EP1602153B1 - Metal foaming material contact for electrical connections - Google Patents

Abstract

The improved life contact mechanism has two conductors (21,23) with an insertion element placed between the two conductor surfaces (22,24). The insertion element (10) is electrically conducting and made of several rubber materials having porosity and high deformability reducing electrical connection resistance.

Description

Technical area

The present invention relates to devices for improving and increasing the conductance of electrical connections and particularly relates to a contact device for improving the service life of electrical connections.

State of the art

In the field of power electrical engineering, the electrical connections of electrolysis tanks or steelmaking furnaces are subjected to currents of high intensity (I> 1000 A) and at high temperatures. This results in significant electrical losses of up to several KW per connection and the resulting loss of efficiency 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. It follows electric losses by Joule effect and by the same an increase in temperatures which accelerates the degradation of the connections but also the drivers 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 areas and points of contact. The contact areas being reduced, the connections then undergo electrical stresses concentrated on these areas and their degradation is even faster.

To recover the contact surfaces of the original connections, the total disassembly of the connections is necessary to re-machine the contact surfaces. But this operation is heavy and expensive.

JA-A-530805890n discloses a metal foam spacer for improving the conductivity of the connection in a capacitor. But this element is not suitable in the context of the invention which relates to the case of connections in which continuous currents of high intensity exceeding 1000 A.

Note that the document US Patent 5360355 discloses an intermediate conductive member having a peripheral seal but which is not made of metal foam.

Presentation of the invention

This is why the first object of the invention is to provide a contact device for electrical connections in order to improve the electrical conductance of these connections and to slow the degradation of the surfaces in contact.

Another object of the invention is to provide a contact device for improving the electrical connections in order to increase the electrical performance of these connections when they are in an advanced state of degradation.

A third object of the invention is to provide a contact device for improving the electrical connections subjected to currents of high intensity greater than 1000 A, to increase the electrical performance of these connections.

The object of the invention is therefore a contact device essentially comprising a conductive element adapted to be interposed between the two contact surfaces of two conductors of an electrical connection. The intermediate conductive element in which circulates a current of an intensity greater than 1000 A is made of silver foam of high porosity and deformability to reduce the electrical resistance of the connection. It also includes minus a peripheral seal creating a seal-proof barrier to external degrading agents at the periphery of the intercalating conductive element.

Brief description of the figures

• La figure la représente de façon microscopique une coupe transversale de la mousse de cuivre,
• La figure 1b représente une plaque de la mousse de cuivre selon un mode de réalisation de l'invention,
• La figure 2a représente une coupe de la connexion électrique selon l'invention avant le serrage,
• La figure 2b représente une coupe de la connexion électrique selon l'invention.

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

• Figure la shows a microscopic cross-section of the copper foam,
• The figure 1b represents a plate of the copper foam according to one embodiment of the invention,
• The figure 2a represents a section of the electrical connection according to the invention before tightening,
• The figure 2b represents a section of the electrical connection according to the invention.

Detailed description of the invention

With reference to the figure 1 the intermediate conductive element used in the device according to the invention is a metal foam 10 preferably manufactured according to the method described in the patent application. WO 02/059396 , it being understood that the device according to the invention is not limited to metal foams obtained by the process described in this document. The metal foam is preferably a copper foam. Its structure is alveolar and its physical properties are mainly a high porosity and deformability and a low density of the order of 400g / m ² . In comparison, the density of a copper sheet of the same thickness is of the order of 15 kg / m ² .

According to figure 1a which illustrates microscopically, schematically and not limiting a section of a copper foam plate 10 according to the invention, the honeycomb structure of the copper foam is such that it consists for the most part of vacuum. As a result, its surface comprises a multitude of contact points 11 of the order of one micron, the number of which reaches 30 points per mm ² . The thickness of the copper foam is of the order of 2 mm.

According to one of the embodiments of the invention, this copper foam constituting the intermediate conductive element according to the invention is cut to the size of the contact surface of the electrical connection described in FIG. figure 2 and has an opening 18 for the passage of the clamping bolt. The copper foam thus cut has two peripheral sealing seals 14 and 16. Peripheral seals 14 and 16 may be made in different ways. They may be impregnated in the foam or made by the removal of an elastomeric sealant on the periphery. But it is also possible to make joints by folding the edges of the foam plate at least once on itself or by rolling the edges of the foam plate.

The Figures 2a and 2b represent an electrical connection according to the invention. According to figure 2a , the conductors 21 and 23 are located on either side of the copper foam 10 so that their surfaces 22 and 24 come into contact with the copper foam. Thus, the copper foam is an intermediate element between the two conductors of the electrical connection. According to figure 2b , the electrical connection between the conductors 21 and 23 is made by close contact by means of a clamping means such as a clamping bolt 25 passing through the two conductors through a hole provided for this purpose and through the opening 18 of the foam of copper 10.

The device according to the invention can be used for a contact of a new electrical connection. In this case, it improves the homogeneity of the passage of the current through the surface in contact. Indeed, in an electrical connection represented for example by the two conductors 21 and 23 in contact with each other, the contact is even more important that it is located near the clamping means or clamping bolt 25. Therefore, the resistance and therefore the electrical losses of the electrical connection consisting of the conductors 21 and 23 in contact is minimal near the clamping means .25 and increases more away from it. This inhomogeneous distribution of the current favors a zone of higher current concentration and therefore a zone more solicited and therefore degraded-more-quickly. The provision of the intermediate conductive element made of copper foam increases the points of contact between the two conductors 21 and 23 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 so no areas more solicited and conducive to a faster degradation.

The device according to the invention can also be advantageously used for a contact of a degraded or deformed electrical connection. 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 in the flow of current through these contacting surfaces. The re-machining of deformed contact surfaces is no longer necessary thanks to the contribution of copper foam. There is thus obtained a significant improvement in the electrical connections having degraded and deformed contact surfaces 22 and 24, even in the case of deformations of the order of one millimeter. Indeed, the deformability of the copper foam allows the whole of the foam 10 to marry the degraded contours of the surfaces in contact 22 and 24, as described on the enlargement of the figure 2b and thus to increase the contact area and distribute the pressure exerted through the clamping means 25. In addition, the tips 11 on the surface of the copper foam multiply the points of contact. This results in improved current flow conditions by reducing electrical losses. In addition, the tips 11 on the surface of the copper foam also pierce the oxide layers that appear on the surface of the metals and therefore the conductors 21 and 23, such as copper oxide or alumina for example. 'aluminum. These layers have an insulating effect and act as resistors and therefore induce electrical losses. As a result, the device according to the invention makes it possible to improve the electrical conductance of a used connection even without first cleaning it.

The peripheral seal 14 and 16 makes it possible to reduce the penetration of degrading external agents into the connection by creating a sealed barrier at the periphery of the connection. Indeed, and in particular in the case of chlor-alkali electrolysis cells, the degrading agents are generally liquids such as sodium hydroxide or washing water or any other pollutant product transported by water.

Copper foam can be improved by removing a product that improves heat transfer and electrical conductivity. Thus, the use of a silver-plated copper foam as an intermediate conductive element improves the efficiency of the device according to the invention. Indeed, the potential drop of a connection of 1 dm ² formed of two copper conductors is of the order of 50 mV for a current of an intensity of 5000 A. With a copper foam, the potential drop decreases to 26 mV and with a silver copper foam, the potential drop is only 5 mV for identical temperature and pressure conditions in all three cases. The silver is deposited on the copper foam by a conventional electrochemical process or under vacuum.

The use of an interposed conductive element composed of a silver foam is also possible without departing from the scope of the invention.

The device according to the invention is all the more advantageous, it sees its efficiency increase with temperature. Indeed, the potential drop of a 1 dm ^{2 connection} using the device according to the invention with a silver copper foam is of the order of a few mV for a current of an intensity of 5000 A and the temperature of 300 ° C. This feature is due to the fact that the tips 11 of the metal foam (copper, silver copper or silver) are soldered under the effect of temperature to the conductors 21 and 23 with which they are in contact.

Although the metal foam is preferably used for the practice of the invention, any other conductive foam composed of one or more materials could be used.

The device according to the invention has many other advantages. Its implementation is fast, easy and clean. It is particularly advantageous for improving the conductance of copper / copper electrical connections but also for connections between two different electrical conductors such as aluminum / copper or steel / aluminum or steel / copper pairs.

By reducing the electrical losses it induces, the device according to the present invention makes it possible to slow down the degradation of the surface state of the electrical connections subjected to currents of high intensity.

The economic advantages of this device are the reduction of the costs due to the reduction of the electrical losses and due to the reduction of the maintenance and the maintenance. In addition, these interests are part of an energy saving policy dictated by environmental standards.

The use of the copper foam according to the invention is also conceivable to improve the thermal conductance of contact and thus avoid thermal losses due to the passage of heat from one material to another.

In addition, other applications are possible and generalizable to the electrical connections and the thermal transfer of electrical components such as diodes, thyristors, etc .... Similarly- to improve crimping lugs on aluminum conductors in the field of the automobile. Therefore, the use of the invention can be generalized to low-intensity electrical connections.

Tests have been carried out to highlight the performance of the metal foam according to the invention called ecocontact conductive foam. The tests were carried out on a connection of 100 mm per 100 mm degraded, that is to say whose contact surfaces are not perfectly flat. Four types of connection have been used with copper, aluminum, and accel for a current ranging from 1000 to 10000 A. The results reported in the table below show that the voltage drop measured at the connection is improved, thanks to ecocontact conductive foam from 82 to 91%. Comparative table of voltage drops between a degraded 100 mm x 100 mm bare connection and the same connection equipped with Ecocontact® conductive foam Voltage drops indicated in mV (mili Vdts) Intensity 1000A 2000A 5000 A 10000 A Copper / Copper Naked connection 20 80 145 280 With Ecocontacty conductive foam 5 10 26 55 Copper / Aluminum Naked connection 13 25 54 115 With Ecocontacty conductive foam 1.3 25 4.7 11 Copper / Steel Naked connection 47 100 210 405 With Ecocontacty conductive foam 11 23 58 118 Aluminum / Aluminum Naked connection 26 54 145 310 With Ecocontacty conductive foam 7 14 37 80

Claims (4)

1. A contact device comprising essentially a conductive insert adapted to be placed between the two contact surfaces (22 and 24) of two conductors (21 and 23) of an electrical connection, said conductive insert consisting of metallic foam (10) with high porosity and deformability and in order to reduce the electrical resistance of the connection;
   said device being characterised in that said conductive insert is silver foam in which flows a current greater than 1,000 A, and in that it includes at least a peripheral_seal (14 and 16) creating a hermetic barrier against external damaging agents along the periphery of said conductive insert.
2. The device according to claim 1, in which said conductive insert is placed between said conductors (21 and 23) whose surfaces (22 and 24) are degraded.
3. The device according to claim 1 or 2, in which said seal (14 and 16) is made by depositing an elastomer type sealing product along the periphery of said conductive insert.
4. The device according to claim 1 or 2, in which said seal (14 and 16) is made by at least a fold on the edge of said conductive insert.

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