EP2593990B1 - Electrical connection device having improved conductance - Google Patents

Description

The present invention relates to improving the conductance of electrical connections. It relates, in particular, a device for electrical connection between two metal conductors.

In all fields where metallic electrical connections are used, and in particular in the field of power electrical engineering, electrical connections in which two metals are brought into contact degrade over time. This results in significant electrical losses. The resulting loss of yield is a major problem. The degradation of these connections is irreversible. Indeed, the degradation of the surfaces in contact induces variations in the density of the current through this surface. This results in electric losses by the Joule effect and, consequently, an increase in temperatures, which accelerates the degradation of the connections but also of the conductors and can even lead to their fusion.

The maintenance of the connections requires disassembly to practice a re-surfacing of the areas in contact. The tools used for these re-surfacing are generally rotary grinding machines. They degrade the total flatness of the surfaces in contact, which has the effect of limiting, on the surface, the zones and the points of contact. The contact areas being reduced, the connections then undergo electrical stresses concentrated on these areas and their degradation is even faster.

In addition, for reasons of cost mainly, copper conductors are replaced today in all connections by aluminum conductors, metal which has electrical conductivity very close to that of copper while being much cheaper. The main disadvantage of aluminum being the formation of a layer of alumina that makes connectivity tricky in connections.

The French patent published under the number 2847391 discloses a contact device comprising a silver foam conductive element adapted to be interposed between the two contact surfaces of two conductors of an electrical connection. Unfortunately, the silver foam, besides being very expensive, does not sufficiently improve the electrical conductance connection and slow down the degradation of the connection device, especially when the device comprises at least one aluminum conductor.

One of the aims of the present invention is therefore to provide an electrical connection device which makes it possible to improve the electrical conductance of the connection and to slow the degradation of the surfaces in contact.

The subject of a first aspect of the invention is therefore an electrical connection device comprising two conductors each having a contact surface and a conductive element interposed between the contact surfaces of the conductors. The intermediate conductive member is an open cell foam skeleton of metal selected from the group consisting of iron, cobalt, nickel and their alloys directly coated with at least one coating of copper, tin, indium or one of their alloys.

In embodiments, the coating is a copper coating itself coated with a coating of tin, indium or an alloy thereof.

According to a second aspect, the present invention provides an electrical connection device comprising two conductors each having a contact surface and a conductive element interposed between the contact surfaces of said conductors, the intermediate conductive element being constituted by a skeleton of foam of open cell metal, in which the metal foam constituting the skeleton of the intermediate conductive element (10) is impregnated with grease.

According to a third aspect, the present invention relates to an electrical connection device comprising two conductors, each having a contact surface and a conductive element interposed between the contact surfaces of said conductors, the intermediate conductive element consisting of a skeleton of foam open-celled metal, wherein the metal foam constituting the skeleton of the intermediate conductive element forms a seal at the periphery of the contact surfaces.

According to a fourth aspect, the present invention is directed to a clamping system which comprises a clamping means adapted to bring two conductors around an interposed conductive element consisting of an open-cell metal foam skeleton for reducing the electrical resistance of the connection, the metal of the metal foam being selected from the group consisting of iron, cobalt, nickel and their alloys directly coated with at least one coating of copper, tin, indium or an alloy thereof.

According to a fifth aspect, the present invention is an electricity meter, which comprises an electrical connection device according to one of the first to third aspect of the present invention or a clamping system object of the fourth aspect of the invention.

According to a sixth aspect, the present invention is directed to a crimping lug lining, which comprises a conductive element consisting of an open cell metal foam skeleton for reducing the electrical resistance of the connection, the metal of the metal foam being selected from the group consisting of iron, cobalt, nickel and their alloys directly coated with at least one coating of copper, tin, indium or an alloy thereof.

Indeed, crimping presents the same problems as the other connections, problems discussed above.

According to a seventh aspect, the present invention aims a method of electrical connection of two conductors each having a contact surface, comprising a positioning step, facing one of the other of said contact surfaces, characterized in that it comprises a step of positioning, between said contact surfaces, an intermediate conductive element consisting of an open cell foam skeleton of metal selected from the group consisting of iron, cobalt, nickel and their alloys directly covered with less a coating of copper, tin, indium or one of their alloys.

• la figure 1 représente une coupe d'un mode de réalisation particulier du dispositif de connexion électrique selon l'invention,
• la figure 2 représente l'élément conducteur intercalaire du dispositif selon l'invention illustré en figure 1 et comportant un joint d'étanchéité périphérique,
• les figures 3A et 3B représentent, respectivement en vue de dessus et en vue de côté, un mode de réalisation particulier d'une cosse à sertir objet du sixième aspect de la présente invention, avant sertissage et
• la figure 4 représente, en vue de côté, la cosse à sertir illustrée en figures 3A et 3B, après sertissage et fixation sur un conducteur.

Other objects, objects and features of the invention will appear more clearly on reading the following description given with reference to the drawings in which:

• the figure 1 represents a section of a particular embodiment of the electrical connection device according to the invention,
• the figure 2 represents the interposed conductive element of the device according to the invention illustrated in FIG. figure 1 and having a peripheral seal,
• the Figures 3A and 3B are respectively a top view and a side view, a particular embodiment of a crimp terminal object of the sixth aspect of the present invention, before crimping and
• the figure 4 represents, in side view, the crimp terminal illustrated in FIG. Figures 3A and 3B , after crimping and fixing on a conductor.

First, we describe Figures 1 and 2 , a first aspect of the present invention. An electrical connection device according to the invention may be the device illustrated on the figure 1 . Two conductors 12 and 14 are separated by an intermediate conductive element 10 of metal foam so that their respective surfaces come into contact with the foam. The electrical connection between the conductors 12 and 14 is achieved by close contact by means of a clamping means such as a clamping bolt 16 passing through the two conductors as well as the intermediate conductive element 10.

In embodiments such as that illustrated in Figures 1 and 2 at least one of the conductors is aluminum. However, the present invention is not limited to this case and applies to all conductors, for example copper.

The metal foam of the spacer element 10 is an open cell foam composed of a metal foam skeleton selected from the group consisting of iron, cobalt, nickel and their alloys directly coated with at least one metal coating such as a coating of tin, indium or one of their alloys.

The skeleton of foam can be obtained by electrolysis. In this case, a plastic foam plate such as a polyurethane foam is made electrically conductive and is used as a cathode in an electrolytic bath, which allows to cover all the surfaces of the cells or open cells of the foam by a layer of metal.

A second method of obtaining the metal foam plate is to deposit the metal by the vacuum deposition technique.

A third method consists in a first step of activating the plastic foam by chemical deposition of a thin metal layer, followed by a second electrolysis step during which a layer of the same metal of adequate thickness is deposited by electrolysis.

After the deposition of the metal layer, the polyurethane is removed by a suitable method, for example by burning in an oven. Polyurethane burns and disappears, leaving only a skeleton made exclusively of metal.

The structure of the foam 10 thus obtained is alveolar and its physical properties are mainly a high porosity and deformability, which has the effect of reducing the electrical resistance of the connection, and a low density of the order of 400 g / m. It is noted that the porosity represents the void ratio on the total volume. Preferably, this ratio is greater than 50% and, even more preferentially, 70%. Deformability is the ratio of the minimum thickness of the foam under pressure to the thickness of the foam before pressurizing. This ratio is preferably less than 50% and, even more preferentially, 10%.

In the embodiment shown, the foam 10 is thus constituted mainly by vacuum because of its cellular structure. As a result, the surface of the foam 10 has a multitude of contact points of the order of one micron, the number of which reaches 30 points per mm ² . The thickness of the foam 10 is of the order of 2 mm. With these tips, the spacer element 10 has many contacts, high conductivity and therefore low resistance. The choice of iron, cobalt, nickel or one of their alloys, which are metals with a high degree of hardness, makes it possible to obtain hard points capable of penetrating the surface of the conductors under the effect of the clamping of these conductors. .

A feature of the invention is that the metal foam skeleton is directly covered with a coating of another metal, by electrolysis or any other method (spraying, immersion in a bath ...) so that the entire surface alveolar is coated with this other metal. Unlike the metal constituting the backbone, the coating metal is preferably ductile in order to increase the contact area of each point of the metal constituting the backbone, to penetrate the ridges of the conductor surface and to improve the electrochemical compatibility between the skeleton of foam and the metal of the conductor, for example aluminum or copper, for the purpose of generating micro-weldings. Thus, the metal of outer skin of the skeleton is preferably tin, indium or one of their alloys.

It will be noted that the first coating may also be covered with another coating of a metal different from that of the first coating, and so on. For example, if the first coating is tin, the second coating may be indium or, if the first coating is copper, the second may be tin.

According to a preferred embodiment of the invention, the intermediate conductive element 10 is composed of a nickel foam skeleton coated with a tin coating.

As illustrated on the figure 2 the spacer element 10 preferably comprises a peripheral seal 20. This peripheral seal 20 can be made in different ways. It can be impregnated into the foam or made by removing an elastomeric sealant on the periphery. It is also possible to make the seal 20 by folding the edges of the foam plate 10 at least once on itself or rolling the edges of the foam plate 10. Under the effect of the pressure, the thickness the foam plate becomes uniform, which implies that the density is at least doubled in the areas of folding of the foam, with the effect of producing the seal considered at the periphery of the intermediate conductive element 10.

The peripheral seal 20 makes it possible to reduce the penetration of degrading external agents by creating a tight barrier at the periphery of the contact. Indeed, and in particular in the case of electrolytic cells, the degrading agents are generally liquids such as sodium hydroxide or washing water or any other pollutant product transported by water.

The device according to the invention can be used for a new electrical connection. In this case, it improves the homogeneity of the flow of current through the surfaces in touch. Indeed, in an electrical connection, the contact is even more important that it is located near the clamping means or bolt 16. Therefore, the resistance, and therefore the electrical losses of the electrical connection consists of conductors 12 and 14 in contact, is minimal near the clamping means 16 and increases further away. This inhomogeneous distribution of the current favors a zone of higher current concentration and therefore an area more stressed and therefore degraded more quickly. The contribution of the intermediate conductive element 10 made of foam increases the points of contact between the two conductors 12 and 14 and thus allows a homogeneous distribution of the current over the entire contact surface. Thanks to this homogeneous distribution, there are no areas of concentration of current and therefore no zone more solicited and conducive to a more rapid degradation.

The device according to the invention can also be advantageously used for a contact of a degraded or deformed electrical connection. Thus, in the case of aluminum conductors, oxygen in the air causes the formation of an aluminum oxide layer, alumina, which increases the resistance of the connection. In order to avoid the formation of the alumina layer, in the prior art, it was thought to weld together the two conductors using an explosion welding method. But this technique is very expensive and difficult to implement. The use of the foam interlayer 10, after or without removal of the alumina, is fast and inexpensive.

In the field of electrolysis cells and steelmaking furnaces, the conductors and the electrical connections are subjected to currents of high intensity and high temperatures. The wear of the connections is concretized mainly by a deformation of the contact surfaces of the electrical connections. This results in significant electrical losses of up to several KW per connection and variations of the current flow through these contacting surfaces. The re-machining of the deformed contact surfaces is therefore no longer necessary using an intermediate conductive element 10 according to the invention.

This provides a significant improvement in electrical connections with deformed and deformed contact surfaces, even in the case of deformations of the order of a millimeter. Indeed, the deformability of the foam 10 allows it to conform to the degraded contours of the surfaces of the conductors 12 and 14 in contact and thus to increase the contact surface and to distribute the pressure exerted by the clamping means 16.

In addition, the tips located on the surface of the foam 10 also pierce the oxide layers such as alumina which form permanently on the surface of the conductors 12 and 14, which improves the electrical conductance of a used connection, even without cleaning it beforehand.

According to an alternative embodiment, the foam constituting the intermediate conductive element 10 is impregnated (charged) with grease which completely fills the cells of the foam, which prevents the penetration of pollutants or agents capable of oxidizing or degrade the surfaces. It is noted that the grease can be conductive, so as to increase the electrical conductance of the foam. Such a grease is, in particular, known under the trademark "Penetrox". In addition, this fat can incorporate anti-oxidation products and metal particles of a few microns increasing its life. Particles can be particles of silver, gold or any other metal that is a good conductor of electricity. Alternatively, the foam component of the intermediate conductive element 10 is impregnated or charged with a component, for example basic, adapted to reduce the formation of a high resistivity layer on the surface of at least one of the conductors 12 and 14, for example alumina on an aluminum conductor, and / or etching the surface of at least one of the conductors 12 and 14.

The device according to the invention is all the more advantageous as its efficiency increases with temperature. Indeed, the potential of a connection drop of 1 dm ² using the apparatus according to the invention with a nickel foam 10 of tin covered is of the order of several mV at a current of an intensity of 5000 A and at a temperature of 80 ° C. This feature is due to the fact that the tips of the foam 10 are welded under the effect of temperature to the conductors 12 and 14 with which they are in contact.

As already mentioned, the device according to the invention is particularly advantageous for improving the conductance of electrical connections in which the two conductors are aluminum, but also when one of the two conductors is copper and the other aluminum or when both conductors are copper.

Finally, by reducing the electrical losses that it induces, the device according to the present invention is particularly suitable for currents of high intensity greater than 1000 A.

Note that the use of resiliently deformable foam also has the advantage of reducing the impact of loosening clamping means since, in this case, the foam relaxes and continues to marry the contact surfaces, the lower pressure on these contact surfaces.

In embodiments, the intermediate conductive member 10 is made of an open-celled metal foam skeleton of high porosity and deformability, selected from the group consisting of iron, cobalt, nickel and their alloys coated directly with metal. at least one copper coating or one of its alloys.

Preferably, the copper coating is itself coated with a coating of tin, indium or one of their alloys. In particular, the inventor has determined that a copper-coated nickel foam, itself coated with tin, has very advantageous electrical connection characteristics.

According to a second aspect, the present invention provides an electrical connection device comprising two conductors, 12 and 14, each having a contact surface and a conductive element 10 interposed between the contact surfaces of said conductors, the intermediate conductive element 10 being constituted an open cell metal foam skeleton, wherein the metal foam constituting the skeleton of the intermediate conductive member 10 is impregnated with grease.

As we have seen, these features allow an improvement of the electrical connection.

Preferably, the fat is a conductive fat.

Preferably, the foam of the intermediate element has a high porosity and deformability, which has the effect of reducing the electrical resistance of the connection thanks to the quality of the contacts formed by the points of contact of the foam on each of the conductor and possibly, thanks to the crossing of the alumina that they allow.

According to a third aspect, the present invention provides an electrical connection device comprising two conductors, 12 and 14, each having a contact surface and a conductive element 10 interposed between the contact surfaces of said conductors, the intermediate conductive element 10 being constituted an open cell metal foam skeleton, wherein the metal foam constituting the skeleton of the intermediate conductive member 10 forms a seal at the periphery of the contact surfaces.

As we have seen, these features allow an improvement of the electrical connection.

According to a fourth aspect, the present invention aims at a clamping system comprising a clamping means, such as a clamping bolt 16, intended to bring the two conductors and the intermediate conductive element 10 closer together. positioning the conductors 12 and 14 around the intermediate conductive member and then clamping the clamping means to achieve the favorable effects of the present invention.

Other features of this second, third or fourth aspect of the invention are essential, preferred or advantageous features of the first aspect of the invention, as described with reference to Figures 1 and 2 .

According to a fifth aspect, the present invention is an electricity meter, which comprises an electrical connection device according to one of the first to third aspect of the present invention or a clamping system object of the fourth aspect of the invention. The inventor has determined that one out of two domestic fire starts from domestic meters. The implementation of the present invention in an electrical connection device associated with an electric meter is therefore particularly advantageous. Indeed, in spite of the thermal cycles, the elastic deformation of the foam 10 ensures the maintenance of an electrical contact avoiding, or at least delaying, the heating due to the Joule effect. The present invention thus applies as well in strong currents as in weak currents.

According to a sixth aspect, illustrated in Figures 3A, 3B and 4 the present invention is directed to a crimp lug liner and a crimp lug provided with such liner, which includes a conductive member 10 consisting of an open cell metal foam skeleton for reducing the electrical resistance of the connection, the metal foam metal being selected from the group consisting of iron, cobalt, nickel and their alloys directly coated with less a coating of copper, tin, indium or one of their alloys.

• une zone 30 à replier pour écraser un câble conducteur 40 et
• une zone de contact 32 destinée à être pressée sur un conducteur 42 par un moyen de serrage 44.

As illustrated in Figures 3A and 3B , in one embodiment, the crimping lug 28 which is the subject of the invention is, before crimping, constituted by a flat foam plate 10 comprising

• a zone 30 to fold to crush a conductive cable 40 and
• a contact zone 32 intended to be pressed on a conductor 42 by a clamping means 44.

For example, the conductor 42 is a battery terminal of a vehicle.

Preferably, the shape of the foam plate 10 corresponds to the shape of a metal plate 34 to which the foam plate is bonded. The foam plate 10 thus provides a crimping lug lining which, when associated with the metal plate 34 forms a crimp lug.

As illustrated in figure 4 after crushing of the zone 30 on the cable 40 and positioning of the clamping means, the lug ensures an electrical contact between the cable 40 and the conductor 42. This electrical contact has a very low resistance compared to the prior art known in the field of crimping. The other features and advantages of the invention set forth with reference to Figures 1 and 2 are also features and advantages of the crimp lug object of the sixth aspect of the invention.

Claims (12)

1. An electrical connection device comprising two conductors (12 and 14) each having a contact surface, a conductive element (10) inserted between the contact surfaces of said conductors, the inserted conductive element consisting of a metal foam skeleton with open cells intended to reduce the electrical resistance of the connection;
   said device being characterized in that the inserted conductive element consists of a foam skeleton of a metal chosen from the group consisting of iron, cobalt, nickel and the alloys thereof directly covered with at least one coating of copper, tin, indium or one of the alloys thereof.
2. The device as claimed in claim 1, in which the coating is a coating of copper or one of the alloys thereof, itself covered with a coating of tin, indium or one of the alloys thereof.
3. The device as claimed in one of claims 1 or 2, in which at least one of the two conductors (12 and 14) is made of aluminum.
4. The device as claimed in one of claims 1 to 3, in which the inserted conductive element (10) comprises a nickel foam skeleton.
5. The device as claimed in claim 4, in which the nickel foam skeleton is covered with a coating of tin.
6. The device as claimed in one of claims 1 to 5, in which a current of intensity greater than 1000 amperes circulates.
7. The device as claimed in one of claims 1 to 6, in which the inserted conductive element (10) comprises at least one seal (20) at its periphery creating a barrier that is tight to degrading external agents.
8. The device as claimed in claim 7, in which the seal (20) is produced by the deposition of a sealing product of elastomer type on the periphery of the inserted conductive element (10).
9. The device as claimed in claim 7, in which the seal (20) is produced by at least one folding-in of the edge of the inserted conductive element (10).
10. The device as claimed in one of claims 1 to 9, in which the metal foam forming the skeleton of the inserted conductive element (10) is impregnated with grease.
11. The device as claimed in claim 10, in which the grease is a conductive grease.
12. The device as claimed in one of claims 1 to 11, in which the metal foam forming the skeleton of the inserted conductive element (10) is impregnated with a component suitable for reducing the formation of a layer of high resistivity on the surface of at least one of the conductors (12, 14) and/or for cleaning the surface of at least one of the conductors.

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