Ag/La_2NiO_4基电触头在直流大电流条件下电弧侵蚀的实验与有限元研究

在电接触试验机上测量Ag/La2NiO4基电触头,得到在直流18V、30A的工作条件下的相关实验数据。并进一步分析电触头对的阴极和阳极的表面形貌、电弧侵蚀和质量变化特点。在此基础上,通过对实验中闭合电弧→接触电阻焦耳热→分断电弧→自然冷却过程的分析,建立一个电触头使用过程中的瞬态温度场的计算模型;根据测得的相关实验数据,采用有限元方法对该模型进行计算,得到电触头的瞬态温度场的分布和演化特点。通过计算结果可以较好预测电弧侵蚀的特点以及材料转移方向,并给出关于材料熔化、汽化等方面的许多重要信息。这些结果对于该电触头材料的侵蚀和使用寿命的研究具有一定参考价值。

Ag/La_2NiO_4基电触头使用中温度场的有限元分析和实验研究

通过对电触头使用过程中闭合电弧→接触电阻焦耳热→分断电弧→自然冷却过程的分析,建立了一个可描述电触头使用过程中,瞬态温度场的统一计算模型。通过对Ag/La2NiO4基电触头的电接触实验机和相关实验的测试、分析和计算,得到进行该电触头使用中瞬态温度场计算所需的基本参数。在此基础上,采用有限元方法进行了计算,得到了该电触头的瞬态温度场的分布和演化特点。通过将计算结果与相关的实验测量结果进行分析和比较,可以发现瞬态温度场对于Ag/La2NiO4基电触头材料的侵蚀机制、使用寿命的研究具有重要参考价值。

Preparation and Anti⁃arc Erosion Property of Ag Matrix Electrical Contact Material Reinforced by Novel Ti_(2)Cd

Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications.In order to further reduce the Cd content under the premise of meeting the high-performance requirements,in this study,high-purity intermediate Ti_(2)Cd powder of MAX phase(Ti_(2)CdC)was synthesized with a pressureless technique and then applied to reinforce the Ag matrix.The Cd content of the as-prepared Ag/Ti_(2)Cd composites was actually reduced by 38.31%compared with conventional Ag/CdO material.Based on the systematic study of the effect of heat treatment temperature on the physical phase,morphology,interface and comprehensive physical properties of Ag/Ti_(2)Cd composites,the preferred samples(heat treated at 400°C for 1 h)showed high density(97.77%),low resistivity(2.34μΩ·cm),moderate hardness(90.8HV),high tensile strength(189.9 MPa),and exhibited good electrical contact performance after 40000 cycles of arc discharging under severe conditions(DC 28 V/20 A).The results of microscopic morphological evolution,phase change and elemental distribution of the electrical contact surface show that the combination of high stability of Ti_(2)Cd reinforcing phase,good interfacial bonding with Ag matrix and improved melt pool viscosity in the primary stage of arc erosion,results in low and stable contact resistance(average value 13.20 mΩ)and welding force(average value 0.6 N),low fluctuation of static force(2.2-2.5 N).The decomposition and absorption energy of Ti_(2)Cd and the arc extinguishing effect of Cd vapor are the main reasons for the stable arcing energy and arcing time of electric contacts in the late stage of arc erosion.

Arc erosion behaviors of AgSnO_2 contact materials prepared with different SnO_2 particle sizes

To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag?4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag?4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag?4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag?4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag?4%SnO2contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.

Production of Ag-ZnO powders by hot mechanochemical processing

Ag–CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties.Nevertheless,considering the restriction on using Cd due to its toxicity,it is necessary to find alternative materials that can replace these composites.In this study,the synthesis of Ag-ZnO alloys from Ag-Zn solid solutions was investigated by hot mechanochemical processing.The hot mechanochemical processing was conducted in a modified attritor mill at 138℃under flowing O2 at 1200 cm3/min for 3.0 h.The microstructure and phase evolution were investigated using X-ray diffractometry,field emission gun scanning electron microscopy and transmission electron microscopy.The results suggest that it is possible to complete the oxidation of Ag-Zn solid solution by hot mechanochemical processing at a low temperature and short time.This novel synthesis route can produce Ag-ZnO composites with a homogeneous distribution of nanoscale ZnO precipitates,which is impossible to achieve using the conventional material processing methods.Considering the fact that the fundamental approach to improving electric contact material performance resides in obtaining uniform dispersion of the second-phase in the Ag matrix,this new processing route could open the possibility for Ag-ZnO composites to replace non-environmentally friendly Ag-CdO.

Influence of operation number on arc erosion behavior of Ag/Ni electrical contact materials

Arc erosion behavior of Ag/Ni materials with different operation numbers was investigated by OM,3DOP and SEM.The results indicated that the arc erosion of Ag/10Ni electrical contact material fabricated by sintering−extrusion technology was more and more serious with the operation numbers increasing from 1000 to 40000.With the same operation numbers,the arc erosion on anode was more serious than that on cathode.Besides,the pores preferred to emerge around the arc effect spot during the first 10000 operations.And the morphology of the molten silver on cathode and anode was different due to the action of gravity and arc erosion.Furthermore,the relationships among arc energy,arc time,welding force,electric resistivity,temperature and mass change on contacts were discussed,which indicated that the mass loss on cathode was mainly caused by the fracture of molten bridge.

Material transfer behavior of AgTiB_2 contact under different contact forces and electrode gaps

To disclose the effect of contact force and electrode gap on the material transfer behavior of Ag-based contact material, arc-erosion tests of the Ag-4wt.%TiB2 contact material were performed for 5000 operations at 24 V/16 A under resistive load on an electric contact material testing system. The arc energy and arc duration were investigated, the surface morphologies of eroded anode and cathode were characterized, the mass changes after arc-erosion tests were determined, and the material transfer behavior was discussed as well. The results show that contact force has a significant effect on the arc energy, arc duration and erosion morphology, but has no impact on the material transfer mode. However, electrode gap not only influences the arc energy, arc duration and surface morphology, but also changes the material transfer mode. At 1 mm, the material transfers from anode to cathode. Nevertheless, an opposite mode presents at 4 mm, which is from cathode to anode.

Smart-microstructures of composites for electrical contacts with frameless packing of Cr and W in copper

W_(45)Cu_(55),Cr_(65)Cu_(35),and Cr_(32)W_(14)Cu_(54)alloys were obtained in order to study the mechanism of“smart response”of the structure of these alloys when using them as arc-resistant circuit-breakers.These alloys differ from industrial ones with frameless packing of Cr and W phases in the copper matrix.The alloy production method is based on the infiltration of copper melt into a mixture of non-compacted Cr and W powders under vibration exposure(80 Hz).The research results show an increase in the arc resistance of contacts when changing from“frame”packing of W to“frameless,”as well as the decisive role of Cr in the processes of self-dispersion of arc-resistant phases and passivation of W and Cu.Based on the obtained results,conclusions are drawn about the advantage of frameless packing of arc-resistant phases in copper and the reasons for the“smart behavior”of the structure of Cr-containing contacts in response to functional loads in the presence of oxygen and an inert atmosphere.

Testing results analysis of contact materials’electrical contact performance

Because of the different ways in which contact materials work, the basic requirements for silver metal oxide contact materials are different. They are anti-welded and anti-erosion when closed, anti-erosion when broken, and arc easily moved and have smaller contact resistance. In this paper, La2O3 is used as a stable oxide in contact material to replace CdO. A new type of Ag/SnO2-La2O3-Bi2O3 contact material is first obtained through using powder metallurgical method. Then electrical contact material parameter tester is used to test the electrical contact performance of the contact material. Through experiments, the arcing voltage and current curves, arcing energy curves, fusion power curves while broken and contact resistance while closed were obtained. Analysis of the results showed that the addition of La2O3 makes the contact material have the following advantages: smaller electrical wear, smaller arc energy, smaller contact resistance and arc is more easily extinguished.

Realization of a novel Ag/SnO_2 electrical contact material with microscopic fiber-like structure

According to the principle that fiber-like arrangement of reinforcing particles SnO2 paralleling to the direction of current is propitious to the electrical and mechanical performance of the electrical contact materials, we proposed and reported a novel precursor route used to prepare Ag/SnO,. electrical contact material with fiber- like arrangement of reinforcing nanoparticles. The mechanism for the formation of fiber-like arrangement of rein- forcing nanoparticles in Ag/SnO2 electrical contact material was also discussed. The as-prepared samples were char- acterized by means of scanning electron microscope （SEM）, optical microscope （OM）, energy-dispersive X-ray spectroscopy （EDX）, MHV2000 microhardness test, and double bridge tester. The analysis showed that the as-prepared Ag/SnO,, electrical contact material with fiber-like arrangement of reinforcing nanoparticles exhibits a high elongation of 24 %, a particularly low electrical resistivity of 2.08 μΩ. cm, and low arcing energy, and thus has considerable technical, economical and environmental benefits.

Study on Restrike Phenomena for 40.5-kV Vacuum Circuit Breakers

When interrupting short circuit fault by 40.5-kV vacuum circuit breakers, it is significant to eliminate multiple restrike phenomena, which occur frequently and result in high overvoltage and even interruption failure. A synthetic circuit that can supply a DC recovery voltage after current zero was used to study multiple restrike phenomena in switching. Some key factors including breaking current, clearance between open contacts, electrode structure and contact material, which may affect restrike characteristics, were studied. Under various clearances, the statistical probability of restrike was obtained. As a result, the best scope of clearance between open contacts was found. The performance of CuCr50/50 and CuCr75/25 material were compared. Two kinds of electrode structures, namely 1/2 coil structure and cup-shaped axial magnetic structure, were tested. After a high-current interruption, conditioning effoct was realized and the probability of restrike decreased.

Preparation of in-situ Cu/NbC nanocomposite and its functionally graded behavior for electrical contact applications

Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.

Contact and injection engineering for low SS reconfigurable FETs and high gain complementary inverters

The newly emerged two-dimensional(2D) semiconducting materials, owning to the atomic thick nature and excellent optical and electrical properties, are considered as potential candidates to solve the bottlenecks of traditional semiconductors. However, the realization of high performance 2D semiconductorbased field-effect transistors(FETs) has been a longstanding challenge in 2D electronics, which is mainly ascribing to the presence of significant Schottky barrier(SB) at metal-semiconductor interfaces. Here, an additional contact gate is induced in 2D ambipolar FET to realize near ideal reconfigurable FET(RFET)devices without restrictions of SB. Benefitting from the consistently high doping of contact region, the effective SB height can be maintained at ultra-small value during all operation conditions, resulting in the near ideal subthreshold swing(SS) values(132 mV/decade for MoTe2 RFET and 67 mV/decade for WSe2 RFET) and the relatively high mobility(28.6 cm2/(Vs) for MoTe2 RFET and 89.8 cm2/(V s) for WSe2 RFET). Moreover, the flexible control on the doping polarity of contact region enables the remodeling and switching of the achieved unipolar FETs between p-type mode and n-type mode. Based on such reconfigurable behaviors, high gain complementary MoTe2 inverters are further realized. The findings in this work push forward the development of high-performance 2D semiconductor integrated devices and circuits.