WO2025229370A1

WO2025229370A1 - Gold-based liquid metal contacts and their manufacturing method for high-current vacuum switchgear

Info

Publication number: WO2025229370A1
Application number: PCT/IB2024/054125
Authority: WO
Inventors: Prytula MYKHAILO
Original assignee: Individual
Current assignee: Individual
Priority date: 2024-04-28
Filing date: 2024-04-28
Publication date: 2025-11-06
Anticipated expiration: 2026-10-28

Abstract

The invention relates to the field of switching devices and provides a method for manufacturing liquid-metal composite contacts with elastic, flexible frameworks made of refractory metal. The invention addresses issues related to the reliability and longevity of contacts in switching devices and simplifies their manufacturing process, allowing for mass production using existing equipment and skilled specialists. The resulting liquid-metal contacts possess high elasticity, improved contact properties, and resistance to welding, enhancing the switching capacity of OLTC and other switching devices. The invention has significant commercial potential and can be applied in various industries that require highly reliable and efficient switching devices.

Description

Gold-Based Liquid Metal Contacts and Their Manufacturing Method for High-Current Vacuum Switchgear

[0001] Gold-Based Liquid Metal Contacts and Their Manufacturing Method for High- Current Vacuum Switchgear introduce a revolutionary approach to the production of contact materials.

[0002] This innovative method not only simplifies the manufacturing process but also facilitates easier integration into industrial applications, significantly enhancing the performance and reliability of high-current vacuum switchgear. The quality and properties of contact materials determine the stability of the entire power supply system, from power plants, including wind and solar power stations, to end consumers in industry and households. Reducing the size and weight of vacuum circuit breakers is critically important for mobile applications such as electric vehicles, and aerospace and air transport.

Technical Field

[0003] Problems with existing contact materials and their impact on the efficiency of vacuum switching devices. Modern vacuum arc extinguishing chambers widely use solid contact materials, which require significant effort to achieve low contact resistance, which is critical for reliable operation of electrical systems. For example, in known devices such as EATON WL-41177, to achieve a contact resistance of about 10 microOhms, contact forces up to 6200 N are required. However, even with such measures, significant energy dissipation occurs at each contact transition, for example, at a current of 4000 Amps, about 160 watts of thermal power is released, which requires the use of forced cooling, as in the model EATON WL-35964W.

[0004] Over the lifetime of vacuum switching equipment, wear of solid contacts due to arc discharge can lead to a loss of contact material of 3-5 mm, which, as known from patent US 11004619B2, leads to a reduction in contact pressure and a decrease in the compressive force of the spring. This reduction in compressive force increases the risk of overheating or explosion during short circuits and faults in circuit interruption.

[0005] In the typical operation of vacuum circuit breakers, the collision of hard solid contacts often results in a rebound effect. This dynamic action induces multiple arc formations at the moment of contact, leading to intense localized heating. Over time, these arcs can cause the contact surfaces to weld together, complicating disengagement and severely impacting the operational integrity and safety of the system.

[0006] To address these issues, engineers are forced to complicate the design of actuation mechanisms, which has its physical limits: increasing the required contact force necessitates the use of more powerful and heavier mechanisms and conductors. This leads to an increase in the inertial forces that must be managed, increasing the complexity and cost of the entire system.

[0007] Using a new contact material with self-restoring capabilities and improved elasticity, which would have almost zero contact resistance even at minimal pressure, could fundamentally change the situation. This would allow for reduced energy consumption, smaller device sizes and weights, and also ensure higher reliability and durability.

[0008] The inventor has been involved in the research and commercialization of liquid-metal composite contact materials with an elastic framework of refractory metals for over 20 years. These developments are aimed at solving problems in the transmission of high power energy and creating a new generation of switching equipment that features improved operational characteristics due to nearly zero contact resistance and low additional contact compression required.

Background Art

[0009] In modem technology of vacuum switching devices, methods of manufacturing liquid-metal composite contacts with elastic frameworks are known, such as those described in patents SU1325590A1, UA62376A, and US7686864B2. These methods involve creating a structure from high-temperature metal wire, forming it into a cylindrical blank, subsequent pressing to achieve desired sizes, and restoration in a vacuum furnace in a hydrogen atmosphere. The structure is impregnated in three stages using alloys of tin, indium, and gallium, which requires strict control of temperatures and processing times.

[0010] A drawback of the known US7686864B2 method of manufacturing liquid-metal contacts is the complexity and costliness of the manufacturing technology, which requires high temperature in high vacuum, changing environments, and precise control of the amount of hydrogen, as well as multiple reloads of the vacuum furnace, achieving vacuum. This method leads to a high percentage of defective products, where part of the framework remains unimpregnated with liquid metal, and the eutectic composition is impossible to adjust. Nearly half of the costly metals are wasted as alloys of In-Ga-Sn form with an unpredictable percentage composition.

[0011] Another drawback of the known method SU1325590A1 is the inability to reliably and rigidly fix the elastic and flexible contact in the contact holder. This method described the creation of a liquid-metal contact with a height of 5 mm and a diameter of 6 millimeters, which due to small sizes, held its shape well, but this method did not provide for a significant increase in the size of the framework needed, for example, for switching tens of thousands or hundreds of thousands of amps. For such switching, the contact would have a diameter, for example, of 150 mm, and being compressed around the circumference, would take on a spherical shape due to its elasticity.

[0012] Soldering to the conductor a framework completely wetted with a low-melting metal is fundamentally impossible. An attempt to solve this task was made in the known SU1644240A1 Composite liquid-metal contact and method of its manufacture, by simultaneous counter impregnation of a porous refractory framework made of tungsten powder from below with the molten metal of the conductor at a temperature above 1083 degrees Celsius (the melting temperature of copper) and from above with the eutectic alloy Indium-Gallium-Tin.

[0013] Practical application of this method showed that the actual impregnation of the porous tungsten framework with copper starts at temperatures above 1130 degrees, above the temperature at which tungsten begins to recrystallize, which reduces the mechanical strength of tungsten and is inapplicable to a framework made of tungsten wire, as it would lead to a loss of strength of the tungsten wire, and the two melts, copper and eutectic alloy In-Ga-Sn, easily diffuse into each other, and the copper base ends up being wetted with gallium eutectic, making it impossible to solder the resulting contact to conductors.

[0014] The next critical drawback of this method is the impossibility of impregnating closed internal pores, which leads to a large amount of irreparable defective products. Such a contact, essentially, remains with a solid surface, although it is covered with liquid metal. A common drawback of known methods SU1325590A1, SU1644240A1, UA62376A, and US7686864B2 in manufacturing liquid-metal contacts is the need to wet all internal surfaces of ready-made tungsten frameworks to retain the liquid phase, while alloys based on gallium under normal conditions do not wet the surface of tungsten and are not retained in the framework structure, therefore ready-made frameworks are placed in a reducing environment, specifically a hydrogen atmosphere, at temperatures above 800 degrees, to remove the oxide layer of the refractory metal and then carry out impregnation directly with the eutectic alloy In-Ga-Sn.

[0015] Disclosure of the Invention

[0016] The basis of the invention claimed in claim 1 of the patent formula lies in the task of developing a simple, repeatable, and economically viable method of mass production of liquid-metal contacts with elastic, flexible frameworks of refractory metal, which will allow manufacturers to widely use the aforementioned unique properties and undeniable superiority over all currently used solid contact materials, increase their reliability, reduce the use of costly high-temperature hydrogen vacuum furnaces, avoid multiple loadings and prolonged vacuuming, and the large amount of defective products that accompany the oxidation-reduction, wetting of the surface, and impregnation of the refractory framework. [0017] This problem is solved in that the refractory framework is manufactured from refractory metal wire preliminarily covered with gold, for example, from commercially produced gold-plated tungsten wire, then [Fig.l] the mentioned framework 1 is placed in a recess in the electrode 2 with solder 3 made of an alloy based on gold or silver, with a melting temperature below the melting temperature of the coating of the refractory metal, and is heated to the melting temperature of the gold or silver solder in a vacuum (vacuum is necessary to protect the refractory metal from oxidation), the gold or silver solder easily connects with the gold-covered tungsten wires. Then the mentioned framework 1 of gold-plated refractory metal, already soldered to the conductor [Fig.2], is impregnated with an alloy based on Gallium, for example known from JPS59123736A alloy In-Ga-Sn-Ag or known from EP0777755B1 alloy In-Ga-Cu-Zn. Impregnation can occur in an air environment, by any convenient method, for example, by applying the necessary amount of low-melting alloy 4 on top [Fig.3], immersion in a bath [Fig.5], immersion in an ultrasonic bath, under additional pressure, etc. It is recommended to carry out impregnation in a vacuum at an elevated temperature, to remove air, increase the fluidity of the low-melting alloy, and better fill the framework to obtain the finished contact 10 [Fig.4]. The time to fill the framework should be sufficient to fill the empty space between the wires, at least 15 minutes.

[0018] In some cases, it is necessary to reverse the procedure to obtain guaranteed wetting of the entire refractory metal wire frame, and to wet the woven refractory metal blank prior to pressing, claim 3 of the patent claims. This will allow visual confirmation of wetting of the entire framework and repair the empty surfaces.

[0019] Measures should also be taken to ensure that the gold surface is not contaminated with foreign impurities, for example, oils, although after soldering the framework in a vacuum it will have the necessary cleanliness. In case of contamination - wash the finished framework with an organic solvent in an ultrasonic bath. One of the advantages of this method, which is favorably distinguished from the known US7686864B2, is the absence of metal waste, full control over the eutectic composition, and the single heating to high temperature during the soldering of the finished framework to the conductor, which is already done by manufacturers of vacuum chambers, who solder solid contacts to conductors in the same way. Thus, all without exception manufacturers of the vacuum contacts chambers in the world already have the necessary equipment and personnel to implement the proposed method of manufacturing contact material. Thus, the impregnation process can be carried out simultaneously for multiple contacts on conductors, for example, as shown in [Fig.l 1],

[0020] In special cases, separate impregnation of the base of the framework with a gold alloy 9 [Fig.9] in vacuum in graphite molds may be required. This may be necessary if the manufacturer of vacuum chambers does not independently manufacture frameworks for liquid-metal contacts, but buys them, for example, from a manufacturer of gold-plated or silver-plated tungsten wire.

[0021] This method practically allows impregnation of the refractory framework with a low-melting alloy not in high-temperature hydrogen and vacuum furnaces, but in the simplest equipment, for example, laboratory vacuum drying ovens, in ultrasonic bath, which significantly reduces the consumption of electricity and other resources, does not occupy the work of high-vacuum furnaces, the amount of defective products is reduced to zero. This method allows the manufacture of flexible elastic contact materials of almost any shape and size for the entire range of vacuum switching equipment, significantly simplifying drive mechanisms, reducing energy losses and maintenance costs. An example of implementation can be known from the patent for an industrial sample UA20612 and patents for utility models UA43517 and UA43518 modular vacuum contactor with a known bistable electromagnet (utility model patent UA43207) as a drive for the moving contact, since after the contacts close, minimal efforts are required to compress the elastic contacts.

[0022] Serial production may consist of manufacturing known method of knitting from tungsten wire 5, covered with gold 6, using a knitting machine [Fig.6]. The weight of the obtained blank from woven tungsten wire should exactly correspond to the project weight of the contact, taking into account the filling with liquid metal. Then the obtained fabric is folded or twisted into a blank 7 of any required shape, for example, cylinder, ring, square, etc. [Fig.7] and placed in a mold 8 [Fig.8] and pressed to the required size and calculated filling of the ready golden plated frame 1 of future contacts [Fig.8]. Then, in the blanks of the conductors, the solder 3 is placed in the production-accepted method and the frameworks of gold-plated tungsten wire are placed on top. The conductors with frameworks are installed in a vacuum furnace in the same way as it is done when reinforcing solid contacts and the process of soldering frameworks to conductors is carried out. After removal from the furnace, protective rings 9 made of material that does not wet with gallium are placed on the upper part of the frameworks [Fig.3], and calculated measuring amounts of low-melting alloy 4 are poured on top and placed in a vacuum cabinet for impregnation. After impregnation, the remnants of the liquid phase are removed from the surface of the contacts, and the contacts are ready for installation in vacuum chambers using the usual technology [Fig.4],

[0023] Calculation of the amount of materials and cost.

[0024] For example, to obtain a contact for a nominal current of 20,000 Amps, it is necessary to make a framework with a diameter of 72 mm and a thickness of 5 mm, while the lower part of the framework will be impregnated to a height of 1 millimeter with a gold alloy. The volume of the framework will be 72x72x3.14/4x5=20347.2 cubic millimeters, or 20.3472 cubic centimeters. Assuming the framework has a tungsten filling of 60%, the rest being gallium-based eutectic, then the weight of the tungsten wire would be 20.3472x19.3x0.6=235.620576 grams, and the weight of the low-melting alloy 20.3472x0.4x6.45=52.495776 grams. The cost of materials for one such contact, not counting the gold-containing solder, would be approximately 1500 US dollars, which is economically viable and does not require any special technological processes.

[0025] Availability of materials.

[0026] The industry that produced tungsten wire for filament bulbs has been declining in recent years due to the switch to LED technologies. However, these production capacities can be utilized to create new types of products. The amount of Indium, Gallium, Tin, and Silver needed in production is small, for example, for a contact with a nominal current of 400 amps, only 1 gram of such an alloy is needed.

[0027] Test Results

[0028] One of the most critical properties of the vacuum arc chamber contacts is their resistance to welding. It is known that metal parts pressed together in a vacuum environment are prone to cold welding since no oxides can form on their surfaces to prevent this process. However, the liquid metal contacts produced by the proposed method inherently cannot form weld seams under any current conditions. For instance, such liquid metal contacts with a diameter of 20 mm withstood a short-circuit current test of 29,000 Amperes for 200 milliseconds without any destruction or welding of the contacts.

[0029] The liquid metal contacts exhibit elasticity and flexibility, making them exceptionally stable under conditions of significant cyclic impact loads, with no contact bounce or chatter observed. Testing for switching overvoltages showed that the liquid metal contacts could maintain a stable arc at low currents to prevent switching overvoltages. The liquid metal contacts with a tungsten framework were installed in a standard vacuum chamber and subjected to extensive wear resistance tests (200,000 switching operations in AC4 mode), demonstrating the contacts' self-restoring capability and maintaining a mirror surface even after 200,000 switchings in AC4 mode.

[0030] These test outcomes not only validate the superior performance and robustness of the proposed liquid metal contact technology but also open new avenues for its application in advanced electrical systems where high reliability and efficiency are paramount. The demonstrated resilience and operational benefits strongly advocate for its adoption in critical infrastructure, paving the way for next-generation vacuum switchgear solutions. [0031] In conclusion, the Gold-Based Liquid Metal Contacts and Their Manufacturing Method for High-Current Vacuum Switchgear revolutionize the field of electrical engineering. By significantly simplifying the production process and enhancing ease of integration, this method offers a substantial advancement over existing technologies. It provides a practical, efficient solution that not only improves the performance and reliability of high-current vacuum switchgear but also promotes greater sustainability and cost-effectiveness in the industry. This innovative approach is expected to set a new standard for contact material technology, supporting the ongoing evolution of the power systems infrastructure.

Claims

[Claim 1] A method for manufacturing contact material for switching devices, comprising an elastic, flexible framework made by pressing from refractory metal wire, previously woven into an organized structure fabric, impregnated at various sections with different alloys for different functional purposes, characterized in that the framework is made from refractory metal wire that is pre-gold-plated, and then impregnated predominantly in a vacuum with a low-melting gallium-based alloy.

[Claim 2] The method for manufacturing contact material according to claim

1, characterized in that after pressing, the framework made from the pre-gold-plated wire is soldered to the conductor and only then impregnated predominantly in a vacuum with the low-melting alloy.

[Claim 3] The method for manufacturing contact material according to claim

1, characterized in that the wetting of the organized structure fabric made of refractory metal wire with the low-melting metal is carried out before pressing.

[Claim 4] The framework for a liquid-metal composite contact, made from refractory metal wire, preliminarily coated with a metal that has good adhesion to gallium alloys, ensuring reliable wetting and retention of the liquid-metal alloy in the framework structure.

[Claim 5] The framework according to claim 4, characterized in that before impregnation with the liquid-metal alloy, the part of the framework intended for attachment to conductors is additionally processed or filled with a metal or alloy that also wets well with gallium alloys, improving the mechanical fixation of the framework in the conductor.

[Claim 6] The method according to any of the preceding claims, wherein the tungsten wire is coated with one or more metals selected from the group consisting of gold, silver, platinum, nickel, palladium, or their combinations.

[Claim 7] The method according to any of the preceding claims, wherein the contact base material is made from alloys based on palladium, silver, platinum, or copper.

[Claim 8] The method according to any of the preceding claims, wherein the framework is impregnated with a known In-Ga-Sn alloy with the addition of silver to enhance conductivity and reduce the specific resistance of the contact material.

[Claim 9] The method according to any of the preceding claims, wherein the impregnation of the framework with a low-melting gallium- based alloy is enhanced by ultrasonic treatment to ensure thorough saturation and uniform distribution of the alloy within the framework.