Vacuum circuit breaker with copper switch contact of weldable design

Abstract

The invention relates to a method for manufacturing an electrical switching contact device for a vacuum circuit breaker, wherein the method comprises at least the following steps: a) providing two electrical contact pieces made of copper or a copper alloy; b) coating the electrical contact pieces with aluminum or an aluminum alloy, respectively, wherein the coating of the contact pieces is effected by a cold gas spraying method; c) welding the sides coated in method step b) to electrical current transition contacts, respectively; d) arranging the unit obtained in method step b) in a vacuum circuit breaker. Furthermore, the invention relates to an electrical switching contact device for a vacuum circuit breaker, having contact pieces manufactured according to the method according to the invention.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for manufacturing an electrical switch contact device for a vacuum circuit breaker, wherein the method comprises at least the following steps: a) providing two electrical contact pieces made of copper or a copper alloy; b) coating the electrical contact pieces with aluminum or an aluminum alloy, wherein the coating of the contact pieces is achieved by a cold gas spraying method; c) welding the sides coated in method step b) to a current transition contact piece each; and d) arranging the unit obtained in method step b) within a vacuum circuit breaker. Furthermore, the invention also relates to an electrical switch contact device for a vacuum circuit breaker, having contact pieces manufactured according to the method according to the invention. BACKGROUND

[0002] Due to the energy transition, the distance between the place of generation and the place of consumption of electrical energy is becoming increasingly large, so that a safe and low-maintenance control of high currents or high voltages is currently becoming more important. As a result, increasingly large electrical currents are being conducted through the existing infrastructure, which has a particularly large impact on the susceptibility to interference of the entire system. In order to counter this, a more secure and more low-maintenance individual component is a basic requirement.

[0003] Vacuum circuit breakers for switching medium and high voltages have been known for a long time. This construction form is robust and has proven itself particularly suitable for the absorption of high currents. However, it is disadvantageous in contrast that, due to the absorption of high switching-off currents and the high forces associated therewith of the emerging arc plasma, only specific materials are suitable for the switch contact. Depending on these constructional boundary conditions, only a very limited material selection and accordingly only a limited manufacturing possibility arises for precisely these components in the direct switching path of the current. Thus, for example, the contact pins of the vacuum switch tube are preferably made of copper or a copper alloy on the basis of thermal and electrical properties, which can then only be mechanically connected to the other components of the vacuum circuit breaker by means of a screw connection or a clamping connection very limitedly. These purely mechanical fastening possibilities can be cumbersome and prone to faults.

[0004] Different approaches for improving the construction of the electrical contacts of a vacuum circuit breaker are also known from the patent literature.

[0005] Thus, for example, EP 0 203 367 A1 describes a contact arrangement for a vacuum switch having two contacts which are arranged coaxially opposite one another and which can be moved relative to one another in the axial direction thereof, the contacts each being composed of a disc-shaped contact piece having a contact face and a disc spaced apart behind the contact piece which is made of a material which is good electrically and which is connected directly to a central feed pin and which has a radially and azimuthally extending conductor by virtue of the design of the circular recess and the slit and which thereby implements means for generating an axial magnetic field, wherein the current is guided from the feed pin via the conductor of the disc to the contact piece, characterized by the following features: a) the slit extends tangentially from the circumference of the disc onto the circular recess, b) the bridges for guiding the current between the disc and the contact piece are each defined by the slit and the recess, c) the contacts which are arranged opposite one another are oriented azimuthally such that the circular recesses of the two oppositely arranged discs coincide in the axial direction, in contrast, the associated tangential slits are only oppositely arranged on the outer diameter of the discs.

[0006] Furthermore, DE 3 347 550 A1 discloses a composite material consisting of chromium and copper, in particular for electrical contacts in vacuum switches in the medium- to high-voltage range of energy technology, wherein the material consists of a chromium skeleton impregnated with copper or a copper alloy, wherein the material contains carbon, which is present partly in the form of free graphite and partly in the form of a bound form of a metal carbide, for which purpose the chromium skeleton additionally has a content of one or more of the metals nickel, cobalt or iron in an amount of 0.05 to 2% by mass.

[0007] EP 1 831 903 B1 discloses a vacuum switch chamber having a first contact and a second contact for switching an electrical current flowing through the vacuum switch chamber in a switched-on switching state, and having at least one heat pipe containing a working medium for conducting away heat generated in the vacuum switch chamber by the electrical current, wherein the heat pipe comprises a section of the heat pipe, which is referred to as evaporator, and a section of the heat pipe, which is referred to as condenser, wherein the heat pipe has a section which is flexible deformable.

[0008] However, this solution known from the prior art for improving the electrical and mechanical properties of the electrical contacts of a vacuum circuit breaker can offer further improvement potential, in particular with regard to the mechanical and electrical connection of the contact pieces to further components of the vacuum switch chamber. SUMMARY

[0009] The technical problem addressed by the present application is to at least partially overcome the disadvantages known from the prior art. The technical problem addressed by the present application is in particular to provide a solution which is characterized in that the electrical contacts are particularly advantageously mechanically and electrically connected to further structures of the vacuum switch chamber.

[0010] According to the application, the solution to the above-mentioned technical problem is achieved at least partially by a method for manufacturing an electrical switch contact device for a vacuum circuit breaker and by an electrical contact device for a vacuum circuit breaker.

[0011] The application therefore relates to a method for manufacturing an electrical switch contact device for a vacuum circuit breaker, which comprises two electrical contact pieces which can be brought into contact with one another, wherein the method comprises at least the following steps:

[0012] a) providing two electrical contact pieces made of copper or a copper alloy;

[0013] b) coating at least one side of the electrical contact pieces respectively with aluminum or an aluminum alloy, wherein the coating of the contact pieces is achieved by means of a cold gas spraying method and the at least one coated side is opposite to the contact sides of the two contact pieces;

[0014] c) welding the sides of the contact pieces which were coated with aluminum in method step b) respectively to a current transition contact;

[0015] d) arranging the unit consisting of the contact pieces and the current transition contact obtained in method step b) in a vacuum circuit breaker.

[0016] It has surprisingly been found that the contact pieces are mechanically connected to the other components of the vacuum switch chamber by means of the layer of cold gas sprayed aluminum, resulting in a vacuum switch chamber which is particularly long-lived and low-maintenance. The clamping connection or the screw connection known from the prior art is therefore superfluous and advantageously a more electrically uniform contact position between the contact pieces and the current lead-out body is produced by means of the connection via the welding. In the design according to the application, the lead-out of high voltages or high currents is achieved by means of the uniform connection of the contact pieces to the current lead-out body, so that the occurring electric and magnetic fields can be uniformly led out. This is more difficult in the design known from the prior art, in which the contact pieces are connected to the current lead-out body asymmetrically. It is thus always possible to form a preferential direction in the lead-out of the current, which can lead to an increased wear of specific regions of the contact pieces. A further advantage is that the cold gas sprayed aluminum coating is very dense, so that the vacuum of the vacuum switch tube can be guaranteed even during a long service life. The connection of the contact pieces to the current lead-out body by means of the welding can withstand a high degree of mechanical stress, so that the reliable service life of the vacuum switch tube can be extended.

[0017] The method according to the invention is a method for manufacturing an electrical switch contact device for a vacuum circuit breaker, the electrical switch contact device comprising two electrical contacts that can contact each other. The vacuum switch tube is typically constructed of a cylindrical, evacuated, insulated ceramic housing containing two switch contacts. One of the two switch contacts is fixed, while the other switch contact is movably arranged. The ends of the ceramic housing are metallized at their end faces and welded to metal flanges. To transmit the movement of the movable contact from the outside to the inside of the vacuum chamber, the movable contact is connected to the housing via a metal bellows. To prevent the accumulation of contact material on the inner surface of the ceramic during the switching process, which could potentially weaken the insulation, a metal vapor shield made of copper or stainless steel is installed in the contact area. Depending on the implementation variant, the metal vapor shield may be non-potentially charged or connected to one of the contacts. For protection, the metal bellows may also be capped. To avoid dielectric problems at the transition from the ceramic to the metal end flange, a corresponding shield may be integrated. Two contacts form the components of a switch contact device, and may or may not be in contact with each other depending on the spacing between them. A current-carrying element can also be included in the switch contact device, continuing to conduct the current carried through the contacts.

[0018] In step a), two electrical contacts made of copper or a copper alloy are provided. The electrical contacts may be entirely made of copper or may also include copper alloys. For example, copper and chromium alloys with a chromium content of, for example, 25 to 50%, have also proven suitable. According to the invention, it is theoretically possible that only one contact is equipped with the aluminum alloy according to the invention. However, it has proven significantly more effective that, according to the invention, both contacts of the vacuum switch tube are equipped with an aluminum coating. Here, the contacts can have any geometry. However, a cylindrical geometry has proven particularly advantageous, having two end sides and a housing surface. One end side is responsible for mechanical and electrical contact with the other contact during operation of the vacuum switch tube, while the other end side of the contact is equipped with an aluminum coating according to the invention and welded to the current-carrying body.

[0019] In step b), at least one side of the electrical contact is coated with aluminum or an aluminum alloy, wherein the coating of the contact is achieved by a cold gas spraying method, and at least one coated side is opposite the contact side of the two contacts. Cold gas spraying is a coating method for metals in which powdered metal materials or metal alloys are applied to a substrate at high speed. Due to the high kinetic energy of the powder, it bonds with the substrate. The gas is preferably nitrogen, and the nitrogen is passed through a high pressure and accelerated to supersonic speed by means of a nozzle. Heating the gas jet can increase the flow velocity of the gas and thus also increase the particle velocity. Similarly, the heating of the particles can cause them to deform upon impact. However, in cold gas spraying, the gas temperature is significantly lower than the melting temperature of the powder used, so that the metal particles do not melt in the gas jet. Surprisingly, this technique can also be used in the construction of vacuum switch tubes, and layers capable of withstanding extreme loads caused by the current and voltage that occur can be produced by this technique. Additionally, it is unexpected that coatings produced by this coating technique can also be used in vacuum applications. The combination of electrical load and environmental conditions is a priori unsuitable for the use of this technology. In this regard, at least one or more switch contacts are coated with cold air spray, wherein the back side refers to the side that does not have direct contact with other switch contacts. The back side of the switch contacts is connected to a current transfer contact that electrically connects the switch contacts to other components of the power grid.

[0020] Powders made of aluminum or aluminum alloys with a narrow particle size distribution are suitable for coating, for example. Thus, aluminum powders with a monodisperse size distribution, for example, having a D50 value (measured by means of dynamic light scattering) around 10 to 250 µm, have proven particularly suitable. These powders can form layers that are particularly capable of withstanding mechanical loads, and these layers also contain only a very small proportion of air inclusions. This can help maintain the best possible vacuum within the vacuum tube.

[0021] In step c), the aluminum-coated sides of the contacts from step b) are welded to the current transfer contacts. Therefore, the mechanical and electrical connection between each contact and the corresponding current transfer contact is achieved not through a copper layer, but through an aluminum layer applied according to the invention by a cold-air spraying method. Direct welding of a copper layer or copper alloy layer to the current transfer contact, which is typically made of copper, is technically impossible. Here, the welding of the aluminum layer to the current transfer contact can be performed using welding methods known in the prior art.

[0022] In step d), the unit consisting of contacts and current transition contacts obtained in step b) is arranged within the vacuum circuit breaker. After the contacts and current transition contacts are joined together by welding, the unit consisting of contacts and current transition contacts can be installed into the vacuum chamber of the vacuum circuit breaker. Furthermore, other components of the vacuum circuit breaker, such as metal bellows or end seals, can be connected to the unit in any manner. Here, after installation, the welded connection can be located inside or outside the vacuum chamber. This is a functional result of the geometry of the contacts and current transition contacts.

[0023] In a preferred embodiment of the method, in step b), in addition to the side opposite the contact side, the areas of the two contacts adjacent to the side can also be coated with aluminum or an aluminum alloy by cold air spraying. According to the invention, the contacts are provided with an aluminum coating at the desired connection point with the current conductor. Besides the coating at this connection point, it has proven particularly suitable that additional surfaces of the contacts are also provided with an aluminum coating. Suitable adjacent areas are, for example, the housing area of ​​the contacts. If the contacts are, for example, cylindrically configured, the coating is applied once to the end side and at least also to a portion of the adjacent cylindrical housing. This coating can help improve the electrical performance of the contacts. Furthermore, this design enables a more uniform coating on the end sides of the contacts.

[0024] In another preferred embodiment of the method, in step b), the side opposite the contact side can be coated with a constant layer thickness. Coating the contact with a constant layer thickness has proven particularly suitable to obtain the most uniform mechanical and electrical properties possible at the connection site between the current conductor and the contact. A constant layer thickness is assumed where the layer thickness varies by less than 10% over the surface under consideration (e.g., the end side). A generally suitable layer thickness range for a reliable connection between the current conductor and the contact is typically between 500 µm and, for example, 3 cm.

[0025] Within the preferred aspects of this method, the cold-gas-sprayed aluminum coating can be machined after application. To obtain the most reproducible strength possible within the welding process, it has proven particularly suitable that the applied aluminum coating undergoes an additional machining step. This machining step may, for example, include smoothing the layer by a grinding process. However, it is also possible that the thickness of the aluminum layer is slightly reduced by an etching process. For this purpose, turning or grinding the layer, for example, may be suitable. However, the aluminum coating can also achieve a particularly suitable low surface roughness, for example, by a smoothing process, which results in improved mechanical adhesion within the welding process.

[0026] In another preferred embodiment of the method, the welding method in step c) can be electron beam welding. Connecting the applied aluminum coating to additional current transition contacts or current emitters by electron beam welding has proven particularly suitable in terms of the mechanical and electrical properties of the connection. Electron beam welding can especially result in a particularly uniform connection between the two parts, which can also contribute to a particularly uniform discharge of current from the vacuum switch chamber. Furthermore, the uniform connection can particularly advantageously absorb any mechanical forces that may arise.

[0027] In a preferred feature of this method, the weldable surface of the current transition contact may have a partially silver-plated contact surface. To improve current conduction through the unit consisting of a current conductor or a current transition contact and a contact element, it has proven advantageous for the current transition contact to have a silver-plated area on the contact surface with the aluminum coating of the contact element. The silver-plated area on the current transition contact is preferably 5% to 25% of the total area of ​​the current transition contact.

[0028] Furthermore, according to the invention, there is an electrical switch contact device for a vacuum circuit breaker, comprising two opposing contacts, each made of at least one two-layer metal composite material having a layer of copper and a layer of aluminum or an alloy thereof. The surfaces of the contacts facing each other have copper layers, and the surfaces of the contacts facing away from the copper layers have aluminum layers. One or both switch contacts of the electrical switch contact device are obtained according to the method of the invention, and the contacts are respectively welded to the current transition contacts of the vacuum circuit breaker. Thus, the electrical switch contact device for a vacuum circuit breaker has two contacts, each having a layer applied individually by means of a cold gas spraying method. The additional aluminum layer adheres very well to the copper and is welded to an additional current conductor by a welding method. This design eliminates the commonly implemented measures for connecting the contacts and the current conductor, such as threaded connections or clamping connections. Uniform adhesion is achieved between the contacts and the current conductor, which in particular results in a uniform and homogeneous current being discharged through the contacts and the current conductor during switching. For further advantages of the switching contact device according to the invention, reference is also made to the advantages of the method according to the invention.

[0029] In a preferred design of the electrical switch contact device, the thickness of the aluminum coating on the side and / or housing surface opposite the contact side can be greater than or equal to 1 mm and less than or equal to 20 mm. These thicknesses of the aluminum coating have proven effective for mechanically and electrically connecting the contacts to the current conductor. This results in a low-maintenance vacuum circuit breaker whose electrical performance is only slightly reduced by the introduced aluminum layer. Smaller layer thicknesses may be disadvantageous because, in this case, insufficient layer thickness for welding may not be available. Larger layer thicknesses may be disadvantageous because, in this case, the electrical characteristics of the unit consisting of the contacts and the current conductor are significantly reduced.

[0030] In a preferred embodiment of the electrical switch contact device, the aluminum coating thickness on the side opposite the contact side can be greater than or equal to 2.5 mm and less than or equal to 20 mm, and the coating thickness on the housing surface can be greater than or equal to 1 mm and less than or equal to 7.5 mm. To obtain the most uniform coating possible, it has proven advantageous that both the end sides of the contact and the housing surface are coated. It is particularly advantageous that the layer thickness on the housing layer of the contact does not reach the same thickness as the coating on the end sides. This difference in thickness can help, particularly advantageously, to guide the current occurring in the area of ​​the unit consisting of the contact and the current-carrying body or current-transfer contact.

[0031] According to another preferred aspect of the electrical switch contact device, the thickness ratio between the copper and aluminum layers of the contact (expressed as the quotient of copper layer thickness / aluminum layer thickness) can be greater than or equal to 4 and less than or equal to 15. To obtain a switch with the best possible performance, it has proven advantageous to maintain the aforementioned range of the relationship between the thickness of the contact and the thickness of the applied aluminum layer. This relationship substantially does not degrade electrical performance and provides improved mechanical properties for the unit comprised of the contact and the current-carrying element.

[0032] For other advantages and technical features of the switching device, refer to the description of the switching device, the accompanying drawings and the description of the drawings, and vice versa. Attached Figure Description

[0033] Further details, features, and advantages of the subject matter of this invention are given by the dependent claims and by the following description and associated examples in conjunction with the accompanying drawings. In the drawings:

[0034] Figure 1 A schematic overview of the components of a vacuum circuit breaker according to the prior art is shown in top view;

[0035] Figure 2 shows a schematic overview of the components of a vacuum circuit breaker according to the prior art in cross-section;

[0036] Figure 3A schematic overview of the components of the vacuum circuit breaker according to the present invention is shown in cross-section;

[0037] Figure 4 A schematic overview of two contacts is shown, each having an aluminum coating on its end side and partially on the housing surface.

[0038] Figure 5 A schematic overview of a contact device consisting of two units according to the invention is shown in cross-section. The unit consists of a contact element and a current-conducting element. Detailed Implementation

[0039] Figure 1 The structure of a vacuum circuit breaker 1 is schematically shown. The vacuum circuit breaker 1 has two contacts 4 and 5, one of which is movably arranged and the other is fixedly arranged. Among other components, the vacuum circuit breaker 1 also has a metal vapor shield 2 and an external insulator 3. Contact 4 is connected to an additional power grid via a current conductor 6. Contact 5 is connected to an additional power grid via a current conductor 7. Contacts 4 and 5 can be connected to the corresponding current conductors 6 and 7, for example, via clamping connections or threaded connections.

[0040] Figure 2 also schematically illustrates the structure of the vacuum circuit breaker 1. The vacuum circuit breaker 1 has two contacts 4 and 5, wherein, in this example, contact 4 is movably arranged and contact 5 is fixedly arranged. Among other components, the vacuum circuit breaker 1 may also include a metal vapor shield 2, a metal bellows 8, a protective cap 9 for the metal bellows 8, and an external insulator 3. Contact 4 is connected to an additional power grid via a current conductor 7. Contact 5 is connected to an additional power grid via a current conductor 6. Contacts 4 and 5 can be connected to the corresponding current conductors 6 and 7, respectively, for example, via clamping connections or threaded connections.

[0041] Figure 3The structure of a vacuum circuit breaker 1 according to the present invention is schematically shown. The vacuum circuit breaker 1 includes two contacts 4 and 5, wherein, in this example, contact 4 is movably arranged and contact 5 is fixedly arranged. Among other components, the vacuum circuit breaker 1 may also have a metal vapor shield 2, a metal bellows 8, a protective cap 9 for the metal bellows 8, and an external insulator 3. Contact 4 is connected to an additional power grid via a current conductor 7. Contact 5 is connected to an additional power grid via a current conductor 6. Contacts 4 and 5 each have a cold-gas-sprayed aluminum coating 10 on their end sides or end faces. Through this cold-gas-sprayed aluminum coating 10, the corresponding contacts 4 and 5 are mechanically connected to the corresponding current conductors or current transition contacts 6 and 7 by welding connections 11. This results in a mechanically extremely stable unit that experiences significantly less mechanical interference and failure. Furthermore, the dimensions of contacts 4 and 5 relative to the thickness of the aluminum coating 10 result in very good electrical characteristics of the unit composed of contacts 4 and 5 and current conductors 6 and 7. In this design, the welding connection position 11 is located inside the vacuum chamber. Alternatively, one of the welding positions 11 can be located inside the vacuum chamber, and another of the welding positions 11 can be located outside the vacuum chamber.

[0042] Figure 4 The diagram schematically illustrates contacts 4 and 5 according to the invention, each having a cold-air-sprayed aluminum coating 10. The coating is applied uniformly, as can be seen here, covering both the end faces of the contacts and the outer casing. This coating contributes to the particularly advantageous electrical and mechanical properties of the vacuum circuit breaker 1.

[0043] Figure 5 The diagram schematically illustrates a design according to the invention for connecting contacts 4, 5 and current conductors 6, 7. The figure shows the cold-gas-sprayed aluminum coating 10 and the welded connection 11 to the current conductors. In this design, the welded connection 11 is located outside the vacuum chamber.

[0044] List of reference numerals

[0045] 1 Vacuum circuit breaker

[0046] 2 Metal vapor shield

[0047] 3 Insulators

[0048] 4 movable contact components

[0049] 5. Fixed contact components

[0050] 6 Current-generating bodies

[0051] 7 Current-generating body

[0052] 8 Metal Corrugated Pipe

[0053] 9 protective caps

[0054] 10. Cold-sprayed aluminum coating

[0055] 11 Welded Connection

Claims

1. A method for manufacturing an electrical switch contact device for a vacuum circuit breaker (1), said electrical switch contact device comprising two electrical contacts (4, 5) capable of contacting each other, Its features are, The method includes at least the following steps: a) Provide two electrical contacts (4, 5) made of copper or copper alloy; b) Coat at least one side of the electrical contacts (4, 5) with aluminum or aluminum alloy, wherein the coating of the contacts (4, 5) is achieved by cold air spraying, and at least one coated side is opposite to the contact side of the two contacts. c) Weld the aluminum-coated sides of the contacts (4, 5) in step b) to the current transition contacts (6, 7) respectively; d) The unit consisting of contacts (4, 5) and current transition contacts (6, 7) obtained in step b) is arranged in the vacuum circuit breaker (1).

2. The method according to claim 1, characterized in that, In step b), in addition to the side opposite to the contact side, the area of ​​the two contacts adjacent to the side is also coated with aluminum or aluminum alloy by cold air spraying.

3. The method according to claim 1 or 2, characterized in that, In method step b), the side opposite to the contact side is coated with a constant layer thickness.

4. The method according to claim 1, characterized in that, The aluminum coating applied by cold air spraying is then machined.

5. The method according to claim 1, characterized in that, The welding method in step c) is electron beam welding.

6. The method according to claim 1, characterized in that, The weldable surface of the current transition contact has a partially silver-plated contact surface.

7. An electrical switch contact device for a vacuum circuit breaker (1), characterized in that, The electrical switch contact device includes two opposing contacts (4, 5), each contact being made of at least one two-layer metal composite material having a copper layer and an aluminum layer or an alloy thereof, wherein the surfaces of the contacts (4, 5) oriented opposite to each other have copper layers, and the surfaces of the contacts (4, 5) facing away from the copper layers have aluminum layers, wherein one or both switch contacts (4, 5) of the electrical switch contact device are obtained by the method according to any one of claims 1 to 6, and the contacts (4, 5) are respectively welded to the current transition contacts (6, 7) of the vacuum circuit breaker (1).

8. The electrical switch contact device according to claim 7, characterized in that, The aluminum coating thickness on the side and / or housing surface opposite the contact side is greater than or equal to 1 mm and less than or equal to 20 mm.

9. The electrical switch contact device according to claim 7 or 8, characterized in that, The aluminum coating has a thickness of 2.5 mm or more and less than 20 mm on the side opposite to the contact side, and a coating thickness of 1 mm or more and less than 7.5 mm on the outer casing surface.

10. The electrical switch contact device according to claim 8, characterized in that, The thickness ratio between the copper layer and the aluminum layer of the contact (4, 5) is greater than or equal to 4 and less than or equal to 15, and the thickness ratio between the copper layer and the aluminum layer of the contact is expressed as the quotient of the copper layer thickness / the aluminum layer thickness.

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