Contact Voltage Drop Research Articles

Influence of normal load, electric current and sliding speed on tribological performance of electrical contact interface

The purpose of this study is to investigate the effect of normal load, electric current and sliding speed on tribological performance of electrical contact interface. Sliding electrical contact tests of H65 material are carried out by using a customized ball-on-flat tribometer. Results show that with the increase of normal load, both the friction coefficient and contact voltage drop show a downward trend. Too low or too high load will not cause the generation of friction-induce vibration (FIV). Although increasing the normal load appropriately can improve the wear behavior of the interface, it will intensify wear if the normal load is overly high. Larger electric current will increase the friction coefficient, contact voltage drop and surface temperature, but reduce the contact resistance. A certain value of electric current will cause the generation of FIV. Larger electric current will destroy the surface lubricating film of interface and intensify wear. With the increase of sliding speed, the friction coefficient firstly increases and then decreases, while the contact voltage drop shows the opposite trend. Strong FIV will be generated at a certain value of sliding speed. Larger sliding speed will cause the formation of a dense film layer, which plays a good lubrication effect.

Physical parameters based analytical I-V model of long and short channel a-IGZO TFTs

This paper presents an analytical model for amorphous In-Ga-Zn-O thin film transistors based on device physics. The proposed model comprises physical parameters including subgap density-of-states (DOS) and is useful for fabrication process optimization. In addition to delocalized free band states, the model accounts for deep and tail trap states and is valid for complete region of operation. Physical parameters are extracted by employing least square (LSQ) curve-fit function and the model is validated by comparing model outcome with measured characteristics of the device. The proposed model is able to predict the I-V characteristics of the long channel devices to good accuracy. Further, this model is enhanced to predict the behavior of the short channel devices by taking contact voltage drop into account. The model accurately reproduces the measured response of long and short channel oxide TFTs with channel length ranging from 20 μm down to 2 μm with channel width fixed to 20 μm. The average error between measured data and model outcome is found to be < 3 %. The proposed model is useful to design oxide TFT based circuits with different channel lengths using a single set of physical parameters through circuit simulator.

Effect of electrical current density, apparent contact pressure, and sliding velocity on the electrical sliding wear behavior of Cu–Ti3AlC2 composites

The purpose of this research was to investigate the potential use of Cu–Ti3AlC2 composites sliding against a Cu–5%Ag alloy as a viable electrical contact couple. Sliding friction and wear tests were conducted in the presence of an electric current using a custom-designed block-on-ring wear testing apparatus. The electrical current density was 0–15 A/cm2 along with an apparent contact pressure of 1.25–7.5 N/cm2 and sliding velocities ranging from 2.5 to 15 m/s. The results indicate that friction coefficient, wear rate, and contact voltage drop measured for the sliding couple increases with an increase in the electrical current density. As the apparent contact pressure increases, the contact voltage drop of Cu–Ti3AlC2 composites increases gradually, while friction coefficient and wear rate first decrease and then increase. With an increase in the sliding velocity, the friction coefficient of the sliding pair decreases and the contact voltage drop increases gradually, while wear rate decreases first, then increases. Adhesive wear and arc erosion wear proposed as the main wear modes. A lubricating film was observed to form on the wear surfaces under each test condition, and that film apparently improves the tribological properties of the sliding couples.

Effect of Ti3AlC2 Content on Electrical Friction and Wear Behaviors of Cu–Ti3AlC2 Composites

The effect of Ti3AlC2 content on electrical friction and wear behaviors of Cu–Ti3AlC2 composites is investigated. Composites with different volume ratios of Ti3AlC2 are prepared by the hot-pressing method, and experiments are performed on a block-on-ring sliding electrical wear tester. The results demonstrate that with increasing Ti3AlC2 content, the contact voltage drops of the Cu–Ti3AlC2 composites increase, the friction coefficient decreases, and the wear rate initially decreases and then increases. A lubricating film forms on the worn surface during the process of electrical sliding wear, which improves the wear resistance of the material. Raman spectroscopy and X-ray photoelectron spectroscopy spectra of the worn surface show that the lubricating film comprises Ti3AlC2, CuO, TiO2 and Al2O3, where the TiO2 and Al2O3 result from decomposition of Ti3AlC2.

Investigation of graphene as a material for electrical contacts in the application of microrelays using finite element modeling

This paper investigates the use of Graphene (Gr) as an electrical contact material for the application of microrelays. Gr is an ideal material for microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS). A microrelay has been considered and electrothermal analysis is carried out based on Finite Element Modeling (FEM) using COMSOL Multiphysics simulation tool. Electrical contact surfaces for the material Al, Cu, Ag and Gr have been analyzed. The electrical contact resistance, voltage drop, current density, resistive losses and temperature of the contact interface has been obtained. The results obtained have been verified using theoretical calculations. Also, the combustion voltage of Gr electrical contact has been obtained as 0.2 V at which the Gr reaches its combustion temperature of 623 K. The results show that Gr electrical contact performs better in terms of electrical and thermal performance parameters which would be used in future electrical components.

Evaluation of Electric–Thermal Performance of High-Power Contact Systems With the Voltage–Temperature Relation

Researchers and engineers use the voltage–temperature ( $V$ – $T$ ) relation to calculate the maximum temperature of electric contacts from contact voltage drop and thus evaluate their performance. However, researchers found deviations from the $V$ – $T$ relation for large contact systems when heat dissipation to the environment becomes significant. We investigated the applicability of the $V$ – $T$ relation to high-power contact systems with spring-loaded contact elements. Such connections with rated normal currents of several kiloamperes and short-time withstand currents of several tens of kiloamperes are used in high-voltage switchgear. We loaded a connector cooled by a potent variable water cooling system with continuous ac up to 6.7 kA to create a multitude of thermally symmetric and asymmetric steady-state operating points. However, temperature differences in the contact system remained below 20 K. Temperature differences calculated with the $V$ – $T$ relation were 23% higher than the measured values, but nevertheless deliver an assessment of the maximum contact system temperature valid for engineering purposes. In the case of a 1-s, 20-kA short-circuit current, a transient temperature rise occurs in the contact system. We numerically calculated the development of the spatial temperature distribution over time and found significant differences to the electric–thermal steady state. While contacts react very quickly and even oscillate with twice the line frequency on ac load, the contact element and conductor continuously heat up and do not reach the steady state.

Effect of Hot Extrusion on Electrical Tribological Behavior of Ag-Cu/MoS2 Composite under Air and Vacuum Conditions

ABSTRACTThe different microstructures of silver–copper/molybdenum disulfide (Ag-Cu/MoS2) composites were manufactured by hot press and hot extrusion processes to investigate the electrical tribological behaviors of both the hot-pressed and hot-extruded composites under air and vacuum. The results showed that microstructures and properties of Ag-Cu/MoS2 composites were improved by hot extrusion, which decreased the wear rates rapidly in both air and vacuum. In air, hot extrusion could improve the transfer layer and tribofilm, resulting in a significant decrease in contact voltage drop, which goes from more than 70 mV in the hot-pressed composite to 30 mV at the hot-extruded composite. Under vacuum condition, some wear debris was melted on the worn surface and then transferred to the counterface to form the transfer layers, which led to the lower contact voltage drops under vacuum, about 6 mV in hot-pressed composites and 3 mV in hot-extruded composites. In addition, the severe adhesive and abrasive wear were attributed to the molten wear debris and transfer layer, resulting in a dramatic fluctuation in the friction coefficient in a vacuum.

Thermostability, mechanical and tribological behaviors of polyimide matrix composites interpenetrated with foamed copper

Polyimide matrix composites interpenetrated with foamed copper were prepared via pressure impregnation and vacuum immersion to focus on their thermostability, mechanical and tribological behaviors as sliding electrical contact materials. The results show that the interpenetrating phase composites (IPC) are very heat-resistant and exhibit higher hardness as well as bending strength, when compared with homologous polyimide matrix composites without foamed copper. Sliding electrical contact property of the materials is also remarkably improved, from the point of contact voltage drops. Moreover, it is believed that fatigue wear is the main mechanism involved, along with slight abrasive wear and oxidation wear. The better abrasive resistance of the IPC under different testing conditions was detected, which was mainly attributed to the successful hybrid of foamed copper and polyimide.

Sliding electrical contact behavior of AuAgCu brush on Au plating

The sliding electrical contact behavior of AuAgCu brush on Au plating was investigated at various normal loads and sliding speeds. The contact voltage drop and electrical noise between the two brushes were measured and the resistance waveforms were recorded. The morphologies of the worn surfaces and wear debris of the brush and plating were observed. The results show that the contact voltage drop and electrical noise decrease with the addition of load whereas increase drastically with increasing sliding speed. With the electrical current in vacuum, the wear process of AuAgCu brush on Au plating involves adhesion, transfer of gold from the plating to the brush, rolling of wear debris between contact surfaces and arc-induced melt at the contact edge, and this gold-on-gold sliding electrical contact system is reliable within experiment period.

Effect of WS2 addition on electrical sliding wear behaviors of Cu–graphite–WS2 composites

Four kinds of Cu-based composites with different mass ratios of graphite and WS2 as lubricants were fabricated by hot-pressing method. Electrical sliding wear behaviors of the composites were investigated using a block-on-ring tribometer rubbing against Cu–5%Ag alloy ring. The results demonstrated that 800 °C was the optimum sintering temperature for Cu–graphite–WS2 dual-lubricant composites to obtain the best comprehensive properties of mechanical strength and lubrication performance. Contact voltage drops of the Cu-based composites increased with increasing the mass ratio of WS2 to graphite. The Cu-based composite with 20% graphite and 10% WS2 showed the best wear resistance due to the excellent synergetic lubricating effect of graphite and WS2. The reasonable addition of WS2 into the Cu-graphite composite can remarkably improve the wear resistance without much rise of electrical energy loss which provides a novel principle of designing suitable sliding electrical contact materials for industrial applications.

Measurement, Control and Evaluation of Low-Power Contactor Switches under Overload Current

Load rating of contactor switches is an important issue for diverse industrial power applications requiring varied connections. This paper presents a simple procedure to evaluate the current-carrying capabilities of contactor switches under overload cyclic stress. An experimental setup is proposed to measure test current, contact voltage drop, and temperature at the contacts and cable connectors. Results are presented for ON–OFF controlled commutated current at 500% and 1000% overload of a contactor in the ON position. The attained results and the criteria for contactors selection in power applications are given.

Effect of current polarity on electrical sliding wear behavior of Cu-WS2-graphite-WS2 nanotube composites in air and vacuum conditions

In this paper Cu-WS2-graphite-WS2 nanotube composites were fabricated by powder metallurgy hot pressing method. The effect of current polarity on the wear rates and contact voltage drops of the composites were investigated using a brush-on-slip ring tribometer rubbing against Cu-5 wt.% Ag alloy ring in air and vacuum, respectively. The worn surfaces of the composites were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Surface profile curves of the worn tracks were measured using the surface profiler. The results demonstrated that the current polarity has a significant effect on the wear rates and contact voltage drops of the composites in both air and vacuum conditions. Positive brush possesses a higher wear rate compared with the negative brush in the air atmosphere since the electrical field direction activates oxidation at the positive brush surface while inhibits oxidation at the negative brush surface. Except for the regular wear losses, the combined effect of molten metal bridge erosion and arc erosion cause the positive brush to lose extra material and the negative brush to gain extra material, so the positive brush shows a higher wear rate in the vacuum condition. The contact voltage drop of the positive brush is lower than that of the negative brush in the air atmosphere, but contrarily, the positive brush shows a higher contact voltage drop in the vacuum condition.

Effect of electrical current on the tribological behavior of the Cu-WS2-G composites in air and vacuum

As the traditional graphite-based composites cannot meet the requirement of rapid developing modern industry, novel sliding electrical contact materials with high self-lubricating performance in multiple environments are eagerly required. Herein a copper-based composite with WS2 and graphite as solid lubricant are fabricated by powder metallurgy hot-pressed method. The friction and wear behaviors of the composites with and without current are investigated under the condition with sliding velocity of 10 m/s and normal load of 2.5 N/cm2 in both air and vacuum. Morphologies of the worn surfaces are observed by optical microscope and compositions of the lubricating films are analyzed by XPS. Surface profile curves and roughness of the worn surfaces are obtained by 2205 surface profiler. The results of wear tests show that the friction coefficient and wear volume loss of the composites with current are greater than that without current in both air and vacuum due to the adverse effects of electrical current which damaged the lubricating film partially and roughed the worn surfaces. XPS results demonstrate that the lubricating film formed in air is composed of oxides of Cu, WS2, elemental S and graphite, while the lubricating film formed in vacuum is composed of Cu, WS2 and graphite. Because of the synergetic lubricating action of oxides of Cu, WS2 and graphite, the composites show low friction coefficient and wear volume loss in air condition. Owing to the fact that graphite loses its lubricity which makes WS2 become the only lubricant, severe adhesive and abrasive wear occur and result in a high value of wear rate in vacuum condition. The formation of the lubricating film on the contact interface between the brush and ring is one of the factors which can greatly affect the wear performance of the brushes. The low contact voltage drop of the composites in vacuum condition is attributed to the high content of Cu in the surface film. This study fabricated a kind of new sliding electrical contact self-lubricating composite with dual-lubricant which can work well in both air and vacuum environments and provides a comprehensive analysis on the lubrication mechanisms of the composite.

The Effect of Electrical Switch Structure to the Contact Voltage-Drop and Temperature Variations

Due to the continuing renovation of the modern technology and the demand for the better consumer products, electricity has become one of the important factors that affect people’s life. The electrical switch is an important element of the electrical device and has been used intensively in industry and transportation devices, such as electrical bicycle, electrical motorcycle, winch etc. As the increasing usage of the electrical switch, the switch quality requirement increases as well. The important factors are contact point mass transferring loss, electric arc energy and contact point resistance and loss. Once the contact point fails to function, the whole electrical device ceases to function. However, regarding the electrical efficiency, in addition to the effect of the contact point materials, the structure is an important factor. In this study the structure of the electrical switch is studied and the effects of spring stiffness, guiding pin and ring to the switch lifespan are discussed. Taguchi method was used to design the experiment. L9(34) Orthogonal Array table was used to perform and discuss the effect of four factors to the desired characteristics; that is to minimize both the contact voltage-drop and the contact temperature increase. Four factors chosen are guiding pin material, compression spring, contact spring and buckle. Test results show that contact spring has the most effectiveness to the contact voltage-drop and temperature increase and is followed by compression spring. Guiding pin and ring type have minimum influence.

Measurement of contact voltage drop and resistance in organic solar cells

Bulk heterojunction organic solar cells based on poly[4,7-bis(3-dodecylthiophene-2-yl) benzothiadiazole-co-benzothiadiazole] and [6,6]-phenyl C71-butyric acid methyl ester are investigated. A prominent kink is observed in the fourth quadrant of the current density-voltage (J-V) response. Annealing the active layer prior to cathode deposition eliminates the kink. The kink is attributed to an extraction barrier. The J-V response in these devices is well described by a power law. This behavior is attributed to an imbalance in charge carrier mobility. An expected photocurrent for the device displaying a kink in the J-V response is determined by fitting to a power law. The difference between the expected and measured photocurrent allows for the determination of a voltage drop within the device. Under simulated 1 sun irradiance, the peak voltage drop and contact resistance at short circuit are 0.14 V and 90 Ω, respectively.

Electrical sliding friction and wear properties of Cu–MoS2–graphite–WS2 nanotubes composites in air and vacuum conditions

Cu–MoS2–graphite–WS2 nanotubes composites were fabricated by the P/M hot pressing method. The tribological properties and contact voltage drops of the composites were investigated using a block-on-ring friction and wear tester in air and vacuum respectively, rubbing against Cu-5wt% Ag alloy ring with different electric current. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results illustrated that the friction coefficients and wear rates in air were lower than those in vacuum due to the synergistic effect of lubrication from the mixture of MoS2 and graphite in air and the limited lubrication properties of graphite in vacuum. The friction coefficients and wear rates increased gradually with the increasing current density because of the additional Joule heat resulting from the release of current. The contact voltage drops were low in the initial stage, and then increased to a stable value owing to the gradual formation of tribo-films on the sliding surface which changed the nature asperities from metal-metal to metal-film-metal type on the contact interfaces of composites and rings.

Correlation analysis of brush temperature in brush-type DC motor for predicting motor life

Some critical components of motors and generators have sliding electrical contacts. Electrical brushes are usually used in these contact points to conduct current between the stationary part and the moving part of the motor. In this paper, studies on brush wear against copper commutators are briefly reviewed. The main influential factors in brush wear are associated with both mechanical wear and electrical wear. Brush wear is affected by various factors, including temperature, material properties, sliding speed, contact force, and interfacial as well as environmental conditions. The mechanical wear of brushes is proportional to brush spring pressure and sliding speed, and the electrical wear of brushes is associated with current and contact voltage drop. For characterization, a brush wear test machine is designed, and influential factors, such as electrical contact resistance, temperature, wear mass loss, and so on, are measured. The wear tests are processed using a small brush-type automotive DC motor. The study primarily aims to investigate the effects of the wear behavior of copper-graphite brushes on small brush-typed DC motors. The variable conditions of electrical current are obtained by changing the brush spring pressure and the sliding speed. The results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear is greatly changed by electrical current, which indicates that high current itself not only produces more Joule heating but also causes an increase in voltage drop that will result in additional Joule heating.

Effect of Lubricant on Lifetime of Au-Plated Slip-Ring and Ag-Pd-Cu Brush System for Small Electric Power

The authors have been investigating degradation process of Au plated slip ring and Ag-Pd-Cu brush system. In almost all cases the lifetime of the sliding system ends, when Au plating layer is worn out, the ring surface is oxidized to be black in color and contact resistance becomes very high. Further, the lifetime is very short without lubricant. So, the lubricant is very effective to make the lifetime longer. However, even with lubricant the lifetime is varied from about 1000 hours to almost 7000 hours in the past experiments. It is an important issue how the lubricant works on the lifetime of the system. In this paper the effect of lubricant on the degradation process of contact resistance is focused on. In the past tests the lubricant is supplied only once before the test. In this test the lubricant is regularly supplied almost every 900 operation hours. Consequently, the operation more than 8000 hours is realized, which is the longest among tests so far. In addition the contact voltage drop increase gradually until 2600 hours and after that it stays almost constant around 70mV. According to the Element Analysis after the test the Ni base plating layer is totally exposed in many tracks. It means that the Au plating layer is gradually worn out probably at the stage of increasing voltage drop. In the previous tests the lifetime ended even when the Ni plating layer remained. So, the reason of long operation in this test is guessed to be that the lubricant not only decreases wear of ring and brush, but also suppresses oxidation of the Ni layer.

Studies on the Effect of Graphite Content on Hardness and Electrical Resistivity of Silver-Graphite Composites

Silver-Graphite composites are attractive materials for electro-mechanical devices to provide noise free rotation between mating surfaces with minimum contact voltage drop. In the present study, the composite was processed through Powder Metallurgy (P/M) route considering that the constituent elements have divergent physical properties without any metallurgical bond between them. The developed composites were evaluated for hardness, electrical resistivity, contact voltage and density. This paper presents a correlation between hardness and electrical resistivity against volume fraction of graphite added, through linear regression which has clearly indicated that the said properties of the composites are highly dependent on the volume fraction of graphite. The hardness and electrical resistivity of the composites were found to obey the relations given below (i) Log H=1.522 + 1.667 Log (1-fg), (ii) 32.36 Log (ρ0/ρ) =1 + 83.74 Log (1-fg), where H is hardness of composites, ρ0 is electrical resistivity of pure silver, ρ is electrical resistivity of composites and fg is the volume fraction of graphite.

Influence of surface finish processing on contact voltage drop in Cu/C electrical sliding contacts

AbstractA sliding contact is normally used to supply current to a rotating or moving object. The surface film formed on the sliding surface is important for ensuring reliability and long life. In the present study, the effects of preoperation conditions and initial surface condition are investigated. We examined the relation between sliding speed and chemical treatment for electrical sliding contact action. The initial surface condition and preoperation conditions greatly influence the contact voltage drop that occurs during operation. It is shown that stability of sliding contact can be achieved by appropriate surface treatment and preoperation conditions. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.