FR2793942A1 - "LOW VOLTAGE" WINDING OF ELECTRIC TRANSFORMER AND ITS MANUFACTURING METHOD - Google Patents

Abstract

The winding, of the type comprising a metal strip (1) wound in the form of turns, separated by an electrically insulating interlayer film (2) also wound in the form of turns, is characterized in that the interlayer film (2 ) has a width appreciably greater than that of the metal strip (1), and in that the projecting lateral parts (5, 5 ′) of the interlayer film (2) are each folded by pressing against the metal strip (1) so as to wrap the edges (9, 9 ') and to cover the edges of the metal strip (1). The invention applies to the production of "Low Voltage" windings of power or distribution transformers electrical energy and in particular avoids the establishment of lateral tamping strips.

Description

"LOW VOLTAGE" COILING of ELECTRICAL TRANSFORMER and its PROCESS

  The invention relates to the field of electrical transformers. More specifically, it relates to the production of so-called "low voltage" windings of power transformers or of electrical energy distribution, that these

  transformers are of the "dry" or "submerged" type.

  Usually, the "Low Voltage" windings of the transformers are produced in the following manner. A strip of a metal that is a good conductor of electricity, such as

  copper or aluminum, is wound in concentric turns around a mandrel-

  support. During the same operation, an insulating strip is wound between said turns in order to separate them electrically. The insulating strip is made of a material with high dielectric characteristics, such as mica, a synthetic film or a paper specially treated by impregnation of a polyepoxy resin. After the winding has been formed, it is heated so as to carry out the polymerization of the resin and

  its bonding to the metal strip in order to maintain the insulating strip. That-

  this thus constitutes a continuous insulating film which is generally called "between-

  layer ". After its realization, the reel seen in section appears in the form of a succession of tight concentric turns where alternate metallic turns and

  interlayer coils preventing contact between two neighboring metal coils.

  In order to precisely avoid any risk of short circuit between two neighboring metal turns, it is necessary to provide an interlayer film slightly wider than the metal strip. For this purpose, an overhang of the insulating film of about ten mm on each side of the coil is generally practiced. To complete the winding, we then have insulating tamping strips in the spaces thus left empty which separate the overhangs of the two consecutive interlayer turns on each side of the metal strip. In this way, these empty spaces are filled and, thanks to these stuffing strips, it is avoided that particles and dirt, more or less conductive, come to infiltrate these interstices to then compromise the insulation of the metal turns. In addition, it thus becomes possible to rest the

  vertical winding without risking damage to the overlaps of the interlayer.

  These strips are put in place during the actual winding. The winding tower is therefore fed simultaneously by four components: the metal strip, the insulating interlayer film and the two tamping strips.

  corresponding to each side of the winding.

  This leads to a relatively complex embodiment of the winding, since the presence of the stuffing strips constitute a source of difficulties which may necessitate stopping the lathe. They can, in fact, break or deviate unexpectedly from their nominal trajectory which must be adjusted with great precision. In addition, their material cost

  represents a non-negligible part of the total cost price of the winding.

  The object of the invention is to propose a type of winding which can be manufactured by a more economical and more reliable manufacturing process than existing processes,

  while maintaining the usual quality of the winding.

  To this end, the subject of the invention is a "Low Voltage" winding for an electric power or electrical energy distribution transformer, of the type comprising a metal strip wound in the form of turns separated by an electro-layer film. insulator also wound in the form of turns and having a width greater than that of said metal strip so as to present lateral overhangs, characterized in that said overhangs are folded while bearing on the metal strip to form folds which envelop the edges and cover the banks of the

metal strip.

  The invention also relates to a method of manufacturing such a winding, according to which one fixes, by superimposing them on the mandrel-support of a winding tower, the end of a metal strip and that of a electro-insulating interlayer film having an extra width in order to define foldable overhangs, an initial overlap fold is formed on each of the edges of said metal strip by folding down and

  fixing said overhangs on the metal strip, and the mandrel is rotated

  support so as to carry out the winding by ensuring the overlapping of the overlaps of the interlayer film on the edges of the metal strip throughout the duration of the operation

winding.

  As will be understood, the invention consists in replacing the tamping strips by a fold of the overhangs of an interlayer film provided substantially wider than usual to form this fold. This withdrawal is pressed against the bank of the

  face of the metal strip opposite the face which is in contact with the interlayer.

  The edges and edges of the metal strip are thus covered, and this during

even winding.

  The invention will be better understood on reading the description which follows, given

  with reference to the following appended figures: - Figure 1, which partially shows, seen in cross section, a "low voltage" winding of a transformer according to the prior art; - Figure 2, which similarly shows a "low voltage" winding according to the invention; - Figure 3, which shows an installation allowing the realization of a winding according to

  the invention, at the first stage of said embodiment.

  In each figure, the same elements are designated by identical references In Figures 1 on the one hand, and 2 and 3 on the other hand, which show the succession of turns of a "Low Voltage" winding produced respectively according to the technique traditional and according to the invention, the axis XX of the support mandrel has been located on which the winding has been wound. For greater clarity of the figures, the winding elements are shown spaced from each other, and not in mutual contact as they

are in reality.

  A metal strip 1, clearly visible in FIG. 3, made of aluminum 1.5 mm thick for example, is wound in concentric turns 10 (only three successive of which are shown in diagrams 1 and 2). These turns are separated by turns 20 of an insulating film 2 (made of mica, synthetic material, or of paper coated or not with a heat-bonding epoxy resin for example), of thickness which can range from 0.1

about 0.5 mm.

  According to known practice (fig.1l), the turns 20 of the insulating film, which we more readily designate by the term "interlayer", slightly protrude by a distance "d" on each side of the winding relative to the limits of the metal strip 1. This distance "d" is conventionally of the order of 10-15 mm. The voids which, due to this extra width, appear on each side of the winding between the ends of two consecutive turns 20 of the interlayer 2 are filled with insulating strips 3 and 3 ', also wound in turns 30 and 30 'during the manufacture of the winding. They are made in principle of the same material as the interlayer 2 and their thickness is close to that of the aluminum sheet 1. It is understood that FIG. 1 only shows in cross section a portion of the winding, which continues both towards the axis XX and opposite to this direction (as symbolized by

  dotted 4, 4 '), and that this portion has its symmetry with respect to the axis X-X.

  The "Low Voltage" winding produced according to the invention is shown in FIG. 2. The winding turn to be implemented can be that used to carry out the winding according to the prior art of FIG. 1, except that no longer has the means

  supply of insulating strips 3, 3 '.

  In this winding, the metal strip 1 has a constitution and dimensions quite usual which have already been mentioned. On the other hand, the interlayer film 2 originally has a width which, to allow the formation of a stable overlap fold, this time markedly exceeds, for example from 3 to 12 cm approximately, that of the metal strip 1. According to the invention, the projecting lateral parts of the interlayer 2 are, during the manufacture of the winding, each folded up by bearing on each corresponding metal turn 10 so as to wrap the edge 9 of said turn and thus cover its bank 11 (and 11 ') on the face

  opposite to that which is entirely in contact with the enveloping coil 20 of the

  layer 2. This covering of edges must be sufficient so that the interlayer film 2 can be firmly held in place by the pressure exerted on its folded blanks 5, 'by the following turns 10 of the metal strip 1. A proposed mode of realization of the "Low Voltage" winding according to the invention is illustrated diagrammatically in FIG. 3. This shows the support mandrel 6 of the winding turn in rotation around its axis X X. At the start of the operation, from the usual way, the ends of the metal strip 1 are fixed, by superimposing them

  and interlayer strip 2 on the surface of the mandrel 6.

  In the example shown, which is a preferred and non-limiting mode of putting the method into practice, the interlayer film 2 is fixed first on the mandrel 6, on

  a width "1" equal to that of the metal strip 1. The latter, narrower than the spacing

  layer, say 20 cm, is superimposed on it, making sure to be centered and well aligned with it. After having made these fastenings, fold over by hand over a length of priming approximately equal to the circumference of the mandrel, the overhanging edges - by 10 cm overhang "r" in this case - of the interlayer 2 on the upper face 7 of the metal strip 1, so as to form an initial overlap 8, 8 ′ (corresponding to the shaded areas of FIG. 3). As this folding is carried out by resting on the metal strip 1, the folded portion comes to apply tightly on the metal without

  formation of voids or spaces between them, in particular in line with the sheet metal edges 9 and 9 ′.

  The width of the covering is therefore equal to that of the initial overhang "r" minus the thickness of the sheet 1. The holding in place of this initial covering 8, 8 ′ is very simply ensured by a piece of adhesive tape, or any other fixing means, even temporary, and the rest of the interlayer film 2 is left free. Then, the mandrel 6

  is rotated so as to initiate the winding of the winding.

  Given the physical properties of the materials used to form the interlayer 2 (flexible film-forming material, non-brittle and non-crumpling, suitable for folding without tearing or creasing), the folding of its edges to form the folded parts 5, 5 'takes place naturally during the winding, without requiring human intervention, because it is initiated by the overlaps 8, 8' made in the first stage of the manufacture of the winding. We can possibly plan to assist the folding down by guides which accompany the folding of the edges of the film 2. Very good results have been obtained with an interlayer film 2 of mica, of the type marketed in France by the company S.E.G. under the name THERNOMID,

  but this material is only an example, in no way limiting.

  The fact of placing, during the winding, the interlayer 2 under the metal strip 1 has the advantage of allowing operators easy access to the zone of formation of the folded parts 5, 5 '. They can easily check at any time whether

  the installation works properly.

  The embodiment according to the invention also has the advantage of in no case leaving the edges 9, 9 ′ of the metal strip 1 exposed to the outside. This makes the winding completely sealed against external agents. On the other hand, the presence of a double layer of insulating film 2 at the edges of the metal strip 1

  (as seen in Figure 2) strengthens the insulation of these edges.

  After the winding has been produced, it can undergo any conventional conventional treatments, such as heat treatments for the polymerization of the resin conventionally impregnating the interlayer paper 2,

  and is then used in the same way as the windings of the prior art.

  It goes without saying that the invention cannot be limited to the example of embodiment described, but that it can have multiple variants or equivalents insofar as is

  respected its definition given by the appended claims.

Claims (5)

  1. "Low Voltage" winding for an electrical power or electrical energy distribution transformer, of the type comprising a metal strip (1) wound in the form of turns (10) separated by an electro-layer film (2) insulator also wound in the form of turns (20) and having a width greater than that of said metal strip (1) so as to have lateral overhangs, characterized in that said overhangs are folded by bearing on the metal strip (1) to form folds (5, 5 ') which wrap the edges (9, 9') and cover the edges (1.1 l ') of the metal strip (1).   2. Winding according to claim 1, characterized in that the covering of   banks (11, 11 ') extends over a width of the order of ten centimeters.   3. Winding according to claim 1, characterized in that said strip between layer (2) is made of mica.   4. Method of manufacturing a "Low Voltage" winding for an electrical power transformer or for distributing electrical energy, according to which one fixes, by superimposing them on the support mandrel (6) of a winding tower, the end of a metal strip (1) and that of an electrically insulating interlayer film (2) having a width greater than that of said metal strip (1) in order to define foldable overhangs (5, 5 '), an initial covering fold (8.8') is formed on each of the edges (11.11 ') of said metal strip by folding down said overhangs, and the support mandrel (6) is rotated so to carry out the winding by ensuring the overhang (5.5 ') of the interlayer film (2) on the edges (11.11') of the strip   metallic (1) during the entire winding operation.   5. Method according to claim 4, characterized in that first fixes on the support mandrel (6) the interlayer film (2), and that the metal strip (1) is superimposed on it.