EP0568415B1 - Insulating method of an electrical conductor and insulated electrical wire obtained by this method - Google Patents

Abstract

The invention relates to a method of insulating electrical conductors. This method is characterised in that it comprises the following steps: a) a layer of a polymer varnish in a solvent and/or diluent medium is deposited on the said conductor; b) then, a powder of a mineral insulation is deposited uniformly over the said layer of varnish in such a way that the said powder adheres to the varnish; and c) the electrical conductor thus coated is subjected to an operation for drying and polymerising the varnish. <IMAGE>

Description

The present invention relates to a method of insulating an electrical conductor and the insulated electrical conductor wire as obtained by the implementation of said method.

More specifically, the present invention relates to the insulation of electrical conductors intended in particular to produce windings of electrical equipment, for example motor windings, in which the insulation is carried out initially on the conductor before it is wound on a support. storage. The conductor thus isolated is then used as an insulated conductor by already known methods.

The electrical conductor wires intended to make the windings of electrical equipment are generally previously isolated by enameling or wrapping or else enameling followed by wrapping.

Enamelling is generally carried out by depositing synthetic polymers in solution in an organic solvent medium. The deposition is carried out in several calibrated layers, each layer being dried and polymerized before the deposition of the next layer by passage through an oven at high temperature of the order of 400 to 500 ° C. The dielectric strength of the insulation thus deposited varies from 60kV per millimeter to 130kV per millimeter depending on the thickness of the polymer called enamel or varnish.

The thermal resistance of this insulator also varies according to the nature of the organic polymer used and does not make it possible to respond to uses in the case where the conductor is subjected to very high stresses, at the same time thermal, electrical and mechanical. Indeed, the electro-dynamic forces, the potential gradients or even the centrifugal forces in the case of windings of rotating machines induce significant stresses on the winding wires in contact which, combined with the increase in operating temperature due to overheating by Joule effect and electromagnetic losses, can cause a short circuit between the wires of the winding thus produced.

In the case of significant mechanical stress, this phenomenon is linked to a creep of the enamel under temperature and pressure which can be simulated by a standardized test called thermoplasticity. This consists of exercising a pressure defined at the intersection of two electrically tensioned wires arranged perpendicularly for a determined period and to repeat the test at different temperatures to determine at what temperature a short circuit occurs.

Under these test conditions, the most efficient enamels to date among those commonly used allow to obtain a thermo-plasticity of the order of 400 ° C to 500 ° C, which, in applications with high thermal stresses and mechanical, remains insufficient due to the absence of mineral matter in the insulation material.

In the case where there are higher electrical stresses corresponding to the medium or to the high voltage. Enamel is most often not used alone but combined with other insulating materials.

One of the reinforcing methods commonly used to overcome these drawbacks consists in covering the enamelled wire, that is to say in winding in the form of a spiral a sheet of continuous fibers impregnated with a polymer in an organic medium. Among the fibers commonly used, mention may be made, for example, of glass fibers or mixtures of glass fibers and polyester fibers.

The covering can also be directly deposited on an unglazed conductor when the operating conditions allow it. It therefore has not only the advantage of improving the connection with the impregnation varnishes of the windings, but, for given specific applications, the presence of a mineral product increases its resistance to high thermal stresses. Compared to enameled winding wire alone, the mineral product increases resistance to intense occasional overloads but limited in duration and increases the safety margin when temperatures occasionally reach 400 to 500 ° C under high mechanical stress.

One solution to improve the electrical insulation would be to add insulating mineral products in enamel varnishes, for example mica. However, this addition would involve certain implementation difficulties: in fact, it is technically excluded to incorporate mineral products with a high concentration in the enamelling varnishes because the phenomena of settling of the charge, on the one hand, and the weak extra thicknesses of calibrated deposits on each layer, on the other hand, (0.01 to 0.02 mm) would not make it possible to obtain regular insulation in composition and thickness according to the different points of the surface of the conductor to be insulated.

It has also been proposed to deposit electrophoresis of the enamel charged with a mineral material such as mica. Such a solution is described in particular in documents US-A-4,058,444, WO-A-89/100765 and FR-A-2,555,599 which all aim to isolate electrical connections by means of a composition consisting of a binder and mica powder in an aqueous medium and deposited by electrolysis. This process, which is difficult to implement continuously, is well suited for shaped parts or windings already made and difficult to insulate, but it is a delicate implementation for the insulation of electrical conductors intended to be wound later on. a storage medium.

To overcome these drawbacks, an object of the present invention is to provide a method which effectively allows the production of electrical insulation comprising mineral insulating materials and which is compatible with a process of insulating the electrical conductor continuously.

• a) de déposer sur ledit conducteur une couche de vernis polymère en milieu solvant et/ou diluant;
     se caractérise en ce qu'il comporte en outre les étapes suivantes :
• b) on produit un nuage localisé de poudre de particules d'un matériau minéral isolant;
• c) on déplace de façon continue ledit conducteur revêtu de la couche de vernis à travers ledit nuage de poudre, par quoi lesdites particules adhèrent à ladite couche de vernis pour former une couche isolante;
• d) on soumet le conducteur électrique ainsi revêtu à une opération de séchage et de polymérisation du vernis.

To achieve this goal, the method of isolating an electrical conductor, according to the invention which comprises the step

• a) depositing on said conductor a layer of polymer varnish in a solvent and / or diluent medium;
  is characterized in that it further comprises the following stages:
• b) a localized cloud of powder of particles of an insulating mineral material is produced;
• c) moving said conductor coated with the layer of varnish continuously through said cloud of powder, whereby said particles adhere to said layer of varnish to form an insulating layer;
• d) the electrical conductor thus coated is subjected to a drying and polymerization operation of the varnish.

It is understood that the method according to the invention effectively allows in-line insulation of the electrical conductor. Indeed, the production of the layer of varnish is made according to conventional means online and the deposition of the mineral insulating powder can conveniently also be carried out in a second step in line in particular using spray nozzles or powder transfer techniques by electrostatic field. We also notice that, like the electrical conductor is not used as an electrode in the insulation process, the method can be used interchangeably depending on whether the electrical conductor is already insulated with enamel or whether it is bare.

Preferably, steps a), c) and d) are repeated several times until the desired thickness of insulation is obtained.

The deposition of the layer of mineral insulation powder is carried out by producing a suspension or a cloud of this powder in an area crossed by the wire to be insulated. This is the meaning to be given to the term spraying in this text as opposed to electrolytic deposition techniques.

Another object of the invention is to provide an insulated electrical conductor wire having insulation of the type obtained by implementing the method according to the invention.

• la figure 1 est une vue en coupe transversale d'un conducteur électrique isolé selon un premier mode de mise en oeuvre de l'invention ;
• la figure 2 est une vue similaire à celle de la figure 1 mais montrant un deuxième mode de mise en oeuvre du procédé selon l'invention ;
• la figure 3 illustre un premier mode de réalisation du dépôt de la poudre de matériau isolant ; et
• la figure 4 illustre un deuxième mode de dépôt de la poudre de matériau isolant selon l'invention.

Other characteristics and advantages of the present invention will appear better on reading the following description of several embodiments of the invention given by way of nonlimiting examples. The description refers to the appended figures in which:

• Figure 1 is a cross-sectional view of an insulated electrical conductor according to a first embodiment of the invention;
• Figure 2 is a view similar to that of Figure 1 but showing a second embodiment of the method according to the invention;
• FIG. 3 illustrates a first embodiment of the deposition of the powder of insulating material; and
• FIG. 4 illustrates a second method of depositing the powder of insulating material according to the invention.

Before describing in detail, different modes of implementing the invention, we will describe the principle.

According to the invention, the electrical insulation of the electrical conductor is carried out in three basic steps. First, the electrical conductor is coated with a layer of polymer varnish in an organic solvent medium or not and / or in a reactive diluent medium. In a second step, the electrical conductor thus covered with varnish is subjected to a spray of a powder of insulating mineral material. This powder adheres to the varnish which has just been deposited, thus achieving a homogeneous layer of mineral insulator since the maintenance of the mineral insulator on the electrical conductor can only be done in direct contact with the layer of varnish initially deposited. In a third step, the electrical conductor thus coated with the initial layer of varnish and the layer of mineral insulation is subjected to a drying and polymerization treatment of the varnish in order to stabilize the assembly. Depending on the desired insulation thickness and therefore the desired insulation characteristics, these three operations are repeated successively.

Referring first to Figure 1, we will describe a first embodiment of the invention. From a bare electrical conductor 12, which can have a circular or rectangular section and be made of copper, aluminum, etc., a first layer of insulating varnish 14 in polymer is produced in an organic or aqueous solvent medium or in an active diluent medium. As varnish, one can use all the varnishes known in the field of the use of insulation of the winding wires. Among these, mention may be made, for example, of varnishes based on modified or unmodified polyester, polyesters, epoxies, polyamide-imides, polyimides, polyurethanes or varnishes based on polyvinyl acetoformal. These varnishes can be applied by conventional techniques, that is to say by passing the conductive wire 12 through the varnish bath, then by calibrating the layer. In a second step, the conductive wire 12 coated with its layer of varnish 14 is made to move in a medium where a powder of mineral insulating material, preferably mica, is present in suspension. The particles adhering to the layer of varnish 14 form a regular uniform layer of particles of mica 16. It is understood that, in fact, only the first layer of particles of mica can adhere to the layer of varnish 14, which allows deposition uniform mineral insulation. Preferably, the mica is in the form of a powder obtained by grinding and it can be of the muscovite or phlogopite type. The average particle size can vary in the particle cleavage plane from 0.05 mm to 0.8 mm and more. Preferably, the maximum dimension in the cleavage plane is 0.4 mm. This maximum dimension is an average dimension corresponding to the statistical dispersion of the particles actually obtained during the operation for preparing the powder. The final content of the mica can be between 10 and 90% of the insulation part thus produced. Preferably, this content is between 40 and 60%. Once this first deposit has been made, a second deposit of varnish layer 18 is carried out, as indicated previously, then a second deposit 20 of a layer of mica, as has already been explained. To complete the production of the insulation, an external layer of insulation can be deposited using the varnish already mentioned, this layer bearing the reference 22. Optionally, several layers of varnish can be deposited successively.

The deposition of the layer of mineral insulation, typically mica, on the electrical conductor 12 already provided with a layer of varnish 14 can be carried out in different ways. FIG. 3 illustrates a first mode of implementation. In this figure, there are shown two spray nozzles 24 and 26 connected to sources of mica in the form of powder and thus allowing circulation in the direction F of the conductive wire 12 inside a cloud of mica powder in suspension. Thus, as already explained, only one layer of mica adheres to the varnish 14, the rest of the mica being unable to adhere to the first layer of insulation mica already obtained.

FIG. 4 illustrates a second mode of deposition of the layer of mica powder. According to this second embodiment, the conductive wire 12 already covered with the layer of varnish 14 circulates in an area 30 in which an atmosphere saturated with mica powder is created by the following means. The mica powder 32 is placed in a hopper 34 open at its lower end 36. The hopper 34 is associated with a vibration generator 38 constituted for example by a wheel 40 associated with a connecting rod 42 which is connected to the hopper 34 by l 'Intermediate of an elastic damping system 44. This causes the progressive descent of the mica powder 32 towards the outlet 36. The creation of the cloud of mica powder in the zone 30 is obtained by the creation of an electrostatic field. For this, preferably, the walls of the hopper 32, which have the general reference 46, are made of an electrically conductive material and the hopper is fixed to an insulating frame 48. A plate opposite the hopper 34 conductive 50 perpendicular to the frame 48 defines the area of creation of the mica cloud 30. The wall 46 of the hopper 34 and the plate 50 are connected to the terminals 52a and 52b of an electric generator 52. The two electrodes formed by the wall 46 and the plate 50 thus define an electric field E which causes displacement of the mica particles in the zone 30. These mica particles adhere to the layer 14 of varnish formed on the conductive wire 12. Preferably, the deposition installation mica powder comprises two modules identical to those shown in Figure 4 but corresponding to electrostatic fields for driving the particles in two opposite directions. This operation associated with the initial deposition of a layer of varnish can be repeated as many times as necessary to obtain the desired thickness of insulation. As already indicated, after each step of depositing a layer of varnish and forming a layer of mica, the electrical conductor is subjected to a heat treatment in order to dry the varnish and polymerize it. this in order to obtain stabilization of the insulating coating. It is important to note that other techniques for spraying mica powder or other mineral insulators on the conductive wire coated with varnish could be used provided that these techniques allow adhesion on the varnish layer of a layer homogeneous uniform of mica or other equivalent mineral insulation. One could for example use a fluidized bed technique.

It is understood that, since the conductive wire to be insulated is not used as an electrode unlike the techniques used most often previously, the electrical conductor can be initially not bare but covered with an initial layer of enamel or a layer covering as shown in FIG. 2. Next, successive depositions of layers of varnish and layers of mica particles are carried out, followed by suitable heat treatment. In particular, this process can be used with an enameled conductive wire whose thermal index is preferably greater than or equal to 180 ° C. As a variant, the method can be implemented on a conducting wire initially covered with a covering layer 60 as defined above. In the latter case, the aim is no longer to provide insulation under preferential economic conditions but to reinforce the proportion of inert materials with a material such as mica known for its good resistance to the corona effect. The outer layer 62 can also be produced by covering.

• teneur en mica de l'isolation :    48 à 52%
• surépaisseur d'isolation :    0,16 à 0,20 mm
• thermoplasticité selon la méthode normalisée CEI supérieure à 500°C
• tension de claquage :    2,5 à 3,3kV par mm
• souplesse de l'isolation : on n'a observé aucune fissuration lors du bobinage du fil sur un mandrin dont le diamètre est égal à trois fois le diamètre du conducteur, ou lors de l'allongement du conducteur de 20%.

In a particular embodiment, the method was implemented under the following conditions. The electrical conductor to be insulated 12 is a copper wire of circular section whose diameter is 2 mm. This conductor is coated with a first layer of varnish of the polyimide type and then covered with mica particles of average maximum dimensions in their cleavage plane equal to 0.4 mm. The conductor then enters the heat treatment oven where it is dried and polymerized and passes twice through the same device for depositing varnish and mica powder for a second and a third application of varnish followed by mica powder. The insulation is completed by depositing in a second device a fourth layer consisting of polyester-imide varnish and of the same mica powder dried and polymerized at a lower temperature, then by a fifth and a sixth layer of polyester-imide varnish dried and polymerized between each deposit under the same conditions as above. The tests carried out on the insulated conductor thus obtained gave the following results:

• insulation mica content: 48 to 52%
• insulation thickness: 0.16 to 0.20 mm
• thermoplasticity according to the IEC standardized method greater than 500 ° C
• breakdown voltage: 2.5 to 3.3kV per mm
• flexibility of the insulation: no cracking was observed during the winding of the wire on a mandrel whose diameter is equal to three times the diameter of the conductor, or during the elongation of the conductor by 20%.

It is understood that, by virtue of the implementation of the method, it is possible to obtain an insulated electrical conductor having electrical insulation properties at least equal to those obtained previously. This process lends itself to the insulation of a continuous conductor and it subsequently allows deformations of the conductor without cracks appearing in the insulation of the latter.

Claims (16)

1. Method of insulating an electrical conductor comprising the following step:

   a) depositing a layer of polymer varnish on said conductor in a solvent and/or diluent medium;
      said method being characterized in that it further comprises the following steps:

   b) creating a localized cloud of powder of particles of an insulating mineral material;

   c) displacing continuously said conductor that is coated with the layer of varnish through said cloud of powder, whereby said particles adhere to said layer of varnish in order to form an insulating layer;

   d) subjecting the electrical conductor coated in this way to an operation of drying and polymerizing the varnish.
2. Method according to claim 1, characterized in that steps a), c), and d) are repeated several times until a desired extra thickness of insulation is obtained.
3. Method according to any one of claims 1 and 2, characterized in that said cloud of powder is created by powdering.
4. Method according to any one of claims 1 to 3, characterized in that said mineral insulator is mica.
5. Method according to claim 4, characterized in that the content by weight of mica is comprised between 40% and 60% of the weight of the final insulation.
6. Method according to any one of claims 4 and 5, characterized in that the mean largest dimension of the mica particles is about 0.4 mm.
7. Method according to any one of claims 1 to 6, characterized in that said electrical conductor is initially bare.
8. Method according to any one of claims 1 to 6, characterized in that the electrical conductor is initially covered in enamel and/or in textile covering.
9. Method according to any one of claims 1 to 8, characterized in that it further includes a final step of depositing at least one layer of varnish.
10. Method according to any one of claims 1 to 8, characterized in that it further includes a final step of implementing at least one layer of textile covering.
11. Method according to claim 3, characterized in that said mineral powder is powdered by means of a device having powdering nozzles.
12. Method according to claim 3, characterized in that the powdering of said cloud of powder is implemented by electrostatically displacing particles of powder, the electric field being created by electrodes that are independent of said conductor.
13. Method according to any one of claims 1 to 12, characterized in that said varnish comprises a polymer selected from the group comprising: modified or non-modified polyester imide; polyesters; epoxies; polyamideimides; polyimides; polyurethanes; polyvinyl acetoformal.
14. Insulated electrical conductor wire, characterized in that it comprises a conductive core, a plurality of layers of varnish (14, 18) and a plurality of layers of insulating powder (16, 20) in alternation, each layer of powder adhering in uniform manner on a layer of varnish.
15. Insulated electrical conductor wire according to claim 14, characterized in that it further comprises at least one layer of enamel and or of textile covering (60) implemented directly on the conductive core (12).
16. Insulated electrical conductor wire according to any one of claims 14 and 15, characterized in that it further comprises outer insulation comprising at least one layer of varnish (22) and/or at least one layer of textile covering (62).

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