Dynamic Contact Resistance Research Articles

Fractal contact resistance model of wind pitch slip ring considering wear and self-excited vibration

Purpose The purpose of this paper is to reveal the dynamic contact characteristics of the slip ring. Dynamic contact resistance models considering wear and self-excited were established based on fractal theory. Design/methodology/approach The effects of tangential velocity, stiffness and damping coefficient on dynamic contact resistance are studied. The relationships between fractal parameters, wear time and contact parameters are revealed. Findings The results show that the total contact area decreases with the friction coefficient and fractal roughness under the same load. Self-excited vibration occurs at a low speed (less than 0.6 m/s). It transforms from stick-slip motion at 0.4 m/s to pure sliding at 0.5 m/s. A high stiffness makes contact resistance fluctuate violently, while increasing the damping coefficient can suppress the self-excited vibration and reduce the dynamic contact resistance. The fractal contact resistance model considering wear is established based on the fractal parameters models. The validity of the model is verified by the wear tests. Originality/value The results have a great significance to study the electrical contact behavior of conductive slip ring. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0300/

Application of DE-ELM Algorithm in SF6 Circuit Breaker Contact Ablation Evaluation

When assessing the ablation status of circuit breaker contacts, the average dynamic contact resistance of the arc contacts of high-voltage SF6 circuit breakers is crucial. The average dynamic contact resistance of arc contacts on circuit breakers under various current levels may be accurately predicted using a method based on a differential evolution algorithm and extreme learning machine (DE-ELM), which is suggested in this research. Combining optimization algorithms yields the ideal input weight and hidden layer bias of the ELM method. The DE-ELM approach has outstanding anticipation performance for anticipation data under various current levels when compared to other anticipation methods. Finally, an expert system for assessing the ablation state of contacts based on the DE-ELM algorithm is created using the average dynamic contact resistance data of arc contacts predicted by DE-ELM. As a guide for the upkeep of high-voltage SF6 circuit breakers, the ablation status of contacts is categorized into four grades: A-level ablation, B-level ablation, C-level ablation, and D-level ablation.

A hybrid coating of organometallic complex with a silane coupling compound to protect galvannealed (GA) steel from white rust without sacrificing weldability

A unique organic-metallic hybrid coating has been formulated to impede white rust formation on galvannealed (GA) steel strips without hindering weldability. With an optimal concentration ratio of methacrylate silane coupling agent to a titanium (IV) lactate metal complex on the surface of zinc were creating of a network-type nanostructure. Controlling the dry film thickness and curing at 120 °C for 60 s with a chemical roll coater produced a thin film coating (<∼2 μm). Spectroscopic instruments like scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), dynamic contact resistance measurement, and electrochemical impedance spectroscopy (EIS) were used to investigate the coating's surface microstructure, interfacial bonding, anticorrosion, and electrical conductivity characteristics for weldability. The welding properties were tested using the AWS D8.9 standard, and the material was subjected to a simulated salt spray test under ASTM B117 to evaluate anti-corrosion (white rust formation). It was observed that ‘Silane’ to ‘Titania complex’ at a ratio of 0.02 in the formulation was providing excellent performance in terms of anti-corrosion and weldability. This coating has the potential to replace the traditionally used harmful chromate passivation coating over zinc and zinc alloy surfaces in the entire steel industries.

Study on the Performance of Liquid-Solid Contact Resistance Based on Magnetohydrodynamic Micro-Angular Vibration Sensor

In this paper, the influence of the contact resistance between the conductive fluid and the metal electrode on the output characteristics of the magnetic fluid micro-angular vibration sensor (MHD sensor) is theoretically analyzed. The contact resistance models based on the solid-solid electric contact theory are established based on the resistivity, temperature, pressure and angular vibration of the materials between the conductive fluid and the metal electrode. The contact resistance was tested by setting up an experimental platform and making conductive fluid rings with electrode materials of Ag, Cu and Ti. The results show that the static contact resistance between the conductive fluid and the metal electrode is positively correlated with the material resistivity and temperature, and negatively correlated with the surface roughness and contact pressure of the metal electrode. The dynamic contact resistance fluctuation is proportional to the amplitude of the input voltage of the angle shaker and inversely proportional to the square of the input frequency. At the same time, reducing contact resistance can improve the MHD sensor's performance.

Investigation on Intermittent Failure Phenomenon of Electrical Connectors Under Repetitive Mechanical Insertion and Withdrawal Operations

Electrical connectors play an indispensable role in electrical and electronic systems. The frequently occurred intermittent failure events seriously affect the reliability of application systems. In this article, the repetitive mechanical insertion and withdrawal experiment of electrical connector is carried out by using our designed test rig and the intermittent failure phenomena recurs. The typical waveforms of contact resistance and force during the mating operation are presented. The variation laws of static contact resistance and dynamic contact resistance under intermittent failure condition are counted and analyzed. And the dynamic contact resistance is proven to be a suitable sensitive parameter to characterize the intermittent failure event. Based on the mathematical model, variation of surface morphology, and element analysis, the failure mechanism of electrical connectors under repetitive operation is proposed.

Fatigue life assessment of dissimilar thickness resistance spot welded C-Mn steel using Weibull distribution

Resistance spot-welding (RSW) is a non-solid-state welding process that is significantly utilized in the self-propelled industry for manufacturing motorized bodies and parts. In this study, current and voltage data were recorded with the help of Miyachi Weld Checker for determining the variation of dynamic resistance over a welding process. Variation in dynamic resistance was analyzed for characterizing the nugget growth. The dynamic contact resistance (DCR) curves delineate that the entire process of nugget progression is composed of contaminants breakdown, asperity softening, resistance increment, growing stage, and stable stage. Further, tensile-shear test and fatigue test were performed for determining peak load and energy absorption, and dynamic behavior of spot-welded samples. Two-parameter Weibull distribution was utilized for statistical analysis of the fatigue test results of the spot-welded joint.

Development of sliding contact resistance testing equipment for carbon brush confluence ring

A carbon brush and a confluence ring form a pair of sliding electrical contacts. To reduce the contact resistance between the carbon brush and the confluence ring, the time for the running-in wear of the carbon brush increased during the machining process to increase the actual contact area. As a result, the welding and ablation failure between the carbon brush and the confluence ring happened under the impact of high current during service. To explore the effect of carbon brush wear on sliding electrical contact performance, it is necessary to monitor the dynamic contact resistance of the carbon brush and the confluence ring. In this paper, a set of 8-channel contact resistance testing equipment is developed. The device uses a relay array to achieve 1-8 channel gating and uses a data acquisition card to detect the contact resistance of each carbon brush and confluence ring pair combining with a four-point method. Based on the Labview software, it realizes the selection of acquisition channels, data acquisition card driving, real-time data processing, displaying, and storage. The range of contact resistance that this set of equipment can detect is 10mΩ ∼2Ω, and the accuracy can reach 1% of the full scale. Finally, the simulation experiments show that the testing equipment meets the technical requirements, and the continuous test runs stably and reliably. It can be used for the testing and research of the sliding contact resistance between the carbon brush and the confluence ring during the running-in wear process.

An arc contacts life assessment method based on dynamic resistance measurement and bp neural network

Arc contacts ablation of high voltage SF6 circuit breaker will cause potential problems for safe operation of the grid. In view of the difficulty of predicting arc contacts life by existing methods, an arc contacts life assessment method based on dynamic contact resistance and BP neural network is proposed. The dynamic contact resistance-travel curve is obtained from the high-current ablation experiments, from which the data characterizing the arc contacts state is extracted as samples to train the neural model. The model is optimized by k-fold cross-validation method, which is finally validated by experimental results. The results show that the arc contacts life prediction value agrees well with the experimental value, which means that the BP neural network can effectively predict the arc contacts life and provide a basis for decision making for arc contacts overhaul and replacement.

Investigations on Mechanical Behaviour and Failure Mechanism of Resistance Spot-Welded DP590 Steel Using Artificial Neural Network

Modelling of the spot weld responses, i.e. shear-tensile strength, coach-peel strength, mean dynamic contact resistance and nugget diameter, was carried out along with the optimization of weld process parameters, i.e. weld current, weld time and electrode force. The experiments for weld fabrication were designed using face-centred central composite design under response surface methodology. Experimental results acquired from the designed experiments were used to generate prediction models of the responses using the artificial neural network approach. Hybrid artificial neural network-genetic algorithm technique was used in order to obtain the optimized welding process parameters. Validation checks were done for the optimized parameters and responses in order to justify the adequacy of the models and optimized value. Failure mode analysis was done to determine the plasticity fraction and to relate this with the mode of failure and microhardness values. The shear-tensile strength, coach-peel strength and nugget diameter increase with the corresponding increase in the amount of heat input during the weld fabrication. The optimum process parameters are 8.98 kA of weld current, 284.92 ms of weld time and 3.04 kN of electrode force leading to the response values as shear-tensile strength of 21.93 kN.

Tungsten-Copper Composites for Arcing Contact Applications

The study presents the research findings on electrical contact materials based on tungsten-copper (W-Cu) composites containing 72 ± 3 wt.% W, rest Cu, and up to 1.5 wt.% Ni. Cylindrical sintered parts with 57 ± 0.5 mm in diameter and 12 ± 0.5 mm in height were manufactured by pressing, sintering, and liquid infiltration route, then were mechanically polished and processed as complex shape protection rings used as arcing contacts in high voltage circuit breakers (HVCBs). The surface elemental composition of the sintered parts was determined by wavelength dispersive X-ray fluorescence spectrometry. The density was determined by hydrostatic weighing in ethanol. The arithmetic mean surface roughness was measured by contact profilometry. The microstructure was studied by scanning electron microscopy. The electrical conductivity was measured by eddy current method. The thermal diffusivity and specific heat were determined by laser flash analysis. Instrumented indentation testing and two computational methods (Oliver &amp; Pharr, and Martens hardness) were employed to study the mechanical properties under quadratic loading and continuous multi cycle (CMC) indentation mode. The functional behavior of the arcing contacts was assessed in terms of static and dynamic contact resistance in operation in minimum oil HVCBs of 110 kV. The properties investigation revealed highly dense contact parts with homogeneous microstructure, Vickers hardness of 260-374, elastic modulus of 185-311 GPa, as well as good electrical and thermal conductivity. The arcing contacts proved a good functional behavior. in service, too. The results endorse the developed sintered contact materials for implementation in practical applications.

Experimental investigation of cold adhesion failure physical mechanism of gold plated contact within the Micro-Electromechanical-Relay

Gold plated contacts are widely used in the Micro-Electromechanical-Relay to improve electric contact reliability. However, the cold adhesion phenomenon between gold plated surfaces is prone to cause normally closed contacts operating failure. In this paper, a novel test rig for measuring dynamic force and contact resistance between spring contact and rod shape contact during breaking process is introduced. The dynamic contact force, displacement and contact resistance during contact breaking process are obtained. From these waveforms, the adhesion force between two contacts in each break is estimated. In order to reveal the failure phenomena occurred in the mechanical vibration screening tests, fretting between the closed contact pairs is generated with different amplitudes and cycles by using the motorized stage. Subsequently, the effects of fretting behaviors on cold adhesion of gold plated contact pairs are investigated explicitly. Next, the associated failure physical model is built with the help of mechanical adhesion theory to explain the nature of surface adhesion. Furthermore, surface quality of gold coating and static contact force are also verified as the key factors influencing the adhesion phenomena. Surface morphologies of contacts prove the substantial increase of adhesion force correlates closely with the features of micro asperities.

Resistance Spot Welding of Dissimilar Interstitial-Free and High-Strength Low-Alloy Steels

The primary aim of this investigation is to examine the resistance spot weldability of dissimilar interstitial-free (IF) and high-strength low-alloy (HSLA) steels. The effect of dynamic contact resistance on the nugget diameter is examined. The mechanical properties of the spot-welded specimens are investigated in both tensile shear and coach peel configurations. These experiments are supplemented by macro- and microstructural examinations, determination of microhardness profiles, and post-failure examinations, including fractography. It is observed that the nugget diameter increases as mean dynamic contact resistance decreases. The heat-affected zone of the HSLA side of the weld joint shows the maximum hardness, whereas the base metal of the IF side shows the minimum hardness. The hardness at the fusion zone of the dissimilar HSLA–IF joint lies in between that of fusion zone of similar HSLA–HSLA and IF–IF joints because of the homogenization of the chemistry of both the grades. The load carrying ability of the IF–HSLA joint is found to be closer to that of IF–IF joint but significantly lower than that of HSLA–HSLA joint; this is because the location of failure for IF–HSLA and IF–IF joint is same, i.e., the HAZ/base metal interface at IF side, while that of HSLA–HSLA joint is the base metal of HSLA steel.

Study of Ablation of Arc Contacts and Dynamic Contact Resistance in High Current Breaker

The fault of power circuit breaker (PCB) can lead very serious problems, especially in high voltage–power grid. The structure of contacts may be composed of main contacts and arc contacts, and this structure can avoid ablation of main contacts efficiently. It is necessary to study the eroded state of the arc contacts and the dynamic contact resistance of arc contacts to estimate the operating state of the PCB. The wear of contacts contains arc ablation and mechanical wear through the characteristics of contacts. The arc ablation is caused by the high temperature of the arc and the mechanical wear is caused by the mechanical friction of static and movable contacts. Some experiments have been done under different size of contacts and different current through them. The results show that the mechanical wear increases, sometimes heavier, with the increase of the size of fixed contacts and the decrease of the size of movable ones because the force between fixed and movable contacts becomes larger. The results also show that the ablation of arc contacts increases with the increase of current, especially when the current is up to 20 kA. With the high temperature of arc reaching the hardness point of copper, the arc ablation and mechanical erosion are increasing obviously since the contacts become soft and easy to wear. Another result of the study shows it is important to choose the material of contacts and the force between movable and fixed contacts. The harder and less resistance the material of contacts, the better the operating situation. To monitor the operating situation of the breaker, the dynamic contact resistance was measured 25 times. As a result, the dynamic contact resistance is sensitive to the current and increasing with the increase of continuous experiment time because of the increasing of metal ions. Furthermore, if the SF6 in the PCB is changes, the dynamic contact resistance would be changed. The dynamic contact resistance in this experiment varies substantially within the range of 80–250 μΩ at the current of 20 kA.

Method to improve the repeatability of dynamic contact resistance measurement test results for high‐voltage circuit breakers

Dynamic contact resistance measurement (DRM) is an effective technique to evaluate the contact condition in substations without dismantling circuit breakers. However, performing DRM tests with unsuitable test parameters will cause low repeatability of the test results, and even lead to the misdiagnosis of contact condition. Performing the DRM tests at high DC injected current can improve the repeatability. This paper studies the mechanism of the DC injected current on the repeatability of the DRM test results, and it also promotes a new determination method of the DC injected current amplitude. The impact of the DC injected current on DRM test results is reviewed. The mechanism of the DC injected current on DRM test results is investigated by analysing the chemical composition of the contact surface, the force exerted on the contacts, and the temperatures of a-spots on the contacts’ surface. Results indicate that not the Lorentz force, but the temperature of a-spots is the primary influencing factor. The amplitude of the DC injected current can be determined by calculating the temperatures of the a-spot on the contacts’ surface. And this method can also be used for other SF6 circuit breakers.

Study on Switching Characteristics and Associated Degradation Mechanism of Contact Material Under Capacitive Load

Electrical lifetime and relative dynamic welding failure mechanisms of an electromechanical relay for a capacitive load are interesting topics in the area of switching devices and contact materials. In this paper, a silver tin oxide contact material has been tested with a capacitive load by using our designed novel model switch. The typical waveforms of contact current and contact voltage at making and breaking are presented. Furthermore, the variations in bounce energy, static contact force, dynamic contact force, arc energy, and contact resistance as a function of operation cycles are plotted and analyzed explicitly. In particular, the intermittent long-duration arcing phenomena during breaking are observed and explained with the variations in local contact asperities. Based on the collected sensitive parameters, an associated physical degradation mechanism of contact materials under the capacitive load is proposed.

Prediction of the dynamic contact resistance of circuit breaker based on the kernel partial least squares

In order to diagnose the ablation characteristics of circuit breakers, the dynamic contact resistance measurement (DRM) has been proposed for almost 20 years. The dynamic resistance curves are easily influenced by two factors: injected current and opening velocity. The two factors are greatly affected the curves and may led a wrong diagnosis in DRM tests. Through analysis of the influence factors, an experimental model is used to simulate the opening process of the breaker in this study. The effective contact area of contact finger which is used in the experimental model under different velocities and current are measured by using the laser scanning microscope. The measurement proves that the changing of effective contact area plays determinative roles in the influencing of injected current and opening velocity. Then, the kernel partial least squares regression method is used to establish the model formula between influencing parameters and the dynamic contact resistance to realise the prediction of the dynamic contact resistance curves. Furthermore, the prediction model also can be used in other current carrying dry sliding friction conditions.

The Mathematical Model of Contact Resistance and Injected Current in DRM Tests of SF6 Circuit Breaker

Dynamic contact resistance measurement (DRM) has been widely used in evaluating the contact condition of circuit breakers from 20 years ago. With the increasing of the injected current, the contact resistance is lower than it was. It is considered that the contact hardness, contact force, and specific resistivity are affected by the injected current. SF6 circuit breaker with self-elastic contact is studied in this paper because of its widely used in high-voltage power system. First, the parameters of the dynamic curves are discussed, and the contact resistance in arcing contact part is concerned because of its susceptibility. Second, the mathematical model of contact force is discussed and calculated, and the change of contact force under a different injected current can be ignored. Finally, the mathematical model of contact resistance and injected current is established, when the breaker contact speed is stable. The mathematical model is proven effective by DRM tests.

Evaluation method of contact erosion for high voltage SF6 circuit breakers using dynamic contact resistance measurement

Dynamic contact resistance measurement (DRM) is an effective technique to evaluate the contact conditions of high voltage SF6 circuit breaker. However, the relations between DRM characteristics and contact performance remain ambiguous, the influence of the electrical stress on the DRM curves is equivocal as well, and there is no contact erosion evaluation method based on DRM.To investigate the relations between DRM characteristics and contact erosion, the DRM results of high voltage SF6 circuit breaker at various degrees of erosion obtained from the designed experiments are presented. The experiments demonstrate that with the degradation of the contacts, the average arcing contact resistance (Ra) increases, and the arcing contact wipe (Da) decreases. Then, the simulation of the erosion test is performed to analyse the relations between Ra and Da and the contact performance. The results show that with the decrease of Ra, the threshold of Da to ensure the success of the current commuting from the main contacts to the arcing contacts becomes shorter. Moreover, the influence of the electrical stress on Ra and Da are investigated. Results demonstrate that Ra reflects the influence of arc by-products and contact geometry caused by electrical stress, and that Da reflects the influence of the interrupted current, the arcing time, the contact geometry, and the contact material. Finally, an evaluation method of the contact erosion for SF6 circuit breaker based on DRM is proposed.

Resistance spot welding of galvannealed high strength interstitial free steel

Variation in dynamic contact resistance with the change in welding process parameters such as weld current, weld time and electrode force were taken into account for establishing the range of adequate nugget formation parameters. Influence of the welding process parameters on the shear – tensile strength, nugget diameter and the observed failure mode was analysed. The adequate resistance spot welding process parameters for galvannealed high strength interstitial free steel sheets of 1.6mm thickness were estimated as 8kA weld current, 250ms weld time and 3.5kN electrode force. Increase in the mean dynamic contact resistance led to a significant reduction in nugget diameter. A critical nugget diameter distinguishing between the IF and PF mode was experimentally determined by failure mode analysis. Different numerical models for estimation of critical nugget diameter were evaluated.

Investigation on the Mathematical Model of Dynamic Contact Resistance of Pantograph-catenary System

Investigation on the Mathematical Model of Dynamic Contact Resistance of Pantograph-catenary System