Method for increasing the effective contact surface of an electrical contact

Abstract

A method for increasing the effective contact surface of an electrical contact comprises applying a conductive coating by spraying a metal powder with the aid of heterophase flow onto the surface of a contact connector of elements of structures which allow the transfer of high-power electrical energy. The coating is applied by a collaborative or industrial robot, with the heterophase flow at subsonic speeds. A heated working gas with an adiabatic index of 1.4-1.6 is used as a carrier for the heterophase flow. Materials with a low yield stress and low resistivity are used for the metal powder to be sprayed, for example, powders of tin, lead, bismuth, gallium and / or alloys thereof, as well as mixtures of said powders. Roughness with an arithmetic mean profile deviation of 0.5-10 μm is formed on the contact surface of the substrate. Once the conductive coating has been applied, the contact surface thereof is increased by imparting roughness with an arithmetic mean profile deviation of 0.5-10 μm thereto. The method makes it possible to increase reliability and energy efficiency and to reduce electrical energy loss by lowering contact resistance in conductive contact connectors.

Description

[0001] METHOD FOR INCREASING THE EFFECTIVE CONTACT SURFACE TO REDUCE THE TRANSITIONAL CONTACT RESISTANCE WHEN MAKING ELECTRICAL CONTACT.

[0002] Field of technology to which the invention relates The invention relates to industrial power systems, namely to a method for contact connection of current-carrying buses to increase the reliability of the connections and reduce losses in current-carrying buses during the transmission of high-power energy and can be used to increase the overall energy efficiency of power systems.

[0003] State of the art

[0004] The prior art discloses the widespread use of lubricants, pastes and compounds to reduce electrical contact resistance, for example (see [1] SU 1756940, IPC H01B1 / 02, published on 23.08.1992 or [2] RU2713155, IPC H01B1 / 12, published on 04.02.2020). The disadvantages of using such materials on contact surfaces include: • the impossibility of uniformly distributing the lubricating-conducting mass and completely filling the gap over the entire contact surface area when making a contact connection;

[0005] • risk of oxidation of the contact in the gap when exposed to elevated temperatures, as well as the environment during operation of the contact connection;

[0006] • during long-term operation and under the influence of external factors, the properties of the lubricant change, which leads to revision of the contact pair and the need to re-use the conductive lubricant.

[0007] The use of coatings to reduce contact resistance is widely known in the prior art, for example, see [3] RU2301847C1, IPC C23C26 / 02, published 27.06.2007 or [4] RU2690086C2, IPC C23C26 / 02, published 30.05.2019. The methods for applying such coatings involve heating the contact parts to carry out the tinning process of the contact pair materials during the formation of the coating. The disadvantage of these analogues is the high labor intensity of the coating application process, due to the human factor and the need to apply a uniform coating layer to the entire contact surface.

[0008] The closest analogue of the claimed invention, adopted as a prototype, is a method for applying a coating (see [5] RU2732367, IPC H01B1 / 02, published 06 / 08 / 2020), which includes preheating compressed air to a temperature of 300-800 °C, feeding it into a supersonic nozzle, forming a supersonic flow of 300-200 m / s in it, introducing copper powder or silver and copper powder and / or a mixture thereof into this flow. The formation of a coating with high adhesion strength occurs due to the high kinetic energy during supersonic application and plastic deformation of the substrate as a result of coating formation. The main disadvantages of the prototype include the following:

[0009] • during the process of coating formation, a high-speed kinetic impact of the sprayed particles occurs, leading to their deformation, but at the same time, high internal stresses arise in the substrate materials, leading to an increase in residual stresses that initiate permanent deformation (warping) of the material of the contact surface of the busbar, thereby reducing the actual contact area of ​​the contacting materials.

[0010] • during the operation of the connections, the process of fretting corrosion is initiated due to the lack of deformation of the coating applied to the contact surface during the formation of contact.

[0011] • during the operation of connections with copper and / or silver coating at elevated heating temperatures (over 100 °C) and exposure to the environment, an increase in the voltage drop in the contact occurs due to the development of the dynamics of the oxidation process of such materials, while a significant decrease in the electrical properties of the resulting coatings occurs according to the % scale of the IACS standard (International Annealed Copper Standard) over time.

[0012] The essence of the invention

[0013] The technical objective of the claimed invention is a method for increasing the actual contact area of ​​the contact surface when implementing electrical contact necessary to reduce the transition contact resistance in the contact connections of busbars during the transmission of electrical energy.

[0014] The technical result is an increase in the reliability of the operation of energy systems and a reduction in electrical energy losses in contact connections of busbars during the transmission of high-power energy by applying a deformable coating in order to increase the actual contact area in the contact connection while reducing the values ​​of the transition contact resistance of the electrical contact.

[0015] The stated problem is solved and the technical result is achieved by a method for increasing the effective contact surface to reduce the transition contact resistance when implementing electrical contact, including preliminary abrasive treatment of the contact surface to a surface roughness with an average arithmetic deviation of the profile of 0.5-10 μm, applying a conductive coating by spraying metal powder with a low yield strength and specific electrical resistance directly onto the surface of the contact connection of structural elements that ensure the transmission of electrical energy, wherein the coating is applied at subsonic velocities of a heterophase flow of 50-5-270 m / s and its temperature of 20-5-280 °C, while the consumption of powder of the sprayed metal is 1.8 g / min + 60 g / min, abrasive treatment of the contact surface of the coating to a surface roughness with an average arithmetic deviation of the profile of 0.5-g-10 μm,assembly of contacts by bolted connection, wherein the contact pressure is less than or equal to the yield strength of the material of the applied coating,

[0016] Furthermore, the technical result is achieved by using materials with low yield strength and electrical resistivity as the sprayed metal powder, such as tin, lead, bismuth, gallium, and / or its alloys, as well as powder mixtures, applied sequentially and / or in a layer-by-layer and / or gradient coating. The actual contact area of ​​the contact surface during electrical contact is increased by the load created by the bolted connection, which exceeds the yield strength of the coating material.

[0017] Furthermore, the technical result is achieved by increasing the contact surface after applying the conductive coating by roughening the surface with an average arithmetic profile deviation of 0.5-5-10 µm. During subsequent assembly of the detachable contact joint, the oxide films formed on the surface of the applied layer during storage are destroyed by the bolt load, which exceeds the yield strength of the coating material.

[0018] Also, the technical result is achieved due to the fact that the coating spraying distance is increased, ensuring a reduction in flow speeds to 50-5-270 m / s and its temperatures of 20-5-280 °C, than when applying a coating using a supersonic heterophase flow with speeds of 330-5-1200 m / s and its temperature of 300-5-800 °C for coating application.

[0019] Also, the technical result is achieved due to the fact that the carrier of the heterophase flow is a heated working gas with an adiabatic index of 1.4-5-1.6 (the adiabatic index is the ratio of the heat capacity at constant pressure to the heat capacity at constant volume).

[0020] Also, the technical result is achieved due to the fact that in order to increase the actual contact surface of the contact connection obtained according to the method described in this invention, a functionally gradient coating can be applied, with a variable gradient of material from the substrate to the peripheral layer according to a linear law.

[0021] Brief description of the drawings

[0022] Fig. 1 - Sketches indicating the dimensions of the sample in mm for forming a detachable bolt contact (a); the area of ​​the contact connection demonstrating a current-transmitting surface with an area of ​​6086 mm 2 (b).

[0023] Fig. 2 - Results of measuring the actual contact area of ​​the surface when implementing a bolted contact connection according to Table 1.

[0024] Implementation of the invention

[0025] In the proposed method, a coating is applied by spraying metal powder directly onto the electrical contact surface of the electrical connection of structural elements that transmit electrical energy to increase the effective contact area during electrical contact, which is necessary to reduce contact resistance. Contacts produced by this method ensure the required reliability, fire safety, and cost-effectiveness.

[0026] Application of this functional coating, which has low electrical resistance and the ability to readily deform under load, is accomplished, for example, using a heterophase flow, which involves generating a subsonic flow of heated working gas with an adiabatic index of 1.4+1.6. The coating is applied using a collaborative or industrial robot to ensure uniformity of the coating. Spraying is performed in the subsonic heterophase flow speed range of 50-5-270 m / s and a temperature of 20-280 °C, with the sprayed metal powder consumption being 1.8 g / min + 60 g / min. To increase the adhesion strength of the coating material to the substrate, the contact surface of the latter is subjected to abrasive treatment to remove contaminants and develop the surface by imparting roughness with an arithmetic mean profile deviation of 0.5-5-10 μm, for example, using abrasive treatment.Materials with low yield strength and specific electrical resistance are used as the powder of the sprayed metal, for example, powder of tin, lead, bismuth, gallium and / or its alloys, as well as mixtures of powders applied sequentially and / or in the version of layer-by-layer and / or gradient coating application.

[0027] Gradient coating is achieved by varying the concentration of the components of the applied powder material during coating formation. The concentration gradient is directed from the substrate material to the peripheral layers of the coating, which is necessary to increase the effective contact surface.

[0028] In order to prevent changes in operational properties due to possible oxidation during storage, after applying the conductive coating, its contact surface is increased by roughening the surface with an average arithmetic deviation of the profile of 0.5-5-10 μm, for example, through abrasive action.

[0029] To confirm the achieved technical result, as well as to compare the proposed solution with an existing analogue, several experiments were conducted, the results of which are summarized in Table 1. Table 1 shows the values ​​of the contact transient resistance measured under normal conditions and after exposure to elevated temperatures of 160 °C for 200 hours with a geometric contact area (see Figures 1 and 2), with the passage of a direct current of 600 A for 10 seconds and with a fixed tightening force of the bolted connection of 35 Nm.

[0030] The essence of the method for measuring the contact resistance (four-pin circuit, Kelvin probe), which occurs between contact surfaces, is to measure the voltage drop on a section of the circuit limited by the contact pad, while an adjustable circuit current is constantly supplied to the section of the circuit, then the contact contact resistance is calculated in accordance with Ohm's law, U = IR (see standard DVS 2929-1 (2014)).

[0031] Example

[0032] Spherical tin powder, obtained by sputtering in a protective atmosphere with a reduced content of oxygen and other non-metallic impurities, is applied to a substrate made of A5M aluminum sheet with dimensions (Fig. 1a). In order to increase the effective contact surface and reduce the contact resistance, the coating is formed only on the surface of the overlap current-transmitting contact (Fig. 16) by applying it using a heterophase flow generated in a nozzle in the subsonic speed range. Before spraying, to increase the adhesion strength, the contact surface is processed to remove contaminants and develop the surface by roughening with an arithmetic mean deviation of the profile R a= 7 μm. The compressed carrier gas (e.g. air) is preheated to 250 °C, generating a flow with a maximum velocity of 236 m / sec, achieved through the use of a subsonic nozzle. Tin powder is fed radially relative to the subsonic flow, where it is captured by the passing flow, forming a heterophase flow of the working gas and the applied powder material. A coating with a thickness of 100 μm is formed at solid phase velocities within the range of 50 27Q m / sec and a powder mass flow rate of 30 g / min. The coating thickness is selected based on the tasks at hand and is controlled by the technological parameters of the coating application process. After applying the conductive coating, its contact surface is increased by abrasive action, thereby achieving a surface roughness of R a= 5 µm. The coating adhesion strength, measured using the ASTM C633 standard, is 36 ± 4 MPa. An increase in the effective contact area of ​​11 ± 4% compared to the uncoated contact is also achieved. These measurements were conducted using the indentation analysis method in the contact zone under bolt load conditions.

[0033] The results of the tests carried out to determine the voltage drop in the contact pair (Fig. 16) at a constant tightening torque of 35 Nm on each of the 4 connecting bolts are shown in Table 1.

[0034] As shown in Table 1, after applying the coating according to the optimal technological parameters according to the invention, the transient contact resistance is significantly reduced.

[0035] Table 1: Results of measuring the contact resistance

[0036]

[0037] Note: A5M grade aluminum sheet is characterized by high purity and chemical neutrality according to GOST 21631-76, subjected to annealing (M - annealed).

[0038] The proposed invention reduces and stabilizes the contact resistance by increasing the actual contact area of ​​the contacting pairs during the bolted connection of the contact pair, including the use of disc springs to stabilize the load of the bolted connection over time. The claimed technical result is achieved by:

[0039] - Application of a uniform and stable functional coating using materials with low yield strength and specific electrical resistance, ensuring a reduction in transient contact resistance.

[0040] By applying a functional coating that exhibits plasticity under the load of the bolted contact joint structure.

[0041] - The formation of a juvenile contact surface occurs due to the destruction of oxide-containing surface layers during the process of plastic deformation of a functional coating with low specific electrical resistance.

[0042] The coating is applied using a robotic system, which includes equipment to ensure the method of applying materials.

[0043] - Formation of a bimetallic coating directly on the current-transmitting surfaces of a detachable contact connection, ensuring the transmission of high-power electrical energy.

[0044] - In order to prevent the influence of oxide films formed during storage, after application of the coating, the coating surface is additionally treated to impart roughness.

[0045] Although the invention has been described with reference to the disclosed embodiments, it will be apparent to those skilled in the art that the specific experiments described in detail are provided merely for the purpose of illustrating the present invention and should not be construed as limiting the scope of the invention in any way. It should be understood that various modifications are possible without departing from the spirit of the present invention.

Claims

CLAUSES OF THE INVENTION 1. A method for increasing the effective contact surface to reduce the transient contact resistance when implementing an electrical contact, comprising applying a conductive coating by spraying metal powder directly onto the surface of the contact connection of structural elements that ensure the transmission of high-power electrical energy, using a collaborative or industrial robot, characterized in that the contact surface is first abrasively processed to a surface roughness with an average arithmetic deviation of the profile of 0.5-10 μm, then the conductive coating is applied by spraying metal powder, with a low yield point and specific electrical resistance, directly onto the surface of the contact connection of structural elements that ensure the transmission of electrical energy, wherein the coating is applied at subsonic heterophase flow speeds of 50-5-270 m / s and its temperature of 20-5-280 °C,in this case, the consumption of powder of the sprayed metal is 1.8 g / min - 5- 60 g / min, then abrasive treatment of the contact surface of the coating is carried out to a surface roughness with an average arithmetic deviation of the profile of 0.5-5-10 μm, then the contacts are assembled using a bolted connection, and the contact pressure is less than or equal to the yield strength of the material of the applied coating.

2. The method according to claim 1, characterized in that the carrier of the heterophase flow is a heated working gas with an adiabatic index of 1.4-1.

6.

3. The method according to claim 1, characterized in that the powder of the sprayed metal is made of materials with low specific electrical resistance and yield strength, such as powder of tin, lead, bismuth, gallium and / or its alloys, as well as mixtures thereof.

4. The method according to claim 1, characterized in that the conductive coating is formed by applying layers of the coating sequentially, or in a gradient manner.

5. The method according to paragraph 1, characterized in that by applying a conductive coating, a bimetallic coating is formed on the surface of the contact area of ​​the connection of the busbar structure elements.

6. The method according to paragraph 1, characterized in that the reduction in the speed of the heterophase flow is carried out by increasing the distance of coating spraying, ensuring a reduction in the flow speed to 50-5-270 m / s and its temperature to 20-5-280 °C.

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