FR2690559A1 - A method of isolating an electrical conductor and insulated electrical conductor as obtained by carrying out the 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.

Description

METHOD OF INSULATING AN ELECTRICAL CONDUCTOR

  AND ISOLATED ELECTRICAL CONDUCTOR AS OBTAINED

BY THE IMPLEMENTATION OF THE PROCESS

  The present invention relates to a method of isolating an electrical conductor and the isolated electrical conductor as obtained by placing

of said method.

  More specifically, the present invention relates to the isolation of electrical conductors intended in particular to produce windings of electrical equipment, for example motor windings, in which the insulation is initially produced on the conductor before winding it on a storage medium. The driver thus isolated is then used as a

  insulated conductor by already known methods.

  Electrical conductors intended to produce windings of electrical equipment are generally isolated beforehand by enameling

  or wrapping or enameling followed by wrapping.

  The enameling is generally carried out by deposition of synthetic polymers in solution in an organic solvent medium The deposition is done in several calibrated layers, each layer being dried and polymerized before the deposition of the next layer by passing through a furnace at a high temperature. the order of 400 to 500 ° C. The dielectric strength of the insulator thus deposited varies from 60 kV per millimeter to 130 kV per millimeter depending on the excess thickness of the polymer.

called enamel or varnish.

  The thermal resistance of this insulator also varies depending on the nature of the organic polymer used and does not meet the needs in the case where the driver is subjected to very high stresses, both thermal, electrical and mechanical Indeed electrodynamic forces, potential gradients or centrifugal forces in the case of rotating machine windings induce significant stresses on the contact winding wires which, combined with the temperature increase of

  functioning due to Joule heating and electromechanical losses.

  This can cause a short-circuit between the winding wires thus produced. In the case of significant mechanical stress, this phenomenon is related to a temperature and pressure leakage of the enamel that can be simulated by a standardized test called thermo-plasticity This consists in exerting a defined pressure at the intersection of two wires under electrical tension arranged perpendicularly for a specified time and to repeat the test at different temperatures to determine at what temperature a short circuit occurs. Under these test conditions, the most effective enamels so far among those commonly used make it possible to obtain a thermoplasticity of the order of 400 ° C. to 500 ° C., which, in applications with high thermal and mechanical stresses, remains insufficient due to lack of materials

  minerals in the insulation material.

  In the case where there are more strong electrical stresses corresponding to

  spawning at medium or high voltage The enamel is most often not

  used alone but combined with other insulating materials.

  One of the reinforcement modes commonly used to overcome these drawbacks consists in guiding the enamelled wire, that is to say, in spirally winding a sheet of continuous fibers impregnated with a polymer in an organic medium. Commonly examples are glass fibers or fiberglass and polyester fiber blends. The covering may also be directly deposited on a non-enamelled conductor when the operating conditions allow it.

  not only the advantage of improving the bond with the varnish

  Winding of the windings but, for specific applications given, the presence of a mineral product increases its resistance to significant thermal stresses. Compared to the enamelled winding wire alone, the mineral product makes it possible to increase the resistance to intense but limited time overloads. and increases the safety margin when temperatures

  occasionally reach 400 to 500 C under strong mechanical stress.

  One solution to improve electrical insulation would be to add

  insulating mineral products in enamels, for example mica.

  However, this addition would entail certain difficulties of implementation: indeed, it is technically impossible to incorporate mineral products with a high concentration in the enamelling varnishes because the phenomena of settling of the load, on the one hand, and the weak thicknesses of deposits calibrated at each layer, on the other hand, (0.01 to 0.02 mm) would not make it possible to obtain regular insulation in composition and in thickness according to the

  different points of the driver's surface to be isolated.

  It has also been proposed electrophoretically depositing enamel loaded with a mineral material such as mica Such a solution is notably

  described in US-A-4,058,444, WO-A-89/100765 and FR-A-

  2555599 all aimed at isolating 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 suitable for shaped parts or windings already made and difficult to isolate but it is a delicate implementation for risolation of electrical conductors to be wound later on a support of

storage.

  To overcome these drawbacks, an object of the present invention is to provide a method that effectively allows the realization of an electrical insulation comprising inorganic insulating materials and which is compatible

  with a process of insulation of the electrical conductor continuously.

  To achieve this goal, the method of insulating an electrical conductor, according to the invention, is characterized in that it comprises the following steps: a) is deposited on said conductor a layer of polymeric varnish in a solvent medium and / or diluent ; b) then, is deposited uniformly on said layer of varnish a powder of a mineral insulator such that said powder adheres uniformly to the varnish; and c) subjecting the electrical conductor thus coated to a

  drying and polymerization of the varnish.

  It is understood that the method according to the invention effectively allows line insulation in the electrical conductor Indeed, the realization of the coating layer is made by conventional means in line and the deposition of the mineral insulating powder can conveniently be also performed in a second step in line, in particular using spray nozzles or techniques for transferring powder by electrostatic field. It is further noted that, since the electrical conductor is not used as an electrode in the insulation process, the process can to be used indifferently

  that the electrical conductor is already insulated with enamel or that it is bare.

  Preferably, steps a), b), c) of the process are repeated several times.

  time until the desired insulation thickness is obtained.

  The deposition of the layer of mineral insulating 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 spray in the

  present text as opposed to electrolytic deposition techniques.

  Another object of the invention is to provide an insulated electrical conductor having an insulation of the type obtained by the implementation of the method according to the invention. Other features and advantages of the present invention

  will appear better on reading the following description of several modes

  implementation of the invention given by way of non-limiting examples

  description refers to the appended figures in which:

  FIG. 1 is a cross-sectional view of an electrical conductor

  isolated trunk 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 mode of depositing the powder of

insulating material according to the invention.

  Before describing in detail, different modes of implementation of

  the invention, we will describe the principle.

  According to the invention, electrical isolation of the electrical conductor is carried out in three basic steps. In a first step, the electrical conductor is coated with a layer of polymer varnish in an organic solvent medium or not and still in a reactive diluent medium. In a second step, the electrical conductor thus coated with varnish is subjected to spraying with a powder of insulating mineral material. This powder adheres to the varnish which has just been deposited thus producing a homogeneous layer of mineral insulator since the maintenance of the mineral insulator on the electrical conductor does

  can be done in direct contact with the varnish layer initially deposited.

  In a third step, the electrical conductor thus coated with the initial layer of varnish and the mineral insulating layer is subjected to a drying and polymerization treatment of the varnish in order to stabilize the assembly according to the desired insulation thickness and therefore the insulation characteristics

  these three operations are repeated successively.

  Referring firstly to FIG. 1, a first embodiment of the invention will be described starting from a bare electrical conductor 12, which may have a circular or rectangular section and be made of copper or aluminum , etc., a first layer of insulating varnish 14 made of polymer in an organic or aqueous solvent medium or in an active diluent medium. As a varnish, it is possible to use all the varnishes known in the field of the use of insulating winding wires. these include, for example, varnishes based on modified or unmodified polyesterimide, 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 in the varnish bath, then by calibration of the layer In a second step, the conductive wire 12 is moved varnish layer 14 in a medium where a powder of mineral insulating material, preferably mica, is present in suspension The particles by adhering to the layer of varnish 14 forms a regular uniform layer of mica particles 16 It is understood that in fact, only the first layer of mica particles can adhere to the varnish layer 14, which allows a uniform deposition of mineral lye. Preferably, the mica is in the form of a powder obtained by grinding and it can The average particle size may vary in the cleavage plane of the particles from 0.05 mm to 0.8 mm and more. Preferably, the maximum dimension in the cleavage plane is 0.4 mm. maximum dimension is an average dimension corresponding to the statistical dispersion of the particles actually obtained during the powder production operation The final mica content may be between 10 and 90% of the Thus, this content is in the range of 40 to 60%. Once this first deposition has been carried out, a second layer of varnish 18 is made, as indicated above, then a second deposit 20 is made. a layer of mica, as has already been explained to finish the realization of the insulation, can be deposited an outer layer of insulation to the already mentioned varnish, this layer bearing the reference 22 possibly several

  layers of varnish can be deposited successively.

  The deposition of the mineral insulating layer, typically mica, on the electrical conductor 12 already provided with a layer of varnish 14 can be achieved in different ways. FIG. 3 illustrates a first embodiment of this embodiment. has represented two spray nozzles 24 and 26 connected to sources of mica in the form of powder and thus allowing the circulation in the direction F of the conductive wire 12 inside a cloud of mica powder in suspension Thus, as already explained, only a layer of mica adheres to the varnish 14, the rest of the mica can not 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 varnish layer 14 circulates in a zone 30 in which a saturated atmosphere is created. mica powder by the following means

  mica powder 32 is placed in a hopper 34 open at its lower end.

  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 means of an elastic damping system 44. the mica powder 32 to the outlet 36 The realization 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 carry the general reference 46 , are made of an electrically conductive material and the hopper is fixed on an insulating frame 48 facing the hopper 34, a conductive plate 50 perpendicular to the frame 48 defines the zone of creation of the cloud of mica 30 The wall 46 of the hopper 34 and the plate 50 are connected to the terminals 52a and 52b of an electrical generator 52. The two electrodes formed by the wall 46 and the plate 50 thus define an electric field E which This mica particles adhere to the layer 14 of varnish formed on the conductive wire 12. Preferably, the depositing installation of the mica powder comprises two modules identical to those which are represented in FIG. 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, may be repeated as many times as necessary in order to obtain the desired excess thickness of insulation. has already indicated, after each step of deposition of a layer of varnish and formation of a layer of mica, the electrical conductor is subjected to a heat treatment to obtain the drying of the varnish and the polymerization thereof. in order to obtain stabilization of the insulating coating It is important to note that other techniques of spraying the mica powder or other mineral insulators on the varnish-bonded conductive wire could be used provided that these techniques permit the adhesion of a uniform homogeneous layer of mica or other equivalent mineral insulator to the coating layer.

  could for example use a fluidized bed technique.

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

by wrapping.

  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 then covered with mica particles of average maximum dimensions in their cleavage plane equal to 0.4 mm The driver then enters the treatment furnace

  where it is dried and polymerized and goes back twice in the same

  positive deposit of varnish and mica powder for a second and third application of varnish followed by mica powder The insulation is completed by a deposit in a second device of a fourth layer consisting of polyester-imide varnish and the same mica powder dried and polymerized at a lower temperature, then with a fifth and a sixth layer of polyester-imide varnish dried and polymerized between each deposit under the same conditions as previously The tests carried out on the isolated conductor thus obtained gave the following results: : mica content of the insulation: 48 to 52% insulation thickness: 0,16 to 0,20 mm thermoplasticity according to IEC standard method greater than 500 C breakdown voltage: 2.5 to 3.3 k V by mm flexibility of isolation: no cracking was observed during the winding of the wire on a mandrel whose diameter is equal to three times the

  driver diameter, or when extending the driver by 20%.

  It is understood that, thanks to 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 method lends itself to insulating a conductor continuously and it allows later deformations of the

  driver without appearing cracks in the insulation of it.

Claims (12)

  A method for isolating an electrical conductor, characterized in that it comprises the following steps: a) depositing on said conductor a layer of polymer varnish in a solvent medium and / or diluent; b) then, a powder of a mineral insulator is uniformly deposited on said layer of varnish so that said powder adheres to the varnish and c) the electrical conductor thus coated is subjected to an operation of   drying and polymerization of the varnish.   2 Method according to claim 1, characterized in that steps a), b) and c) are repeated several times until one obtains the extra thickness desired insulation.   Process according to one of Claims 1 and 2, characterized   in that said powder is deposited by spraying.   Process according to one of Claims 1 to 3, characterized   in that said mineral insulator is mica.   Process according to Claim 4, characterized in that the weight content of mica is between 40% and 60% of the weight of the insulation produced.   6 Process according to any of claims 4 and 5, characterized   in that the mica particles have a larger average dimension of 0.4 mm.   Insulating method according to any of claims 1 to 6,   characterized in that said electrical conductor is initially bare.   8 Process according to any of claims 1 to 6, characterized   in that the electrical conductor is initially covered with enamel and / or guipe.   9 Process according to any of claims 1 to 8, characterized   in that it further comprises a final step of depositing at least one layer of varnish.   Process according to any one of Claims 1 to 8, characterized   in that it further comprises a final step of producing at least one covering layer.   Process according to claim 3, characterized in that the spraying of said mineral powder is carried out by a spray nozzle device. 12 Process according to claim 3, characterized in that the spraying of said powder is performed by electrostatic displacement of the powder particles and displacement of said conductor in the powder cloud thus created.   Process according to any one of claims 1 to 12, characterized   characterized in that said varnish comprises a polymer selected from the group consisting of: modified or unmodified polyesterimide; polyesters; epoxy; polyamide-imides; polyimides; polyurethanes; polyvinyl acetoformal. Insulated electric conductor, characterized in that it comprises a conductive core (12), at least one layer of varnish (14, 18) and at least one layer of a directly deposited mineral insulating powder (16, 20). in a way uniform on said varnish.   An insulated electrical conductor according to claim 14, characterized in that it comprises a plurality of varnish layers (14, 18) and a plurality of alternating layers of insulating powder (16, 20), each layer of powder   adhering uniformly on a layer of varnish.   16 Isolated electrical conductor according to any one of   claims 14 and 15, characterized in that it further comprises at least one   layer of enamel and / or covering (60) made directly on the conductive paste (12).   17 Isolated electrical conductor according to any of the   Claims 14 to 16, characterized in that it further comprises an insulation   external material comprising at least one layer of varnish (22) and / or at least one covering layer (62).