EP0096058B1 - Electric transformer and method for making it - Google Patents

Abstract

The transformer comprises a magnetic circuit (8) as well as, for each phase, a high voltage electric circuit (17) and a low voltage electric circuit (18), both wound about at least one section of the magnetic circuit (8). The electric circuits (17, 18) are arranged in at least one electrically insulating annular frame (11) which, in operation, is between the electric circuits (17, 18) and the above mentioned section of the magnetic circuit (8). Utilization particularly for improving the occupation of electric windows by the magnetic circuit and of magnetic windows by the electric circuit.

Description

The present invention relates to an electrical transformer intended in particular but not limited to the so-called “average” powers, that is to say ranging from 5 to 1000 kVA approximately, and for single-phase or polyphase circuits. This transformer comprises a magnetic circuit comprising at least one strip of magnetic material wound in a ring defining in its middle a circular window, as well as, for each phase, a high voltage electrical circuit and a low voltage electrical circuit both wound around at least one section of the magnetic circuit.

The adjectives "high" and "low" have only a relative meaning here to designate the circuits connected to the terminals of the device between which the voltage is respectively the highest and the lowest.

The present invention also relates to a method for manufacturing this transformer. Such a transformer is known for example from DE-C-691531 or from JP-A-5 632 709. The advantage of circular magnetic cores is that they can be rolled very automatically around circuits after having finished and insulated these.

However, the rolling of such a magnetic core implies that it is rotated around the section of electrical circuits around which it must be located. Thus, great precautions must be taken to avoid injuring the electrical circuits and their insulation during this operation.

According to the known technique, these precautions consist in surrounding the electrical circuits with tape or insulating paper, and in making sure that during its rolling or even after it, in the completed transformer, the magnetic circuit may come into contact with the electrical circuit.

During manufacture, the installation of the aforementioned insulation is delicate and difficult to automate. Once the circuits are complete, they must be subjected to a long vacuum drying to extract the moisture from the paper present in large quantities, which can only fulfill its role as electrical insulator when it is dry.

Furthermore, the efficiency of a transformer is all the better when the windows of the electrical circuits are completely occupied by the magnetic circuit. The gap that the state of the art requires to provide between magnetic circuit and electrical circuits plays a detrimental role in this regard. It is also harmful with regard to the weight and size of the device. In addition, this interval involves fixing the electrical and magnetic circuits independently of each other, which is all the more difficult since the fasteners have to withstand sudden and violent forces which can result from the appearance of a short circuit. in the network served by the transformer.

US-A-2 498 747 describes a three-phase transformer in which the magnetic circuit consists of rolled strips, but this magnetic circuit delimits oval windows. To manufacture such a transformer, the magnetic circuit must first be produced and the electrical circuits then put in place by winding them around the magnetic core and cutting it to introduce the circuits and re-solder it after this introduction. The first method is very long and according to the second the welds introduce additional reluctances detrimental to the efficiency of the transformer. Furthermore, FIG. 2 clearly shows that the magnetic windows of the transformer are particularly poorly filled by the electrical circuits.

The object of the present invention is to provide a transformer of the type specified at the start in which the magnetic circuit can be conveniently and efficiently formed on the electrical circuit.

According to the invention, the electric transformer is characterized in that the electric circuits are arranged in at least one electrically insulating annular carcass which, in service, is interposed between the electric circuits and the section of the magnetic circuit which they surround, the carcass having a profile substantially coinciding with a part of the circular profile of the window of the magnetic circuit.

Thus, the carcass effectively protects the electrical circuits, so that the precautions to be taken during winding are almost nonexistent and in addition the space between the electrical circuits and the carcass can be extremely reduced or even nonexistent which is very advantageous. with regard to the weight, the efficiency and the size of the transformer thus produced.

The presence of the carcass considerably facilitates first of all the winding of the electrical circuits, and also the production of the magnetic circuit which can form with the carcass a practically rigid interlocking whereas, according to the state of the art, any mutual support of the magnetic circuits and Avoid electrical damage to the insulation of electrical circuits. The carcass can without any difficulty be securely fixed to any piece of frame such as a tank covering the transformer.

It is true that FIG. 2 of US Pat. No. 2,498,747 seems to represent that the electrical circuits are coated in a sort of carcass. However, it is not described and it is not understood how it can be placed around the pillars of the magnetic circuit after it has been formed.

In any case, as seen above, the carcasses suggested by this document, used in a fundamentally different structure, do not provide the technical effects sought according to the present invention.

It is also true that, according to GB-A-540869, the magnetic core consists of a steel or nickel wire (page 2, lines 85 to 89), itself intended to be traversed by a certain current, and wound around a carcass k. Such a carcass is provided in the embodiment of FIG. 2 but not in the other embodiments. Whether or not this first carcass has been provided, the electrical windings are then wound around other carcasses (FIG. 3) and in a manner analogous to that provided for in US-A-2 498 747, and with the same drawbacks .

According to GB-A-540 869 as according to US-A-2 498 747, the elements constituting the cores do not define circular windows and although differing in the way of making the core, they teach exactly the same thing as to how to make the electrical windings.

Finally, none of the prior documents describes a carcass having a profile substantially coinciding with a part of the circular profile of the window of the magnetic circuit.

In an advantageous version of the invention, adapted to the case of single-phase transformers in which the high and low voltage windings are wound around two separate sections of the magnetic circuit, or in the case of polyphase transformers, the magnetic circuit has at least one window passed through. by two carcasses surrounding two sections of magnetic circuit which are opposite relative to this window, each carcass having a profile substantially coinciding with the half-profile of the window considered of the magnetic circuit.

Thus, the two carcasses together form around the electrical circuits an insulating sheath which completely separates them from the magnetic circuit.

According to another object of the invention, the method for manufacturing a transformer of the kind described above, with multiple carcasses, is characterized in that the electrical circuits are wound in the carcasses, the carcasses are fixed together by a at least of their edges, and in that at least one strip of magnetic material suitably slit is wound around each of at least some of the locations where two carcasses are mutually fixed, the carcasses serving as a guide for the winding of the strip .

According to this method, the carcass, in addition to its many advantages set out above, greatly facilitates the production of the magnetic circuit which can be rolled directly on it without risk of damaging the electrical insulation.

Other features and advantages of the invention will also result from the description below.

• la figure 1 est une vue en élévation latérale d'un transformateur triphasé conforme à l'invention ;
• la figure 2 est une vue de dessus du transformateur de la figure 1 ;
• la figure 3 est une vue schématique en perspective montrant l'arrangement des circuits électriques et magnétique du transformateur des figures 1 et 2 ;
• la figure 4 est une vue de dessus plus détaillée du transformateur, le couvercle de la cuve étant ôté ;
• la figure 5 est une vue de dessous du transformateur, le fond de la cuve étant supposé ôté ;
• la figure 6 est une vue en coupe selon le plan VI-VI de la figure 4, les deux anneaux magnétiques non situés dans ce plan étant supposés ôtés ;
• la figure 7 est une vue schématique d'une carcasse avant assemblage ;
• la figure 8 est une vue en coupe selon le plan VIII-VIII de la figure 9 d'une carcasse avec ses circuits électriques ;
• la figure 9 est une vue de dessus de la carcasse de la figure 8 ;
• les figures 10 et 11 sont des vues à échelle agrandie des détails X et XI de la figure 8 ;
• la figure 12 est une vue partielle du circuit magnétique, en coupe selon le plan XII-XII de la figure 6 ;
• la figure 13 est une vue schématique montrant les différents feuillards utilisés pour réaliser un anneau magnétique :
• la figure 14 est une vue en perspective éclatée, avec arrachement, montrant le montage de la prise basse tension sur le dessus des carcasses ;
• la figure 15 est une vue en perspective du commutateur de réglage du rapport de transformation ;
• la figure 16 est une vue schématique du câblage des plots de réglage de tension ;
• la figure 17 est une vue de dessus, d'un transformateur monophasé avec coupe axiale du circuit magnétique ;
• la figure 18 est une vue analogue à la figure 17 mais représentant un transformateur dans lequel les circuits électriques haute tension et basse tension sont montés dans deux carcasses distinctes ;
• la figure 19 est une vue d'une variante du transformateur de la figure 18, les circuits électriques étant vus en coupe selon le plan XIX-XIX de la figure 18 ; et
• la figure 20 est une vue analogue à la figure 18, mais représentant un transformateur triphasé dans lequel tous les anneaux du circuit magnétique sont situés dans un même plan.

In the appended drawings, given by way of nonlimiting examples:

• Figure 1 is a side elevational view of a three-phase transformer according to the invention;
• Figure 2 is a top view of the transformer of Figure 1;
• Figure 3 is a schematic perspective view showing the arrangement of the electrical and magnetic circuits of the transformer of Figures 1 and 2;
• Figure 4 is a more detailed top view of the transformer, the cover of the tank being removed;
• Figure 5 is a bottom view of the transformer, the bottom of the tank being assumed removed;
• Figure 6 is a sectional view along the plane VI-VI of Figure 4, the two magnetic rings not located in this plane being assumed to be removed;
• Figure 7 is a schematic view of a carcass before assembly;
• Figure 8 is a sectional view along the plane VIII-VIII of Figure 9 of a carcass with its electrical circuits;
• Figure 9 is a top view of the carcass of Figure 8;
• Figures 10 and 11 are views on an enlarged scale of the details X and XI of Figure 8;
• Figure 12 is a partial view of the magnetic circuit, in section along the plane XII-XII of Figure 6;
• FIG. 13 is a schematic view showing the different strips used to make a magnetic ring:
• Figure 14 is an exploded perspective view, broken away, showing the mounting of the low voltage socket on the top of the carcasses;
• FIG. 15 is a perspective view of the switch for adjusting the transformation ratio;
• Figure 16 is a schematic view of the wiring of the voltage adjustment pads;
• Figure 17 is a top view of a single-phase transformer with axial section of the magnetic circuit;
• Figure 18 is a view similar to Figure 17 but showing a transformer in which the high voltage and low voltage electrical circuits are mounted in two separate carcasses;
• Figure 19 is a view of a variant of the transformer of Figure 18, the electrical circuits being seen in section along the plane XIX-XIX of Figure 18; and
• Figure 20 is a view similar to Figure 18, but showing a three-phase transformer in which all the rings of the magnetic circuit are located in the same plane.

In the example shown in Figures 1 to 16, the three-phase transformer is arranged in a triangular section tank with rounded tops, having a bottom 2 and a cover 3 whose periphery is constituted by an oblique wall 4 bearing in an angularly distributed arrangement the three high voltage terminals 6 of the device. In service, the tank 1 is filled with electrically insulating mineral oil.

The transformer proper comprises a magnetic circuit 7 consisting of three circular rings 8 made of magnetic sheet, each of which has a frustoconical face 7 by which it is attached to the frustoconical face 7 of two other rings so that the planes of the rings 8 are arranged along the lateral faces of a prism. The structure of the magnetic rings 8 will be described in detail below.

The transformer also includes electrical circuits 9 arranged around the magnetic circuit, each around one of the sections where two rings 8 are joined.

According to the invention, the electrical circuits 9 are arranged in carcasses 11 having a tubular central part 12, of circular section, around which the electrical circuits are wound, and reserving a window 13 inside for the passage of the magnetic rings. 8. At each end of the central part 12 is provided a flange 14 directed radially outwards, intended to laterally hold the electrical windings. The part 12 and the two edges 14 together give the carcass a semi-circular profile.

The carcasses 11 are made of insulating material such as plastic. As shown in FIG. 7, the carcasses 11 are produced in two parts fitted into one another according to a fitting surface 16 which surrounds the central part 12 equidistant from the edges 14. The joint surface 16 forms a step whose height can be adjusted so as to reserve between the window 13 and the annular housing reserved for the electrical circuits, a sufficiently long escape route so as not to allow the electrical ignition between the electrical coils and the magnetic rings.

Each carcass 11 contains a high voltage circuit 17 (FIG. 8) and a low voltage circuit 18. According to an important feature of the invention, the high voltage circuit 17 is formed of turns of copper or aluminum wire located at the bottom of the carcass 11, that is to say against the central part 12. As shown in FIGS. 8 and 10, the turns of the circuit 17 are arranged in rows 19 separated by sheets of insulating paper 21. At each layer, the sheets 21 have a width slightly greater than the width available inside the carcass. This excess width serves to make on each side of the layer of turns lying above the sheet 21 a rim of paper 22 between this layer 19 and the wall of the carcass 11.

The low voltage circuit 18 consists of an aluminum strip 23 wound around the high voltage circuit 17. Between each layer of the strip 23 and each edge 14 of the carcass is interposed a strip of cardboard 24. The strip 23, the strips 24 as well as a sheet of paper 26 for the separation of the layers are rolled up in a single operation, the sheet 26 having, like the sheets 21, a flange 27 on each side of the strip 23.

Between the high voltage circuit 17 and the low voltage circuit 18 is formed an annular channel 28 allowing the passage of the oil as coolant. The channel 28 is delimited by two sheets of cardboard 29 braced by wooden sticks (not shown) parallel to the axis of the carcass. Opposite each annular end of the channel 28, the edges 14 of the carcass 11 have a series of orifices 31 allowing the communication of the channel 28 with the exterior of the carcass 11.

Each carcass 11 further carries two chimneys 32 directed axially towards the cover 3 of the tank 1, which each allow the exit from one of the ends of the high-voltage winding 17. Furthermore, each carcass 11 has a square notch 33 (FIGS. 8 and 9) directed towards the axis ZZ of the apparatus (FIG. 4), by which protrude towards the cover 3 two tabs 34 welded to the ends of the low voltage circuit 18.

In the fully assembled device, the three carcasses 11 are located in the same horizontal plane parallel to the bottom 2 of the tank and are fixed to each other by their two edges 14. For this purpose, each edge 14 has a tongue 36 offset 30 ° relative to the notch 33, and a correspondingly shaped housing 37 located opposite the tongue 36 relative to the notch 33. The tongues 36 and the housings 37 of the different carcasses are fitted one into the other. the others and ultrasonically welded or glued.

As shown in FIGS. 4, 8 and 9, the positioning of the active part of the transformer in the tank can be carried out exclusively by means of the carcasses 11 resting on the side wall of the tank 1. Thus, the carcasses 11 lead to both the electrical circuits 17, 18 and magnetic 8, which is particularly advantageous in the case of the use of magnetic materials substantially losing their magnetic qualities under the effect of mechanical stresses. The carcasses 11 which are arranged concentrically with the rounded edges of the side wall of the tank 1 are each carried by four brackets 81 welded in an angular manner distributed in this rounded edge. Between the carcass 11 and each bracket 81 is interposed an insulating wedge 82 screwed to the square 81 by means of a screw 83 which, once mounted, has its head embedded in a well 84 of the wedge 82 so as to avoid risk of electric ignition. The shims 82 are shouldered so as to ensure at the same time the centering of the active part of the transformer in the tank 1. A sheet of rubber may be interposed between each bracket 81 and the shim 82 to absorb the operating vibrations of the transformer.

A single socket 38 is connected at the same time to the six blades 34 connected to the six ends of the three low voltage windings 18 contained in one of the carcasses 11. From the socket 38, which contains the internal connections to the transformer between the low voltage windings, leave three phase conductors 39 each connected to a low voltage phase terminal 41 arranged on a flat of one of the rounded corners of the transformer tank. A fourth conductor (not shown), located under the conductors 39, connects it. socket 38 to a neutral terminal (no shown), arranged under the terminals 41. As shown in FIG. 14, the socket 38 carries three tongues 42 intended to be welded by ultrasound or glued at locations 43 of the coils 11. Once this fixation has been achieved, the blades 34 are then riveted to the socket 38.

The underside of the carcasses 11 has, approximately in line with the blades 34, a series of four studs 43 arranged in an arc centered on the axis ZZ (Figure 5). The apparatus further comprises a switch with three star branches 44, mounted in rotation about the axis ZZ by means of a control rod 45 (FIG. 14) passing through the apparatus along this axis, and supported by two bearings arranged in triangular plastic frames 46 (Figure 5), 47 (Figure 4) fitted between the magnetic rings 8, one 46 below the other 47 above the carcasses 11. The socket 38 has a bore 48 to allow the passage of the rod 45 which also passes through the cover 3 of the device and is connected outside of the latter to a control wheel 49 (Figures 1 and 2).

Each branch 51 of the switch 44 carries at its end a ball 52 pushed by a spring 53 and bearing on the internal wall of a tubular roller 54 which can take as desired three rest positions in which it is astride between two successive studs 43 between which it establishes a short circuit. As shown in FIG. 16, the studs 43 are connected to the high-voltage winding 17 so that two successive studs 43a, 43b are connected to the same turn, the stud 43c being separated from the studs 43a, 43b by a number of turns and the pad 43d being separated from the pad 43c by a double number of turns. Thus, the switch 44 makes it possible from the dial 49 to adjust the number of active turns of the high voltage circuit, and consequently the transformation ratio of the transformer.

As shown in FIG. 6, in the assembled transformer, the circular window 56 that each magnetic ring 8 presents is occupied almost entirely by two pairs of electrical circuits 17, 18 at the location where the carcasses 11 which contain them, assembled by the tongues 36, housings 37, together have a circular profile. As the electrical circuits which are thus juxtaposed in the plane of each ring 8 are the low voltage circuits 18, the space 57 reserved between them can be very thin without risk of short circuit.

As shown in Figures 4 and 12, in addition to their frustoconical face 7, the magnetic rings 8 also have a substantially semi-toric face 58 whose profile is inscribed in a semicircle whose diameter corresponds substantially to the diameter of the window 13 carcasses 11. Each substantially semi-toric face 58 is connected by its two annular edges 59, 61 to the frustoconical face 7 of the sleeve 8. Thus, in the window 13 of each carcass 11, the two rings 8 joined together have a circular profile which occupies almost all of window 13.

In the embodiment shown, the rings 8 are produced by means of magnetic sheet metal sheets rolled around the geometric axis of the ring. To achieve the desired profile of the rings 8, five strips are rolled around each other. The first 62 has the shape of a rectangular trapezoid whose bases are perpendicular to the longitudinal direction of the strip. This strip is rolled first, from its small base, and its inclined edge 63 being directed towards the outside of the device. The following strip 64 is rectangular, it is rolled with a slight offset towards the outside of the device at each turn so that the face 7 of the ring has the desired taper with 60 ° angle at the top. The next strip 66 has again the shape of a rectangular trapezoid, its inclined edge this time being on the side of the interior of the device. The strips 67 and 68, which are then rolled, are both trapezoidal.

The trapezoidal strips can be made without falling from a strip of constant width equal to the sum of the large base and the small base of the desired trapezoidal strips. By slitting this strip along an oblique longitudinal line, two strips in the shape of a rectangular trapezoid are obtained, both having the desired dimensions and which can be used in the context of the production of two of the magnetic rings. This principle of slitting is shown diagrammatically by the strip 62 'shown in dotted lines in FIG. 13. The strips 67 and 68 which constitute non-rectangular trapezoids can be produced in the same way from rectangular trapezoids which are inclined slightly.

• - on prépare par refendage les bandes de tôle magnétique nécessaires à la réalisation du circuit magnétique ;
• - on bobine sur un mandrin circulaire ayant sensiblement le diamètre du profil des carcasses 11, les feuillards de tôle magnétique dans la position qu'ils devront ensuite occuper dans le transformateur assemblé ;
• - on détend des anneaux magnétiques ainsi préassemblés en les soumettant à un traitement thermique de recuit ;
• - on déroule les anneaux magnétiques du mandrin précité en les réenroulant au fur et à mesure selon un diamètre d'enroulement plus large ;
• - avant, pendant ou après les opérations que l'on vient de décrire, on bobine sur les carcasses 11 les enroulements électriques à haute puis à basse tension ;
• - on assemble les carcasses entre elles, on réalise les différentes connections entre les enroulements, notamment en posant la prise 38, et les interconnexions 77 (figure 4) entre les enroulements 17 ;
• - on soumet l'ensemble des trois carcasses ainsi assemblées à un étuvage ou à un séchage sous vide destiné à assécher totalement le papier d'isolation des circuits électriques ;
• - on bobine ensuite les anneaux magnétiques 8 autour des carcasses 11. Les feuillards destinés à constituer les anneaux 8 prennent d'eux-mêmes la forme voulue puisqu'ils ont été recuits dans cette position ;
• - on fixe les carcasses 11 dans-la cuve 1, on connecte les bornes 6 et 41 avec la prise 38 et le réseau d'interconnexions 77, on remplit d'huile et on ferme le couvercle 3.

We will now describe the process for manufacturing the transformer above:

• - The magnetic sheet strips necessary for the realization of the magnetic circuit are prepared by slitting;
• - It is wound on a circular mandrel having substantially the diameter of the profile of the carcasses 11, the magnetic sheet metal strips in the position which they must then occupy in the assembled transformer;
• - The magnetic rings thus preassembled are relaxed by subjecting them to an annealing heat treatment;
• - The magnetic rings of the aforementioned mandrel are unwound by rewinding them progressively according to a larger winding diameter;
• - Before, during or after the operations just described, the high and low voltage electrical windings are wound on the carcasses 11;
• - The carcasses are assembled together, the various connections between the windings are made, in particular by fitting the socket 38, and the interconnections 77 (FIG. 4) between the windings 17;
• - All three carcasses thus assembled are subjected to steaming or vacuum drying intended to completely dry the insulation paper of the electrical circuits;
• - The magnetic rings 8 are then wound around the carcasses 11. The strips intended to constitute the rings 8 themselves take the desired shape since they have been annealed in this position;
• - the carcasses 11 are fixed in the tank 1, the terminals 6 and 41 are connected with the socket 38 and the interconnection network 77, the oil is filled and the cover 3 is closed.

The description which has just been made of the example of FIGS. 1 to 16 has made it possible to identify the numerous advantages of the invention, namely: gain in weight and size, gain in efficiency and yield of the transformer, ease of manufacture and elimination of the numerous risks which existed until then of damaging the electrical circuits during this manufacture, solid and easy fixing of the active part in the tank thanks to the carcases which can be firmly fixed to the tank without risk of short circuit or risk of damaging the circuits. Until now, numerous methods consisting in rolling the magnetic circuits after having wound the electric circuits had been proposed. However, these methods, which were intended to allow magnetic circuits to be without any discontinuity, had never received practical application since it was not possible to carry out this rolling without damaging the electrical circuits. The invention has remedied this impossibility. In addition, the rolling of magnetic circuits which can be carried out without taking much care with regard to electric circuits, is very fast. This saves time, and also makes it possible to steam the electrical circuits before laying the magnetic circuits. Parboiling, which is already greatly shortened because of the much smaller amount of insulating paper which must be provided, is further shortened in the absence of the magnetic circuits. The very rapid rolling of the magnetic circuits does not give the insulating paper time to re-soak in moisture before the assembly is immersed in the oil of the tank.

All these advantages obtained in the context of the preferred embodiment of FIGS. 1 to 16 can also be obtained in the context of other embodiments such as those represented in FIGS. 17 to 20.

In FIG. 17, the single-phase transformer comprises a circular magnetic circuit 69 whose circular profile fits exactly in the circular window 71 of a carcass 72 of semi-circular profile, which contains at its bottom a high voltage electrical circuit 73 and on its periphery a low-voltage electrical circuit 74. The circuit 74 greatly exceeds the carcass so that the carcass assembly 72, circuits 73 and 74 has a substantially circular section which roughly corresponds to the window 76 of the magnetic circuit 69. However, of course, contact between the circuit 74 and the ring 69 must be avoided. A relatively small interval is sufficient for this purpose since the circuit 74 is the low voltage circuit.

In the example of FIG. 18, the circuit 69 is surrounded, in two diametrically opposite sections, by two carcasses 72 situated substantially in the same plane. One of the carcasses contains the high voltage electrical circuit, the other the low voltage electrical circuit. The magnetic ring 69 can be circular like the rings 8 of FIGS. 1 to 16.

However, as shown in FIG. 19, the ring 69 can also be rectangular or square, in which case, the carcasses 72 are cylindrical with flat edges. This advantageous solution in terms of size, however has the drawback that the magnetic circuit cannot be produced according to the method which has been described with reference to FIGS. 1 to 5. It must either be carried out by means of stacked sheets assembled for example with a tab, as shown in FIG. 19, or else made of sheets rolled directly around the carcasses, without the possibility of annealing since this would of course damage the electrical circuits.

The example in Figure 20 is similar to that in Figure 18 but applied to a three-phase transformer. The magnetic rings 69 have a semi-circular profile externally limited by a cylindrical surface 76. There are four of them all arranged in the same plane with their axes in the same plane. The carcasses 72, three in number, each contain a high voltage circuit and a low voltage circuit, are each of semi-circular section. They each surround one of the sections of the magnetic circuit where two rings 69 are tangent. The carcasses 72 are also located in the same plane with their geometric axes in the same plane.

It can therefore be seen from these succinctly described examples that the carcasses according to the invention are applicable to a very large number of transformer structures, providing substantial advantages in each case.

Of course, the invention is not limited to the examples shown, and numerous modifications can be made to these examples without departing from the scope of the invention.

Thus, the invention is not limited to single-phase or three-phase transformers, and devices with a greater number of phases can naturally be produced with the same advantages.

The invention advantageously lends itself to the use of amorphous magnetic materials - also called metallic glasses - to produce the magnetic rings. Indeed, metallic glasses which are in the form of a strip of 1 / 100th, of approximately mm, offer their excellent magnetic qualities only when they are free from mechanical stresses. This condition, usually difficult to achieve, is on the contrary fulfilled by itself thanks to the invention when the carcasses are alone fixed to the tank and carry the magnetic circuits. The metallic glass sheet can be routed in a structure close to those shown in the figures, the number of winding turns being naturally much greater.

Furthermore, the strip used to make the low voltage electrical circuits may be made of copper. The cooling channels 28 can be produced from a profiled piece of flexible plastic material, having substantially the shape of a ladder, which is deformed to surround the high voltage electrical circuit before rolling the strip of the low electrical circuit. voltage. The three studs 43a, belonging to the three carcases 11 can be electrically connected, which makes it very simple to mount the high voltage circuit in a star.

Claims (18)

1. An electrical transformer comprising a magnetic circuit (8, 69) comprising at least one band of magnetic material wound into a ring defining at its centre a circular window (56) and, for each phase, a high-voltage electrical circuit (17, 73) and a low-voltage electrical circuit (18, 74) both wound around one section at least of the magnetic circuit, characterised in that the electrical circuits are formed in at least one electrically insulating annular frame (11, 72) which, in operation, is interposed between the electrical circuits (17, 18, 73, 74) and the said section of the magnetic circuit (8, 69), the frame having a profile which substantially coincides with a part of the circular profile of the window (56) of the magnetic circuit.

2. A transformer according to claim 1, characterised in that each frame (11) is made by fitting together two half-frames along a junction surface (16) which between the electrical circuits (17, 73) and the magnetic circuit (8, 69) forms a leakage path whose length is sufficient to prevent electrical flashover between these circuits.

3. A transformer according to claim 1 or 2, characterised in that the magnetic circuit (8, 69) has at least one window (56) through which extend two frames (11) surrounding two sections of the magnetic circuit (9) which are opposed relatively to said window, each frame (11) having a profile coinciding substantially with the half- profile of the associated window of the magnetic circuit.

4. A transformer according to claim 3, characterised in that the two frames (11) are fixed to one another in the window (56) of the magnetic circuit (9).

5. A transformer according to claim 3 or 4, characterised in that for each phase it comprises a frame (11), a high voltage circuit (17) made from conductive wires wound at the bottom of the frame (11), and a low voltage circuit (18) made from a conductive band (23) wound in the same frame (11) around the high voltage circuit (17).

6. A transformer according to claim 5, characterised in that the wire of the high voltage circuit (17) is made from copper while the band of the low voltage circuit (18) is made of aluminium.

7. A transformer according to claim 5 or 6, characterised in that an annular cooling duct (28) is formed in each frame (11) between the high voltage electrical circuit (17) and the low voltage electrical circuit (18) and communicates with the exterior of the frame (11) via ports (31) formed in the wall (14) thereof.

8. A transformer according to any one of claims 5 to 7, characterised in that the layers of turns of wire of the high voltage circuit (17) and the turns of the low voltage circuit (18) are all separated from one another by insulating paper (21, 26).

9. A polyphase transformer according to any one of claims 3 to 8, characterised in that its magnetic circuit is formed of circular rings (8) of which there is one per phase, each having a substantially frustoconical face (7) by which it is adjacent to the frustoconical face (7) of two other adjacent rings (8) so that the planes of the rings (8) are disposed along the lateral surfaces of a prism, and in that the electrical circuit is formed in an equal number of frames (11), each of which surrounds two rings (8) at the place where they are adjacent to one another.

10. A transformer according to claim 9, characterised in that the rings (8) of the magnetic circuit have a semi-toric face (58) connected by its two annular edges (59, 61) to the two annular edges of the frusto-conical face (7), and in that the frames (11) are circular and of semi-circular profile.

11. A transformer according to claim 9 or 10, characterised in that each frame (11) bears a series of studs (43) all connected to the high voltage circuit (17) but with some offset in respect. of the turns, and in that the transformer also bears a rotary switch (44) having one arm (51) per phase, each of its arms (51) being in contact with two successive studs (43) of one of the frames (11) so as to allow the transformer transformation ratio to be adjusted by rotation of the switch (44).

12. A transformer according to claim 11, characterised in that it comprises a tank (1) which contains the magnetic circuit (8) and the electrical circuits (17, 18) so that the plane of the frames (11) is substantially parallel to the base (2) of the tank (1), in that the studs (43) and the switch (44) are situated on that side of the frames (11) which extends towards the base of the tank (1), the arms (51) of the switch (44) being connected to a control rod (45) which is taken out of the tank (1) at the end remote from the base (2).

13. A transformer according to any one of claims 9 to 12, characterised in that each frame (11) has at least one shaft (32) enabling the wire of the high voltage electrical circuit to pass from the high voltage winding (17) to the high voltage connection terminals (6) of the apparatus.

14. A transformer according to any one of claims 9 to 13, characterised in that the two ends of each low voltage circuit (17) are connected to pins (34) formed on an edge (14) of the frame remote from the tank base (2) near the central axis (ZZ) of the transformer, and in that during operation a single tapping (38) containing the connections required between the low voltage windings (18) is connected to all the pins (34).

15. A transformer according to any one of claims 3 to 14, characterised in that it is arranged in a tank (1) which supports the operative part (8, 17, 18) solely through the agency of the frames (11).

16. A method of making a transformer according to any one of claims 1 to 15, to produce a transformer having multiple frames (11), characterised in that the electrical circuits (17, 18) are wound in the frames (11), the frames are fixed together by at least one of their edges (14), and in that at least one suitably split strip of magnetic material (62, 64, 66 to 68) is then wound around each of at least some of the places where two frames (11) are fixed together, the frames (11) acting as a guide for the winding of the strip.

17. A method according to claim 16, in which the magnetic material is sheet metal, characterised in that the strips (62, 64, 66 to 68) are wound on a circular mandrel before being wound on the frames (11) and are relaxed by heat treatment and then unwound from the mandrel.

18. A method according to claim 16 or 17, characterised in that before the magnetic circuit (8) is produced the connections (38) between the electrical circuits (17, 18) are made and the resulting assembly is dried.

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