EP2693447A1 - Method for manufacturing an electric cable comprising a hydrophobic coating - Google Patents

Abstract

The method involves forming an alumina porous hydroxide layer (2) having pores. An elongated electric conductive element (1) is positioned around the hydroxide layer, where the conductive element is made of aluminum or alloy from aluminum. The pores of the alumina porous hydroxide layer are partially filled with a hydrophobic material (3) that is selected among fluorinated polymers, esters and the fatty-acids. The aluminum hydroxide layer porous is partially dissolved in an acid solution including chromic acid and phosphoric acid to form a hydrophobic coating (4). An independent claim is also included for an electric cable.

Description

The present invention relates to a method for manufacturing an electric cable comprising a hydrophobic coating, and an electric cable obtained by said method.

It typically, but not exclusively, applies to high-voltage electrical transmission cables or overhead power transmission cables, well known under the OHL " OverHead Lines ".

More particularly, the invention relates to an electric cable capable of reducing the corona effect.

Overhead lines are traditionally made up of one or more bare electrical conductors, stretched over an appropriate set of towers. These lines are conventionally intended for the transport of electrical energy under an alternating high voltage (225 to 800 kV). Each electrical conductor has a diameter of a few centimeters and can be composed of several assembled metal son. Along the bare electric conductor, there is always an effect called corona effect. The corona effect indeed occurs on all electrical conductors and overhead lines, subjected to high voltage. As soon as the electric field on the surface of the electrical conductor, in particular depending on the local radii of curvature, becomes sufficiently large locally (ie greater than the ionization field of the humid air, of the order of 10 kV / cm, or even greater than the ionization field of dry air, of the order of 30 kV / cm), the air ionizes and forms around the electrical conductor a luminous crown.

In the operational configuration of the electrical conductor, one of the consequences of the corona effect is the production of noise when the driver is wet. Therefore, the electrical conductor can become a source of significant discomfort and inconvenience for those who are or remain in the vicinity of this type of driver. Indeed, under these conditions, the conductivity of the air increases, and because of this, it produces a more intense and more effective ionization. The corona effect also causes energy losses and can cause health risks related to electromagnetic radiation, acoustic noise and power losses.

In order to overcome this problem, one solution is to make the surface of the electrical conductor hydrophobic. The hydrophobicity of the surface makes it possible to prevent water retention at the level of the electrical conductor in order to reduce for example the formation of frost or the deposition of asperities on the outer surface of the electrical conductor, and thus to limit the phenomenon of effect crowned.

To do this, the document WO 2006/072648 proposes to surround an aluminum electrical conductor with a hydrophobic plastic coating such as a polymer wax, obtained by atomization.

However, the disadvantage of this type of hydrophobic coating is that it requires periodic surface reprocessing to ensure its effectiveness.

The object of the present invention is to overcome the drawbacks of the techniques of the prior art by proposing in particular a method of manufacturing an electrical cable comprising a hydrophobic coating to guarantee a significantly diminished corona effect while being easy to put implemented and having good stability over time.

1. i.former une couche d'hydroxyde d'alumine (i.e. hydroxyde d'oxyde d'aluminium) poreux comprenant des pores, autour dudit élément électriquement conducteur allongé,
2. ii.remplir au moins en partie les pores de la couche d'hydroxyde d'alumine poreux, par un matériau hydrophobe, et
3. iii.dissoudre partiellement la couche d'hydroxyde d'alumine poreux, de manière à former ledit revêtement hydrophobe.

The present invention relates to a method of manufacturing an electric cable comprising at least one elongated electrically conductive element, surrounded by a hydrophobic coating, characterized in that the method comprises the following steps:

1. i.forming a porous alumina hydroxide (ie aluminum hydroxide) hydroxide layer around said elongated electrically conductive member,
2. ii.filling at least a portion of the pores of the porous alumina hydroxide layer with a hydrophobic material, and
3. partially dissolving the porous alumina hydroxide layer so as to form said hydrophobic coating.

With the method of the invention, a hydrophobic coating can be easily formed around the surface of at least one electrically elongated conductor, while having a very good long-term chemical stability not requiring in particular surface reprocessing. The corona effect of the electric cable thus formed advantageously decreases significantly.

In the present invention, the term "hydrophobic" means a coating or a layer whose surface has a contact angle (or drop angle) strictly greater than 90 °, and preferably at least 110 °.

The measurement of the contact angle accounts for the ability of a liquid to spread over a surface by wettability. The method consists in measuring the angle of the tangent of the profile of a drop deposited on the coating or the layer, with the surface of the coating or of the layer.

This contact angle is typically measured using a goniometer at 25 ° C using distilled water.

Step i

The porous alumina hydroxide layer surrounding the elongated electrically conductive member is preferably a layer that is in direct physical contact with the elongate electrically conductive member. In other words, the electrical cable thus formed does not preferably comprise a layer interposed between the porous alumina hydroxide layer and the electrically conductive element.

In a particularly advantageous embodiment, step i is an anodizing step, especially when the elongated electrically conductive element is an aluminum or aluminum alloy element.

Anodizing is a surface treatment (of conversion type) which makes it possible to form, by anodic oxidation, from the electrically conductive element, the alumina hydroxide layer. Thus, the anodizing will consume a portion of the electrically conductive element to form said alumina hydroxide layer.

During anodization, the alumina hydroxide layer is formed from the surface of the electrically conductive element towards the core of said electrically conductive element, unlike an electrolytic deposition.

Anodizing is conventionally based on the principle of electrolysis of water. It consists of immersing the electrically conductive element in an anodizing bath, said electrically conductive element being placed at the positive pole of a DC generator.

The anodizing bath is more particularly an acid bath, preferably a phosphoric acid bath or a sulfuric acid bath. These are respectively phosphoric anodizing or sulfuric anodizing.

In step i, when the porous alumina hydroxide layer is advantageously formed by anodization, the current density applied for the anodization may be at most 10 A / dm ² , preferably may be 0, 5 to 6 A / dm ² , and particularly preferably may range from 1 to 4 A / dm ² .

This current density makes it possible to guarantee that a sufficient quantity of pores has been formed during step i. Said pores may be ordered or unordered pores.

Step ii

In a particular embodiment, step ii is a step in which the elongated electrically conductive member coated with said porous alumina hydroxide layer may be immersed in a solution of said hydrophobic material.

By way of example, the hydrophobic material may be chosen from fluorinated polymers, such as, for example, a polytetrafluoroethylene (PTFE), esters and fatty acids, or a mixture thereof.

In a particularly advantageous embodiment, the pores of the porous alumina hydroxide layer are preferably not completely filled with the hydrophobic material. In other words, the hydrophobic material does not completely cover the alumina hydroxide layer. porous. Indeed, it is not necessary to fill the pores completely for several reasons.

The first reason is the saving of hydrophobic material that can be achieved.

The second reason is with regard to the dissolution step iii which can lead to dissolving, in addition to the porous alumina layer, the hydrophobic material.

The third reason is that, even if the drop angle is well above 90 °, thus proving the hydrophobic character of the coating, the drop is said to be "sticky" because it tends to adhere to the surface of the hydrophobic coating.

The person skilled in the art will be able to play on various parameters, such as the particle size or the size of the powder of the hydrophobic material, the concentration of the hydrophobic material in the solution, the temperature of the solution, the impregnation time, in order to fulfill the least partially said pores, and in particular so as not to fill them completely.

• si il n'y a pas de matériau hydrophobe dans les pores, l'angle de contact sera alors inférieur à 90° : le revêtement ne sera alors pas considérer comme hydrophobe;
• si le matériau hydrophobe rempli partiellement les pores, sans les remplir en totalité, l'angle de contact sera alors supérieur à 90° et la goutte aura tendance à glisser à la surface du revêtement hydrophobe: le revêtement obtenu sera donc bien hydrophobe ;
• si le matériau hydrophobe rempli totalement les pores, l'angle de goutte sera alors supérieur à 90°, mais la goutte sera dite « collante » car elle aura tendance à adhérer à la surface du revêtement hydrophobe, ce qui n'est pas le mode de réalisation préféré de la présente invention.

It will be easy to verify the hydrophobic character of the hydrophobic coating, and more particularly of the (outer) surface of the hydrophobic coating, by measuring the drop angle, namely:

• if there is no hydrophobic material in the pores, the contact angle will then be less than 90 °: the coating will not be considered as hydrophobic;
• if the hydrophobic material partially filled the pores, without filling them completely, the contact angle will then be greater than 90 ° and the drop will tend to slip on the surface of the hydrophobic coating: the coating obtained will therefore be hydrophobic;
• if the hydrophobic material completely fills the pores, the drop angle will then be greater than 90 °, but the drop will be called "sticky" because it will tend to adhere to the surface of the hydrophobic coating, which is not the mode preferred embodiment of the present invention.

When the hydrophobic material completely fills the pores, it means in particular that said pores are filled homogeneously with a more than 90% filling of the pore volume by the hydrophobic material, and preferably 100% of the pore volume by the hydrophobic material.

Step iii

In step iii, the hydrophobic coating formed is in particular an alumina hydroxide layer comprising on its surface protuberances (i.e. protuberances) of said hydrophobic material.

Thus, during the dissolution of the alumina hydroxide, the alumina hydroxide is dissolved partially, but not completely, in order to keep enough alumina hydroxide in order to ensure good adhesion of the hydrophobic material to the alumina hydroxide. electrically conductive element, thanks to the layer of alumina hydroxide.

The dissolution of the alumina hydroxide is also sufficient to obtain the hydrophobic properties of the hydrophobic coating, so as to obtain a coating with a contact angle strictly greater than 90 ° (measured using a goniometer, at 25 ° C, with distilled water). More particularly, the dissolution of the alumina hydroxide in step iii is sufficient to allow the hydrophobic material to form protuberances flush with the surface of the hydrophobic coating.

In a preferred embodiment, step iii is a step in which the porous alumina hydroxide layer is dissolved in an acidic solution. Those skilled in the art may vary the acid concentration of said solution and the temperature of said solution to affect the dissolution kinetics of the porous layer.

By way of example, mention may be made, as acid solution, of a solution comprising chromic acid and phosphoric acid.

Those skilled in the art will readily be able to determine the proper immersion time and solution temperature in order to dissolve the necessary amount of the alumina hydroxide layer to achieve the hydrophobicity of the surface of the hydrophobic coating.

In a particularly advantageous embodiment, the hydrophobic coating of the electric cable of the invention is the most outside the electrical cable. This coating is therefore in direct contact with the external environment of the electric cable. In other words, the electrical cable formed in step iii preferably has no element surrounding the hydrophobic coating.

Concerning the elongate electrically conductive element of the invention, it is intended for the transport of energy (i.e. high voltage electrical transmission).

It may preferably be metal, especially based on aluminum, namely either only aluminum or aluminum alloy such as for example aluminum alloy and zirconium.

Aluminum or aluminum alloy has the advantage of having a significantly optimized electrical conductivity / specific weight pair, particularly with respect to copper.

The electrically conductive element of the invention may conventionally be an assembly of wires (or strands) of metal whose cross section may be of round shape or not, or a combination of both. When they are not round, the cross section of these son may be for example of trapezoidal shape or "Z" shape. The different types of form are defined in IEC 62219.

The electrically conductive element may be positioned preferentially in the center of the electric cable or coaxially with the longitudinal axis of the electric cable.

In a particular embodiment, the elongated electrically conductive element has not undergone treatment intended to structurally modify the state of its outer surface, in particular to increase the surface roughness, prior to step i.

By way of example, there may be mentioned as a treatment intended to structurally modify the state of its external surface a physical etching such as the application by press of a pattern, directly on the outer surface of said conductive electrical element, or an etching chemical such as oxidative etching.

1. a. dégraisser l'élément électriquement conducteur, et/ou
2. b. décaper l'élément électriquement conducteur.

The method of the invention may further comprise at least one of the following steps, prior to step i:

1. at. degreasing the electrically conductive element, and / or
2. b. etch the electrically conductive element.

Preferably, step a and step b can be performed concomitantly.

• c. neutraliser l'élément électriquement conducteur.

Moreover, the method of the invention may furthermore comprise the following step, prior to step i:

• vs. neutralize the electrically conductive element.

In a particularly preferred embodiment, the method of the invention may comprise said three steps a, b and c, step c being performed after steps a and b.

Step a

The purpose of the degreasing step is to eliminate the various bodies and particles contained in the greases that may be present on the surface of the elongated electrically conductive element.

It can be performed chemically or electrolytically.

By way of example, the degreasing step a may be carried out by at least partially immersing the electrically conductive element in a solution comprising at least one surfactant as a degreasing agent.

Step b

The pickling step serves to remove oxides that may be present on the surface of the elongate electrically conductive member. There are several methods of stripping: chemical, electrolytic or mechanical.

Preferably, it will be possible to use a chemical etching consisting in removing the oxides by dissolution, or even bursting of the oxide layer, without attacking the material of the underlying electrically conductive element.

By way of example, the stripping step b may be carried out by at least partially immersing the electrically conductive element in a solution comprising a base as a stripping agent.

When step a and step b are performed concomitantly, a single solution comprising a degreasing agent and a etchant may be used to both etch and degrease the electrically conductive element.

Step c

The neutralization step makes it possible to condition the electrically conductive element, before the deposition of step i is carried out.

More particularly, when step i is an anodizing step, step c of neutralization consists in conditioning the electrically conductive element by plunging it at least partially into a solution identical to the anodizing bath provided in step i in order to put the surface of the electrically conductive element at the same pH as the anodizing bath of step i.

This solution also makes it possible, on the one hand, to eliminate certain traces of oxides that can hinder anodization, and on the other hand to eliminate any residues of the etchant agent. Neutralization makes it possible to put the surface of the aluminum at the same pH as the anode bath.

By way of example, the neutralization step c can be carried out by at least partially immersing the electrically conductive element in a solution comprising an acid as neutralizing agent.

Another object of the invention is an electric cable obtained from the method as described above.

More particularly, the electrical cable of the invention comprises at least one elongated electrically conductive element, surrounded by a hydrophobic coating, characterized in that the hydrophobic coating is an alumina hydroxide layer comprising on its surface protuberances (ie protrusions) of said hydrophobic material. In other words, the hydrophobic material does not completely cover the alumina hydroxide layer.

The electric cable according to the invention may have an apparent diameter (i.e. outer diameter) ranging from 10 to 100 mm.

The electrical cable of the invention may be more particularly a high-voltage electrical transmission cable, in particular of high-voltage overhead line (OHL) type of at least 225 kV and up to 800 kV. This type of cable is usually stretched between two pylons.

By way of example, the electrical cable of the invention may comprise an elongated central element of the electrically conductive element type and / or reinforcement element, this elongated central element being surrounded by a first elongated element of the elongated electrically conductive element type surrounded by the hydrophobic coating according to the present invention. In addition, the electrical cable may comprise a second element of the elongated electrically conductive element, positioned between the central element and the first element: the first element then surrounds the second element. The element or elements surrounding the elongated central element may be positioned coaxially around said elongate central element.

• La figure 1 représente de façon schématique la succession des étapes du procédé de fabrication selon l'invention.
• La figure 2 représente une imagerie FEG (Field Emission Gun) d'une coupe transversale d'un fil en aluminium traité par anodisation phosphorique.
• La figure 3 représente de façon schématique un câble électrique, en coupe transversale, obtenu selon le procédé de l'invention.
• La figure 4 représente de façon schématique un autre câble électrique, en coupe transversale, obtenu selon le procédé de l'invention.

Other features and advantages of the present invention will appear in light of the examples which follow with reference to the annotated figures, said examples and figures being given for illustrative and not limiting.

• The figure 1 schematically represents the succession of steps of the manufacturing method according to the invention.
• The figure 2 represents an FEG ( Field Emission Gun ) imaging of a cross section of an aluminum wire treated by phosphoric anodizing.
• The figure 3 shows schematically an electric cable, in cross section, obtained according to the method of the invention.
• The figure 4 schematically represents another electric cable, in cross section, obtained according to the method of the invention.

For the sake of clarity, the same elements have been designated by identical references. Similarly, only the essential elements for understanding the invention have been shown schematically, and this without respect of the scale.

The figure 1 illustrates the schematic representation of the succession of steps i, ii and iii, of the method of the invention.

By way of example, an aluminum wire with a diameter of 3 mm will be anodized (step i) by forming an alumina hydroxide layer all around said wire, by phosphoric anodization (8-30% by weight). phosphoric acid in distilled water) at room temperature (ie 25 ° C), under the application of a current density of between 1 and 4 A / dm ² . The aluminum wire obtained is thus covered with a layer of porous alumina hydroxide. This coated aluminum wire is shown in cross-section on the figure 2 .

Then, the hydrophobic material (step ii) will be implanted in the pores of the porous alumina hydroxide layer by dipping the aluminum wire coated with said porous alumina hydroxide layer in a solution of PTFE ( 1-5% by weight of PTFE in distilled water) at room temperature (ie 25 ° C) for 15 minutes.

Finally, the porous alumina hydroxide layer will be partially dissolved (ie not completely) by immersing the wire obtained in the previous step (see step ii) in an acidic solution comprising acid. phosphoric acid (3-6% by weight of phosphoric acid in distilled water) and chromic acid (1-2% by weight of chromic acid in distilled water) at a temperature of between 30 and 60 ° C, the dissolution rate being 0.5 μm / min at 30 ° C, to form a hydrophobic coating.

The surface of the hydrophobic coating obtained has contact angles of the order of 130-140 °, measured with distilled water using a goniometer, at 25 ° C.

Prior to step i, it is preferable first of all to strip and degrease said aluminum conductive wire (step not shown), by immersing it in a solution of soda and surfactants such as, for example the GARDOCLEAN referenced solution marketed by CHEMETALL (30-50 g / L sodium hydroxide) at 40-60 ° C for 30 seconds. Then, the conductive wire is immersed in a solution of sulfuric acid (20% by weight of sulfuric acid in distilled water) for the neutralization step (step not shown), at ambient temperature (ie 25 ° C. ) for 10 seconds.

In order to schematically visualize the hydrophobic coating formed according to the process described above, the figure 3 has a cross section of an electric cable 10a obtained according to the method of the invention, wherein the elongated electrically conductive element 1 is covered with said hydrophobic coating 4. This hydrophobic coating 4 comprises a layer of alumina hydroxide 2 and protuberances of hydrophobic material 3 flush with the surface of said layer of alumina hydroxide 2.

The figure 4 represents for its part another electric cable 10b of OHL type, obtained according to the method of the invention.

This OHL cable comprises a first elongated electrically conductive element 1 covered by said hydrophobic coating 4. This hydrophobic coating 4 comprises a layer of alumina hydroxide 2 and protrusions of hydrophobic material 3 flush with the surface of said hydroxide layer. alumina 2.

In addition, the electrical cable 10b comprises an electrically conductive and / or reinforcing elongated central element 5, surrounded by a second elongate electrically conductive element 6, the first element 1 surrounding the second element 6.

Claims (13)

A method of manufacturing an electric cable comprising at least one elongate electrically conductive element (1), surrounded by a hydrophobic coating (4), characterized in that the method comprises the following steps: i. forming a porous alumina hydroxide layer (2) comprising pores around said elongate electrically conductive member, the electrically conductive member being an aluminum or aluminum alloy member, ii. at least partially filling the pores of the porous alumina hydroxide layer (2) with a hydrophobic material (3), and iii. partially dissolving the porous alumina hydroxide layer to form said hydrophobic coating (4). Process according to claim 1, characterized in that step i is an anodizing step. Process according to Claim 2, characterized in that the current density applied for the anodisation is at most 10 A / dm ² . Process according to claim 2 or 3, characterized in that step i is a phosphoric or sulfuric anodizing step. A method as claimed in any one of the preceding claims, characterized in that step ii is a step in which the electrically conductive element coated with said porous alumina hydroxide layer is immersed in a solution of said hydrophobic material. Process according to any one of the preceding claims, characterized in that hydrophobic material (3) of step ii is chosen among fluorinated polymers, esters and fatty acids, or a mixture thereof. A process according to any one of the preceding claims characterized in that step iii is a step in which the porous alumina hydroxide layer is dissolved in an acidic solution. Process according to claim 7, characterized in that the acid solution comprises chromic acid and phosphoric acid. Method according to one of the preceding claims, characterized in that the hydrophobic coating (4) is the outermost layer of the electric cable. Method according to any one of the preceding claims,
characterized in that the electrically conductive element (1) has not undergone treatment to structurally change the state of its outer surface, prior to step i. Electric cable obtained from the process as defined in
Claims 1 to 10, comprising at least one elongate electrically conductive element (1), surrounded by a hydrophobic coating (4), characterized in that the hydrophobic coating is an alumina hydroxide layer comprising on its surface protuberances of said material hydrophobic (3). Electrical cable according to claim 11, characterized in that it is a
high voltage electrical transmission cable. Electrical cable according to claim 12, characterized in that
comprises an elongated central member of the electrically conductive member type and / or reinforcing member, said elongated central member being surrounded by a first elongate electrically conductive member member surrounded by said hydrophobic coating.

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