EP3224840B1 - Basic module for magnetic core of an electrical transformer, magnetic core comprising said basic module, method for manufacturing said magnetic core, and transformer comprising said magnetic core - Google Patents

Description

The invention relates to the field of electrical transformers capable of being carried on board aircraft. Their function is the galvanic isolation between the source network and the on-board electrical and electronic systems, as well as the voltage transformation between the primary circuit (network side supplied by the on-board generator(s)) and one or more several secondary circuits. In addition, these transformers can be "rectifiers" by a downstream functionality based on electronic components, in order to deliver a constant voltage to certain on-board devices.

Low-frequency on-board transformers (≤ 1kHz) consist mainly of a magnetic core in soft magnetic alloy, laminated, stacked or wound according to construction constraints, and primary and secondary winding(s) in copper. The primary supply currents are variable over time, periodic but not necessarily of purely sinusoidal form, which does not fundamentally change the needs of the transformer.

The constraints weighing on these transformers are multiple.

They must have a volume and/or a mass (in general the two are closely linked) as small as possible, therefore a volumetric or mass power density as high as possible. The lower the operating frequency, the greater the section of the magnetic yoke and the volume (thus also the mass) of this yoke, which exacerbates the interest in miniaturizing it in low-frequency applications. As the fundamental frequency is very often imposed, this amounts to obtaining the highest possible magnetic working flux or, if the electrical power delivered is imposed, to reducing as much as possible the passage section of the magnetic flux (and therefore the mass of the materials), always to increase the specific power by reducing the on-board masses.

They must have a sufficient longevity (10 to 20 years minimum depending on the applications) to enable them to be profitable. Therefore, the thermal operating regime must be taken into account with respect to the aging of the transformer. Typically a minimum lifetime of 100,000 hours at 200°C is desired.

The transformer should be operated on a roughly sinusoidal frequency supply network, with an amplitude of the output rms voltage which may vary transiently by up to 60% from moment to moment, and in particular during the energization of the transformer or during the sudden engagement of an electromagnetic actuator. This has the consequence, and by construction, of a current inrush at the primary of the transformer through the nonlinear magnetization curve of the magnetic core. The elements of the transformer (insulators and electronic components) must be able to withstand strong variations in this inrush current without damage, which is called the “inrush effect”.

The noise emitted by the transformer due to electromagnetic forces and magnetostriction must be low enough to comply with current standards or to meet the requirements of users and personnel stationed near the transformer. Increasingly, pilots and co-pilots of aircraft wish to be able to communicate no longer using headsets but by direct voice.

The thermal efficiency of the transformer is also very important to consider, since it fixes both its internal operating temperature and the heat flows that must be evacuated, for example by means of an oil bath surrounding the windings and the cylinder head, associated with oil pumps sized accordingly. The sources of thermal power are mainly Joule effect losses from the primary and secondary windings, and magnetic losses from variations in the magnetic flux over time dΦ/dt and in the magnetic material. In industrial practice, the thermal power density to be extracted is limited to a certain threshold imposed by the size and power of the oil pumps, and the internal operating limit temperature of the transformer.

Finally, the cost of the transformer must be kept as low as possible in order to ensure the best technical and economic compromise between material, design, manufacturing and maintenance costs, and optimization of the electrical power density (mass or volume ) of the device by taking into account the thermal regime of the transformer.

In general, it is advantageous to seek the highest possible mass/volume power density. The criteria to be taken into consideration to assess it are mainly the saturation magnetization Js and the magnetic induction at 800 A/m B ₈₀₀ .

Two manufacturing technologies are currently used for on-board low-frequency transformers.

According to a first of these techniques, the transformer comprises a wound magnetic circuit when the power supply is single-phase. When the power supply is three-phase, the core structure of the transformer is made by two toroidal cores of the previous type joined, and surrounded by a third torus wound and forming an "8" around the two previous toric cores. This form of circuit imposes in practice a small thickness of the magnetic sheet (typically 0.1 mm). In fact, this technology is only used when the power supply frequency makes it necessary, taking into account the induced currents, to use strips of this thickness, that is to say typically for frequencies of a few hundred Hz.

According to the second of these techniques, a stacked magnetic circuit is used, whatever the thicknesses of the magnetic laminations envisaged. This technology is therefore valid for any frequency below a few kHz. However, particular care must be taken with deburring, juxtaposition, and even efficient electrical insulation of the sheets, in order to reduce both the parasitic air gaps (and therefore optimize the apparent power) and limit the induced currents between the sheets. .

• les alliages Fe-3% Si (les compositions des alliages sont, dans tout le texte données en % pondéraux, à l'exception de celle des alliages nanocristallins dont il sera question par la suite) dont la fragilité et la résistivité électrique sont principalement contrôlées par la teneur en Si ; leurs pertes magnétiques sont assez faibles (alliages à grains non orientés N.O.) à faibles (alliages à grains orientés G.O.), leur aimantation à saturation Js est élevée (de l'ordre de 2T), leur coût est très modéré ; il existe deux sous familles de Fe-3% Si utilisées soit pour une technologie de noyau de transformateur embarqué, soit pour une autre :
  • ∘ les Fe-3% Si à Grains Orientés (G.O.),utilisés pour les structures de transformateur embarqué de type « enroulé » : leur perméabilité élevée (B800 = 1.8 - 1.9 T) est liée à leur texture {110} <001> très prononcée ; ces alliages ont l'avantage d'être peu coûteux, faciles à mettre en forme, de grande perméabilité, mais leur saturation est limitée à 2 T, et ils présentent une non-linéarité très marquée de la courbe d'aimantation qui peut provoquer des harmoniques très importantes ;
  • ∘ les Fe-3% Si à grains Non Orientés (N.O.), utilisés pour les structures de transformateur embarqué de type « découpé-empilé » ; leur perméabilité est plus réduite, leur aimantation à saturation est similaire à celle des G.O. ;
• les alliages Fe-48% Co-2% V, dont la fragilité et la résistivité électrique sont principalement contrôlées par le vanadium ; ils doivent leurs perméabilités magnétiques élevées non seulement à leurs caractéristiques physiques (anisotropie magnétocristalline K1 faible) mais aussi au refroidissement après recuit final qui règle K1 à une valeur très basse ; du fait de leur fragilité dès qu'ils séjournent quelques secondes entre 400 et 700°C, ces alliages doivent être mis en forme à l'état écroui (par découpe, estampage, pliage...), et une fois seulement que la pièce possède sa forme finale (rotor ou stator de machine tournante, profil en E ou I de transformateur) le matériau est alors recuit en dernière étape ; de plus, à cause de la présence de V, la qualité de l'atmosphère de recuit doit être parfaitement contrôlée pour ne pas être oxydante ; enfin le prix de ce matériau, très élevé (20 à 50 fois celui du Fe-3% Si - G.O.), est lié à la présence de Co et est grossièrement proportionnel à la teneur en Co.

In one or the other of these technologies, a soft magnetic material with high permeability is used in the on-board power transformers, and whatever the thickness of the band envisaged. Two families of these materials exist in thicknesses of 0.35 mm to 0.1 or even 0.05 mm, and are clearly distinguished by their chemical compositions:

• Fe-3% Si alloys (the compositions of the alloys are, throughout the text given in % by weight, with the exception of that of the nanocrystalline alloys which will be discussed later) whose fragility and electrical resistivity are mainly controlled by the Si content; their magnetic losses are quite low (alloys with non-oriented grains NO) to low (alloys with oriented grains GO), their magnetization at saturation Js is high (about 2T), their cost is very moderate; there are two sub-families of Fe-3% Si used either for an embedded transformer core technology or for another:
  • ∘ Grain Oriented (GO) Fe-3% Si, used for “wound” type on-board transformer structures: their high permeability (B800 = 1.8 - 1.9 T) is linked to their very texture {110} <001>pronounced; these alloys have the advantage of being inexpensive, easy to shape, of high permeability, but their saturation is limited to 2 T, and they have a very marked non-linearity of the magnetization curve which can cause very important harmonics;
  • ∘ Fe-3% Si with Non-Oriented (NO) grains, used for “cut-stacked” type on-board transformer structures; their permeability is lower, their saturation magnetization is similar to that of GOs;
• Fe-48% Co-2% V alloys, whose fragility and electrical resistivity are mainly controlled by vanadium; they owe their high magnetic permeabilities not only to their physical characteristics (low magnetocrystalline anisotropy K1) but also to the cooling after final annealing which sets K1 to a very low value; because of their fragility as soon as they remain for a few seconds between 400 and 700°C, these alloys must be shaped in the work-hardened state (by cutting, stamping, bending, etc.), and only once the part has its final shape (rotor or stator of a rotating machine, E or I profile of a transformer) the material is then annealed in the last step; moreover, because of the presence of V, the quality of the annealing atmosphere must be perfectly controlled so as not to be oxidizing; finally the price of this material, very high (20 to 50 times that of Fe-3% Si - GO), is linked to the presence of Co and is roughly proportional to the Co content.

In addition to these two families of high permeability materials (Fe-3% Si G.O. and Fe-48% Co-2% V) mainly currently used in on-board low-frequency power transformers, iron-based amorphous materials are sometimes encountered when the requirement on the thermal (dissipation, magnetic losses) is very high, which then imposes a significant degradation of the power density (Js = 1.88 T). Amorphous are only used in wound circuits.

It has also been known for a long time that additions of Co to iron increase the magnetic saturation of the alloy, up to 2.4 T towards 35 to 50% Co, and one would therefore have expected to see the use other materials based on FeCo and containing less cobalt than Fe-48%Co-2%V in on-board transformers.

Unfortunately, it turns out that these alloys with a lower Co content have a magnetocrystalline anisotropy of several tens of kJ/m ³ , which does not allow them to have a high permeability in the case of a random distribution of the final crystallographic orientations. . In the case of magnetic sheets with less than 48% Co for medium-frequency on-board transformers, it has therefore been known for a long time that the chances of success necessarily pass through a sharp texture characterized by the fact that in each grain, an axis <100> is very close to the rolling direction. The {110}<001> texture obtained by Goss in 1946 in Fe-3% Si by secondary recrystallization is an illustrious case: however the sheet must not have contained any cobalt.

More recently, we have shown in the document US-A-3,881,967 than with additions of 4–6% Co and 1–1.5% Si, and also using recrystallization secondary, high permeabilities could also be obtained: B800 ≈ 1.98 T, i.e. a gain of 0.02 T/% Co at 800 A/m compared to the best current Fe-3% Si GO sheets (B10 ≈ 1.90 T ). It is however obvious that an increase of only 4% of the B ₈₀₀ is not sufficient to significantly lighten a transformer. For comparison, an Fe-48% Co-2% V alloy optimized for transformer has a B800 of approximately 2.15 T ± 0.05 T, which allows an increase in magnetic flux to 800 A/m for the same cylinder head section approximately 13% ± 3%, at 2500 A/m approximately 15%, at 5000 A/m approximately 16%.

It should also be noted the presence in the Fe-3% Si GO of large grains due to secondary recrystallization, and of a very slight disorientation between crystals allowing a B ₈₀₀ of 1.9 T, coupled with the presence of a coefficient of magnetostriction λ ₁₀₀ very clearly greater than 0. This makes this material very sensitive to assembly and operating constraints, which in industrial practice brings the B800 of a Fe-3% Si GO in operation in an on-board transformer to around 1.8 T. This is also the case for alloys of US-A-3,881,967 . On the other hand, Fe-48%Co-2%V has magnetostriction coefficients of amplitude still 4 to 5 times higher than Fe-3%Si, but random distribution of crystallographic orientations and small average grain size. (a few tens of microns), which makes it much less sensitive to low stresses, and therefore does not significantly reduce the B800 in operation.

In operation, it must therefore be considered that the replacement of a Fe 3% Si GO by a Fe-48% Co-2% V leads to an increase in the magnetic flux at constant section of the on-board transformer of the order of 20 to 25% for operating field amplitudes of 800 to 5000 A/m, i.e. approximately 0.5% increase in magnetic flux per 1% of Co. The alloy of US-A-3,881,967 allows an increase of 1% of the magnetic flux by 1% of Co, but as we said, this total increase (4%) was considered much too low to justify the development of this material.

It has also been proposed, in particular in the document US-A-3,843,424 , to use an Fe-5 alloy with 35% Co, comprising less than 2% Cr and less than 3% Si, and having a Goss texture obtained by primary recrystallization and normal grain growth. Fe-27% Co-0.6% Cr or Fe-18% Co-0.6% Cr compositions are cited as making it possible to reach 2.08 T at 800 A/m and 2.3 T at 8000 A/m. These values would allow in operation, compared to an Fe-3% Si-GO sheet operating at 1.8 T at 800 A/m, and at 1.95 T at 5000 A/m, to increase by 15% at 800 A/m and by 18% at 5000 A/m the magnetic flux in a given yoke section, and therefore to reduce the volume accordingly or transformer ground. Thus, several compositions and manufacturing processes for Fe-low Co alloys have been proposed (with possible additions of alloying elements) generally making it possible to obtain magnetic inductions at 800A/m close to those accessible with alloys commercial Fe-48% Co-2% V, but with significantly lower Co contents (and therefore cost prices) (18 to 25%).

In summary, the various problems with which the designers of aeronautical transformers are confronted can thus be posed.

In the absence of strong requirements on the noise due to magnetostriction, the compromise between the requirements on a low inrush effect, a high mass density of the transformer, a good efficiency and low magnetic losses lead to the use of solutions putting involving wound magnetic cores of Fe-Si G.O., Fe-Co or iron-based amorphous, or solutions involving cut-and-stack magnetic cores of Fe-Si N.O. or Fe-Co.

But these requirements on a low noise of magnetostriction being more and more widespread, it is not possible to satisfy them with the preceding technologies other than by increasing the volume and the mass of the transformer, because one does not know how to lower the noise other than by reducing the average working induction B _t , therefore increasing the section of the core and the total mass to maintain the same working magnetic flux. B _t must be lowered to approximately 1 T, instead of 1.4 to 1.7 T for Fe-Si or Fe-Co in the absence of noise requirements. It is also often necessary to pad the transformer, resulting in an increase in its weight and its size.

Only a material with zero magnetostriction would, at first sight, make it possible to solve the problem, and on the condition of having a work induction greater than that of current solutions. Only the Fe-80% Ni alloys which have an induction at saturation Js of about 0.75 T and the so-called “coated or cut cycle” nanocrystalline alloys whose Js is about 1.26 T have such a low magnetostriction. But Fe-80%Ni alloys have too low a work induction B _t to provide lighter transformers than traditional transformers. Only nanocrystalline would allow this lightening with the low noise required.

It is recalled that a material with a lying or cut hysteresis cycle is a material whose hysteresis cycle B = f(H) is such that its slope is relatively low, up to, possibly, intersecting the abscissa axis H.

But these nanocrystallines pose a major problem in the case of an “on-board transformer” solution. Their thickness is about 20 µm and they are wound in a torus in the flexible amorphous state around a rigid support, so that the shape of the torus is retained throughout the heat treatment leading to nanocrystallization. And this support cannot be removed after the heat treatment, always so that the shape of the toroid can be preserved, and also because the toroid is then often cut in two to allow a better compactness of the transformer by using the technology of the circuit wound previously described. Only resins for impregnating the wound torus can maintain it in the same shape in the absence of the support which is removed after polymerization of the resin. But after a C cutout of the impregnated and hardened nanocrystalline torus, a deformation of the C is observed which prevents the two parts from being placed exactly face to face to reconstitute the closed torus, once the windings have been inserted. The fixing constraints of the Cs within the transformer can also lead to their deformation. It is therefore preferable to keep the support, which weighs down the transformer.

• A l'intérieur, un enroulement de Fe-Si G.O. ;
• A l'extérieur un enroulement d'un matériau à plus faible magnétostriction que le Fe-Si G.O et qui ne représente que au plus 50% de la section du noyau et peut être un alliage Fe-Si 6,5%.

JP H03-268311 describes a low-noise wound transformer core formed by the superposition of two strip materials:

• Inside, a winding of Fe-Si GO;
• On the outside, a winding of a material with lower magnetostriction than Fe-Si GO and which represents only at most 50% of the section of the core and can be a 6.5% Fe-Si alloy.

In this document, it appears that the two materials can have relatively little different magnetostrictions and magnetic losses. The respective saturation magnetizations of the materials are not considered, nor the influence of the construction of the core on the inrush effect.

JP H08-250337 describes a coiled core of Si steel (for example 6.5% Si) with low noise, fragile, the cracking of which is to be avoided under the effect of vibrations and thermal stresses. To this end, this core is surrounded on its two internal and external peripheries by sheets of Si steel with lower magnetostriction than those of the central part of the core, containing 3% of Si, grain oriented (see § 9° They represent 4-20% of the total mass of the core.The core therefore has three superimposed windings.The respective magnetostrictions of the different materials are not specified quantitatively, nor are the details of their respective magnetic properties.An influence of the construction of the nucleus on the inrush effect is not mentioned.

DE-A-1 813 643 discloses a low-noise suppression coil having a bilayer closed core, in particular for the suppression of semiconductor circuits, for which the properties required are not the same as those of the cores of aeronautical transformers, in particular on magnetic losses which, in the cores of interference suppression coils, must be high to result in the creation of induced currents. A low magnetostriction material is effectively required in the cores of DE-A-1 813 643 , but it must be placed inside the kernel.

US-A-5,160,379 describes a soft magnetic alloy applicable in particular to transformers, mainly comprising Fe, which may contain Ni or Co, containing Cu, Si and/or B, and at least one metal chosen from Nb, W, Ta, Zr, Hf, Ti, Mo, and a crystal size of less than 1000 Å.

JP H03-271 346 describes a soft magnetic alloy relatively comparable to those of the previous document, but necessarily containing Nb, W, Ta or Mo.

JP S55-88313 describes a three-phase Evans-type transformer core fitted locally with spacers to stiffen its assembly, and thus reduce the noise caused by its oscillations. It relates, essentially, to the classic three-phase transformer core design that the invention aims to improve,

EP-A-1 742 232 shows three-phase transformer cores consisting of two elementary modules and an additional winding surrounding them. These cores are composed of magnetic laminations of different characteristics, arranged in such a way as to obtain a uniform distribution of the magnetic flux inside the core. This makes it possible to reduce the no-load losses (iron loss) of the transformer. The problems of magnetostriction noise reduction and the inrush effect are not mentioned, as well as the means which would make it possible to obtain them.

JP H4 074403 describes a transformer of small size and reduced weight, of the "armored transformer" type, comprising two cores which interpenetrate and one of which is made of a "low magnetostriction" material such as Fe-Si 6.5 %.

WO-A-2011/107387 (D9) describes non-immersed transformer cores, in amorphous material, provided on their surface with a coating which encapsulates them and protects them from their environment (humidity, oxidation). This coating is at least one wound strip having interruptions.

The object of the invention is to propose a design of low-frequency electrical transformer, suitable for use in aircraft, and making it possible to best solve the technical problems just mentioned, and at the lowest cost.

To this end, the subject of the invention is an elementary magnetic core module of an electric transformer according to claim 1.

The elementary module preferably comprises one or more of the characteristics of claims 2 to 5.

The invention also relates to a magnetic core of a single-phase electric transformer according to claim 6.

The invention also relates to a single-phase electrical transformer according to claim 7.

The invention also relates to a magnetic core of a three-phase electric transformer according to claim 8.

The magnetic core preferably includes one or more of the features of claims 9 to 15.

The invention also relates to a three-phase electrical transformer according to claim 16.

The invention also relates to a method of manufacturing a single-phase electric transformer core according to claim 17.

The invention also relates to a method of manufacturing a three-phase electrical transformer core according to claim 18.

The method preferably includes one or more of the features of claims 19 to 23.

• une bonne tenue mécanique de l'ensemble du noyau composite, sous l'effet des contraintes d'enroulage, des contraintes thermiques lors des recuits, des contraintes de maintien lors de la découpe en C du noyau (qui n'est qu'optionnelle mais est préférée), des contraintes de maintien lors des opérations de surfaçage des zones coupées, des contraintes de maintien des C en position stable sous entrefer réglé ;
• une réduction significative du nombre d'opérations de fabrication et du coût global de fabrication, notamment par la moindre consommation de matériau nanocristallin (toutes choses étant égales par ailleurs), et par l'utilisation du support d'enroulage de l'invention non seulement comme support mécanique, mais aussi comme amortisseur d'effet d'inrush et comme transformateur d'énergie en régime permanent de transformation, en complément du circuit nanocristallin ;
• une densité de puissance volumique et/ou massique équivalente, voire légèrement meilleure, vis à vis de la solution utilisant 100% de nanocristallin, et très supérieure aux autres solutions mono-matériau encore très utilisées à base de FeCo ou FeSi enroulée, et où le bruit suffisamment faible émis est obtenu en dégradant l'induction de travail, et donc en alourdissant nécessairement le transformateur.

The inventors were surprised to find that, with a view to transforming electrical energy at frequencies of the order of a few hundred Hz, or even a few kHz, for example in aeronautical transformers, where it is required both a high volumic and/or mass power density, low to very low noise emitted, low magnetic losses in sinusoidal waves coming from the magnetic core (less than 20 W/kg at 400Hz, preferably less than 15 W/kg and preferably less than 10 W/kg, for a maximum induction of 1 T) and by Joule effect (from the conductors) and sufficient damping of the inrush effect (inrush current when a transformer is started) , the "composite" wound magnetic core configuration, that is to say made up of a wound magnetic core using at least two materials of clearly different natures in terms of composition or properties and such that at least one of these materials is at a time s majority in volume and has a low apparent magnetostriction at saturation (typically λ _sat ≤ 5ppm, preferably ≤ 3 ppm, and better still ≤ 1ppm) with low magnetic losses at 40Hz and that at least one other of these materials has a magnetization at high saturation, typically Js ≥ 1.5 T, preferably ≥ 2.0 T, and better still ≥ 2.2 T), has the following advantages (particularly with reference to the most efficient current solution and using 100% material nanocrystalline):

• good mechanical strength of the entire composite core, under the effect of winding stresses, thermal stresses during annealing, holding stresses during C-cutting of the core (which is only optional but is preferred), holding constraints during surfacing operations of the cut zones, holding constraints of the Cs in a stable position under a regulated air gap;
• a significant reduction in the number of manufacturing operations and in the overall manufacturing cost, in particular by the lower consumption of nanocrystalline material (all other things being equal), and by the use of the winding support of the invention not only as a mechanical support, but also as an inrush effect damper and as an energy transformer in steady state transformation, in addition to the nanocrystalline circuit;
• an equivalent volume and/or mass power density, or even slightly better, with respect to the solution using 100% nanocrystalline, and much higher than the other mono-material solutions still widely used based on wound FeCo or FeSi, and where the sufficiently low noise emitted is obtained by degrading the working induction, and therefore by necessarily making the transformer heavier.

• la figure 1 qui montre schématiquement un exemple de noyau de transformateur triphasé selon l'invention, avec les bobinages du transformateur ;
• la figure 2 qui montre schématiquement un exemple de sous-noyau du transformateur triphasé de la figure 1, qui peut aussi être utilisé pour constituer un noyau de transformateur monophasé ;
• la figure 3 qui montre les relations entre bruit, indice d'inrush et masse du noyau dans les exemples de référence et les exemples selon l'invention présentés dans la description.

The invention will be better understood on reading the following description, with reference to the following appended figures:

• the figure 1 which schematically shows an example of a three-phase transformer core according to the invention, with the windings of the transformer;
• the picture 2 which schematically shows an example of the sub-core of the three-phase transformer of the figure 1 , which can also be used to form a single-phase transformer core;
• the figure 3 which shows the relationships between noise, inrush index and mass of the core in the reference examples and the examples according to the invention presented in the description.

It has been said that one of the main problems with the usual transformers used in aircraft is their noise level which interferes with conversations between crew members.

Transformer noise comes from two sources: magnetic forces and magnetostriction from the magnetic materials used in the cores of these transformers.

The noise resulting from the magnetic forces can be reduced quite easily in a closed magnetic circuit with very low distributed air gaps, by mechanical systems suitable for holding the various elements made of electromagnetic materials (conductors and magnetic sheets).

• soit choisir un matériau à caractéristiques de magnétostriction faibles ou nulle (exemple : l'alliage FeNi80 dit « Mumétal ») ;
• soit disposer d'un matériau magnétique et d'une structure de transformateur pour lesquels le flux magnétique ne se propagera que suivant la même direction cristallographique.

On the other hand, the noise of magnetostrictive origin is based on the very often non-zero and anisotropic magnetostriction characteristics of the ferromagnetic crystal, and also on the magnetic flux which often changes direction in these crystals. Logically, to reduce or even eliminate this type of noise, you must:

• either choose a material with low or zero magnetostriction characteristics (example: the FeNi80 alloy called “Mumetal”);
• or have a magnetic material and a transformer structure for which the magnetic flux will only propagate along the same crystallographic direction.

Magnetostrictive phenomena must be considered with several magnitudes of deformation (λ ₁₀₀ , λ ₁₁₁ , λ _sat ) or energy.

The magnetostriction constants λ ₁₀₀ and λ ₁₁₁ represent the amplitude of the coupling between local magnetization and lattice deformation along the crystallographic axes <100>, respectively <111>. This coupling is therefore also anisotropic with respect to the crystallographic reference, so that for a supposedly uniform magnetization of the metal (and, therefore, of direction given in the reference of the sample, and therefore also of specific direction in each of the crystals considered ), each crystal would tend to deform differently from its neighbor (the crystallographic orientations being necessarily different), but will be prevented from doing so by intergranular mechanical cohesion. The resulting elastic stresses, which can be represented in a simplified way by a quantity σ _i , generate a magnetoelastic energy, of order of magnitude (3/2)λσ _i which partially demagnetizes the material (in this expression, λ approximately represents an average magnetostriction of the same order of magnitude as the constants λ ₁₀₀ and λ ₁₁₁ ). Except in certain cases (for example traction exerted on FeSi-GO alloys) the application of an external stress also degrades performance: this is the opposite effect of magnetostriction. These magnetostriction constants λ ₁₀₀ and λ ₁₁₁ very mainly depend on the composition, and also on the crystallized fraction in the case of a nanocrystalline material, and they are known for a certain number of materials.

λ _sat is the apparent saturation magnetostriction. The quantities λ ₁₀₀ and λ ₁₁₁ relate to the magnetostriction deformations along the <100> and <111> axes of a monocrystal free to deform. The behavior of an industrial material (therefore generally polycrystalline) introduces the internal elastic stress σ _i due to the different crystallographic orientations present, which amounts to hindering the deformation of each of the crystals. This results in an overall magnetostriction, called "apparent magnetostriction" of the material, measured from the demagnetized state, and having no rigorous explicit relationship with the constants λ ₁₀₀ and λ ₁₁₁ , other than the same order of magnitude. This apparent magnetostriction λ _sat is determined after saturation, and therefore represents the maximum amplitude of deformation of the material when it is magnetized, relative to its starting state "demagnetized" or not, which is in all cases an initial state of deformation unknown. λ _sat is therefore a variation in the state of deformation between two poorly identified states. λ _sat is thus a use value which intervenes in the first order in the vibration of the magnetic laminations, the noise emitted or the compatibility of deformation between the magnetic material and its immediate vicinity (for example the packaging of a magnetic component core passive, field sensor, signal transformer, etc.).

In a material without pronounced texture (the effect of a texture will be seen below) and having magnetostriction coefficients very different from 0, such as an Fe3% Si-NO electrical steel which is devoid of texture or does not have a little pronounced texture, then according to the excitation phases of the material in the transformer, the magnetic magnetization will alternate periodically at any point of the material between its direction of easy magnetization (no or little excitation field) and a direction local more or less close to the Direction de Laminage DL. This alternation, which is different from one grain to another in the metal, associated with different magnetostriction coefficients λ ₁₀₀ and λ ₁₁₁ , generates cyclic deformations of the metal, which are at the origin of the acoustic noise emitted by these vibrations. .

• l'induction accessible B(Hm) qui est située vers 90% de la saturation afin d'utiliser au maximum le matériau tout en limitant les A.tr magnétisants et les harmoniques générées par la non linéarité B-H ;
• et les pertes magnétiques.

Concerning the low magnetic losses at medium frequency, it should be noted that two quantities influence the choice of the most suitable material:

• the accessible induction B(Hm) which is located around 90% of the saturation in order to make maximum use of the material while limiting the magnetizing A.tr and the harmonics generated by the non-linearity BH;
• and magnetic losses.

In aeronautics, the on-board network was for a long time at a fixed frequency of 400 Hz, but the variable frequency (typically 300 Hz to a few kHz) supplied directly by the generators is increasingly being used. In these relatively low "medium frequencies", it is advantageous to have a material with high induction and low losses (the thermal dimensioning also conditions the volume and mass of the transformer), such as thin Fe-Co alloys, thin Fe-Si electrical steels GO or NO high saturation amorphous, possibly Fe-6.5%Si. This domain frequency corresponds to skin thicknesses of less than 1/10 mm, which is completely compatible with the need for thicknesses of this type in the case of a wound-type magnetic core technology according to the invention. Above 0.1 mm, it is more and more difficult to roll the metal in toroidal form.

Also, if only the magnetic losses of material at high Js are considered in order to reduce the mass and the volume of the magnetic core, the choice of the main known accessible materials corresponds to table 1 below. High Js materials are used in the invention to operate very mainly in transient state in order to dampen the inrush effect. Consequently, it is mainly the materials with low magnetostriction, ensuring the main part of the steady-state operation of the transformer, which will emit the magnetic losses.

Due to the thermal confinement of the transformer cores, the magnetic losses must remain low as well as the losses by Joule effect of the conductors, in order to maintain an ambient temperature of the internal transformer below 150°C, in a cooling regime without forced convection. Typically, it is usual to consider that the magnetic losses of an on-board transformer core should not exceed 20 W/kg of installed magnetic material, preferably less than 15 W/kg, and better still less than 10 W/kg, for a maximum induction of 1 T under a sinusoidal field at a frequency of 400 Hz (this corresponds to 2 T/400 Hz at respectively less than 80 W/kg, and preferably less than 60 W/kg and, better still, less than 40 W /kg). This condition must be met by the materials of all the transformer core windings.

It can be seen in Table 1 below that amorphous or nanocrystalline materials comply with the strictest limitations on magnetic losses (<5 W/kg).

The nanocrystalline material FeCuNbSiB given as an example in the various tables has the typical composition Fe _73.5 Cu ₁ Si ₁₅ B _7.5 Nb ₃ . Table 1: Technical characteristics of different magnetic materials for embedded transformers Material Thickness (mm) _ρel (µΩ.cm) ρ _vol (kg/m ³ ) Magnetic losses at 1T (in W/kg) B _t (T) Hm (B _t ) (in A/m) 400Hz 1kHz 5kHz 400Hz 1kHz FeSi-NO 0.1 48 7650 11 33 350 1.8 5000 5500 FeSi-GO 0.05 48 7650 8 22 200 1.8 80 90 Fe-50%Co 0.1 45 8200 7.5 23 250 2.1 500 550 Amorphous 2605SC 0.025 125 7320 1.6 6 65 1.5 40 64 Amorphous 2605CO 0.025 130 7560 4.5 18 210 1.6 40 60 Fe-6.5/Si 0.1 75 7400 6 17 180 1.2 60 60 Fe-50%Ni (Supra 50) 0.05 48 8200 3 10 150 1.5 56 70 Nanocrystalline FeCuNbSiB 0.02 115 7300 0.3 1 30 1.1 8 8.5 with ρ _el : electrical resistivity at 20°C and ρ _vol : density at 20°C

The work induction B _t is used to dimension the magnetic circuits (FeSi, FeCo) when the frequency does not exceed 1 kHz, because the magnetic losses remain modest, therefore easy to evacuate. Beyond 1 kHz, the losses make it necessary to use a larger cooling system or to impose a reduction in B _t (due to the fact that the losses are linked to the square of B _t ): the iron-based amorphous then appear as an alternative interesting (lower B _t but much lower losses): indeed the lower saturation magnetization Js of amorphous metals is then no longer a disadvantage, while their low magnetic losses represent a strong advantage.

The trend in civil aeronautics is to design on-board transformers with increasingly low acoustic noise emitted, even very low when it is located next to the cockpit and pilots work without a headset to communicate. . Like any on-board component, the transformer must be as light and as compact as possible, consume as little current as possible and heat as little as possible, and also be able to withstand strong variations without damage to its integrity (its insulators, its electronic components). load, i.e. large variations in the inrush current of the transformer. This inrush current, called “inrush current”, must be as low as possible.

It is established in recent literature that the maximum inrush current (transient magnetizing current of a transformer) is proportional to (2B _t + B _r - B _s ) where B _t is the nominal work induction (resulting from the sizing of the magnetic circuit), B _r is the remanent induction of the magnetic circuit (namely of the assembly consisting of the ferromagnetic core and the air gaps located or distributed according to the construction structure of the core), and B _s is the saturation induction of the core.

• un matériau à forte aimantation à saturation (FeSi ou FeCo, de préférence à FeNi et aux nanocristallins) ;
• un circuit magnétique à faible rémanence, ce qui peut être obtenu soit directement par le choix du matériau qui le constitue (exemple du cycle d'hystérésis couché des alliages nanocristallins), soit par un effet de construction de la culasse (entrefers répartis ou localisés, produisant suffisamment de champ démagnétisant) ;
• une induction de travail B_t faible ; mais cela est antinomique avec la densité de puissance élevée, la miniaturisation et l'allègement des transformateurs, et ne constitue donc pas une solution satisfaisante au problème posé ;
• une faible section de noyau magnétique ce qui conduirait à utiliser un matériau à haute saturation ;
• une forte section d'aire des bobines.

To obtain a low maximum current of Inrush, it is necessary:

• a material with strong saturation magnetization (FeSi or FeCo, preferably FeNi and nanocrystals);
• a magnetic circuit with low remanence, which can be obtained either directly by the choice of the material which constitutes it (example of the hysteresis cycle coated in nanocrystalline alloys), or by a construction effect of the yoke (distributed or localized air gaps, producing sufficient demagnetizing field);
• a low work induction B _t ; but this is contradictory with the high power density, the miniaturization and the lightening of the transformers, and therefore does not constitute a satisfactory solution to the problem posed;
• a small section of the magnetic core which would lead to the use of a material with high saturation;
• a strong cross section of the coils.

In short, if we only consider the question of the inrush, the ideal magnetic circuit comprises an alloy with high saturation magnetization (FeSi, FeCo) and low remanence, used at reduced induction: this requires optimized design and sizing of the magnetic circuit and an adequate calibration of the air gap(s) from these materials with high magnetization at saturation Js.

If we combine the constraints of small size and low mass, low magnetic losses, low to very low acoustic noise and low inrush effect in an on-board aeronautical transformer, it remains to cross-check the most interesting solutions to optimize each quantity. constraining seen previously. Table 2 summarizes this in the case of a structure with a magnetic core wound and cut into two C-shaped elements, with a small and calibrated air gap (hence a low B _r ) and for the same mass of core magnetic, in the various cases where a single material is used to constitute the core. The characteristics of certain materials are given for different values of B _t and/or Hc. Table 2: Expected properties of materials that can be used to form a single-material core Material Thickness (mm) H c (A/m) B _t (T) Power density Acoustic noise emitted Magnetic losses A.tr and conductor losses Inrush effect Cost ideal material excellent excellent excellent excellent excellent excellent Fe3%Si-NO 0.1 40-50 1.8 very good poor poor poor poor excellent Fe3%Si-GO 0.1 20 1.8 very good weak good good poor excellent Fe3%Si-GO 0.05 25 1.8 very good weak very good good poor excellent Fe3%Si-GO 0.05 25 1 weak good very good Very well good excellent Fe3%Si-GO 0.05 25 0.5 Wrong Very well excellent excellent excellent excellent Fe-50%Co 0.1 56 2.1 excellent Wrong poor poor poor weak Fe-50%Co 0.05 54 2.1 excellent Wrong weak poor poor weak Fe-50%Co 0.05 54 0.5 poor good Very well Very well excellent weak Amorphous base iron 2605CO 0.025 4 1.6 very good poor Very well very good weak weak Amorphous base iron 2605CO 0.025 4 1 weak good excellent excellent excellent weak Fe-6.5/Si 0.1 10 1.5 very good good good weak good good Fe-50%Ni {100}<001> 0.05 8 1.5 very good very good Good good poor good Fe-50%Ni {100}<001> 0.05 8 0.7 poor excellent very good very good excellent Good Nanocrystalline FeCuNbSiB 0.02 1 1.1 good excellent excellent excellent poor Good Nanocrystalline FeCuNbSiB 0.02 1 0.6 poor excellent excellent excellent excellent good Cobalt-based amorphous 0.025 1 0.7 poor excellent excellent excellent poor Wrong Cobalt-based amorphous 0.025 1 0.3 Wrong excellent excellent excellent excellent Wrong Fe-81%Ni-5%Mo Mumetal 0.05 1 0.7 poor excellent very good excellent poor poor (ratings of decreasing interest: excellent > very good > good > weak > mediocre > bad)

• soit on se met dans des conditions de matériau à faibles pertes magnétiques associées à de faibles épaisseurs et de faibles inductions (Fe-3% Si-G.O. à B_t de 0,5 T, Fe-50% Co à B_t de 0,5 T, Fe-50% Ni {100}<001> à B_t de 0,7 T, nanocristallin Fe_73,5Cu₁Si₁₅B₇,₅Nb₃ (les chiffres en indice correspondant à des pourcentages atomiques comme il est d'usage dans la définition de tels matériaux) à B_t de 0,6 T, amorphe base cobalt à B_t de 0,3 T), et alors on atteint de bonnes à très bonnes performances en pertes dissipées, bruit acoustique émis, A.tr, pertes conducteurs et effet d'inrush, mais on dégrade alors fortement la densité de puissance ;
• soit on se place à induction élevée (1,5 à 2 T) dans différents matériaux et on atteint de bonnes à très bonnes densités de puissance, mais alors l'effet d'inrush et le bruit acoustique sont notablement accrus, et en tout cas bien au-delà de ce qui est maintenant accepté ;
• soit on utilise un matériau nanocristallin du type précisé, ceux-ci se distinguant par une induction de travail d'environ 1 T et permettant de satisfaire de façon au moins acceptable tous les besoins fondamentaux avec un inrush acceptable, un bruit faible, des pertes magnétiques faibles, des A.tr (et donc des pertes conducteurs) faibles, mais avec une densité de puissance moyenne.

It appears that with such single-material solutions thus known from the prior art, the types of choice are the following three:

• either we put ourselves in material conditions with low magnetic losses associated with low thicknesses and low inductions (Fe-3% Si-GO at B _t of 0.5 T, Fe-50% Co at B _t of 0, 5 T, Fe-50% Ni {100}<001> to B _t of 0.7 T, nanocrystalline Fe _73.5 Cu ₁ Si ₁₅ B _{7 .5} Nb ₃ (the subscript figures correspond to atomic percentages as it is customary in the definition of such materials) at B _t of 0.6 T, amorphous cobalt base at B _t of 0.3 T), and then good to very good performance in terms of dissipated losses, acoustic noise emitted , A.tr, conductor losses and inrush effect, but the power density is then greatly degraded;
• either we place ourselves at high induction (1.5 to 2 T) in different materials and we reach good to very good power densities, but then the inrush effect and the acoustic noise are significantly increased, and in any case far beyond what is now accepted;
• either a nanocrystalline material of the specified type is used, these being distinguished by a work induction of approximately 1 T and making it possible to satisfy in an at least acceptable manner all the fundamental needs with an acceptable inrush, low noise, low magnetic losses, low A.tr (and therefore conductor losses), but with an average power density.

As a wound torus, the nanocrystalline crystals known for this use therefore constitute the best compromise solution. But to make it even more interesting, it would be necessary to find a way to do without the conservation of the winding support to reduce the total mass. Also an even better compromise between the mass and the different usage values required of an aeronautical on-board transformer with a magnetic yoke with a wound core, subjected to a medium frequency of a few hundred Hz to a few kHz, whether single-phase or three-phase, would be desirable.

This objective can be achieved by the following general solution according to the invention, developed here in the most restrictive case of a three-phase transformer, illustrated in the figure 1 . This figure is only a block diagram, and does not represent the mechanical support and assembly parts allowing the maintenance of the various functional parts. However, those skilled in the art can easily design these parts by adapting them to the precise environment in which the transformer according to the invention is intended to be placed.

The elementary module of the invention is a magnetic core, of the wound type known per se, but made by combining two different soft magnetic materials, in different proportions. One, majority in cross section (in other words in volume since all the elements of the module have the same depth), is distinguished by a weak magnetostriction, the other, minority in cross section, is distinguished by a strong magnetization at saturation Js and serves as a mechanical support for the first material, as an inrush limiter, and has a minor but not insignificant participation in the transformation of energy in steady state. These materials may optionally be present with identical sections/volumes, but the material with high saturation magnetization Js must not exceed in section/volume the material with low magnetostriction.

The inventors were, in fact, surprised to find that in such a configuration, the nanocrystalline cores (materials with low magnetostriction) wound around the first core wound and previously manufactured in crystalline material with high saturation magnetization (Fe, Fe-Si , Fe-Co...) not only were well held mechanically since the support is preserved here (not only as a mechanically useful part, but above all as an essential part for the electromagnetic operation of the transformer), but that the power density obtained remained at the same level as that of an unsupported nanocrystalline core. Of course, we don't have not, here, the disadvantages which would be linked to an absence of support, namely the geometric instability of the nanocrystalline core, and the possible alterations in the operation of the transformer which would result therefrom. If the material of the crystalline core is well chosen, in addition to the support function of the nanocrystalline core, significant advantages are obtained on the overall operation of the transformer. These advantages are a limitation of the inrush effect during the transient state and, in steady state, a good transformation of the energy under an alternating medium frequency, so that the power density of the transformer is not degraded by compared to what it would be with a “nanocrystalline material alone” solution assuming that, in the latter case, it is possible to maintain good geometric stability under stress of the two C half-cores.

We will now describe, in the order of manufacture of a three-phase magnetic core according to the invention (association of three elementary modules), the various possible constituents and the characteristics of a transformer structure according to the invention resulting from this manufacturing. This structure is schematically illustrated in the figure 1 .

We begin by manufacturing a composite wound structure of an internal magnetic sub-core, this sub-core being composed of two elementary modules placed side by side. The term “composite structure” means that the structure uses several magnetic materials of different natures. It is constituted as follows, and assembled in the order which will be exposed.

The structure first comprises a winding 1, 2 of two magnetic sub-cores each made from a strip of material consisting of a material with high magnetization at saturation Js and low losses, such as Fe-3% alloys Grain-oriented Si, Fe-6.5% Si alloys, Fe-15 alloys with a total of 55% Co, V, Ta, Cr, Si, Al, Mo, Ni, Mn, W textured or not, the soft iron and ferrous steels and alloys consisting of at least 90% Fe and having a coercive field Hc of less than 500A/m, ferritic Fe-Cr stainless steels containing 5 to 22% of Cr, 0 to 10% in total of Mo, Mn, Nb, Si, Al, V and more than 60% Fe, non-oriented Fe-Si-Al electrical steels, Fe-Ni alloys containing 40-60% Ni with not more than 5% additions total amounts of other elements, Fe-based magnetic amorphs containing 5-25% total B, C, Si, P and more than 60% Fe, 0-20% total Ni and Co and 0-10% d other elements.

These two windings 1, 2 each constitute the (inner) winding support of one of the two internal magnetic sub-cores of the transformer. Preferably, this winding is self-supporting after extraction from the winding machine, but it can itself be wound on a more rigid support that is as light as possible so as not to weigh down the transformer too much, this support being made of any type of material, magnetic or not.

The function of these windings 1, 2 of the inner magnetic sub-core is to dimensionally stabilize the final magnetic circuit in C, and also to absorb the very high A.trs and the transients which occur during power-up, during connection of the transformer to the network, during the sudden inrush of power from a load... and which cause a high inrush current in the transformer (inrush effect). This sub-part 1, 2 in high Js material, in a transformer sized for a much lower nanocrystalline work induction (slightly below the Js of a low magnetostriction material, i.e. ≤ 1.2 T) will be then magnetized to saturation for the duration of the inrush (which varies from a few seconds to 1 to 2 min.) from B _t . This makes it possible to store a lot of magnetization energy in this form in these high Js materials, and prevents this energy from being transferred to a hypersaturation of the section of material with low magnetostriction and low Js, which would cause excitation fields and huge inrush currents.

Materials with high Js are desirable, because if the requirement were only to withstand the transient A.tr by a large energy storage, it would be enough to have a minimum permeability µ _r of at least 10 to 100 in the transient field period H during the inrush phenomenon, which will quickly become greater than the permeability under the inrush field of materials with high permeability, low magnetostriction and low Js, falling from very high values (µ _r > 100,000) to a value close to unity in the hypersaturation BH zone.

However, the requirement is not only to withstand the transient A.tr for these high Js materials, but also not to shield the internal materials of the transformer magnetic yoke in steady state. Indeed, for variable frequencies ranging from 300 Hz to 1 kHz (or even more) which are increasingly found on aeronautical on-board networks, the skin thickness is 0.05 to 0.2 mm (depending on the material, frequency and permeability of the medium). Therefore, a winding of material with high Js having an insufficiently low thickness compared to the thickness of the skin would shield the external field coming from the windings, and this all the more so as there would be a large number of turns of metal with high Js in the winding. It is therefore preferable to use a material with high Js of low thickness (0.05 to 0.1 mm).

In addition, we want to remain with a very low acoustic noise during the operation of the transformer in steady state, despite the presence of a part of the magnetic yoke in material with high Js and magnetostriction ranging from “medium” to “strong”. It is therefore necessary that these latter materials are not magnetically active in the steady state of the transformer, or at least that they operate at a sufficiently low induction operating point for the acoustic noise emitted to be very low. This requires that the permeability of materials with low magnetostriction is much higher (by 1 to 2 orders of magnitude) at 300 Hz-1 kHz than the permeability of materials with high Js. This is achieved by using nanocrystalline or cobalt-based amorphous on the one hand (µ _r at 1 kHz > 50,000 - 100,000) and thin FeSi or FeCo alloys (µ _r at 1 kHz < 3000), or also Fe-80% Ni alloys by sufficiently reducing their thickness (≤ 0.07mm) on the other hand.

• FeSi-G.O. pour Grain Oriented (grains orientés) ;
• et FeSi-HiB pour High Induction (induction élevée), dont les textures sont les plus resserrées et les performances de µ_r et de pertes sont les meilleures.

High Js materials can be, for example, all Fe-3% Si alloys with a {110}<001> so-called Goss texture, known in “electrical steels” under the names of the two sub-families:

• FeSi-GO for Grain Oriented;
• and FeSi-HiB for High Induction, which has the tightest textures and the best µ _r and loss performance.

These performances are obtained only in the rolling direction of the materials, which is very suitable for wound magnetic cores, whereas when one deviates from this direction, the performances decrease very quickly.

It is also possible to use in particular the Fe-49% Co-2% V-0 alloy with 0.1% Nb, the V possibly being replaced partially or totally by Ta and/or Zr. The performance, unlike previous FeSi, is not related to texture but to composition and optimization heat treatment, and its performance is approximately isotropic in the plane of the sheet. Performance is largely retained when strip thickness is lowered towards 0.05-0.1mm

• Fe-10 à 30% Co, de préférence 14 à 27% Co, de préférence 15 à 20% Co, contenant aussi :
  • 0 à 2% (Si, Al, Cr, V), de préférence 0 à 1% (Si, Al, Cr, V) ;
  • 0 à 0.5% Mn, de préférence 0 à 0.3% Mn.
  • 0 à 300 ppm C, de préférence 0 à 100 ppm C ;
  • 0 à 300 ppm de chacun de S, O, N, B, P, de préférence 0 à 200 ppm de chacun de S, O, N, P, B ;
• Le reste est du Fe, accompagné par des impuretés résultant de l'élaboration. On peut mettre en forme et traiter ces matériaux par :
  • laminage à chaud se terminant en phase ferritique, de préférence à une température de moins de 900°C ;
  • puis deux séquences de laminage à froid : la première passe avec un taux de réduction de 50 à 80%, la seconde passe avec un taux de réduction de 60 à 80%
  • recuit en phase ferritique après laminage à chaud, et diminution rapide de température après recuit (> 200°C/h entre Ac1 et 300°C)
  • recuit intermédiaire (entre les deux séquences de laminage à froid) en phase ferritique, avec une montée lente en température (< 200°C/h entre 300°C et Ac1).

It is also possible to use in particular an Fe-10 alloy at 30% Co with little texture or with a Goss texture like the previous Fe-3% Si. In the case of a Goss texture, which makes it possible to increase the permeability and to reduce the magnetic losses (but this is not particularly required for the part of the magnetic yoke with high Js operating mainly transiently or at very low permanent induction ), the following materials may, in particular, be used:

• Fe-10 to 30% Co, preferably 14 to 27% Co, preferably 15 to 20% Co, also containing:
  • 0 to 2% (Si, Al, Cr, V), preferably 0 to 1% (Si, Al, Cr, V);
  • 0 to 0.5% Mn, preferably 0 to 0.3% Mn.
  • 0 to 300 ppm C, preferably 0 to 100 ppm C;
  • 0 to 300 ppm each of S, O, N, B, P, preferably 0 to 200 ppm each of S, O, N, P, B;
• The remainder is Fe, accompanied by impurities resulting from processing. These materials can be shaped and treated by:
  • hot rolling ending in the ferritic phase, preferably at a temperature of less than 900°C;
  • then two cold rolling sequences: the first pass with a reduction rate of 50 to 80%, the second pass with a reduction rate of 60 to 80%
  • annealing in the ferritic phase after hot rolling, and rapid temperature drop after annealing (> 200°C/h between Ac1 and 300°C)
  • intermediate annealing (between the two cold rolling sequences) in the ferritic phase, with a slow rise in temperature (< 200°C/h between 300°C and Ac1).

The various ferrous materials with high Js, described previously, are illustrated by examples in the following table 3. When a content of one of the elements mentioned is not specified, this means that this element is present only in trace amounts, or at a relatively low content which makes it without a very significant influence on the Js of the material. The possible contents of the elements other than Co, Si, Cr and V present in the alloys have not been specified, because these elements have little influence on the targeted magnetic properties.

We cite here the induction at 800 A/m (B800), because in this type of material with high Js, the application of a field of 800 A/m makes it possible to reach an induction B located towards the elbow of the curve B = f(H). However, it is around the elbow of the curve B = f(H) that the best compromise is reached between volume reduction (high B) and low transformer consumption (low A.tr). The B8000 (induction at 8000 A/m) accounts, on the contrary, for the approach induction to saturation, used not only in the power density potential (B _t < B8000) but also in the reduction of the inrush effect. Table 3: examples of materials with high Js that can be used in the invention In weight In ppm Alloy Co Whether CR V VS min Al O NOT S B800(T) B8000(T) 1 15 0.02 0.05 < 0.005 0.017 0.25 0.01 70 22 8 2.08 2.24 2 15 1.0 0.03 0.1 0.016 0.27 0.02 48 17 11 1.95 2.18 3 18 0.05 0.04 < 0.005 0.017 0.32 0.02 56 31 7 2.12 2.30 4 18 1.0 0.007 < 0.005 0.017 0.29 < 0.01 62 25 < 5 2.00 2.23 5 10 0.03 0.05 < 0.005 0.019 0.33 < 0.01 47 22 < 5 2.01 2.12 6 27 0.03 0.5 < 0.005 0.015 0.30 0.01 82 28 6 2.03 2.28 7 48 0.008 0.07 2.0 0.019 0.28 0.02 63 19 9 2.10 2.35 8 0 3.0 0.007 < 0.005 0.017 0.27 0.01 51 18 < 5 1.90 2.00

The structure then comprises two additional windings 3, 4. They are each superimposed on one of the windings 1, 2 of high Js material previously described, "superposed" meaning that the additional winding 3, 4 is arranged around the corresponding winding 1, 2 of high Js material which was previously produced. These additional windings 3, 4 are made with a strip of a material having both low magnetic losses and low magnetostriction, such as polycrystalline alloys Fe-75 at 82% Ni-2 at 8% (Mo, Cu, Cr, V), cobalt-based amorphous alloys, and, very preferably, FeCuNbSiB and similar nanocrystalline alloys.

A particularly recommended polycrystalline material with about 80% Ni is also known as Mumetal. It achieves very low magnetostriction for a composition of 81% Ni, 6% Mo, 0.2 to 0.7% Mn, 0.05 to 0.4% Si, the remainder being iron, and for appropriate heat treatment d optimization of magnetic performance, well known to those skilled in the art.

A particularly recommended nanocrystalline material, known to those skilled in the art since the 1990s, is renowned for its very low magnetic losses from low frequencies down to 50-100kHz and for its ability to tune its magnetostriction, via the compositions adequate and adequate heat treatments, to a value of zero or very close to 0. Its composition is given by the formula (the subscript figures corresponding to atomic percentages as is customary in the definition of such materials):

[Fe _1-a Ni _a ] _{100-xyz-α-β-γ} Cu _x Si _y B _z Nb _α M' _β M' _γ

with a ≤ 0.3; 0.3 ≤ x ≤ 3; 3 ≤ y ≤ 17, 5 ≤ z ≤ 20, 0 ≤ α ≤ 6, 0 ≤ β ≤ 7, 0 ≤ γ ≤ 8, M' being at least one of the elements V, Cr, Al and Zn, M" being at least one of the elements C, Ge, P, Ga, Sb, In and Be, having a relative permeability µ _r of between 30,000 and 2,000,000, a saturation of more than 1 T, and even 1.25 T when the composition is optimized to achieve zero magnetostriction.

Upon annealing, the nanocrystalline material shrinks approximately 1% from its initial amorphous band state. This phenomenon must therefore be taken into account in advance in the winding of the amorphous strip around the first part 1, 2 of the inner sub-core made of high Js material, before the nanocrystallization annealing. Otherwise the 1% shrinkage on the first part of the core can lead to very strong internal stresses on the two materials of the core, which makes the whole fragile to the point of risking breakage and increases the magnetic losses. Conversely, this retraction promotes the mechanical joining of the two types of materials, and therefore promotes, if it is not excessive, a better dimensional stability of the C-shaped parts after impregnation and cutting.

Each of these bi-material windings (1, 3; 2, 4) constitutes an internal magnetic sub-core (called “elementary module”), defining a space 5, 6 in which two of the primary windings 7, 8, 9 will be inserted. of the three phases of the transformer and two of the secondary windings 10, 11, 12 of the three phases of the transformer.

It should be noted that if the transformer is single-phase, only one of these elementary modules alone constitutes the magnetic core of the transformer.

The structure then comprises a winding 13, which is disposed around the assembly formed by said two internal magnetic sub-cores closely joined along one of their sides. The winding 13 is formed from a strip of material with low magnetic losses and low magnetostriction, such as Fe-75 alloys at 82% Ni - 2 at 8% (Mo, Cu, Cr, V), alloys cobalt-based amorphous alloys, and very preferably nanocrystalline FeCuNbSiB and related alloys as defined above. This winding 13 forms part of the external magnetic sub-core.

Up to and including this stage, it is preferable to only hold all the materials together by means of added metal parts that can mechanically withstand annealing at 600°C. It is in fact the maximum nanocrystallization temperature that will have to be applied, preferably at the end of this step, to the whole of the transformer core in constitution, when the materials of the windings 3, 4, 13 so require. If resins or glues are used before to immobilize the magnetic tapes wound relative to each other, then they will probably be degraded during the nanocrystallization annealing. Their use must therefore preferably be postponed until a step subsequent to the nanocrystallization annealing.

For reasons of conservation of the magnetic flux, it is preferable to wind in this step a section of material 13, denoted S ₁₃ , more or less identical to each of the sections S ₃ or S ₄ which have been wound in material with low magnetostriction in the inner subnuclei. It is also preferable to minimize the void zones situated between the three windings of material with low magnetostriction. We will take as recommended ratios S ₃ /S ₁₃ or S ₄ /S ₁₃ a value of 0.8 to 1.2 to compensate for the differences in the perimeter of the winding and the possible differences in air gap between the different materials which we will talk about later. far.

The structure then comprises a new winding 14 superimposed (in the sense seen above with regard to the internal magnetic sub-cores) around this part 13 with low magnetic losses and low magnetostriction of the external magnetic sub-core. This new winding 14, whose section will be denoted S ₁₄ , is formed from a strip of material with high Js and low losses, such as Fe-3% Si-GO, Fe-6.5% Si, Fe-15 at 55% (Co, V, Ta, Cr, Si, Al, Mn, Mo, Ni, W) textured or not, soft iron and various steels, ferritic stainless steels Fe-Cr at 5 to 22% Cr, 0-10% total Mo, Mn, Nb, Si, Al, V and more than 60% Fe, Fe-Si-Al NO (non-oriented) electrical steels, Fe-Ni alloys close to 50% Ni, iron-based magnetic amorphous. This final winding 14 completes the supply of magnetic material in what constitutes the wound yoke of the transformer.

It is preferable to wind in this step a section S ₁₄ of material 14 with high Js and low losses not too different from those S ₁ or S ₂ , which are themselves close to each other or identical, and which have been wound in 1.2 high Js material in the internal sub-cores, in order to have the same inrush attenuation effect in all three phases of the transformer. We will take 0.3 ≤ S ₁₄ /S ₁ ≈ S ₁₄ /S ₂ ≤ 3 because the material of the winding 14 with high Js and low losses has a winding path (perimeter) which can be very different from that of the materials windings 1 or 2 placed in the center of the subassemblies, and this must be taken into account in the dimensioning of the composite core (this results from the application of Ampère's theorem).

Thus the parts 3, 4 and 13 with low magnetic losses and low magnetostriction will have identical sections, or of the same order of magnitude, whereas the sections of materials with high Js and low losses of the first windings of the two sub-cores, 1 and 2 on the one hand, and the final winding 14 on the other hand, can be quite significantly different within the limits which are specified.

The nanocrystallization heat treatment of the windings 3, 4, 13 with low magnetic losses and low magnetostriction, if necessary, can be carried out at At the end of this stage, all the metallic materials having been assembled. But due to the contraction of the material 3, 4, 13 during the nanocrystallization, one is exposed after annealing to a detachment of the second winding 14 of the external sub-core with respect to the first winding 13 of the external sub-core, making much more difficult the "joining together" of the assembly before cutting. It is therefore preferable to apply this annealing at the end of the previous step, as said previously.

At the end of this step of setting up the winding 14 with low magnetic losses and low magnetostriction of the external sub-core, it is, on the other hand, advisable to apply by deposition, or by prior bonding of the strips, or by impregnation under vacuum (or any other suitable process) a resin, an adhesive, a polymer, or another comparable substance, which will transform the whole of the magnetic yoke wound into a resistant one-piece body with high dimensional stability under stress. Hooping can possibly replace this bonding or this impregnation, or precede it.

Then the magnetic yoke thus formed is cut so as to divide the different sub-cores into two parts 15, 16 to form two elementary "half-circuits", after using the different technologies for immobilizing the strips of material and the sub-cores previously cited. These two parts 15, 16 are intended to be separated by an air gap 17 as shown in the figure 1 . The cutting must be done by firmly holding the magnetic yoke, within the limit of the mechanical resistance of the solidified core, and by any cutting process such as wire abrasion, cutting, water jet, laser, etc. . It is preferable to divide the cylinder head into two symmetrical parts as shown, but an asymmetry would not be contrary to the invention.

Then, shaping and surfacing of the future surfaces of the air gap 17 are carried out, then the replacement, facing each other, of the two parts 15, 16 of the cut-out magnetic yoke (to find the starting structure) after a possible wedging of the air gap 17, and after insertion of the pre-made primary 7, 8, 9 and secondary 10, 11, 12 windings of the transformer.

The air gap 17 has the function of naturally demagnetizing any part of the magnetic core at the instants of the electrical period when the magnetic excitation becomes weak or zero. Thus, if the transformer is initially stopped and, therefore, the entire magnetic yoke is demagnetized by the air gap (B _r = 0), the inrush effect observed when the transformer is abruptly reloaded will be reduced.

The surfacing or the calibration of the air gap 17 are not absolutely necessary for the invention, but they allow a better adjustment of the performance of the transformer. This makes it possible to increase inrush performance, and to make the characteristics of the transformers of a production series more reproducible.

The "replacement" or "assembly" of the two parts 15, 16 of the cut magnetic circuit, and possibly surfaced and wedged, can in particular be carried out by means of tightening by shrinking also using a high Js material having properties comparable to those of the material used in the winding 14, and therefore also participating (but without air gap) in attenuating the inrush effect like the other high Js materials. This option is particularly interesting because it makes it possible to further lighten the magnetic circuit, while giving it strong mechanical cohesion.

The section of material with high Js compared to the total section, on the one hand for each sub-core taken alone, and, on the other hand, for the magnetic core taken as a whole, is worth from 2 to 50%, and preferably 4 to 40%. Therefore, this section is most generally in the minority, and in any case not in the majority, in the elementary module defined externally by the winding 14 of strip of material with high Js superimposed on the winding 13 of strip of low magnetostriction and in each of the elementary modules of the internal sub-kernel.

$$2\le \frac{100.{\mathrm{S}}_2}{{\mathrm{S}}_2+{\mathrm{S}}_4}\le 50,\mathrm{de}\mathrm{préférence}4\le \frac{100.{\mathrm{S}}_2}{{\mathrm{S}}_2+{\mathrm{S}}_4}\le 40$$

$$2\le \frac{100.{\mathrm{S}}_{14}}{{\mathrm{S}}_{13}+{\mathrm{S}}_{14}}\le 50,\mathrm{de}\mathrm{préférence}4\le \frac{100.{\mathrm{S}}_{14}}{{\mathrm{S}}_{13}+{\mathrm{S}}_{14}}\le 40$$

In other words, the ratio of the winding sections between materials with high Js (S ₁ , S ₂ , S ₁₄ ) and materials with low magnetostriction λ (S ₃ , S ₄ , S ₁₃ ) must be maintained for each elementary module in a range determined for the invention to be implemented satisfactorily. The proportion of high Js material (in terms of section ratios), relative to the total of the sections of the two types of materials, must be between 2 and 50%, and preferably between 4 and 40%. This can result in the following inequalities: $$2\le \frac{100.{\mathrm{S}}_1}{{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3}\le 50,\mathrm{of}\mathrm{<figure-callout\; id="4"\; label="preference"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">preference</figure-callout>}4\le \frac{100.{\mathrm{S}}_1}{{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3}\le 40$$

$$2\le \frac{100.{\mathrm{S}}_2}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_4}\le 50,\mathrm{of}\mathrm{<figure-callout\; id="4"\; label="preference"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">preference</figure-callout>}4\le \frac{100.{\mathrm{S}}_2}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_4}\le 40$$

$$2\le \frac{100.{\mathrm{S}}_{14}}{{\mathrm{<figure-callout\; id="13"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{13}+{\mathrm{<figure-callout\; id="14"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{14}}\le 50,\mathrm{of}\mathrm{<figure-callout\; id="4"\; label="preference"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">preference</figure-callout>}4\le \frac{100.{\mathrm{S}}_{14}}{{\mathrm{<figure-callout\; id="13"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{13}+{\mathrm{<figure-callout\; id="14"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{14}}\le 40$$

, de préférence $$4\le \frac{100.\left({\mathrm{S}}_3+{\mathrm{S}}_{\mathrm{4}}+{\mathrm{S}}_{14}\right)}{{\mathrm{S}}_1+{\mathrm{S}}_2+{\mathrm{S}}_{13}+{\mathrm{S}}_3+{\mathrm{S}}_4+{\mathrm{S}}_{14}}\le 40$$

And also $2\le \frac{100.\left({\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_4+{\mathrm{S}}_{14}\right)}{{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2+{\mathrm{<figure-callout\; id="13"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{13}+{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_4+{\mathrm{<figure-callout\; id="14"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{14}}\le 50$

, preferably $$4\le \frac{100.\left({\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{4}}+{\mathrm{S}}_{14}\right)}{{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2+{\mathrm{<figure-callout\; id="13"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{13}+{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_3+{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_4+{\mathrm{<figure-callout\; id="14"\; label="S"\; filenames="imgf0001.png"\; state="\{\{state\}\}">S</figure-callout>}}_{14}}\le 40$$

To obtain proper operation of the transformer, passing through a good balance of the masses of the different materials between the different magnetic circuits, and not to weigh it down too much while benefiting from the advantages of the invention provided by the presence of the material with high Js in all the sub-cores, it is therefore necessary to respect the proportion in section of material with high Js of 2 to 50%, better 2 to 40%, both for the transformer core taken as a whole, which is reflected in the last inequality , that for each of its subsets (the two internal sub-kernels (1, 2; 3, 4) and the external sub-kernel (13, 14)) taken in isolation, which is reflected in the first three inequalities.

Since the different elements of the transformer normally all have the same depth p, these section ratios are equivalent to the volume ratios of the different materials.

In order for the invention to function as required, it must be possible to constitute a winding "mandrel" 1, 2 of high Js material for the low magnetostriction material 3, 4, and therefore a minimum of high Js material is necessary. . Participation in the damping of the inrush effect also requires a minimum section of high Js material. For these two reasons, we set at 2%, preferably 4%, the minimum value of the section of material at high Js with respect to the total section of material, for each of the sub-cores and for the core taken as a whole. .

If the material with high Js becomes predominant in section in the sub-cores and/or the core (≥ 50%), then its mass unnecessarily weighs down the structure. As has been said, it only actively participates significantly in damping the inrush effect, whereas in steady state of the transformer, we want the material with high Js to only magnetize weakly. so as not to emit noise (it inevitably has medium to strong apparent magnetostriction). Thus, the sizing of the transformer to achieve the desired power is essentially based on the material with low magnetostriction λ. If we had less than 50% low λ material (50% or more high Js material), essentially only this minority section would participate in the electrical transformation. Consequently, the high Js material is limited to a maximum of 50% of the total section of magnetic materials present in the sub-cores and the core of the transformer, as stated above.

• Si on utilise 100% de Fe49Co49V2 (exemples 2 à 5) pour constituer le noyau du transformateur, il faut abaisser B_t (induction de travail du transformateur en régime permanent) à moins de 0,3 T pour obtenir un bruit de 55-60 dB (alors qu'on verra qu'un bruit de 55 dB au maximum est souhaitable) ce qui correspond à une masse de plus de 18,7 kg pour pouvoir transformer la puissance électrique demandée ; dans cet exemple la densité de puissance massique du noyau de transformateur peut être évaluée à un taux de 46 kVA/18,7 kg= 2,46 kVA/kg de noyau magnétique, ce qui est une densité de puissance trop basse pour être acceptable ;
• Dans l'exemple 21 avec 53,3% de section Fe49Co49V2 (donc 46,7% de section de matériau nanocristallin), le bruit (58 dB) est encore trop élevé pour être conforme au cahier des charges ; la masse totale est de 6,4 kg, soit 28% plus grande que celle de l'exemple 12 entièrement en nanocristallin, ce qui serait acceptable, et l'indice d'inrush est de -0,35, ce qui est bon ;
• Les exemples 19 et 20 montrent qu'un bruit acceptable peut être obtenu avec plus de 50% de Fe49Co49V2, mais pour une masse totale trop forte, qui est de respectivement 7,4 et 7,1 kg (donc 40 à 50% plus élevée qu'avec la solution en nanocristallin seul de l'exemple 12) ;
• A l'inverse dans les exemples 18 et 18B, à respectivement 23,6 et 39% de section de FeCo27, le bruit est un peu trop fort (56 et 58 dB) alors que les masses ont été réduites jusqu'à un niveau convenable ; ainsi, avoir moins de 50% de la section magnétique en matériau à haute Js est une condition nécessaire mais pas suffisante pour une mise en œuvre satisfaisante de l'invention ; par exemple les exemples 15 et 18C avec respectivement 23,6 et 39% de section de FeCo27 émettent un bruit suffisamment bas, pour des masses faibles de, respectivement, 5,1 et 5,8 kg, soit seulement 2 et 16% de section de plus que la solution en nanocristallin seul de l'exemple 12, mais en permettant de bénéficier de tous les avantages de l'invention.

The following examples, which will be detailed later in Table 4, and the related comments, illustrate this point well:
Taking, for example, the Fe49Co49V2 material as the high Js material:

• If 100% Fe49Co49V2 (examples 2 to 5) is used to constitute the core of the transformer, it is necessary to lower B _t (work induction of the transformer in steady state) to less than 0.3 T to obtain a noise of 55-60 dB (while we will see that a noise of 55 dB maximum is desirable) which corresponds to a mass of more than 18.7 kg in order to be able to transform the electrical power required; in this example the mass power density of the transformer core can be evaluated at a rate of 46 kVA/18.7 kg= 2.46 kVA/kg of magnetic core, which is too low a power density to be acceptable;
• In Example 21 with 53.3% Fe49Co49V2 section (therefore 46.7% nanocrystalline material section), the noise (58 dB) is still too high to comply with the specifications; the total mass is 6.4 kg, ie 28% greater than that of example 12 entirely in nanocrystalline, which would be acceptable, and the inrush index is −0.35, which is good;
• Examples 19 and 20 show that an acceptable noise can be obtained with more than 50% Fe49Co49V2, but for too high a total mass, which is 7.4 and 7.1 kg respectively (therefore 40 to 50% higher than with the single nanocrystalline solution of example 12);
• Conversely in examples 18 and 18B, at 23.6 and 39% FeCo27 section respectively, the noise is a little too loud (56 and 58 dB) while the masses have been reduced to a suitable level. ; thus, having less than 50% of the magnetic section in high Js material is a necessary but not sufficient condition for satisfactory implementation of the invention; for example examples 15 and 18C with respectively 23.6 and 39% section of FeCo27 emit a sufficiently low noise, for low masses of, respectively, 5.1 and 5.8 kg, i.e. only 2 and 16% section more than the single nanocrystalline solution of example 12, but making it possible to benefit from all the advantages of the invention.

The elementary half-circuits formed by the parts 15, 16 are very dimensionally stable, in particular after impregnation with a varnish and polymerization, even under the constraints of maintaining the two C-shaped parts of the elementary magnetic core. This would not be the case if the high Js parts 1, 2 were removed, which serve as mechanical supports for the low magnetostriction windings 3, 4, and stiffen each elementary core.

The magnetic alloys with low magnetostriction and low magnetic losses of the windings 3, 4 make it possible to satisfy most of the required requirements, in particular the very low acoustic noise emitted, even when one places oneself at a work induction B _t close to saturation. This makes it possible in this case to maximize the power density, in particular in the case of nanocrystalline materials where it is possible to work up to 1.2 T. This is the other material, at high Js, of the winding 14 the outer part of the core which contributes the most to the damping of the inrush effect.

But we notice, with surprise, that thanks to the high Js magnetic support material of the internal windings 1, 2 of the sub-cores, the inrush effect is distributed over the two types of material. Thus the operating induction of the majority nanocrystalline material can be increased almost to saturation, which makes it possible to lighten the transformer accordingly.

High Js alloys are characterized by medium (FeSi, FeNi, iron-based amorphous) to high (FeCo) amplitude magnetostriction, which makes it necessary to reduce the work induction B _t very significantly (typically to at most 0.7T) to achieve low acoustic noise.

It has been realized that by using together, in a clever way, alloys with low magnetostriction and low magnetic losses and alloys with high Js, in particular, preferably, by the differentiated adjustment of the air gap 17 which is provided, advantageously but not necessarily, between the materials of each pair of C, so as to give it a value ε1 at the level of the first material and a value ε2 at the level of the second material, and also by the respective proportions of the materials, it was possible at the same time on the one hand set a high work induction in the part with low magnetostriction, and on the other hand set a low work induction in the part with high Js. By proceeding in this way, the inrush effect is sufficiently damped and distributed over the two types of material, and the noise emitted by each of the materials remains low, while allowing a fairly high power density, in any case better than what is known in the state of the art for solutions in which a low magnetostriction noise is primarily sought.

We will now describe examples of application of the invention and reference examples, based on the figures 1 and 2 and on the experimental results of table 4 which translates the picture 3 .

We consider on the figure 2 a single-phase transformer core 18, characterized by a rectangular-oblong shape of height h, width l and depth p, on which rests the winding of the main active material of the transformer: the material with low magnetostriction. This elementary core 18 can also be integrated into a three-phase transformer circuit as shown in the figure 1 as an elementary module.

This oblong circuit single-phase transformer module is made with a first material with high Js, of winding thickness ep1, and with a second material with low magnetostriction wound around the first material itself wound beforehand, and having a thickness of winding ep2. The small and large inner sides of the winding 3 (second material), and which are also the small and large outer sides of the winding 1 (first material) when it is present (as in the examples according to the invention and in some of the reference examples), are denoted “a” and “c” respectively, and are respectively worth, for all the examples tested, a=50 mm and c=125 mm. a and c are also the dimensions of the inner sides of the windings 3, 4 of the second material, with low magnetostriction, arranged around the windings 1, 2 of the material with high Js. For all the tests, ep2 is equal to 20 mm. and ep1 is comprised, according to the tests, between 0 (absence of material at high Js) and 20 mm.

The depth p is variable according to the tests, because it is designed so that the power transferred is substantially the same in all the tests (of the order of 46 kVA), taking into account that the values of a and c are also the same in all tests. It will be noted (see Table 4) that p can reach values as high as 265 mm for a reference test 4 using an Fe49Co49V2 alloy alone and 176 mm for the reference test 8 using a FeSi3 alloy alone. The reference solutions making use of a single nanocrystalline and the solutions of the invention which make use of a nanocrystalline and a material with high Js have a depth p that is markedly lower. In the examples according to the invention, it is of the order of 60 to 80 mm.

The transformer is supplied with electric current of nominal frequency 360 Hz. The primary supply current has an intensity of 115 A with a number of turns N ₁ generally equal to 1 turn, but being 5 turns in reference example 1 and 2 turns in reference examples 2, 3 and 4, taking into account the considered air gaps of each winding 1 and 2 on the one hand, 3 and 4 on the other hand, also taking into account the material considered for each winding (therefore of its permeability), in order to reach the work induction B _t . A voltage of 230 V is applied to the primary. The secondary winding has, in all the examples described, a number N ₂ =64 turns, and the nominal voltage expected at the secondary is 230 V. In all cases, the energy conversion system in which the transformer is integrated requires that to provide a constant voltage variation V ₁ of 230 V. This also amounts to supplying a constant three-phase power of 46 kVA.

• d'un premier matériau à haute saturation ;
• et, en complément, d'un deuxième matériau à basse magnétostriction, enroulé autour du premier matériau.

The magnetic core is therefore made from a wound structure of strips consisting of:

• a first high saturation material;
• and, in addition, a second material with low magnetostriction, wrapped around the first material.

In order to always deliver the same secondary voltage of 230 V, we play on the section of the magnetic core, via the depth p of the core, while the rolled thickness ep2 of the second material is kept identical for all the tests, equal to 20 mm and corresponds to a constant magnetic circuit length of 430 mm. By contrast, the length of the magnetic circuit of the first material, with variable thickness according to the examples, ranges from 270 to 343 mm in all the examples according to the invention and also in all the reference examples with an elementary bi-material module. If we consider that P is the transformed power, as P = I.fem (intensity of the primary current multiplied by the electromotive force fem generated at the secondary) is a dimensioning constraint (P = constant), and that the electromagnetic force is imposed by the electrical circuit and since “emf = N ₂ .B _t .section of the core.2π.frequency”, then the section must be increased when one is obliged to reduce B _t to lower the noise.

It is recalled that it is the second material with low magnetostriction which operates very mainly in steady state, and therefore ensures the output voltage and power of the transformer. On the other hand, the inrush effect comes from the combination of the magnetic behaviors of the two materials, and in order to appreciate the innovative contribution of the presence of another magnetic material (the first material) in the core, the rolled thickness ep1 of this first material varies from 0 (which corresponds to an absence of the first material) to 20 mm depending on the tests. This corresponds to a magnetic circuit length which varies from 0 to 343.2 mm.

où S₁ et S₂ sont les sections des enroulements des premier et deuxième matériaux respectivement, B_r,2 est l'induction rémanente du deuxième matériau, seul actif en fin de période de régime permanent lorsqu'intervient la coupure du transformateur et le passage du noyau magnétique à l'état rémanent, B_t,1 et B_t,2 sont les inductions de travail, J_s,1 et J_s,2 sont les aimantations à saturation des premier et deuxième matériaux respectivement. La formule peut être aisément adaptée au cas où plus de deux matériaux sont utilisés.The noise comes from the magnetostriction of the materials and their level of magnetization, and therefore the noise will be mainly linked in steady state to the magnetic behavior of the second material. The inrush index is given by the known formula: I _n =2.B _t +B _r -B _s for a magnetic core with a single magnetic material. This formula is generalized to the case of two materials according to: $$\left({\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2\right).{\mathrm{I}}_{\mathrm{not}}={\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2.{\mathrm{B}}_{\mathrm{r},2}+{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_1.\left(2{\mathrm{B}}_{\mathrm{you},1}-{\mathrm{J}}_{\mathrm{s},1}\right)+{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0002.png"\; state="\{\{state\}\}">S</figure-callout>}}_2.\left(2{\mathrm{B}}_{\mathrm{you},2}-{\mathrm{J}}_{\mathrm{s},2}\right)$$

where S ₁ and S ₂ are the sections of the windings of the first and second materials respectively, B _r,2 is the remanent induction of the second material, the only one active at the end of the steady state period when the transformer is cut off and the passage of the magnetic core in the remanent state, B _t,1 and B _t,2 are the work inductions, J _s,1 and J _s,2 are the saturation magnetizations of the first and second materials respectively. The formula can easily be adapted in the event that more than two materials are used.

We call dΦ/dt the voltage induced (in other words the electromotive force emf) by the transformer. It is thanks to it that the electrical power P requested is transformed: P = fem.I where I is the intensity of the magnetizing current of the transformer.

The noise emitted by the various examples made of wound transformer cores is measured by a set of microphones placed around the transformer, in the mid-plane of the magnetic yoke. The various examples of magnetic cores use a single (references) or two (certain references and the invention) materials, namely soft magnetic materials (FeCo27, Fe49Co49V2, Fe-3%Si-GO, grain-oriented FeSi electrical steel, nanocrystalline FeCuNbSiB of the type [Fe _1-a Ni _a ] _{100-xyz-α-β-γ} Cu _x Si _y B _z Nb _α M' _β M"γ with a = 0; x = 1; y = 15; z = 7.5, α=3, β=γ=0. The material(s) is (are) rolled up according to the basic structure defined previously.

The examples in table 4 below are sized and supplied in such a way as to always transform substantially the same power, namely approximately 46kVA. This three-phase power being given by √3.I ₁ .dΦ/dt with dΦ/dt = N ₂ .(B _t,1 .S ₁ + B _t,2 .S ₂ ).ω = 230V, where I ₁ = 115A , N ₂ (number of secondary turns) equal to 64, ω (pulsation) = 2.π.f, f being the frequency, here equal to 360 Hz, S ₁ and S ₂ (magnetic yoke sections of the first and second materials respectively) equal respectively to (H.ep1) and (H.ep2), and B _t,i is the work induction of material i.

Another possibility consists in precisely adjusting the air gaps (after cutting) ε1 and ε2 between the half-circuits of the windings of the first and second materials respectively, by giving them, if necessary, different values during the shaping of the cutting zones, in order to to be able to limit the magnetization of one material relative to the other. Otherwise certain uncontrolled levels of magnetization of material 1 could increase the magnetostriction or the inrush effect too much. It should, however, be remembered that the increase in an air gap increases the current necessary for the magnetization at the level B _t , and therefore degrades the efficiency of the transformer. A balance will therefore have to be found between the advantages and disadvantages of the practical use of this solution.

). Si l'entrefer ε2 avait été dix fois plus large (100 µm), on aurait une perméabilité intrinsèque µ_r,eq,mat2 = 3760, soit quatre fois moindre que précédemment. Or (selon le théorème d'Ampère), H.L = N₁.I (L étant la longueur moyenne de circuit magnétique) et H = B/µ_r,eq tant que le matériau travaille avec une courbe B = f(H) approximativement linéaire (cas du transformateur). Donc en maintenant B_t constant (pour maintenir la force électromagnétique et la puissance transférée constantes, comme dit précédemment), il faut compenser une augmentation de l'entrefer (et donc une baisse de µ_r,eq) par une hausse de l'intensité I du courant magnétisant, ce qui entraine une dégradation du rendement du transformateur.For example in example 13 of the invention, the minimum residual air gap ε2 between the two half-circuits of the second material (the nanocrystalline material) is evaluated at 10 μm, and then the equivalent relative magnetic permeability μ _{r,eq, mat2} of the “material 2 + air gap” magnetic circuit increases the intrinsic permeability µ _r,mat2 of material 2 from 30,000 to 17,670 in the case of the example (by applying the formula $\frac{1}{{\mathrm{\mu }}_{\mathrm{r}\mathrm{,eq}\mathrm{,<figure-callout\; id="2"\; label="mast"\; filenames="imgf0002.png"\; state="\{\{state\}\}">mast</figure-callout>}2}}\approx \mathrm{air\; gap}+\frac{1}{{\mathrm{\mu }}_{\mathrm{r}\mathrm{,mast}2}}$

). If the air gap ε2 had been ten times wider (100 µm), we would have an intrinsic permeability µ _r,eq,mat2 = 3760, ie four times less than previously. However (according to Ampère's theorem), HL = N ₁ .I (L being the average magnetic circuit length) and H = B/µ _r,eq as long as the material works with a curve B = f(H) approximately linear (case of the transformer). So by keeping B _t constant (to keep the electromagnetic force and the transferred power constant, as said previously), it is necessary to compensate for an increase in the air gap (and therefore a drop in µ _r,eq ) by an increase in the intensity I of the magnetizing current, which leads to a deterioration in the efficiency of the transformer.

If we consider on the same example 13 the air gap ε1 of magnetic circuits with high Js material, we conclude that an air gap ε1 of 3.5 mm makes it possible to limit the equivalent permeability of the first material (here FeCo) to 0.05 T (see the formula µ _r,eq above), and therefore a low noise of 43 dB. If the air gap ε1 is reduced to 10 µm, therefore to a value equal to that of ε2, then the material with high Js FeCo greatly exceeds the induction of 1 T in the steady state of the transformer, and the noise of the FeCo then becomes predominant and unsatisfactory (much higher than 55 dB), but may be admissible for the duration of the Inrush effect (ie from a few fractions of a second to a few seconds).

The general rule for limiting inrush effects and noise is that, as the work induction B _t has a degrading influence on both the inrush effect and the magnetostriction noise, it is necessary to lower B _t to mitigate these effects. But this drop in B _t must be compensated by an increase in the magnetic section to keep dΦ/dt and the transformed power at the same level.

The specifications for this aeronautical transformer are that the noise must be a maximum of 55 dB, at least outside the periods during which the inrush effect is felt, and the inrush factor less than or equal to 1, with the lowest possible magnetic core mass. Also, the total mass of magnetic materials should not exceed about 6.5 kg. We will see that for this last condition to be fulfilled at the same time as the other two, the total section of the high Js material relative to the total section of magnetic materials in the core exceeds 50%. This condition must also be respected if we reason on each of the internal and external sub-nuclei taken in isolation. In order not to complicate Table 4, only the ratio of the total sections has been specified there, but it must be understood that all the examples according to the invention also meet the condition for each of their sub-cores.

The examples in Table 4 show the following. Those denoted “ref” are reference examples, those denoted “inv” are examples according to the invention.

Examples 1 to 12, 18, 18B, 19 to 21 inclusive of Table 4 are therefore reference examples, and Examples 13 to 17 inclusive, 18C, 22 to 24 inclusive are examples according to the invention which meet all the criteria of the specifications as defined above.

It will be noted that for reference examples 1 to 12, no air gap has been provided in the second material. For all the other examples, whether reference or according to the invention, an air gap ε2 of 10 μm has been provided in the second material. For examples 13 to 24, whether they are reference or according to the invention, both an air gap ε2 of 10 μm in the second material and an air gap ε1 in the first material have been provided, ε1 being able to take various values according to the tests, and ε1 being different from ε2, except for example 24 where ε1 = ε2 = 10 μm. It must be understood that in these examples, ε1 and ε2 are the same for all the elements of the kernel: the two internal sub-nuclei and the external sub-nucleus.

To calculate the volumes and deduce the sections of the different materials, we took as densities 7900 kg/m ³ for FeCo27, 8200 kg/m ³ for FeCo50V2, 7650 kg/m ³ for FeSi3, 7350 kg/m ³ for nanocrystalline.

The Js of the different materials are 2.00 T for FeCo27, 2.35 T for FeCo50V2, 2.03 T for FeSi3, 1.25 T for nanocrystalline. Table 4: Performance of different core configurations tested Second material First material Steady state Mass and section Ex. Materials 2 + 1 thickness 2 mm thickness 1 mm P mm B, matte. 2 B _t,2 (T) Br matt. 2 Br (T) B _t matt. 1 B _t,1 (T) dΦ/dt (V) Noise (dB) Inrush index Matt mass. 1 (kg) Matt mass. 2 (kg) Total mass (kg) % weight of mat. 1 (at high Js % section of mat. 1 (at high Js) Three-phase power (kVA) Matt air gap. 2ε2 (µm) Matt air gap. 1ε1 (µm) 1 ref FeCo27 20 0 40 2 0.95 - 231.62 105 2.95 0 2.7 2.7 0 0 46.14 0 0 2 ref Fe49Co49V2 20 0 40 2 1.3 - 231.62 115 2.95 0 2.8 2.8 0 0 46.14 0 0 3 references Fe49Co49V2 20 0 53 1.5 0.975 - 230.18 96 1.63 0 3.7 3.7 0 0 45.85 0 0 4 references Fe49Co49V2 20 0 80 1 0.65 - 231.62 75 0.3 0 5.6 5.6 0 0 46.14 0 0 5 references Fe49Co49V2 20 0 265 0.3 0.195 - 230.16 61 -1.56 0 18.7 18.7 0 0 45.85 0 0 6 ref FeSi3 20 0 53 1.5 1.05 - 230.18 92 2.02 0 3.5 3.5 0 0 45.85 0 0 7 ref FeSi3 20 0 72 1.1 0.77 - 229.31 85 0.94 0 4.7 4.7 0 0 45.67 0 0 8 ref FeSi3 20 0 176 0.3 0.21 - 229.31 57 -1.22 0 19.0 19.0 0 0 45.67 0 0 9 ref FeSi3 20 0 72 1.1 0 - 229.31 85 0.17 0 4.7 4.7 0 0 45.67 10 0 10 ref Coated or cut cycle nanocrystalline 20 0 72.3 1.1 0.055 - 230.26 40 1.01 0 4.6 4.6 0 0 45.87 10 0 11 ref Coated or cut cycle nanocrystalline 20 0 94 0.85 0.0425 - 231.33 40 0.49 0 5.9 5.9 0 0 46.06 10 0 12 ref Coated or cut cycle nanocrystalline 20 0 79.5 1 0.05 - 230.18 41 0.8 0 5.0 5.0 0 0 45.85 10 0 13 inv Coated or cut cycle nanocrystalline + Fe49Co49V2 20 2 72 1.10 0.06 0.05 230.35 43 0.71 0.40 4.6 5.0 8.0 10.8 45.88 10 3500 14 inv Coated or cut cycle nanocrystalline + FeCo27 20 1.7 70 1.1 0.055 0.4 229.83 46 0.8 0.33 4.4 4.7 7.0 9.3 45.78 10 360 15 inv Coated or cut cycle nanocrystalline + Fe49Co49V2 20 5 66.3 1.1 0.055 0.4 230.35 49 0.49 0.90 4.2 5.1 17.6 23.6 45.88 10 360 16 inv Coated or cut cycle nanocrystalline + Fe49Co49V2 20 2.1 68.3 1.1 0.055 0.6 229.98 48 0.8 0.40 4.3 4.7 8.5 11.2 45.81 10 220 17 inv Coated or cut cycle nanocrystalline + Fe49Co49V2 20 2.5 66.5 1.1 0.055 0.75 229.84 52 0.8 0.46 4.2 4.7 9.8 13.1 45.78 10 160 18 ref Coated or cut cycle nanocrystalline + FeCo18 20 5 60 1.1 0.055 0.9 230.18 56 0.69 0.81 3.8 4.6 17.6 23.6 45.85 10 120 18B ref Coated or cut cycle nanocrystalline + FeCo18 20 10 56.7 1.1 0.055 0.6 229.83 58 0.29 1.44 3.6 5.0 28.8 39 45.78 10 120 18C reverse Coated or cut cycle nanocrystalline + FeCo18 20 10 66 1.1 0.055 0.2 229.31 53 0.02 1.68 4.2 5.88 28.6 39 45.67 10 120 19 ref Coated or cut cycle nanocrystalline + Fe49Co49V2 20 20 69 1.1 0.055 0.05 229.74 53 -0.62 3.06 4.4 7.4 41.4 57.8 45.76 10 3500 20 references Coated or cut cycle nanocrystalline + FeCo27 20 17 69.5 1.1 0.055 0.05 229.90 52 -0.49 2.73 4.4 7.1 38.5 53.3 45.79 10 3500 21 ref Coated or cut cycle nanocrystalline + FeCo27 20 17 69.5 1.1 0.055 0.2 229.90 58 -0.35 2.46 4.0 6.4 38.4 53.3 45.78 10 800 22 inv Coated or cut cycle nanocrystalline + FeSi3 20 5 71.5 1.1 0.055 0.05 230.30 47 0.42 0.90 4.5 5.4 16.7 23.6 45.87 10 3500 23 inv Coated or cut cycle nanocrystalline + FeSi3 20 5 71.5 1.1 0.055 0.05 230.30 50 0.42 0.90 4.5 5.4 16.7 23.6 45.87 10 3500 24 inv Coated or cut cycle nanocrystalline + FeSi3 20 5 59 1.1 0.055 1 230.61 52 0.8 0.74 3.7 4.5 16.4 23.6 45.93 10 10

An entirely nanocrystalline circuit (reference examples 10 to 12) certainly makes it possible to meet the requirements of the specifications in terms of noise and inrush, for a mass alone of the magnetic circuit which can go down to 4.6 kg, which would be satisfactory to first sight. However, this mass does not include the non-magnetic supports of the magnetic circuit, which can be made, for example, of wood, Teflon or aluminum, and which can constitute a mass of several hundred grams.

The nanocrystalline solution alone necessarily requires the use of a temporary or permanent winding support. In the case where it is permanent, it increases the mass of the nanocrystalline circuit as we have just said.

In all cases (permanent support or not), this support must be made, even though it does not participate in any way in the electrical operation of the transformer, unlike the cases relating to the invention. The cost of producing the support is therefore not made profitable in the design of the transformer, unlike the cases of the invention. Examples 10 to 12 are therefore not considered to fully meet the specifications of the invention, and are classified as references.

To clarify this important point, reference examples 12 (nanocrystalline alone) and 17 according to the invention (nanocrystalline composite core cycle coated or cut + FeCo27) can be compared. These two examples are chosen because they can be considered to be the most efficient for their respective technological choices, since they have the same Inrush index. The noise emitted is lower for the 100% nanocrystalline solution (41 dB against 52 dB for the coated or cut cycle nanocrystalline composite core solution + FeCo27), but in both cases the noise is below the admissible threshold of 55 dB.

Example 12 uses a mass of nanocrystalline material of 5.0 kg, to which must be added a minimum mass of 200 to 300 g of non-magnetic Teflon, aluminum or stainless steel. Two possible cases have been considered for this example: permanent support and non-permanent support.

Table 5 cites the successive operations in these three embodiments, and compares the orders of magnitude of the costs of each step (from +: inexpensive to +++: expensive; 0: step absent from the embodiment) of the solutions in the case of making a functional sub-assembly of a single toroid (single-phase transformer type): Table 5: Cost comparison of solutions 12 (reference) and 17 (invention) Step no. 100% nanocrystalline solution (n°12), non-permanent support Stage cost 100% nanocrystalline solution (n°12), permanent support Stage cost Solution according to the invention (No. 20) Stage cost 1 Realization of a non-permanent magnetic core support ++ Realization of a permanent magnetic core support + Realization of a FeCo magnetic metal support ++ 2 Winding of the amorphous strip on an extractable metal support (shell) + Winding of the amorphous strip on an extractable metal support (“ferrule”) + Winding of the nanocrystalline strip on the support, with a nanocrystallization contraction wedge (approximately 1%) removed at the end of winding + 3 Annealing of nanocrystallization and contraction of the amorphous ribbon on the ferrule + Annealing of nanocrystallization and contraction of the amorphous ribbon on the ferrule + Annealing of nanocrystallization and contraction on the FeCo support + 4 Extraction of the nanocrystalline core from the ferrule + Extraction of the nanocrystalline core from the ferrule + 0 0 5 Nanocrystalline core placed on the non-permanent support with minimal clearance + Nanocrystalline core placed on the permanent support with minimal clearance + 0 0 6 Impregnation of the “core + support” assembly ++ Impregnation of the “core + support” assembly ++ Impregnation of the “core + support” assembly ++ 7 Polymerization of the whole + Polymerization of the whole + Polymerization of the whole + 8 Extraction of non-adherent support + 0 0 9 Cutting into two equal Cs of the impregnated core alone ++ Cutting into two equal Cs of the core + impregnated support + Cut into two equal Cs + 10 Surfacing of the cutting faces of the Cs + Surfacing of the cutting faces of the Cs + Surfacing of the cutting faces of the Cs + 11 Mechanical assembly with regulated air gap (wedge if necessary) +++ Mechanical assembly with regulated air gap (wedge if necessary) ++ Mechanical assembly with regulated air gap (wedge if necessary) ++

Table 5 shows that there are fewer operations in the case of the invention, and, moreover, some of the operations common to the various solutions are less costly in the case of the invention. Indeed, when cutting and assembling C parts in 100% nanocrystalline material (example 12 without permanent mechanical support), the absence of stiffening mechanical support (case "without permanent support") requires maintaining the C carefully, therefore using appropriate clamping jigs so as not to deform and damage the parts.

In the case of Reference Example 12 with a permanent support, the precautions are the same as for the invention, but in this case, the final core is made heavier, and the cost of the support is added to each magnetic core produced.

In the case of example 17 according to the invention, the FeCo support constitutes a mechanical core avoiding irreversible mechanical deformations, and is at the same time used functionally on the electromagnetic and electrical plane.

In the end, compared to the invention, the 100% nanocrystalline solution of the prior art (example 12) is either a little more expensive because of the greater number of operations and heavier because of the mass of the support ( case of the permanent support), or (case of the non-permanent support) of equal or slightly higher mass, but in any case much more expensive to produce. It therefore does not constitute, overall, a satisfactory solution to the problems which the invention sought to solve.

Returning to Table 4, we see that a circuit mainly in nanocrystalline with an additional circuit in Fe-27% Co alloy in certain limited proportions makes it possible to achieve equivalent or even slightly better mass performance (final mass close to 4, 5 kg in the best case), while also respecting the inrush and noise specifications, if it is compared to a 100% nanocrystalline solution with a non-permanent support (see above). This sizing optimum corresponds, in the case of the examples according to the invention, to a proportion by section of FeCo or FeSi of approximately 9 to 40%, and from 7 to 29% by weight approximately, compared to all the magnetic materials of the core. This optimum is also valid at the level of each of the sub-nuclei taken separately.

By further increasing the proportion of FeCo, and therefore by making the magnetic circuit heavier (case of more than 30% by weight and more than 50% by section of FeCo, examples 19, 20 and 21), we see that the effect of inrush can be drastically reduced to a negative index. In this case, the magnetic circuit reaches a mass of around 7 kg (for a zero inrush index). This mass can however be considered a little too high for this technical solution to be fully satisfactory, especially since, moreover, the noise is only relatively slightly below the acceptable maximum of 55 dB (examples 19 and 20 ) or is above this acceptable maximum (example 21). A mass of the order of 6.5 kg would generally be considered acceptable, but only if, moreover, the noise and inrush conditions are respected. This explains why Example 21 is not considered to be part of the invention.

The use of FeSi-G.O. (Grain Oriented Fe-3% Si electrical steel), replacing FeCo, in the previous case shows the same trend results as the previous case, but making the magnetic circuit somewhat heavier if one wants to obtain an index of comparable inrush.

The use alone and without a localized air gap (i.e. with an uncut magnetic circuit), and at high induction, of the traditional materials of aeronautical on-board transformers (FeCo27, Fe49Co49V2, FeSi3) leads to very low masses magnetic circuit (examples 1, 2, 3, 6), but also to very high noise (92 to 115 dB), well above the admissible limit of 55 dB, and to a very high inrush effect (index d 'inrush from 1.63 to 2.95) which will lead to the degradation of certain electronic components on the on-board network. Note that if the circuit were cut to obtain a localized air gap and a very low remanence Br, then the inrush effect would be much less significant. But the noise would still be loud and the implementation cost would be much higher.

The use of these same crystalline materials alone, but at a significantly lower induction, makes it possible to significantly reduce the inrush effect and the noise (examples n° 4, 5, 7, 8, 9) until approaching ( noise) or reach (inrush) the admissible limits of the specifications. However, when this situation is obtained (examples n°5 and 8), the mass of the magnetic circuit is of the order of 18-19 kg, i.e. three times greater than those of the reference solutions based on nanocrystalline alone and with induction. high, or solutions according to the invention where the nanocrystalline is combined with FeCo or FeSi.

The picture 3 summarizes the performance of different possible magnetic circuit solutions in an inrush-noise index diagram where the transformer masses corresponding to the different points are also specified.

The dotted lines show the maximum noise values of 55 dB and the inrush index of 1 required by the specifications cited above. The zone in which the examples are found which meet these points of the specifications and present, moreover, a section of material with high Js compared to the total section of magnetic materials of 50% at most, and sections of materials with high Js reported to the total sections of the magnetic materials of each sub-core by 50% at most. This last point, which is also part of the specifications, also makes it possible to guarantee that the core of the transformer is very light, of the order of 6.5 kg or less.

It clearly appears that the invention makes it possible, by the use of a nanocrystalline circuit combined with FeCo or FeSi, to respect the limitations in noise and inrush effect by using magnetic circuits much lighter than the solutions in traditional crystalline materials (FeSi, FeCo comparable) used alone. As for the solutions using a single nanocrystalline, their performance, at equal mass, is fairly comparable to that of the invention in terms of noise and inrush index, but we have seen in table 5 that the cost of producing these solutions was substantially higher than that of the embodiments according to the invention.

The Inrush Index is always a strictly decreasing function of the mass of the magnetic yoke. But this curve is not linear, and it makes it possible in the case of the example analyzed to determine magnetic yoke solutions with fairly low mass (4 to 6.5 kg) for an already very low inrush index. In a different way, the noise depends not only on the mass, but also on the choice of the material(s) used (via their magnetostrictive properties).

It thus appears clearly that the solutions of the invention based on nanocrystalline associated with another material (FeCo or FeSi in particular) make it possible to combine a low mass (4 to 6.5 kg), a low noise and a low index of 'inrush, and for a cost and manufacturing complexity as moderate as possible.

Variants of the invention can be envisaged.

Several high Js materials can be used in the same magnetic core, for example a Goss textured Fe-3%Si alloy in the inner winding of the inner sub-cores and an Fe-50%Co alloy in the outer winding of the sub - outer core.

Several materials with low magnetostriction can be used in the same magnetic core, such as, for example, a nanocrystalline FeCuNbSiB alloy of the composition specified above, in the inner winding of the inner sub-cores and an amorphous cobalt base in the winding. exterior of the outer subnucleus. It is best to use the same material for both inner sub-cores. It is preferable to keep the rule of conservation of the magnetic flux “J _s .Section” between the three sub-parts concerned with materials with low magnetostriction.

According to the invention, the use of nanocrystalline materials is recommended with respect to the use of other types of materials with low magnetostriction.

Indeed, the nanocrystalline materials of FeCuNbSiB composition mentioned, which constitute privileged but not exclusive examples of materials that can be used for the implementation of the invention, are known to make it possible to adjust their magnetostriction to 0 by an adequate heat treatment, while their magnetization at saturation remains relatively high (1.25 T), therefore conducive to not making the transformer too heavy (see the dimensioning principles already mentioned influencing dφ/dt and the inrush).

The invention is not only valid for a three-phase structure with two sub-cores placed side by side and nested in a third sub-core, but is also applicable to a simple magnetic core of a single-phase transformer, or to any other nesting of a higher number of magnetic sub-cores, for example in the case of polyphase transformers with more than three phases. A person skilled in the art will be able without difficulty to adapt the design of the transformer according to the invention to this latter case.

The cutting of the finished magnetic core, forming the air gap 17, so as to better fill the winding window and therefore to reduce the mass/volume of the magnetic core, is not essential, but it is very preferable both for the previous reason since the power density is increased, via the optimal filling of the winding window, but also to lower the remanent induction of the magnetic circuit. An additional advantage of the cut is to be able to possibly differentiate the air gaps ε1 and ε2 of the two materials, in order to better control the maximum level of magnetization of the first material with high Js and high magnetostriction.

The adjustment of the air gap can therefore be different between materials with low magnetostriction and materials with high Js, as we have seen on most of the examples according to the invention in table 4 and as represented on the figures 1 and 2 . If the magnetostriction is very low, the cyclic deformation of the materials will be very low and the air gap wedging will only propagate and amplify little noise. On the other hand for materials with high Js, very magnetostrictive, even for low work inductions in steady state (less than 0.8 T, or even less than 0.4 T) the vibrations may still be sufficient to generate noise above the highest requirements. In this case it may be preferable to machine a slight air gap, greater than that of the material with low magnetostriction, so that the materials with high Js are not in contact with the wedge, which makes it possible to reduce the emission of noise.

If we see an interest in it, we can also provide different values of ε1 and/or ε2 for the various parts of the core, in other words. that the air gaps (ε1, ε2) separating the two parts of the various windings (1, 2, 3, 4, 13, 14) are not all identical between the internal magnetic sub-core and the external magnetic sub-core.

The surfacing of the cut faces of the magnetic core is not essential, but it is preferable because it allows a better dimensioning of the performances of the transformer. This makes it possible to increase inrush performance, and to make transformers more reproducible during industrial production.

Calibrating the air gap using a wedge is not essential, but it is preferable to precisely adjust the remanent induction (linked in particular to the inrush effect) and the maximum level of magnetization accessible in each material, and to make more reproducible processors in industrial production.

The cutting symmetry of the magnetic core is not essential.

In the event of non-cutting, it is not essential to glue, impregnate, fix the various metal parts of the cylinder head, more rigidly and tightly than the various tight windings and the heat treatment(s) allow. ).

The different materials do not necessarily have the same width. For example, three strips of FeCuNbSiB nanocrystallizable amorphous of width l each can be wound around a pre-wound torus of internal FeSi or FeCo sub-core of width 3l. This brings the advantage of providing the same mechanical winding support for the FeCuNbSiB strips which are especially easy to produce and use when their width is less than 20-25 mm, whereas the needs for the magnetic cores of on-board transformers can greatly exceed such widths.

As an alternative to the previous solution, it is also possible to stack different magnetic cores with the same widths of material, in order to also obtain in the end a wider macro-torus before gluing, fixing, impregnation, mechanical wedging or other, then cutting, surfacing then assembly of the prefabricated windings.

All materials, or only some of them, can be wound in the amorphous or work-hardened or partially crystallized state (depending on the case), or else be wound in the nanocrystallized state (FeCuNbSiB), relaxed (amorphous iron base or cobalt base) or crystallized (Fe-80%Ni, FeCo, FeSi, other polycrystalline materials).

Claims (23)

1. - An elementary module of a magnetic core of an electrical transformer of the wound type, made up of a first (1; 2) and second (3; 4) superimposed winding, respectively made from a first and second material, said first material being a crystalline material with a saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum inductance of 1 T, preferably less than 15 W/kg, preferably less than 10 W/kg, said first material being chosen from among Fe-3% Si alloys with oriented grains, Fe-6.5% Si alloys, Fe-15 to 55% total of Co, V, Ta, Cr, Si, Al, Mn, Mo, Ni, W alloys, textured or not, soft iron and ferrous alloys made up of at least 90% Fe and having Hc < 500 A/m, ferritic stainless steels Fe-Cr with 5 to 22% Cr, 0 to 10% total Mo, Mn, Nb, Si, Al, V and with more than 60% Fe, non-oriented electric steels Fe-Si-AI, Fe-Ni alloys with 40 to 60% Ni with no more than 5% total additions of other elements, Fe-based magnetic amorphous materials with 5 to 25% total B, C, Si, P and more than 60% Fe, 0 to 20% Ni + Co and 0 to 10% other elements, all of these content levels being given in percentages by weight.

   and said second material being a material with an apparent saturation magnetostriction (λ_sat) less than or equal to 5 ppm, preferably less than or equal to 3 ppm, better still less than or equal to 1 ppm, and magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably less than 15 W/kg, preferably less than 10 W/kg, said second material being chosen from among Fe-75 to 82% Ni - 2 to 8% (Mo, Cu, Cr, V) alloys, cobalt-based amorphous alloys, and FeCuNbSiB nanocrystalline alloys,

   characterized in that the cross-sections (S₁; S₂) of the first winding (1; 2) and (S₃; S₄) of the second winding (3; 4) are such that the ratio (S₁/(S₁ + S₃); S₂/(S₂ + S₄)) of each cross-section of the first material with a high saturation magnetization (Js) compared to the cross-section of the set of the two materials of the elementary module is comprised between 2 and 40%.
2. - The elementary module according to claim 1, wherein said second material is a nanocrystalline alloy with composition:
   
           Fe_1-aNi_a]_{100-x-y-z-α-β}-γCu_xSi_yB_zNbαM'βM''γ
   
   with a ≤ 0.3; 0,3 ≤ x ≤ 3; 3 ≤ y ≤ 17, 5 ≤ z ≤ 20, 0 ≤ α ≤ 6, 0 ≤ β ≤ 7, 0 ≤ γ ≤ 8, M' being at least one of the elements V, Cr, Al and Zn, M" being at least one of the elements C, Ge, P, Ga, Sb, In and Be, the index numbers corresponding to atomic percentages.
3. The elementary module according to one of claims 1 or 2, including an air gap (17) dividing it into two parts.
4. - The elementary module according to claim 3, wherein the air gap (ε1) separating the two parts of the first windings (1; 2) is different from the air gap (ε2) separating the two parts of the second windings (3; 4).
5. - The elementary module according to claim 3 or 4, wherein said two parts are symmetrical.
6. - A single-phase electric transformer magnetic core, characterized in that it is made up of an elementary module according to one of claims 1 to 5.
7. - A single-phase electric transformer, including a magnetic core and primary and secondary windings, characterized in that the magnetic core is of the type according to claim 6.
8. - A three-phase electric transformer magnetic core, characterized in that it includes:

   - an inner magnetic sub-core made up of two elementary modules according to one of claims 1 to 4, alongside one another; and

   - an outer magnetic sub-core made up of two additional superimposed windings (13, 17), positioned in this order around the inner magnetic sub-core:

   ▪ a first winding (13) made from a strip of the material with low magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably below 15 W/kg, preferably below 10 W/kg, and with a saturation apparent magnetostriction (λ_sat) less than or equal to 5 ppm, preferably less than or equal to 3 ppm, better still less than or equal to 1 ppm, said first winding (13) of the outer magnetic sub-core being made from a material chosen from among Fe-75 to 82% Ni - 2 to 8% (Mo, Cu, Cr, V) alloys, cobalt-based amorphous alloys, and FeCuNbSiB nanocrystalline alloys;

   a second winding (14) made from a strip of the material with a high saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and low magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably below 15 W/kg, preferably below 10 W/kg; said second winding (14) of the outer magnetic sub-core being made from a material chosen from among Fe-3% Si alloys with oriented grains, Fe-6.5% Si alloys, Fe-15 to 50% total of Co, V, Ta, Cr, Si, Al, Mn, Mo, Ni, W alloys, textured or not, soft iron and ferrous alloys made up of at least 90% Fe and having Hc < 500 A/m, ferritic stainless steels Fe-Cr with 5 to 22% Cr, 0 to 10% total Mo, Mn, Nb, Si, Al, V and with more than 60% Fe, non-oriented electric steels Fe-Si-AI, Fe-Ni alloys with 40 to 60% Ni with no more than 5% total additions of other elements, Fe-based magnetic amorphous materials with 5 to 25% total B, C, Si, P and more than 60% Fe, 0 to 20% Ni + Co and 0 to 10% other elements, these contents being given by weight percent the cross-section (S₁₃) of the first winding of the outer magnetic sub-core and the cross-section (S₁₄) of the second winding (14) of the outer magnetic sub-core being such that the ratio (S₁₄/(S₁₃ + S₁₄)) of the cross-section of the material with a high saturation magnetization and the cross-section of the set of the two materials of the outer magnetic sub-core is comprised between 2 and 50%, preferably between 4 and 40%, and the cross-section of material with a high saturation magnetization (Js) in the assembly of the core, in terms of ratio of cross-sections, relative to the total cross-sections of the two types of materials in the assembly of the core $\left(\frac{\left({\mathrm{S}}_3+{\mathrm{S}}_4+{\mathrm{S}}_{14}\right)}{{\mathrm{S}}_1+{\mathrm{S}}_2+{\mathrm{S}}_{13}+{\mathrm{S}}_3+{\mathrm{S}}_4+{\mathrm{S}}_{14}}\right)$

   

   being comprised between 2 and 50%, preferably between 4 and 40%.
9. - The three-phase electric transformer magnetic core according to claim 8, wherein said first winding (13) of the outer magnetic sub-core is made from a nanocrystalline material with composition: $${\left[{\mathrm{Fe}}_{1-\mathrm{a}}{\mathrm{Ni}}_{\mathrm{a}}\right]}_{100-\mathrm{x}-\mathrm{y}-\mathrm{z}-\mathrm{\alpha }-\mathrm{\beta }-}\mathrm{\gamma }{\mathrm{Cu}}_{\mathrm{x}}{\mathrm{Si}}_{\mathrm{y}}{\mathrm{B}}_{\mathrm{z}}\mathrm{Nb}\mathrm{\alpha }\mathrm{M}\prime \mathrm{\beta }\mathrm{M}"\mathrm{\gamma }$$

   

   with a ≤ 0.3; 0,3 ≤ x ≤ 3; 3 ≤ y ≤ 17, 5 ≤ z ≤ 20, 0 ≤ α ≤ 6, 0 ≤ β ≤ 7, 0 ≤ γ ≤ 8, M' being at least one of the elements V, Cr, Al and Zn, M" being at least one of the elements C, Ge, P, Ga, Sb, In and Be, the index numbers corresponding to atomic percentages.
10. - The magnetic core according to one of claims 8 or 9, including an air gap (17) dividing it into two parts.
11. - The magnetic core according to claim 10, wherein the air gap (ε1) separating the two parts of the first windings (1; 2) of the inner magnetic sub-core and the two parts of the second winding (14) of the outer magnetic sub-core is different from the air gap (ε2) separating the two parts of the second windings (3; 4) of the inner magnetic sub-core and the two parts of the first winding (13) of the outer magnetic sub-core.
12. - The magnetic core according to claim 10 or 11, wherein the various air gaps (ε1, ε2) separating the two parts of the various windings (1, 2, 3, 4, 13, 14) are not all identical between the inner magnetic sub-core and the outer magnetic sub-core.
13. - The magnetic core according to one of claims 8 to 12, wherein the ratio between the cross-section (S₁₃) of the first winding (13) of the outer magnetic sub-core and the cross-section (S₃; S₄) of the second windings (3, 4) of the inner magnetic sub-core is comprised between 0.8 and 1.2.
14. - The magnetic core according to one of claims 8 to 13, wherein the ratio between the cross-section (S₁₄) of the second winding (14) of the outer magnetic sub-core and the cross-section (S₁; S₂) of the first windings (1, 2) of the inner magnetic sub-core is comprised between 0.3 and 3.
15. - The magnetic core according to one of claims 10 to 12, wherein said two parts are symmetrical.
16. - A three-phase electric transformer, including a magnetic core and primary and secondary windings, characterized in that the magnetic core is of the type according to one of claims 8 to 15.
17. - A method for manufacturing a single-phase electric transformer magnetic core according to claim 6, characterized in that it includes the following steps:

    - manufacturing a magnetic metal support in the form of a first winding (1) made from a first material, said first material being a crystalline material with a high saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and low magnetic losses of less than 20 W/kg at a frequency of 400 Hz in sinusoidal waves, for a maximum induction of 1 T;

    - winding, on said metal support, a second winding (3) made from a second material having, or being intended to have, after a nanocrystallization annealing, a saturation apparent magnetostriction (λ_sat) less than or equal to 5 ppm, preferably less than or equal to 3 ppm, better still less than or equal to 1 ppm and magnetic losses less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably less than 15 W/kg, preferably less than 10 W/kg and 2 to 40% in proportion of cross-section of first material with a high saturation magnetization (Js) compared to the section of the assembly of the first and second materials;

    - optionally, performing a nanocrystallization and contraction annealing of said second winding (3) on said support;

    - securing the two windings (1, 3), for example by sintering, or by gluing, or by impregnating using a resin and polymerization of said resin.
18. - A method for manufacturing a three-phase electric transformer magnetic core according to claim 8, characterized in that it includes the following steps:

    - producing an inner magnetic sub-core made up of two elementary modules, each elementary module being produced as follows:

    • manufacturing a magnetic metal support in the form of a first winding (1; 2) made from a first material, said first material being a crystalline material with a high saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and low magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T;

    • winding, on said metal support, a second winding (3; 4) made from a material having, or being intended to have, after a nanocrystallization annealing, a saturation apparent magnetostriction (λ_sat) less than or equal to 5 ppm, preferably less than or equal to 3 ppm, better still less than or equal to 1 ppm, and magnetic losses less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably less than 15 W/kg, preferably less than 10 W/kg, the ratio of the cross-section of first material with a high saturation magnetization (Js) to the total of the cross-sections of the materials of the first (1; 2) and second (3; 4) windings being from 2 to 40%;

    • optionally, performing a nanocrystallization and contraction annealing of said second winding (3; 4) on said support;

    - placing said elementary modules alongside one another along one of their sides, in order to form said inner magnetic sub-core;

    - producing an outer magnetic sub-core as follows:

    • positioning, around the inner magnetic sub-core, a third winding (13) made from a strip of material having, or being intended to have, after a nanocrystallization annealing, a saturation apparent magnetostriction (λ_sat) less than or equal to 5 ppm, preferably less than or equal to 3 ppm, better still less than or equal to 1 ppm, and magnetic losses less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, preferably less than 15 W/kg, preferably less than 10 W/kg;

    • optionally, performing a nanocrystallization and contraction annealing of said third winding (13) on the inner magnetic sub-core;

    • positioning, around said third winding (13), a fourth winding (14) made from a material with a high saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and low magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T, the ratio of the cross-section of material with a high saturation magnetization (Js) to the total of the cross-sections of the materials of the third (13) and fourth (14) windings being from 2 to 50%, preferably from 4 to 40%, and the proportion of material with a high saturation magnetization (Js) in the entire core, in terms of ratios of cross-sections, relative to the total cross-sections of the two types of materials, being comprised between 2 and 50%, preferably between 4 and 40%;

    • and securing said windings (1, 2, 3, 4, 13, 14), for example by sintering, or by gluing, or by impregnating using a resin and polymerization of said resin.
19. - The method according to claim 17 or 18, wherein said magnetic transformer core is cut so as two form to elementary cores, said elementary cores next being intended to be reassembled so as to define an air gap between them (17).
20. - The method according to claim 19, wherein the two elementary cores are symmetrical.
21. - The method according to claim 19 or 20, wherein the surfaces of the elementary cores intended to define the air gap (17) are worked and surfaced before the elementary cores are reassembled.
22. - The method according to claim 21, wherein the working and surfacing are done such that the surfaces intended to define the air gap (17) separating the first windings (1; 2) of the two elementary cores define an air gap (ε1) different from the air gap (ε2) separating the second windings (3; 4) of the two elementary cores.
23. - The method according to one of claims 19 to 21, wherein the two elementary cores are reassembled by sintering using a crystalline material with a high saturation magnetization (Js) greater than or equal to 1.5 T, preferably greater than or equal to 2.0 T, better still greater than or equal to 2.2 T, and low magnetic losses of less than 20 W/kg in sinusoidal waves with a frequency of 400 Hz, for a maximum induction of 1 T.

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