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This article presents the results of research on the thermal state of vacuum switch contacts during the conduction of short-circuit currents. This state is directly related to the value of the flowing current and the operating conditions of the switch. These conditions are mildest in the case of the conduction of operating currents through closed contacts. The situation worsens significantly when short-circuit currents are conducted, and the greatest destructive effects occur during commutation processes. Exceeding a certain level of contact destruction usually leads to the loss of the switching capacity of the switch. In vacuum switches, tracking the thermal state of the contacts is particularly difficult due to the inaccessibility of transducers or measurement sensors inside the chamber. In such a case, simulation studies verified by experimental results are important. This paper presents the results of such studies, directed at their practical implementation in the design and operation of vacuum switches. Simulation studies were conducted to analyze the thermal processes occurring in the contacts of vacuum switches during the conduction of short-circuit currents. Special attention was paid to the influence of contact parameters on the thermal processes occurring during the conduction of short-circuit currents. In addition to simulations, experimental studies were carried out to verify the simulation results. Ultimately, the research results presented are intended to provide practical knowledge of the design and operation of vacuum switches, particularly with regard to the contact heating processes during the conduction of short-circuit currents. [ABSTRACT FROM AUTHOR]

Micro-Electromechanical-Relay (MER) has widely achieved application in the field of engineering thanks to the excellent features and ever-growing interest in microelectronic products. However, the adhesion phenomenon between gold-sputtered contact pairs in MER usually brings about operating failure of normally closed contacts limiting the reliability level of MER. In this paper, various contact combinations between electrical contact pairs are assembled to simulate real contact conditions, and associated failure type is built by taking advantage of mechanical adhesion theory to reveal failure mechanism about cold adhesion. It is found that the adhesion force is correlated closely with the surface roughness of contact pairs. The specific contact combination is a significant effective strategy to reduce the adhesion failure between electrical contacts. [ABSTRACT FROM AUTHOR]

The contact finger electrical connection structure is a crucial component of high voltage bushings, and its safety and reliability directly impact the operational stability of the bushing. To investigate electrical contact performance of the contact finger under eccentric conditions, a three‐dimensional electrical, thermal, and force multi‐physics coupling calculation model was established. Additionally, a test platform was constructed to measure electrical contact characteristics of the contact finger. The contact characteristics of the contact finger when the male head was axially deflected and radially offset compared to the female head were obtained. The research findings indicate when the male head deflects axially, the contact force changes of the contact finger blades on both sides are opposite. Moreover, as the axial deflection angle of the male head increases, the resistance of the electrical connection structure shows a rising‐slow decreasing‐fluctuating trend. The resistance is highest at 3°, with a resistance increase rate of 7.35%. Furthermore, the resistance of the electrical connection structure varies with the radial offset of the male head, following a power function. Contact failure occurs when the radial offset is 1.31 mm, and the resistance increase rate reaches 24.9% at a radial offset of 1.58 mm. [ABSTRACT FROM AUTHOR]

The article presents the results of laboratory measurements of Ud breakdown voltages in a high-voltage vacuum insulating system for different pressures, contact gaps, type of electrode contacts and type of residual gas inside the discharge chamber. First of all, the electrical strength of the discharge chamber with a contact system terminated with contact pads made of W70Cu30 and Cu75Cr25 material was compared for selected values of contact gaps. It was found that below a pressure of p = 3.0x10-1 Pa the electrical strength reaches an approximately constant value for each of the set contact gaps d. Analytical relationships were determined to calculate this value for each of the contact pads used. Above a pressure of p = 3.0 x 10-1 Pa, the measured values of Ud breakdown voltages decrease sharply. The values of breakdown voltages in the discharge chamber with residual gases in the form of air, argon, neon and helium were also determined for selected values of contact gaps d. Depending on the residual gases used, significant differences were noted in the values of pressure p at which the loss of insulating properties in the discharge chamber occurred. These values were 3.3 x 10-1 Pa for argon, 4.1 x 10-1 Pa for air, 6.4 x 10-1 Pa for neon, and 2.55 x 100 Pa for helium, respectively. [ABSTRACT FROM AUTHOR]

In this study, hard wear-resistant Ti-Si-C coatings were deposited on Cu-Cr materials to improve their performance as sliding electrical contact materials. A ceramic disk composed of Ti3SiC2 and TiC phases was used as a target for DC magnetron sputtering to deposit the coatings. The influence of the power supplied to the magnetron on the chemical composition, structure, and friction coefficient of the coatings was examined. The coatings demonstrated high hardness (23–25 GPa), low wear rate (1–3 × 10−5 mm3/N/m) and electrical resistance (300 μOhm·cm), and fair resistance to electroerosion. The coating deposited at 450 W for 30 min displayed optimal properties for protecting the Cu-Cr alloy from the arc effect. [ABSTRACT FROM AUTHOR]

High electrical and thermal contact resistances can ruin a thermoelectric device's performance, and thus, the use of effective diffusion barriers and optimization of joining methods are crucial to implement them. In this work, the use of carbon as a Cu11Mn1Sb4S13 tetrahedrite diffusion barrier, and the effectiveness of different fixation techniques for the preparation of tetrahedrite/copper electrical contacts were investigated. Contacts were prepared using as jointing materials Ni and Ag conductive paints and resins, and a Zn-5wt% Al solder. Manual, cold- and hot-pressing fixation techniques were explored. The contact resistance was measured using a custom-made system based on the three points pulsed-current method. The legs interfaces (Cu/graphite/tetrahedrite) were investigated by optical and scanning electron microscopies, complemented with energy-dispersive X-ray spectroscopy, and X-ray diffraction. No interfacial phases were formed between the graphite and the tetrahedrite or Cu, pointing to graphite as a good diffusion barrier. Ag water-based paint was the best jointing material, but the use of hot pressing without jointing materials proves to be the most reliable technique, presenting the lowest contact resistance values. Computer simulations using the COMSOL software were performed to complement this study, indicating that high contact resistances strongly reduce the power output of thermoelectric devices. [ABSTRACT FROM AUTHOR]

This review summarizes the advancement on sintered composites based on tungsten–copper (W–Cu) reinforced with graphene (Gr) or its derivative such as reduced Gr oxide (rGO) for use as electrical contacts applied in switching devices. Main synthesis approaches for preparing Gr or rGO reinforced W–Cu composite powders and their consolidations by using various powder metallurgy techniques are presented. The nature of the initial materials, synthesis conditions, processing parameters, and the relevant findings are disclosed and discussed. The improvement in microstructure and technical characteristics like density, electrical conductivity, hardness, coefficient of friction, wear rate, and arc ablation behavior of W–Cu–Gr/rGO composites are highlighted comparatively with that of unreinforced composites. This review reveals an insight into a novel class of composites as candidates for electrical contact applications. [ABSTRACT FROM AUTHOR]

In this work, the wear and melt erosion behavior of tin-plated copper alloy contacts are investigated under fretting at current loads ranging from 0.1 to 12.5 A. Three typical variations in the average values of contact resistance and contact temperature with fretting cycles are recorded and interpreted explicitly. The material melt erosion in the contact interface is observed clearly at currents higher than 5 A due to substantial Joule heat. The increment of contact temperature together with the distortion of transient friction force are considered as the degradation characteristics in the fretting. The produced scars and oxides between the contact interface eventually lead to the electric circuit disconnection. The distinct physical mechanism of contact interface fretting wear and melt erosion at high current loads is presented. [ABSTRACT FROM AUTHOR]

A silicon microparticulate material (SiMP) used as the anode for lithium‐ion batteries promises higher volumetric capacity and less interfacial reactions than its costly nanoparticulate counterpart. However, what mostly hinders its practical use is its expansion and pulverization during cycling that induces electrical disconnection and electrode polarization. A liquid metal (LM) is proposed as a remedy for these problems that acts as an adaptive conducting continuum to cure both short‐ and long‐range electrical disconnection. LM encapsulated in a carbon layer constructs a local electrical "ocean" adaptively connecting pulverized Si "islands" upon cycling. Furthermore, carbon nanofibers grown on the LM provide long‐range conducting bridges between the microparticulates, which allow the production of thick electrodes that can be used with SiMPs. With the increased tap densities (4.15 and 1.75 g cm−3 respectively for the composite and the electrode), these thick electrodes give highly stable and superior volumetric lithium storage. These results pave the way for practical compact lithium batteries with SiMPs that have a high‐volumetric energy density. [ABSTRACT FROM AUTHOR]

The purpose of the proposed course is to enhance students' knowledge, engineering skills and understanding in the field of electrical contacts power engineering – the currents of contact welding. The main goal for students is to acquire brief skills concerning measurements of certain parameters using static layout: currents that cause contact welding, clamping force of contacts joints and breaking force. Moreover, students are encouraged to obtain soft skills like confidence in the mentioned field and creativity. Student work during the exercise is evaluated on the basis of report from laboratory work and test. Essential aspect is safety training while working with HV and MV switchgears – that is another obligatory feature which participants will obtain from this course. Course results were evaluated as significant on the basis of concluded statistical analysis and comparison to previous formula employed during the classes. [ABSTRACT FROM AUTHOR]

The electrical contact resistance (ECR) of copper (Cu‐ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20–550 °C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature‐dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electroless Ag, Ni and Cr layers were successfully obtained on Cu particles. • Electroless plating layers were detected at the grain boundaries of Cu-based materials. • Electrical contact performances were improved over conventional electrical contacts. • Thanks to electroless Ni, wear performance was increased 3 times compared to Cu. • FGM design with Ni showed 10 times higher arc erosion performance compared to Cu. In this study, hot pressing was used to fabricate the novel copper based functionally graded electrical contact materials synthesized by silver, nickel and chrome plated copper core particles. For the fabrication of functionally graded materials (FGMs) by hot-pressing; pure copper, two and three layered metallic powders were used in the lower, middle and upper layer, respectively. The wear and arc-erosion performances of the developed materials increased from 3 to 10 times as compared to that of pure copper. Wear tests showed that the abrasive wear mechanism was dominant for the FGMs including electroless nickel and chromium coating layer. The highest specific wear rate (SWR) value was found in Cu f -Ag′ (4.9 × 10−4 mm3/Nm) materials under the load of 20 N while the lowest SWR value belongs to Cu f -Ag-Ni′ (2.3 × 10−4 mm3/Nm) materials under the load of 10 N. While severely melted and deformed regions are dominant on arc erosion surfaces of pure copper and copper-silver containing contacts, flatter and relatively less melted regions were detected on the surfaces of FGMs containing nickel and chromium. The arc-erosion loss values (cm3 × 10−4) measured for FGM 1 sample were 0.75 and 0.70, 0.99 and 0.88, 1.21 and 1.04 at 3000 cycles under the current of 5 A, 10 A and 15 A in fixed and moving contacts, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a computer vision inspection methodology is presented for the detection and segmentation of areas of wear by electric arc on the surface of electrical contacts using segmentation by instances. Cadmium is a toxic metal frequently used in the manufacture of alloys for electrical contact, so efforts have been made to replace or eliminate this element from the industry. Our work proposes an approach oriented to the automation of the inspection process, which reduces the subjectivity of the repetitive task of inspecting electrical contacts, allowing to compare two different alloys, such as one with Cadmium (Cd) and the other with Copper (Cu)., subjected to the same conditions and determine which of them presents less wear by electric arc. In this way you can know if the new part is better, equal or worse in terms of performance. Initially, an adaptation was made of the source code hosted in a github repository of mask R-CNN of the Matterport corporation, where variables, classes were modified, and directories were created according to our needs. The results obtained show that the masks generated by the algorithm adjust very well to contact wear, despite the irregular shape of the damage. However, the "charred" edge was probably not considered, because in training images it was a feature that few images presented, so segmentation may not be considering this factor. [ABSTRACT FROM AUTHOR]

In this article, an attempt is made to explore the effects of normal force and temperature on the threshold displacement amplitudes of tin-plated electrical contacts at elevated temperatures. Fretting tests were conducted at 323, 348, and 373 K at normal forces of 1, 1.25, 1.5, and 2 N. Riders and flats made from a 0.3-mm-thick brass sheet were coated with $10~\mu \text{m}$ of tin. Dimples were commonly found at the center of the contact area of the test specimens corresponding to an unlimited lifetime. In the testing temperature range, the threshold displacement amplitude decreases with an increase in the temperature and with a decrease in the normal force. In this range, the threshold displacement amplitude was found to be controlled by the oxidation of a tin-plated surface. The activation energy was found to be 7.5 kJ/mole, which is close to the value of the activation energy for the growth of tin oxide film. The threshold displacement amplitude can be represented in the form of an Arrhenius equation and is proportional to the normal force. [ABSTRACT FROM AUTHOR]

Various types of electrical connectors are available globally. Electrical connectors are one of the critical components in many applications, including the automotive sector. They are primarily used to supply high power (or high currents) to other connected devices, such as batteries, electronics, and motors. in both conventional and hybrid/electric vehicles. Finite element modeling (FEM) is one of the tools through which better electrical connector designs can be created, and thus, enhanced performance of these connectors can be achieved. This article presents a comprehensive review of the FEM of electrical connectors performed until now in both the bulk regions as well as the contact regions by researchers worldwide. [ABSTRACT FROM AUTHOR]

Herein, the electrical contact formation between the electrodes of the micro four‐point technique and a semiconducting sample is described. It is shown that the contact is formed in two stages: a voltage‐induced electrical contact formation, followed by a current‐induced decrease in contact resistance. Moreover, a method is proposed allowing for precise control of the final contact resistance. Finally, it is demonstrated that the contacting process is similar on 1D fin structures, where the demonstrated control of the electrical contact is needed while measuring on nanometer‐wide fins in arrays with a pitch smaller than the electrode contact size. [ABSTRACT FROM AUTHOR]

An axial magnetic field (AMF) plays an important role in the process of vacuum arc stabilisation during the current breaking process in the vacuum circuit breakers (VCBs) of the AMF type. To minimise the contacts erosion special attention should be paid to reach a possibly high value of the AMF density (between contact plates), especially in the outer electrode region. Various contact geometries are patented all over the world to improve the AMF distribution. Nevertheless, there is an issue which is not raised in the literature as yet. It is the mutual orientation (rotation) of the moving and fixed contacts. This orientation can have an influence on the AMF distribution. The above problem is analysed here numerically using Maxwell (ANSYS) software package based on the finite element method. The own (patented) contact design is considered in the analysis mentioned. However, the beneficial influence of AMF on the arc behaviour is well known for VCB designers, the explanation of this phenomenon is described (in the literature) rather seldom and very cursorily. Therefore, a simplified model accounting for the role of AMF in vacuum arc diffusion is shortly presented at the beginning of this study. [ABSTRACT FROM AUTHOR]

The work addresses a particular case of interaction between adhesive and abrasive wear in the electrical contact field, characterized by a selective adhesive transfer layer. The system studied is composed of a resistive element (NiCr thin layer) and a contactor (AgPd), forming an angular position sensor lubricated with a standard silicone oil/PTFE grease. The angular position/electrical resistance relationship is disturbed by wear of the NiCr surfaces, enhanced by the formation on the AgPd contactor of a third body enriched in Ni. From a practical point of view, it has been found that this detrimental Ni-selective transfer formation can be controlled by inserting tumble finishing with lamellar alumina powder as the last step of NiCr track manufacturing. Acting like a solid lubricant, alumina clusters of 1–5 µm in size adhere to NiCr surface giving rise to a delay or cancel of Ni adhesion on the contactor which lead to a significant improvement of electrical behavior of the position sensor. • We studied the wear mechanisms taking place in an electrical contact inside a sensor. • The resistance degradation of AgPd/NiCr contact is related to the wear process. • Selective transfer layer rich in nickel adhered on the AgPd surface is point out as the major factor limiting the electrical performances of the contact. • Tumble finishing treatment using Alumina particles was found to improve the electrical performances of the contact by stopping the growth of the transfer layer (3rd body). [ABSTRACT FROM AUTHOR]

Electrical contacts are basic components of electrical systems. They are applied in various conditions, which can influence the lifetime of the electrical contacts significantly. Fretting corrosion is one of the main failure mechanisms of electrical contacts with micro-motion. During this operation, the coating on electrical contacts is worn, generating wear debris. If the coating consists of non-noble material, for instance tin, which is a widely used coating material for electrical contacts, the wear debris will be oxidized and subsequently form an electrically highly resistant oxide layer after long-term service. Two decisive factors for the lifetime of electrical contacts are the number of cycles of motion and the time required to form this thick oxide layer. In many power semiconductor components, the housing is firstly pumped to vacuum condition, and then filled with nitrogen. The higher degree of vacuum leads to a substantially reduced amount of oxygen, a lower oxygen partial pressure and a longer mean free path of oxygen molecules, which retards the oxidation process. Therefore a remarkable improvement of fretting corrosion behavior is theoretically expected. The subject of this study is to investigate the effects of atmosphere and vacuum on fretting corrosion behavior. In order to investigate the fretting corrosion performance and the lifetime of these tin coated electrical contacts, a series of wear and fretting corrosion tests are conducted under various degrees of vacuum. The correlation between the lifetime of electrical contacts and pressure is analyzed. The results indicate that with an increasing degree of vacuum, the lifetime of electrical contacts in fretting tests is, as expected, prolonged. • The higher vacuum level leads to a remarkable improvement in fretting corrosion behavior of tin coated electrical contacts. • A relationship between the oxygen partial pressure and the lifetime is proposed based on theoretical derivation and then verified by the experimental data. • The lifetime can be significantly influenced by the vacuum condition. • It is possible to predict the lifetime of tin coated electrical contacts under various vacuum conditions. • The common model of fretting corrosion can be validated quantitatively by the results of this study. [ABSTRACT FROM AUTHOR]

Highlights • Modifying electrical contacts by electropolymerization of MMA is studied. • Ten times increase in the corrosion resistance of electrical contacts is observed. • The electrical resistance increased, but remained well below the accepted limit. • Cathodic electrodeposition of PMMA effectively sealed the pores of Au top-layer. Abstract Cu/Ni-P/Au multi-layer systems are employed as electrical contacts. The Au top-layer is thin and porous. These pores deliver the corrosive media to the under-layer, which induces the corrosion by a galvanic coupling mechanism. Therefore, filling these pores is essential to improve the lifetime of electronic devices. The pores can be sealed by the electrodeposition of poly(methyl methacrylate) that decreased the porosity index (about 97%) and increased the corrosion resistance (about 10 times) of electrical contacts after 10 cycles of electropolymerization. A non-uniform polymeric film, however, was formed at higher number of polymerization cycles (> 50) that decreased the corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract Cu/Ni(Ni-P)/Au systems are extensively used to serve as electrical contacts due to their exceptional combination of excellent electrical conductivity, corrosion resistance, and mechanical behavior. Cu has a unique electrical conductivity that made it the most used metal in electronics. However, protective coatings must be applied on Cu due to its poor corrosion resistance. Au films are widely used to secure a proper lifetime of electrical contacts. Ni barrier films are also essential to avoid the diffusion of Cu into the Au deposits that deteriorate the desired properties of noble metal films. The main aspects for improving these systems are the corrosion and wear resistance, the electrical conductivity, lowering the surface roughness and designing a morphology with hemispherical features. In this review, recent studies about the deposition of different Ni films, including Ni alloys and Ni composites, noble metal films, and possible post-treatments to optimize the performance of multi-layer films are presented with special attention to the above-mentioned criteria. Graphical abstract Unlabelled Image Highlights • The deposition of various Ni alloys and Ni composite films is studied. • The deposition of different noble metal thin films is studied. • Dispersing methods of particles to make composite films are described. • The importance of post-treatment techniques on thin films is explained. [ABSTRACT FROM AUTHOR]

Abstract The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi 2 Te 3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi 2 Te 3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi 2 Te 3 is ~0.47 and optimized Bi 1.95 Pb 0.05 Te 3 exhibit p-type conduction with enhanced ZT of ~0.63 at 386 K. The conversion efficiency of Bi 1.95 Pb 0.05 Te 3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be ~4.9% for a temperature difference (Δ T) of 200 K. The efficiency was further enhanced to ~12% (at Δ T ~ 494 K) in the segmented thermoelement consisting of Bi 1.95 Pb 0.05 Te 3 and (AgSbTe 2) 0.15 (GeTe) 0.85 (i.e. TAGS-85). Graphical abstract Unlabelled Image Highlights • Bi 2 Te 3 exhibits n- to p-type transition by substituting Bi with small amount of Pb. • p-Type Bi 1.95 Pb 0.05 Te 3 exhibit improved ZT ~ 0.63 w.r.t. n-type Bi 2 Te 3 (ZT ~ 0.47). • Bi 1.95 Pb 0.05 Te 3 with Ni/Ag contacts exhibited η of ~4.9% (at Δ T ~ 200 K). • Segmented Bi 1.95 Pb 0.05 Te 3 /TAGS-85 design exhibited η of ~12% (Δ T ~494 K). [ABSTRACT FROM AUTHOR]

This paper reports on the performance and tribological mechanisms in a newly developed design for an electrical sliding contact in terms of sliding velocity, normal force and electrical current during 24-h experiments. Copper discs were run against hard-carbon graphite, electrographite and polymer-bonded graphite. The average wear rates of the copper discs against the three graphite materials were reduced to 10 −8 and 10 −7 mm 3 /Nm, and the graphite discs to 10 −6 mm 3 /Nm, which is for 1 and 1–2 orders of magnitude less, than copper slip-rings and carbon brushes in conventional systems, respectively. The coefficient of friction was 0.2–0.4, depending on the conditions, which is comparable to the values of conventional electrical sliding contact. Tribofilms are generated in almost all contacts, and crucially determine the contact performance. The polymer-bonded-graphite/Cu formed the most compliant tribofilms that unify and decrease the local contact pressures and temperatures, and have the largest surface coverage that reduces the wear and contact resistance, which in turn reduces the contact instabilities and so the friction. [ABSTRACT FROM AUTHOR]

The thermal stability and contact resistance of TaAlN thin films as electrical contacts to SiGe thermoelectric elements are reported. We demonstrate that a sharp interface is maintained after the device annealed at 800 ° C for over 100 h, indicating that no interdiffusion takes place between TaAlN and SiGe. A specific contact resistivity of (2.1 ± 1.3) × 10 −6 Ω-cm 2 for p-type SiGe and (2.8 ± 1.6) × 10 −5 Ω-cm 2 for n-type SiGe is demonstrated after the high temperature annealing. These results show that TaAlN is a promising contact material for high temperature thermoelectrics such as SiGe. [ABSTRACT FROM AUTHOR]

Ag/W composite materials have been widely utilized as electrical contacts in low voltage circuit breakers. In this review, the corrosion, oxidation and erosion behavior of Ag/W contacts are examined with a special emphasis on the materials properties. For comparison, the oxidation/corrosion characteristics of the two main elemental constituents, Ag and W, are also reviewed. We limit ourselves to the effects of atmospheric corrosion and provide some examples for field and standard simulated laboratory tests that give insights into the long-term stability of contact materials. The effects of arcing and erosion on the performance of Ag/Refractory contacts are also discussed. [ABSTRACT FROM AUTHOR]

The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20 MW of RF power from two antennas in the 40–55 MHz frequency range during long pulses of up to 3600 s and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250 °C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-Contact ® LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62 MHz pulse ending in a 300 s flat top at 1.9 kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3 mm stroke at 175 °C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low. [ABSTRACT FROM AUTHOR]

This paper presents technological trials aimed at producing Ag-W, Ag-WC, Ag-W-C and Ag-WC-C composite contact materials and characterizing their properties. These materials were obtained using two methods, i.e. press-sinter-repress (PSR) at the refractory phase content of less than 30% by weight as well as press-sinter-infiltration (PSI) at the refractory phase content of ≥50% by weight). The results of research into both the physical and electrical properties of the outcome composites were shown. They include the analysis of the influence of the refractory phase content (W or WC) on arc erosion and contact resistance changes for the following current range: 6 kAmax in the case of composites with a low refractory phase content, 10 kAmax in the case of composites with the refractory phase content of ≥50% by weight. [ABSTRACT FROM AUTHOR]

Maintenance and repair of circuit breakers (CBs) due to their protective role in the power systems is the centre of attention and assessing their condition is tremendously important. The interruption chamber of the CBs including main contacts is highly subjected to erosion over time due to friction, and excessive heat produced by an arc during the interruption of the currents. This study presents a new high‐frequency (HF) non‐intrusive diagnostic technique for the deterioration of contacts used in high‐voltage CBs. The most striking result to emerge from the investigations is that the resonance frequency highly relies on the condition of contacts. The proposed approach is implemented in Computer Simulation Technology Studio Suite software and compared with the measured data obtained through the static resistance measurement. In addition, a HF model based on the transmission line theory has been developed for the interruption chamber of CBs. The comparison of the obtained results via a novel HF‐based approach with the experimental data validates the feasibility and accuracy of this approach in analysing the ablation of contacts used in the interruption chamber of CBs. [ABSTRACT FROM AUTHOR]

Break operations of AgSnO2 contact pairs were conducted in dc inductive (L = 5.7 mH) and resistive load circuits at 14 V and up to around 10 A under different contact opening speeds from 0.5 to 200 mm/s and with/without external magnetic field application in air. Break arc voltage waveforms were observed, and total break arc durations and metallic phase durations were determined based on the observed arc voltage waveforms. After the experiments, averages for total arc durations as well as the metallic phase and gaseous phase (when observed) durations were calculated at each condition. The results show that increases in the contact opening speeds lead to reductions in metallic phase durations, while the application of external magnetic field causes gaseous phases to become shorter. [ABSTRACT FROM PUBLISHER]

A copper-graphite brush is used as a sliding part in the electrical contacts of electrical machines and usually operates at elevated temperatures. This experimental research relates the dynamic properties of the copper-graphite brush to its wear rate at elevated temperatures. The dynamic and material properties were researched using a dynamic response analysis, hardness test and differential scanning calorimetry. The results show that there is a key temperature range where the material properties of copper-graphite brush was changed and which reflects on the increases of damping by 15% and hardness decreases by 50 %. [ABSTRACT FROM AUTHOR]

In this paper, a model problem that can be used for mathematical modeling and investigation of arc phenomena in electrical contacts is considered. An analytical approach for the solution of a two-phase inverse spherical Stefan problem where along with unknown temperature functions heat flux function has to be determined is presented. The suggested solution method is obtained from a new form of integral error function and its properties that are represented in the form of series whose coefficients have to be determined. Using integral error function and collocation method, the solution of a test problem is obtained in exact form and approximately. [ABSTRACT FROM AUTHOR]

The commercialization of nanocrystalline metals and alloys is currently entering a renaissance period. Many of the processing and consolidation challenges that have haunted them are now more fully understood, opening the doors for stabilized nanocrystalline metals to be produced on a bulk scale. While challenges remain, the increased volume at which these materials are being supplied is for the first time allowing for investigations into more traditional methods of metal working, such as extruding, rolling, forming, and forging. Recently, the manufacturing science has been developed to allow nanocrystalline Cu-Ta alloys to progress to this point. This article therefore builds upon the last decade of evolutionary progression within the family of stabilized nanocrystalline Cu-Ta alloys by presenting some of the first findings related to scaled powder synthesis, production of billets, thin sheets, and foils. The mechanical performance and physical properties relevant to forming electrical contacts and pins including, tensile, J-integral fracture toughness, Charpy Impact, bi-axial tension, and conductivity are reported. This introductory investigation into forming such a novel material, provides evidence to these alloys potential at bridging the gap between being a scientific curiosity to that of a real engineering material. • The commercialization of nanocrystalline metals and alloys is currently entering a renaissance period. Many of the processing and consolidation challenges that have haunted them are now more fully understood, opening the doors for stabilized nanocrystalline metals to be produced on a bulk scale. While challenges remain, the increased volume at which these materials are being supplied, is for the first time allowing for investigations into more traditional methods of metal working, such as extruding, rolling, forming and forging. Recently, the manufacturing science has been developed to allow nanocrystalline Cu-Ta alloys, to progress to this point. This article therefore builds upon the last decade of progression within the family of stabilized nanocrystalline Cu-Ta alloys by presenting some of the first findings related to scaled powder synthesis, production of billets, thin sheets and foils. The mechanical performance and physical properties relevant to forming electrical contacts and pins including, tensile, J-integral fracture toughness, Charpy Impact, bi-axial tension, and conductivity are reported. This introductory investigation into forming such a novel material, provides evidence to these alloys potential at bridging the gap between being a scientific curiosity to that of a real engineering material. [ABSTRACT FROM AUTHOR]

Manufacturable nanodevices must now be the predominant goal of nanotechnological research to ensure the enhanced properties of nanomaterials can be fully exploited and fulfill the promise that fundamental science has exposed. Here, we test the electrical stability of Au nanocatalyst-ZnO nanowire contacts to determine the limits of the electrical transport properties and the metal-semiconductor interfaces. While the transport properties of as-grown Au nanocatalyst contacts to ZnO nanowires have been well-defined, the stability of the interfaces over lengthy time periods and the electrical limits of the ohmic or Schottky function have not been studied. In this work, we use a recently developed iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the electrical, structural, and chemical properties when the nanowires are pushed to their electrical limits and show structural changes occur at the metal-nanowire interface or at the nanowire midshaft. The ohmic contacts exhibit enhanced quantum-mechanical edge-tunneling transport behavior because of additional native semiconductor material at the contact edge due to a strong metal-support interaction. The low-resistance nature of the ohmic contacts leads to catastrophic breakdown at the middle of the nanowire span where the maximum heating effect occurs. Schottky-type Au-nanowire contacts are observed when the nanowires are in the as-grown pristine state and display entirely different breakdown characteristics. The higher-resistance rectifying I-V behavior degrades as the current is increased which leads to a permanent weakening of the rectifying effect and atomic-scale structural changes at the edge of the Au interface where the tunneling current is concentrated. Furthermore, to study modified nanowires such as might be used in devices the nanoscale tunneling path at the interface edge of the ohmic nanowire contacts is removed with a simple etch treatment and the nanowires show similar I-V characteristics during breakdown as the Schottky pristine contacts. Breakdown is shown to occur either at the nanowire midshaft or at the Au contact depending on the initial conductivity of the Au contact interface. These results demonstrate the Au-nanowire structures are capable of withstanding long periods of electrical stress and are stable at high current densities ensuring they are ideal components for nanowire-device designs while providing the flexibility of choosing the electrical transport properties which other Au-nanowire systems cannot presently deliver. [ABSTRACT FROM AUTHOR]

This paper presents a systematic analysis of the electrode configuration influence on the electrical properties of organic semiconductor (OSC) thin-film devices. We have fabricated and electrically characterized a set of planar two-terminal devices. The differences in I-V characteristics between the top and bottom contact structures are presented and analyzed. Top-contact configurations have a linear current vs. electric field behavior, while the bottom-electrode devices display a transition from ohmic to space-charge-limited conduction regime. The transition is temperature- and thickness-dependent. Finite-element calculations show that when the OSC film is connected using top electrodes, the current flows through the OSC bulk region. On the other hand, the bottom-electrode configuration allows most of the current to flow near the OSC/substrate interface. The current probes interfacial states resulting in a space-charge conduction regime. The results shed some light on the so-called “contact effects” commonly observed in organic thin-film transistors. The findings presented here have implications for both the understanding of the charge transport in OSC films and the design of organic semiconductor devices. [ABSTRACT FROM AUTHOR]

The influence of grain size on degradation of electrical contacts during fretting wear was investigated. Copper polycrystals with grain sizes of 2–162 µm were used to examine friction, wear, and electrical contact resistance. The results showed that the electrical contact failure was caused by the compact oxide layer produced at the contact junction. Copper specimens with smaller grains had a longer lifecycle because of grain-size strengthening. However, this strengthening effect was limited to a critical grain size and, with further increase in grain size, plastic deformation underneath the contact surface played a major role in delaying the contact failure caused by oxide formation on the fretting surface. [ABSTRACT FROM AUTHOR]

A mechanical thermostat is a device that switches heating or cooling appliances on or off based on temperature. For this kind of use, electronic or mechanical switching concepts are applied. During the production of electrical contacts, several irregularities can occur leading to improper switching events of the thermostat electrical contacts. This paper presents a non-obstructive method based on the fact that when the switching event occurs it can be heard and felt by human senses. We performed several laboratory tests with two different methods. The first method includes thermostat switch sound signal analysis during the switching event. The second method is based on sampling of the accelerometer signal during the switching event. The results show that the sound analysis approach has great potential. The approach enables an accurate determination of the switching event even if the sampled signal carries also the switching event of the neighbour thermostat. [ABSTRACT FROM AUTHOR]

Fretting of silver coated electrical contacts has been studied in a crossed cylinder contact model setup at varying displacement amplitude. The contacts have been tested dry (unlubricated) and lubricated with lithium complex (LiX) and polypropylene (PP) thickened greases. The same polyalphaolefin (PAO) base oil blend was used, hence the thickener is the only difference between the greases. At low displacement amplitude no large difference between dry and lubricated conditions was found. Contact welding occurs for all contacts, also the lubricated. The grease is ejected from the contact area after only a few fretting cycles and the contact welds. A positive effect of grease lubrication on friction and wear is primarily seen at high vibration amplitude, where gross slip is the prevailing fretting regime. For the LiX grease lubricated contacts, fretting at intermediate displacement amplitudes show to be the most critical and the wear marks show much surface damage. Here, the PP grease showed better lubricating effect than the LiX grease. [ABSTRACT FROM AUTHOR]

Selecting the electrical properties of nanomaterials is essential if their potential as manufacturable devices is to be reached. Here, we show that the addition or removal of native semiconductor material at the edge of a nanocontact can be used to determine the electrical transport properties of metal-nanowire interfaces. While the transport properties of as-grown Au nanocatalyst contacts to semiconductor nanowires are well-studied, there are few techniques that have been explored to modify the electrical behavior. In this work, we use an iterative analytical process that directly correlates multiprobe transport measurements with subsequent aberration-corrected scanning transmission electron microscopy to study the effects of chemical processes that create structural changes at the contact interface edge. A strong metal-support interaction that encapsulates the Au nanocontacts over time, adding ZnO material to the edge region, gives rise to ohmic transport behavior due to the enhanced quantum-mechanical tunneling path. Removal of the extraneous material at the Au-nanowire interface eliminates the edge-tunneling path, producing a range of transport behavior that is dependent on the final interface quality. These results demonstrate chemically driven processes that can be factored into nanowire-device design to select the final properties. [ABSTRACT FROM AUTHOR]

Cu–Cr alloys produced by powder metallurgy are widely used as contact materials in vacuum interrupters. The efficiency of these devices depends on material characteristics, in particular porosity and oxygen content. This paper focusses on densification and oxygen evolution in Cu and Cu–25 wt%Cr compacts during sintering. Chemical reactions and their relationships with sintering are studied by dilatometric and thermogravimetric analyses coupled with mass spectrometry. High density Cu compacts swell during sintering, due to the gas released in closed pores by Cu oxide reduction reactions. The addition of Cr hinders the sintering kinetics by a mechanical effect but prevents swelling phenomena by trapping the released oxygen in solid chromium oxide. The furnace atmosphere has a major effect as its reducing degree determines the chemical reactions. Under neutral atmosphere such as secondary vacuum, copper oxide reduction occurs at high temperature, when densification has already produced close pores. In Cu compacts, this leads to large swelling while in Cu–25 wt%Cr compacts the oxidation of Cr traps the oxygen in CR 2 O 3 interfacial nodules. A reducing atmosphere such as diluted hydrogen flux reduces the Cu oxide at lower temperature, so that part of the released oxygen is evacuated out of the compact. This leads to lower swelling in Cu compact and to a reduced amount of chromium oxide in lower oxygen Cu–25 wt%Cr compacts, which results to better bonding between Cu and Cr particles. [ABSTRACT FROM AUTHOR]

The scope of this work is the calculation of a coefficient of friction as a function of wear cycles for a degrading coated contact. The coating system guarantees a specific number of insertions and withdrawals with a constant low electrical resistance. Another requirement is a low friction force. In the last years the importance of this demand has considerably increased. The number of pins per connector increased because of miniaturization and integration. Since the insertion and withdrawal forces are the sum of the force per pin, the total forces increased equally. A mathematical analysis of the coefficient of friction for hemispherical and cylindrical geometries is given. Experimental results confirm the theoretical considerations. [ABSTRACT FROM AUTHOR]

Sliding electrical contact behavior of the brass fiber brush with 23% packing fraction was investigated as sliding against coin-silver and Au plating under vacuum and air conditions. The friction coefficient, contact resistance and electrical noise of the brushes were analyzed. The microstructure and worn surfaces of the brass fiber brush and counter discs were observed to discover the involved wear mechanisms. The friction coefficients in vacuum are much higher than those in air. The contact resistances and electrical noises of the brush against both discs in vacuum are extremely low. The contact resistance against coin-silver quickly increases as the sliding condition varies from vacuum to air, which is much higher than that against Au plating. Sliding speed has an insignificant effect on the contact resistance and electrical noise of fiber brush. Formation of oxide film and loose oxide particles on the worn surfaces of fibers and the coin-silver disc leads to the increase of contact resistance and electrical noise. The transfer of gold from Au plating to worn surfaces of brass fibers is used to prevent the oxidation of fibers and keep the contact resistance and electrical noise in a relatively low level. The multi-contact mechanism of brass fiber brush has been also discussed. [ABSTRACT FROM AUTHOR]

Most fretting studies analyze material׳s responses using criteria directly issued from characteristic parameters of the fretting loops (loop aperture, dissipated energy, contact stiffness…). The present study concerns the influence of the device, first element of the tribological triplet, on the gross slip response of a ball-on-flat contact. The role of the static and dynamic device stiffness (vibratory analysis), of the control system mode (imposed displacement or imposed actuator force) and of the material type (ductile or brittle) on the loop shape is analyzed in order to distinguish the respective contributions of devices and materials. [ABSTRACT FROM AUTHOR]

The article considers the substitution of silver in interrupting electrical contacts by a nonprecious metal on the basis of copper. Technical specifications for the material capable of replacing silver are formulated, including high softening temperature and weak adhesion of oxides to the base metal. As a result, a composite nanomaterial on the basis of copper is offered to substitute silver. Microstructure, mechanical, thermî-mechanical, physical properties of the nanocomposite was studied. Changes of contact resistance during the formation of oxides on the surfaces of copper, silver, and the nanocomposite was studied, as well as losses of volume when exposing these materials to an electric arc. The prospects of substituting silver by the nanocomposite on the basis of copper were proven by the results of comparative bench testing of materials. [ABSTRACT FROM AUTHOR]

A novel powder metallurgy method, based on preparation of powder mixtures of copper with 0.5, 1, 1.5, 2, 2.5, 3, and 5 wt.% of nanographite particles ~50 nm in size, is used to produce Cu-nanographite electrical contact materials with flake microstructure. The dispersion of graphite nanoparticles in the Cu matrix is examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Morphology, particle size, and apparent density of flake powders are investigated. Microstructure, density, electrical conductivity, and hardness are studied for green and sintered samples. The composites reinforced with lower graphite nanoparticles content (0.5 wt.%) exhibit much lower agglomeration content, while the composites reinforced with higher graphite nanoparticles content (5 wt.%) showed higher agglomeration content. It is found out that the electrical conductivity of the sintered Cu-nanographite electrical contact materials decreased from 76.92 to 68.28 IACS by graphite nanoparticle addition. The maximal (~34) and minimal (~20) Brinell hardness is obtained for the monolithic Cu sample and 5 wt.% graphite nanoparticle reinforced Cu electrical contact materials, respectively. [ABSTRACT FROM AUTHOR]

The photoelectric work function of nearly stoichiometric (111) and (100) hydrothermally grown UO2 was measured to be 6.28 ± 0.36 eV and 5.80 ± 0.36 eV, respectively. Candidate metals for electrical contacts are identified for both rectifying and non-rectifying contacts based on work function, lattice compatibility, and electrical conductivity. [ABSTRACT FROM AUTHOR]

Electrostatic charge due to inter‐particle and particle‐to‐wall contacts may generate significant hazards during the processing of particulates within the pharmaceutical industry. Although charge behaviour of particulates is erratic and not easy to predict, it would be desirable to characterise the tendency of tribocharging prior to manufacturing. The work reported in this study concentrates on a new and novel technique for the detection of the active ingredient and excipient in a bipolar material. Three different case studies are presented for demonstration of the applicability of the method in different practical situations. Work confirmed through an experimental rig set‐up indicates that materials that accumulate opposite charge via contact and rubbing can be detected from their charge sign as well as their relative magnitude. The results reported clearly demonstrated that the developed method for charge characterisation is a useful tool to understand how the charges are distributed in a population of particles showing a number of advantages over conventional methods. [ABSTRACT FROM AUTHOR]

In order to obtain a better understanding of the welding mechanism in contact separation, electrical endurance tests were conducted with AgSnO2 and AgNi contacts on a simulation test device. Waveforms of contact displacement, contact voltage, and current were recorded with LabVIEW during the tests, and changes in a contact gap and heights of pips with increases in operation cycles were observed through charge-coupled device cameras. The resultant test results show that welding in separation is accompanied with a preceding voltage pulse which represents arc rather than contact bounce arc. [ABSTRACT FROM PUBLISHER]

In this study, the spark discharge risks on small relays in low‐voltage circuits are evaluated based on the test current magnitude and the rate of current change of surge current. For the risk assessment of spark discharge caused by the high‐voltage switching surge on the small relay in low‐voltage circuits, there are fewer papers relevant to the topic. First of all, this study presents the construction of a test circuit model, in which the open contacts of small relays are energised by a set of spark discharge generators. The actual current waveforms are measured and analysed. This study provides a manner to evaluate the risk degree of the small relay in low‐voltage circuits damaged by the surge current. Referring to the relevant IEEE standards concerning surge protection, a surge protection circuit of a signal line is applied. The test is done after installing this surge protection circuit, the test of spark discharge is done after installing this surge protection circuit, and the test result confirms that the use of surge protection devices can suppress the surge current, so this study can be applied to reduce the hazards of the low‐voltage equipment. [ABSTRACT FROM AUTHOR]

Sliding electrical contacts transferring current between stationary and rotating components are also tribological systems. Although low contact resistance and noise are prioritised, lower wear rates reduce material usage, and lower friction reduce energy loss. In this paper a slip-ring assembly with wires contacting a silver–graphite ring is investigated with the aim to optimize the wire material to displace all wear to the ring. Uncoated wires and wires coated with nanocomposite Ti–Ni–C or TiN are tested at 100 mA current. Tribofilms, consisting mainly of silver and carbon, form on the wires and a contact resistance of around 0.5 Ω is measured for all wire materials. The properties of the tribofilms control the overall performance and the similarity between them, regardless of wire material, is the reason for the similar contact resistance. The Ti–Ni–C coating wear least on the silver–graphite. Both coatings degrade and wear off during testing, exposing the steel substrate. The steel itself also wears, although not at a rate excluding it as a possible wire material. None of the three surfaces fully displaces wear to the ring only. Considering the performance of the uncoated steel wire, coatings cannot be motivated on behalf of either improved electrical performance or wire protection. [ABSTRACT FROM AUTHOR]