Movable Contact Research Articles

Elucidation of the synergistic mechanism of nano silicon carbide and titanium nitride as highly efficient additives of polyalphaolefin on strengthening the lubrication performance of movable contact interface

This study comprehensively investigated physicochemical and tribological performance of polyalphaolefin (PAO4) oil introducing oleic acid (OA)-functionalized SiC/TiN hybrid nanomaterials. The dispersion stability, wettability, thermal stability, and friction properties of the nanolubricants (NL) system were greatly improved following the application of hybrid NL. Additionally, the anti-wear and reducing-friction behavior were assessed via a four-ball tribometer. The results showed that the COF and WSD values of wear scar lubricated by hybrid NL were greatly reduced by approximately 32.7% and 35.1%, respectively, compared with the base oil. Finally, it is strongly confirmed that the significant improvement of friction performance is mainly due to improved interfacial effect of NL, the stable chemical tribo-film generated onto the friction surface, and the synergistic effect among SiC, TiN nanoparticles, and OA surfactant.

Influence of Mineral Oil-Based Nanofluids on the Temperature Distribution and Generated Heat Energy Inside Minimum Oil Circuit Breaker in Making Process.

The enhancement of the thermal properties of insulating oils has positively reflected on the performance of the electrical equipment that contains these oils. Nanomaterial science plays an influential role in enhancing the different properties of liquids, especially insulating oils. Although a minimum oil circuit breaker (MOCB) is one of the oldest circuit breakers in the electrical network, improving the insulating oil properties develops its performance to overcome some of its troubles. In this paper, 66 kV MOCB is modeled by COMSOL Multiphysics software. The internal temperature and the internally generated heat energy inside the MOCB during the making process of its contacts are simulated at different positions of the movable contact. This simulation is introduced for different modified insulating oils (mineral oil and synthetic ester oil) with different types of nanoparticles at different concentrations (0.0, 0.0025, 0.005, and 0.01 wt%). From the obtained results, it is noticed that the thermal stress on the MOCB can be reduced by the use of high thermal conductivity insulating oils. Nano/insulating oils decrease internal temperature and generate heat energy inside the MOCB by about 17.5%. The corresponding physical mechanisms are clarified considering the thermophoresis effect.

Optimal Design and Dynamic Analysis of a Spring-Actuated Cam-Linkage Mechanism in a Vacuum Circuit Breaker

This study attempted to establish an optimal design and perform dynamic analysis for a spring-actuated cam-linkage composite mechanism in a rated 12 kV, 25 kA vacuum circuit breaker (VCB). The optimal design of the VCB mechanism involves two steps: the first step involves the optimal design of the stiffness of closing springs and the cam profile, based on three-order polynomial motion curve of the follower; the second step involves the optimal design of a four-bar linkage. To minimize the surplus work in the VCB operating mechanism, the overall difference between the general output force and general resistant force of the VCB operating mechanism during the closing operation was adopted as the objective function to be minimized. Furthermore, the differential evolution algorithm with the golden ratio (DE-gr), an efficient and accuracy metaheuristic algorithm, was employed as the optimization method. The dynamic analysis of the optimal operating mechanism was conducted using a MATLAB-coded program and verified by the multibody dynamic software MSC-ADAMS. The dynamic analysis revealed that the optimal design of the VCB mechanism can considerably decrease the average closing velocity of the movable contact and the Hertz stress between the contact surface of the cam and the roller follower.

How to charge while driving: scheduling point-to-point deliveries of an electric vehicle under overhead wiring

Electrifying road-based long-haul transportation is an intricate task. Given the current state of battery technology, either the driving ranges of electric commercial vehicles (ECVs) are too short or high-capacity batteries are costly and so heavy that payloads are limited. An old, yet recently revitalized, charging infrastructure currently evaluated on multiple test tracks around the globe alternatively suggests charging of electric trucks while driving. Analogously to trams, trolley buses, or trains, ECVs are powered by an electric motor connected to overhead wires via a movable contact arm and supported by a battery or an extra conventional drive, which steps in on non-electrified road segments. This paper is dedicated to the routing of a single ECV executing full-truckload point-to-point deliveries along a highway main line where charge-while-drive infrastructure is fixedly installed along some but not all parts of the road. We formulate the resulting optimization problem, investigate computational complexity, and provide suitable solution procedures based on decomposition. Once all this is available, we explore the induction effect of charge-while-drive technology, i.e., the amount of charging detours required to gather enough energy for the next job. Our results show that the induction effect can be considerable and may lead to substantial extra traffic compared to conventional charge-while-park technology.

Vacuum arc characteristics of an AMF–TMF composite contact with fixed AMF contacts under different opening velocities

The objective of this paper is to determine the vacuum arc characteristics of a novel axial magnetic field (AMF)–transverse magnetic field (TMF) composite contact under different opening velocities. The AMF–TMF composite contact consists of a pair of outer fixed AMF contacts and a pair of inner movable TMF contacts. Drawn arc experiments were carried out in an L–C discharging circuit with this composite contact system to observe the differences in the arc development process under different opening velocities. The opening velocity of the inner movable contact was set to 1.3, 1.8, and 2.3 m/s. The arc current was up to 20 kA rms. In the experiments, the arc behavior was recorded using a high-speed camera. The arc current of each contact and the arc voltage were measured. Then the arc characteristics, including the arc current transfer characteristics, diffused arc duration, and mental droplet distribution before zero current, were quantitatively analyzed. Furthermore, magnetic field calculation was carried out to explain why the arc characteristics are different under different opening velocities. Experimental results show that with an increase in the opening velocity from 1.3 to 2.3 m/s, the diffused arc duration before zero current increases from 1.05 to 1.75 ms when the cathode is on the fixed side and increases from 1.30 to 1.90 ms when the anode is on the fixed side. In addition, the quantity of mental droplets between contacts before zero current is less with high opening velocity. It indicates stronger short-current breaking capacity under higher opening velocity. From the simulation results, it can be seen that during the arcing period, more current transfers to the fixed AMF contact under higher opening velocity and generates a stronger AMF. It could explain the earlier diffusion of the vacuum arc column under higher opening velocity.

A Novel Nonlinear Dynamic Model for Predicting Contact Bounce of Electromagnetic Relays With Flexible Spring Components

Contact bounce is a common phenomenon in the closing process of electromagnetic relays, which seriously affects the electrical contact reliability of the system. The whole closing process of flexible spring components consists of the free movement stage and the contact bounce stage, which increases the complexity of analyzing the electrical contact behaviors of electromagnetic relays. In this study, a novel nonlinear dynamic model of the flexible spring components in electromagnetic relays is established to analyze the physical mechanism of the electrical contact bounce. Considering the electromagnetic effect, flexible deformation, contact collision, and welding force, the proposed mathematical model can capture the dynamic closing process accurately and collect bounce parameters efficiently. The Kelvin–Voigt viscoelastic contact model is employed to evaluate the nonlinear contact force between the static and movable contacts. Based on the Galerkin method, the nonlinear equations of motion for the movable spring within electromagnetic relays are formulated. A series of experimental work are designed to measure the typical waveforms of displacements of the movable contact and currents in the coil during the closing process of the movable spring. Furthermore, the theoretical results are validated by comparing with the experimental data. The dependences of some key factors, including the structural, material, and electrical contact parameters on the contact bounce characteristics, are investigated explicitly. The theoretical results attest that the proposed model can accurately predict the dynamic behaviors of the movable spring, and the contact bounce can be effectively suppressed by adjusting the parameters of the flexible spring component.

Contact resistance based tactile sensor using covalently cross-linked graphene aerogels.

A movable electrical contact between two materials is one of the most fundamental, simple, and common components in electronics that is used for binary control of a conducting path in an electrical circuit. Here, variable contact resistance between a highly elastic graphene aerogel and a rigid metal electrode is used for the analysis of non-binary pushing and pulling mechanical forces acting on the contact, enabling superior strain and pressure measurements. The variable contact resistance based electromechanical sensors demonstrate superfast, ultrasensitive and quantitative measurements of compressive and tensile stress from -1.18 MPa to 0.55 MPa. The sensors can operate over the temperature range of -60 to 100 °C, cover the whole skin and human motion range, and determine the weight of a grasped object. The measurement of such high forces has only been possible due to the high-temperature induced covalent cross-linking of graphene in the aerogel that provides high strength, durability, and fast response (<0.5 ms) to the sensing element. The study demonstrates the great potential of the contact resistance-controlled sensing, which enables high-precision and reliable measurement of strain and pressure over a remarkable large sensing range, providing new opportunities for applications in human-machine interfaces, robotics, flexible electronics, and haptic technology.

Research on 500kV Transformer on-load Tap Changer Fault Treatment and Physical Properties Testing

This article introduces the intermittent increase of acetylene content in the oil during the operation of a 500kV start-up substation of a power generation company. It is preliminarily judged that there is spark discharge in the oil chromatographic analysis and on-site partial discharge test. After returning to the factory for maintenance and internal inspection, it was found that the movable contact and the fixed contact of the selected part of the on-load tap-changer were not connected in place, which caused intermittent spark discharge and continued to increase acetylene. The problem is solved by adjusting the number of turns of the gear when the tap switch is switched forward and backward, and the transformer resumes normal operation.

Research on the Contact Bounce During the Closing Process of a Repulsion Mechanism Applied in a Superconductivity Direct-Current Vacuum Circuit Breaker

This paper studies the contact bounce during the closing process of a repulsion mechanism applied in a superconductivity direct-current vacuum circuit breaker. A multi-physics field coupling simulation model is established to describe the whole closing process for the repulsion mechanism. The relationship between the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> is obtained for the repulsion mechanism, where the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> is an instantaneous closing velocity for the movable contact just mating with the stationary contact at the first time, and the D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> is the maximum contact bounce distance. According to this relationship, the critical instantaneous closing velocity V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cri</sub> for the case of no contact bounce is determined. According to V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cri</sub> , a novel oil buffer is designed to adjust the closing displacement of the repulsion mechanism to realize a nonclosing bounce. A prototype repulsion mechanism with an oil damper is developed. Its closing characteristics are tested and compared with the simulation results to verify the absence of a contact bounce.

Development of GIS Switch State Judgment System Based on Image Recognition

Aiming at the fast opening and closing speed of the GIS isolation/grounding switch, manual observation is more difficult, so it is difficult to judge the current switch status. This paper proposes an OpenCV-based image identification algorithm to identify the position of the switch movable contact during the opening and closing process of the isolating switch, thereby judging the state of the isolating switch. This system uses Raspberry Pi as the main hardware core, the server drives the CMOS camera through Raspberry Pi 4B, collects image information in the GIS optical observation window, and performs simple processing, and transmits it to the Raspberry Pi 4B based on the UDP protocol as the main core. In the upper computer and adopt the target detection algorithm based on OpenCV to track the current isolation/grounding switch contact position and determine the current opening and closing state.

A New Method for Measuring Stress Inside Movable Element in Contact

Subsurface stress plays an important role in the damage of a movable contact element, but subsurface stresses are usually obtained with numerical calculation according to the theory of contact mechanics. In the present paper, a new method to measure the subsurface stress of the movable element is proposed with using photoelastic technology. Although the technology has been widely used in measuring the stress in the static state, it is seldom used in a moving body because the observed point is moving. After the experimental tester is introduced in detail, the principles of the photoelastic technology are presented. The tester is designed to be able to working in three conditions, the static, the rolling, and the sliding, in the line or surface contacts. The experimental results, that is, the interference fringes, of the three states are then presented in different loads and rotational speeds. Because the fringe figure indicates the maximum shear stress distribution in the body of the moving element, we can find what the real stress distribution in the rolling or sliding element is alike.

Optimizing the electrification of roads with charge-while-drive technology

Given the current state of battery technology, applying electric trucks for long-haul transportation is a cumbersome task. Either the driving ranges are too short or high-capacity batteries are so heavy that payloads are limited. An old, yet recently revitalized charging infrastructure, currently evaluated on multiple test tracks all around the globe, allows to charge electric trucks while driving. However, installing the charging infrastructure along highways, namely, overhead wiring or road-embedded power lines both accessed by trucks equipped with a movable contact arm, is costly. This paper provides a detailed modeling approach based on continuous variables to minimize the installation costs for electrified highway kilometers while still providing sufficient energy for a given set of representative tours of electric vehicles. We apply our solution approach to show that investment costs can considerably be reduced along a European highway mainline while still allowing electrified transport among most adjacent major cities. Furthermore, we quantify the loss in precision, if instead of our detailed approach a more aggregate model based on discrete decision variables is applied.

ГИДРОДИНАМИЧЕСКИЙ РАСЧЕТ КЛИНОВИДНОЙ СИСТЕМЫ «ПОЛЗУН - НАПРАВЛЯЮЩАЯ», РАБОТАЮЩЕЙ НА СЖИМАЕМОМ СМАЗОЧНОМ МАТЕРИАЛЕ В УСЛОВИЯХ НАЛИЧИЯ РАСПЛАВА НА ПОВЕРХНОСТИ НАПРАВЛЯЮЩЕЙ

Recently, various methods have been used to ensure the hydrodynamic mode of lubrication, one of the methods is devoted to this scientific article. In the article, on the basis of the equation of motion of a compressible, truly viscous liquid for a "thin layer", the equations of state, the continuity equation, as well as the equations describing the profile of the molten contour of the surface of the support ring, an asymptotic and self-similar solution is found for the zero (without taking into account the melt) and the first (taking into account the melt) approximation, for determining the velocity field and pressure in the lubricating layer. For the profile of the molten contour and the pressure, the solution is found by the method of sequential approximation, for the extreme and non-extreme case. As a result, a refined mathematical calculation model of a wedge-shaped sliding support with a low-melting metal coating on the movable contact surface is developed, which compensates for the emergency lack of lubricant and provides a stable hydrodynamic lubrication mode, which allows determining the bearing capacity and friction force. As a result of numerical analysis, the obtained refined mathematical calculation model of a wedge-shaped sliding support with a low-melting metal coating on the surface of the support ring, taking into account the compressibility of the liquid lubricant and the coating melt, and experimental research, the effectiveness of the obtained complex of refined models that allow performing both pre-design evaluation and design engineering calculations, in a wide range of operational load-speed modes, as well as the mechanism and stages of transition to lubrication with metal sprays is established, providing an increase in the level of the main tribotechnical parameters and the resource of tribosystems.

Гидродинамический расчет клиновидной системы «ползун-направляющая», работающей на сжимаемом смазочном материале в условиях наличия расплава на поверхности направляющей

In the article on the basis of the equation of motion of the compressible lubricant for the «thin layer», continuity, state, and the equation describing the profile of the molten contour taking into account the formula of mechanical energy dissipation the asymptotic and self-similar solution is found for the extreme (when the speed tends to infinity) and non-extreme case. As a result of solving the problem, a refined mathematical calculation model of a wedgeshaped sliding support with a low-melting metal coating on a movable contact surface is obtained, which compensates for an emergency lack of lubricant and provides a stable hydrodynamic lubrication mode

Investigation of the Possibility of Using X-Rays to Control the Technical Condition of High-Voltage Low-Oil Switches

The capabilities of the X-ray method of nondestructive testing of high-voltage oil-filled equipment are investigated using the example of a low-oil switch of the VMT series of 110-kV voltage class (VMT-110) with porcelain external insulation. A list of characteristic types of defects based on the analysis of the causes of failure of VMT-110 switches was compiled, and a special defective sample (SDS) for laboratory research was created. The following types of defects were simulated: contact bar deformation, contact wear, burning of the contact surface and reducing the height of the contact part of the movable contact, cracks in the casing of the fixed contact, crimping failure and rope unwinding, mechanical damage to the bottom rollers, fracture of the upper roller spring, bearing defects, cracks in the insulating rods of the control system of the movable contact, and cracks on the inner and outer surfaces of the porcelain insulator of the arcing chamber. The X‑ray examination of SDS was performed using a monoblock X-ray device with a constant voltage on the tube and directed radiation output. The optimal parameters of the X-ray device were selected experimentally. The information content of the SDS radiographs for monitoring the SDS technical condition was evaluated by comparing the actual defects with the images obtained on the radiographs. The results of the SDS study have shown that the proposed technical solution can detect at least 75% of the characteristic types of defects in the internal structural elements of the VMT-110 switch. The proposed instrumentation can be used to monitor the technical condition of other types of high-voltage equipment (gas-insulated switches, gas-insulated switchgear, measuring transformers, and cable couplings) onsite without disassembly.

A Sequential Adaptive Control Strategy for the Contact Colliding Speed of Contactors Based on Fuzzy Control

In the making process of a contactor, the fast collisions of the movable contact and the static contact lead to the contact bounce, which greatly reduces the electrical life of the contactor. In this article, a neural network model is used to estimate the contact colliding speed and a fuzzy logic controller is designed with the contact colliding speed as the feedback. By controlling the excitation time of the contactor, the contact colliding speed successively approximates a given smaller reference value, thus, the contact bounce is inhibited. The results of the cosimulation show the theoretical feasibility of the proposed scheme. In addition, three contactors of different types are used for an experiment, and the results show that the reduction in the contact bounce time is more than 70% and that the proposed control strategy is universal.

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.

Analysis of small intermediate relays from leading manufacturers

This paper presents a comparative analysis of technical characteristics and designs of small intermediate relays from various manufacturers. The following main characteristics of relay are considered: operation and release values; weight and dimensions; power consumption; time parameters; reliability characteristics. The design of the relays of the Russian and international manufacturers are being discussed, their design features that affect the technical characteristics are considered. It is noted that the fastening of movable contacts directly to the armature (relays from Finder, Relpol, Irkutsk Relay Plant) requires a flexible connection with the relay contacts, which leads to more complicated assembly and calibration of relays. It is shown that the kinematic diagram in the presence of free travel with no mechanical coupling with the contact pusher, used in the relay from Schrack, can reduce power consumption and increase the vibration and shock resistance of the relay break contacts. In Schrack AC relays, the operating clearance zone is configured to create a short-circuited loop with reduced electrical resistance and to provide optimum conditions for reducing armature vibration. The appropriate relay designs in terms of improving technical characteristics are proposed. The advantage of a flat return spring over cylindrical coil springs in terms of manufacturing technology and stability of mechanical characteristics of relay is shown. It was revealed that the electromagnetic drive of the Schrack relay compares favorably with electromagnetic drives of other companies in terms of the use of stray magnetic fluxes to create a useful electromagnetic torque. Based on the results of the comparative analysis and experimental study of existing relay designs, recommendations were formulated for the development of a new series of the Russian small intermediate relays within the framework of the import substitution program.

A Reliable and Controllable Motor Actuator Without Permanent Magnetic for 40.5 kV Vacuum Circuit Breakers

In order to solve the disadvantages of long start-up time and demagnetization of the traditional permanent magnetic (PM) actuators, this article presents a high reliable and controllable novel motor actuator without PM, which includes driving motor and its control circuit. The proposed driving motor is similar to the switched reluctance motor, which has the advantages of small rotational inertia and fast start-up. The difference is that there is an auxiliary coil, which is placed between the two-stator sets, can be energized by controllable direct current to adjust the air-gap flux density and then the output torque of motor and the velocity of movable contact are easier to control. Furthermore, a prototype of the novel motor actuator has been developed according to the analysis and calculation results of the dynamic characteristics of 40.5-kV vacuum circuit breaker (VCB), and which is tested on the platform in conjunction with a 40.5-kV VCB prototype to showcase the success of the proposed motor actuator and its control method.

Modeling and Experimental Verification of Contact Sliding Behavior for Flexible Spring Components Within Electromechanical Relays

The electrical contact reliability of electromechanical relays is affected by the mechanical contact sliding behavior greatly. The whole contact sliding behavior of spring components involves the free travel stage and the overtravel stage. In this paper, a novel mathematic model of the typical flexible spring components within electromechanical relays is built to calculate the contact sliding distance (SD). Two variant types of this model are presented to satisfy different spring components configurations. The main influencing factors of contact SD, including the length of the movable spring, contact gap between two contacts, the head height, and diameter of the movable contact, are studied in detail. Furthermore, the contact SD and broadside lines of contact pair are captured in situ and measured by introducing a charge-coupled device (CCD) camera with a highpixel resolution. The comparison between analytical calculation results and experimental results shows the accuracy of the built model. Finally, the interrelation between contact force, electrical contact resistance, and contact SD is experimentally investigated. It is found that approximately linear relationships exist between the contact SD, contact force, and the forward distance of the push rod.