contact surface and buffer impedance force, are investigated and their effects on the train derailment are also evaluated. The simulation results indicate that during a train collision the longitudinal impact force is so large that the coupler-buffer device reveals a weak ability to anti-jackknifing. As a result, in some cases the coupler rotation angle is very large and equal to its designed max-angle. Under the effect of this large coupler rotation angle, the collided trains have a risk to derail. In order to improve the collided train’s safety against derailment, a high friction force at the coupler arc contact surface and a low coupler max-angle are suggested.

Temperature field modelling in the form grinding of involute gear based on high-order function moving heat source

Grinding is one of the primary methods to enhance the tooth surface quality. For gear form grinding, due to the complexity of grinding movement and nonuniform grinding conditions of the tool and workpiece geometry, the accurate prediction for gear grinding temperature is difficult to achieve by using a single specific heat source shape. Therefore, a new temperature model based on high-order function curve moving heat source distribution in the grinding zone was established. Compared with the traditional models, using the new model can avoid assuming the heat source distribution shape in advance and greatly reduce the disadvantages caused by improper heat source shape assumptions under the nonuniform grinding conditions along the tooth profile. In this model, the analysis of geometry model of gear form grinding, characteristic parameters of abrasive grains and moving point heat source theory were comprehensively considered. Additionally, the finite element numerical simulation and gear grinding experiments were outperformed to analyze the gear grinding temperature. Comparison results show the highest temperature based on high-order function curve heat source appears earlier and closer to the front of the grinding contact arc compared with triangular and rectangular heat source distribution shapes. Furthermore, the tooth surface temperature in the grinding zone obtained by new model has better consistency with the experimental measurement results. The relative errors of the analytical and numerical simulation results of the maximum temperature are within 5.2 % and 6.4 %, respectively. These findings prove the accuracy and superiority of the temperature prediction model based on high-order function moving heat source distribution for gear form grinding, and it has a guiding role in the optimization of the workpieces with complex profiles in form grinding.