EP0497681A1 - Transformer torus and method of making such a torus - Google Patents

Abstract

Transformer torus comprising a magnetic circuit consisting of a plurality of segments of sheet metal strip (2) permanently having the general shape of a slit cylinder, the various sheet metal segments (2) being arranged concentrically and being assembled in this position at at least one point (4) of their circumference, for example by welding. Application: in particular to measurement transformers, for example for detecting faults in electrical cables. <IMAGE>

Description

The present invention relates to a transformer toroid, in particular a measurement transformer, for example for the detection of faults on electric cables, comprising a laminated magnetic circuit constituted by a plurality of superposed sections of sheet metal tape. The invention also relates to a method of manufacturing such a torus.

For the detection of faults on electric cables, so-called circular passage transformers are used. Such a transformer comprises a laminated magnetic circuit in the shape of a torus, the circular passage of which is crossed by a cable constituting the primary of the transformer, the secondary being formed by a winding surrounding the magnetic circuit.

At the present time, the toroids of such transformers are either closed toroids or opening toroids, the latter possibly being of the split type or of the split type.

The closed toroids have the main drawback that the cables on which the fault detection must be carried out must be disconnected to allow the placement of the toroids around the cables.

The divided toroids include two rigid torus halves produced by spiral winding with contiguous turns of a sheet metal strip, by impregnating this winding with varnish, by drying the varnish, which makes the winding rigid, and by cutting the winding in two halves and rectifying the cutting edges. The two rigid winding halves are then overmolded using plastic and are assembled, for example, by a hose clamp.

These divided toroids have a high cost price and make it possible to produce transformers with an accuracy which is much higher than that required for example for measurement transformers for detecting faults on cables.

The split toroids comprise a laminated magnetic circuit constituted by a plurality of flat sections superimposed with ribbon of sheet metal. To bring these sections of sheet metal ribbon in the form of a torus, it is necessary to elastically deform the packet of sections of ribbon into a cylinder around a cable, and then to block the packet of sections of ribbon in this form, for example by overlapping its ends and immobilizing them using pliers.

These split toroids have multiple drawbacks.

On the one hand, the cylindrical conformation of the initially flat sections of ribbon implies a high degree of deformation, which, in the case of oriented crystal sheets, involves risks of destabilization. In addition, this cylindrical conformation by elastic deformation implies, when laying the body around a cable, significant efforts to overlap the two ends of the sections of ribbon, the clamp then having to be locked on the two ends, the ribbons still being energized. The installation of such a torus therefore presents considerable difficulties, in particular when the installation must be made in places of difficult access. In addition, the risk of injury from the sections of elastic sheet metal is not negligible.

The subject of the present invention is a transformer core which is both of reduced cost and of simple installation, involving only low efforts on the part of the personnel responsible for the installation, reducing the risk of injury to the worker. personnel and eliminating the risk of destabilization when using oriented grain sheets.

The invention also relates to a simple process for the manufacture of such toroids.

The transformer toroid according to the invention, in particular a measurement transformer, for example for the detection of faults on electric cables, comprises a laminated magnetic circuit constituted by a plurality of superposed sections of sheet metal tape, in particular of gray sheet metal oriented. According to the invention, the sections of sheet metal tape have a generally permanent shape in a split cylinder, are arranged concentrically so that their ends lie substantially in the same plane and are assembled in this position, at at least one point of their circumference. distant from at least one of their ends, so that the different sections of sheet metal are free from each other on at least one part of their circumference located between said assembly point and said end.

Thus, the fitting of the torus according to the invention around a cable involves a first elastic deformation, of reduced amplitude, of the torus of cylindrical shape in one direction in view of the spacing of the ends of the sections of sheet metal tape, to allow the engagement of the torus around the cable, followed by a second elastic deformation of reduced amplitude of the torus in the opposite direction with a view to overlapping the ends of the sections of ribbon, to allow the blocking of the two ends one by compared to the other, for example using pliers. Each of these two deformations of reduced amplitude requires only a small effort, practically entails no risk of injury, and cannot cause destabilization when using oriented grain sheet.

Of course, the degree of deformation that the sections of sheet metal tape undergo during installation is all the lower the more the elastically deformable part or parts of the torus, that is to say the or the part (s) located between the point or points of assembly of the sections of sheet metal tape and the end of these sections is longer.

In principle, it is sufficient for the sections of sheet metal strip of the torus to be assembled at a point on the circumference, in which case this point of assembly may preferably be in a diametrically opposite position relative to the two ends of the sections of sheet metal. Thus, the ribbon tones are free from each other between the assembly point and each of the ends, which gives the torus two flexible branches of 180 ° each.

However, in particular in the case of tori of relatively large diameter, it is also possible, in the context of the invention, to assemble the sections of sheet metal tape at more than one point, for example at two points of the circumference , said points being preferably at a maximum from the ends of the sections of sheet metal tape in order to obtain flexible branches of maximum length.

It is also possible, within the framework of the invention, to ensure that the point or points of assembly of the sections of sheet metal tape is not (s) arranged symmetrically with respect to the ends. It is indeed sufficient in principle, for the installation of the torus, that the latter has a single flexible branch of sufficient length. However, the assembly which causes a stiffening of the sections of sheet metal tape should preferably be carried out at a point distant from the subsequent blocking location of the ends of the torus.

According to a preferred embodiment from the manufacturing point of view, the sections of sheet metal tape are assembled by welding.

Preferably, the sections of sheet metal tape are assembled by at least one pair of opposite welds provided on the two edges of the torus.

For the manufacture of a transformer core according to the invention, a sheet metal strip is wound in a spiral with a plurality of contiguous turns on a support, for example a cylindrical mandrel. Then, the turns are assembled together in at least one point of the circumference of the winding. The ribbon is then subjected in the wound state to an annealing heat treatment to stabilize it in the wound state. Finally, the winding is cut, preferably at a location remote from the assembly point.

• la figure 1 est une vue de côté d'un tore de transformateur conforme à l'invention;
• la figure 2 est une vue de côté du tore de la figure 1 après mise en place du secondaire sur le tore et après fermeture du tore autour d'un câble;
• la figure 3 est une coupe partielle à plus grande échelle suivant III-III de la figure 2.

Referring to the appended schematic drawing, an illustrative and nonlimiting embodiment of a transformer core according to the invention will be described below in more detail; on the drawings:

• Figure 1 is a side view of a transformer core according to the invention;
• Figure 2 is a side view of the toroid of Figure 1 after placement of the secondary on the torus and after closing the torus around a cable;
• FIG. 3 is a partial section on a larger scale along III-III of FIG. 2.

As illustrated in FIG. 1, a torus 1 intended to constitute the magnetic circuit of a measurement transformer, for example for the detection of faults on electric cables, is constituted by a plurality of sections 2 of sheet metal tape shaped as split cylinder. The sections 2 of sheet metal tape are arranged concentrically so that their ends 3 lie substantially in the same radial plane. The different sections 2 of the torus 1 are held in this position by two welds 4 produced on the two opposite edges of the torus 1, in a position diametrically opposite the ends 3 of the sections 2.

The sheet metal sections 2 are free from one another in the two branches 5 extending from the welds 4 to the ends 3, that is to say over approximately 180 ° each. Consequently, each of these two branches 5 is elastically deformable both in the direction of opening and closing of the torus 1.

Figure 2 shows the implementation of the toroid 1 as a magnetic circuit of a measurement transformer, for example for the detection of faults on an electric cable 6. For this purpose, the torus 1 is equipped with a secondary winding 7 threaded on one of the branches 5. The torus 1 thus equipped is placed around the cable 6, which can be achieved in a simple manner by spacing the ends 3 of the branches 5, thanks to the flexibility of these branches. Then, the torus 1 is tightened around the cable 6, until its ends 3 overlap, which is also easily possible thanks to the flexibility of the branches 5. Finally, the torus 1 is locked in the closed position using 'a clamp 8 engaged on the ends 3 in the overlapping position.

As it appears above all in FIG. 3, the clamp 8 comprises a massive piece 9 in the form of a U-shaped fork and a locking screw 10 allowing the tightening of the sheets 2 of the two branches 5 at the location of their overlapping ends 3 . In the example shown, the screw 10 is a hexagon socket screw which, after tightening, can be locked using a lock nut 11.

The torus 1 according to the invention is remarkable for the permanent cylindrical shape of its concentric sheet metal sections 2, which are free relative to each other over the length of the branches 5 extending from the assembly point 4 of the sheets 2 to the ends 3. This results in great flexibility of the branches 5, which, in combination with the permanent open-cylinder shape of the sheets 2, implies only a reduced elastic deformation of the sheets 2 as well during the opening of the torus 1 for its placement on the cable 6 only when it is tightened with a view to overlapping its ends 3, for blocking the torus 1 in the closed position around the cable 6.

For the manufacture of the torus 2 according to the invention, a strip of sheet metal, for example of sheet with oriented grains, is wound in a spiral with a plurality of contiguous turns on a support, for example a cylindrical mandrel. Then after having provisionally fixed the ribbon in the wound state in this position for example by welding points, the different turns of the ribbon are assembled together at at least one point of the circumference, for example by the two opposite welds 4 on the winding slices. The rolled up tape is then subjected to an annealing heat treatment, to stabilize the sheet metal tape in the rolled up state, that is to say to give it this shape permanently. Finally, the ribbon winding is cut in an axial plane, for example by sawing, at a location remote from the assembly point, for example at a location diametrically opposite to the welds 4. The assembled and split sheet winding thus obtained constitutes the split torus 1 according to FIG. 1.

It should be noted that the embodiment described above and illustrated by the accompanying drawings has been given only by way of an indicative and non-limiting example and that numerous modifications and variants are possible within the framework of the invention.

Thus, the sheet metal sections 2 of the torus 1 can be assembled for example by the welds 4 in positions other than positions diametrically opposite the ends 3. In this case, the two branches going from the assembly point to the free ends 3 of the sheet metal sections 2 can be of different lengths. It is also possible, in particular in the case of large-diameter toroids, to assemble the sheet metal sections 2 at several points distributed over the circumference.

Furthermore, the welds 4 can be replaced, in the context of the invention, by any other means ensuring an assembly of the sheet metal sections, for example rivets, bonding or a clamp similar to the locking clamp 8.

Finally, the screw clamp 8 used for blocking the ends 3 in the overlapping position can be replaced by any other means for blocking one relative to the other the ends 3 of the sheet metal sections 2, so as to obtain a closed torus.

Claims (6)

Transformer toroid, in particular of measurement transformer, for example for the detection of faults on electric cables, comprising a laminated magnetic circuit constituted by a plurality of superimposed sections of sheet metal tape, in particular of oriented grain sheet, characterized by the fact that the sheet metal sections (2) have a generally permanent shape in a split cylinder, are arranged concentrically so that their ends (3) lie substantially in the same plane and are assembled in this position, at at least one point of their circumference distant from at least one of their ends, so that the different sections are free from each other over at least part of their circumference situated between said assembly point and said end. Toroid according to claim 1, characterized in that the sheet metal sections (2) are assembled by welding. Toroid according to claim 2, characterized in that the sheet metal sections (2) are assembled by at least one pair of opposite welds (4). Toroid according to any one of the preceding claims, characterized in that it further comprises a clamp (8) for locking the ends (3) of the sections in the overlapping position. Toroid according to any one of the preceding claims, characterized in that the sheet metal sections (2) are assembled in a place substantially diametrically opposite their ends (3). Method of manufacturing a transformer core according to any one of the preceding claims, characterized in that
that a sheet metal strip is wound in a spiral with a plurality of contiguous turns,
that the turns are assembled together at at least one point on the circumference of the winding,
that said ribbon in the wound state is subjected to an annealing heat treatment to stabilize it in the wound state, and
that the winding is cut at a location remote from said assembly point.

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