EP3198617B1 - Magnetic core of rotating transformer - Google Patents

Description

Background of the invention

The present invention relates to the general field of "U-shaped" rotary transformers used to achieve an electric power transfer by electromagnetic induction between two elements.

A "U-shaped" rotary transformer typically consists of two radially superimposed circular geometry elements, namely an inner core having one or more outer annular grooves in which toric coils are housed and an outer core mounted around the core internal being concentric with it and having one or more internal annular grooves facing the outer grooves of the inner core and in which are housed toric coils. These two elements with circular geometry are mounted concentrically in such a way that one of the elements can rotate relative to the other around a common longitudinal axis.

Existing solutions for the manufacture of such a "U-shaped" rotary transformer consist in producing the inner and outer cores from a sintered ferrite material or, in the case of small size transformers, by machining cast iron high resistivity. In the case of the inner core, the O-coils must then be formed by winding them directly into the outer grooves thereof. As for the outer core, the toroidal coils are most often housed in the internal grooves by deformation.

Such a rotating transformer architecture, however, poses a number of problems. In particular, in the case of toric coils having a large section, it is not always possible to deform them to accommodate them in the inner grooves of the outer core, so that it is then necessary to form the outer core around these reels. Moreover, the materials used (sintered ferrite or cast iron) are fragile and do not always withstand severe vibration environments such as can be found in particular in the field of aeronautics.

The document FR 1 306 964 A discloses a magnetic core according to the preamble of claim 1.

Object and summary of the invention

The main object of the present invention is therefore to propose a rotating transformer magnetic core architecture which does not cause such disadvantages.

This object is achieved by means of a rotary transformer magnetic core, comprising bars arranged along a longitudinal axis of the core and at least two cheeks spaced axially from one another and extending radially from the bars to delimit with these at least one annular groove in which an O-coil is intended to be housed, and in which, in accordance with the invention, each cheek consists of a bundle of circular magnetic sheets which are arranged radially and in that the bars each consist of a plurality of stacks of magnetic sheets, the stacks of sheets forming the bars being arranged axially and assembled on the packets of circular sheets being spaced angularly from each other around the longitudinal axis of the core .

The core according to the invention is remarkable in that it comprises an arrangement of magnetic sheets allowing the magnetic flux to travel, firstly radially in the circular sheets forming the cheeks, and secondly axially in the sheets forming the bars. Such a structure thus facilitates the assembly and industrialization of the "U-shaped" rotary transformer, in particular by limiting manufacturing tools and recovery operations. In particular, with such a core, the toroidal coils can be made and isolated prior to the constitution of the core. Furthermore, the eddy current losses are minimized here by the lamination and the insulation between the different sheets. In addition, it is possible to create special points to allow the passage of the transformer coil connections by making openings on the sheets.

According to an advantageous arrangement, the circular sheets forming each cheek may be segmented. Such a segmentation of the circular sheets makes it possible to cancel the effects of the appearance in each circular sheet of a counter-electromotive force due to the magnetic field which embraces it. In fact, the sectoring of the circular sheets makes it possible to eliminate the induced circular currents due mainly to the alternating field lines which enclose the sheets.

Alternatively, always to counter the effects of the appearance in each circular sheet of a counter-electromotive force, the circular sheets forming each cheek may each comprise radial notches forming internal baffles for extending the path of the current loops.

According to another advantageous arrangement, the circular sheets forming each cheek may have recesses. The presence of these recesses provides a gain in mass, a reduction of leakage inductances and free passages for possible connections.

The sheets of the stacks forming each bar can be stacked in radial directions. Alternatively, these sheets can be stacked in tangential directions.

The packets of circular sheets forming the cheeks may comprise axial notches in which are assembled the stacks of sheets forming the bars.

In this case, the core may advantageously further comprise shims of non-magnetic material disposed between the flanks of each stack of sheets forming the bars and the sides of the notches of the circular plate packets. The presence of such wedges reduces the appearance of eddy currents in the cheeks by reducing the input of a magnetic flux in a direction normal to the plane of the sheets.

Furthermore, the core may advantageously furthermore comprise an insulating material arranged in a bottom of the notches of the circular plate packets. The presence of such an insulating material makes it possible to avoid creating an electrical contact between the segments of circular sheets at the level of the connection between the cheeks and the bars of the core.

The invention also relates to a rotary transformer comprising an inner annular core and an outer annular core concentrically mounted around a common longitudinal axis so that one of the cores can rotate relative to the other about said longitudinal axis at least one of the nuclei being a nucleus as defined above.

Brief description of the drawings

• la figure 1 est une vue schématique montrant un exemple de transformateur tournant en U à laquelle s'applique l'invention ;
• la figure 2 est une vue en perspective d'un noyau externe de transformateur tournant selon un mode de réalisation de l'invention ;
• la figure 3 est une vue en coupe longitudinale du noyau de la figure 2 ;
• la figure 4 est une vue en perspective et en coupe longitudinale d'un noyau externe de transformateur tournant selon un autre mode de réalisation de l'invention ;
• la figure 5 montre la segmentation d'une joue de noyau externe selon une disposition avantageuse de l'invention ;
• la figure 6 montre la réalisation de chicanes dans une joue de noyau externe selon une autre disposition avantageuse de l'invention ;
• la figure 7 montre la présence de cales amagnétiques et de matière isolante entre les joues et les barreaux d'un noyau externe selon encore d'autres dispositions avantageuses de l'invention ; et
• la figure 8 montre la réalisation d'évidements dans une joue de noyau externe selon encore une autre disposition avantageuse de l'invention.

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate embodiments having no limiting character. In the figures:

• the figure 1 is a schematic view showing an example of a U-shaped transformer to which the invention applies;
• the figure 2 is a perspective view of an outer transformer core rotating according to an embodiment of the invention;
• the figure 3 is a longitudinal sectional view of the nucleus of the figure 2 ;
• the figure 4 is a perspective view in longitudinal section of an outer transformer core rotating according to another embodiment of the invention;
• the figure 5 shows the segmentation of an outer core cheek according to an advantageous arrangement of the invention;
• the figure 6 shows the realization of baffles in an outer core cheek according to another advantageous arrangement of the invention;
• the figure 7 shows the presence of nonmagnetic wedges and insulating material between the cheeks and the bars of an outer core according to still other advantageous provisions of the invention; and
• the figure 8 shows the realization of recesses in an outer core cheek according to yet another advantageous arrangement of the invention.

Detailed description of the invention

The invention applies to any rotating transformer (single-phase or polyphase) type "U" used to achieve an electric power transfer by electromagnetic induction between a fixed element and a rotary element such as the rotating three-phase transformer 10 shown in FIG. figure 1 .

In a manner known per se, this rotating transformer 10 comprises an inner annular core 12 and an outer annular core 14 which are mounted concentrically about a common longitudinal axis 16 so that one of the cores can rotate relative to the other around said longitudinal axis 16.

The inner core 12 comprises two outer annular grooves 18 in which are housed toric coils 20, while the outer core 14 comprises two internal annular grooves 22 facing external grooves 18 of the inner core and in which are also housed toroidal coils 24 .

A radial air gap 26 is provided between the inner diameter of the inner core 12 and the outer diameter of the outer core 14 so that it can rotate inside the inner core without physical contact with it.

Of course, the invention also applies to rotary single-phase transformers in which the cores comprise only one groove and two cheeks to accommodate a single toroidal coil. In the same way, the invention applies to other polyphase rotary transformers by varying the number of grooves and cheeks.

The figures 2 and 3 represent an external core 14 of such a rotating transformer according to one embodiment of the invention. Of course, the invention also applies to the realization of the inner core.

According to the invention, the outer core 14 comprises bars 142 (also referred to as magnetic links, crowns or yokes) which are arranged along the longitudinal axis 16 of the rotating transformer, these bars being each constituted by a plurality of stacks of magnetic sheets, for example of rectangular shape, which are arranged axially.

So, on the example of figures 2 and 3 these stacks of sheets forming each bar are 12 in number, are regularly distributed around the longitudinal axis 16 and are each composed of 17 rectangular sheets joined together with the interposition of an insulating layer. Of course, these numbers could be different, as the shape of the sheets of these stacks is not necessarily rectangular. In these stacks of rectangular plates 142, the magnetic flux flows axially.

Still according to the invention, the outer core 14 also comprises three cheeks 144 (also referred to as circular cheeks or flanks) which are spaced axially from one another and which extend radially from the bars to delimit with them the two internal annular grooves 22 in which the toroidal coils 24 are intended to be housed, each cheek 144 being constituted by a bundle of circular magnetic sheets which are arranged radially and assembled between they with interposition of a layer of insulation.

In the example of figures 2 and 3 each flange 144 is thus constituted of a pack of 10 circular magnetic sheets in which the magnetic flux circulates radially.

More specifically, the packets of circular sheets forming cheeks 144 each comprise axial notches 146 in which are assembled the stacks of sheets forming the bars 142.

Moreover, in the exemplary embodiment of figures 2 and 3 , the sheets of the stacks forming the bars 142 of the core are stacked in radial directions (that is to say that these sheets are arranged in a radial direction).

The figure 4 shows an alternative embodiment of an outer core 14 'in which the laminations of the stacks forming the bars 142' of the core have a different orientation, namely that they are stacked in tangential directions (i.e. these sheets are arranged in a tangential direction).

Here, the cheeks 144 'also comprise each of the axial notches 146' in which are assembled the stacks of sheets forming the bars 142 ', these sheets being for example 5 in number by stacking.

Note that the plates forming the bars and circular sheets forming the cheeks of the core are typically non-oriented grain magnetic sheets which are covered with a layer of insulation and pressed together to allow their assembly in the form of packets and dies. stacks.

In liaison with Figures 5 to 8 various advantageous characteristics of the magnetic core according to the invention will now be described.

In particular, each circular sheet of circular plate packets forming cheeks 144, 144 'has the disadvantage of being the seat of a counter electromotive force due to the magnetic field that embraces it.

In order to cancel the induced circular current loops (current loops whose approximate center is the longitudinal axis 16), it is possible, as shown in FIG. figure 5 to segment the circular sheets of the circular plate packets forming the flanges 144, 144 '. Thus, as shown in these figures, each pack of circular sheets is segmented, for example into 4 segments 144a, 144'a, which are held together by means of gluing or mechanical holding via fastening elements such as screws, rivets or others, these fasteners having an insulation system with respect to the sheets so as to avoid a "re-looping" of the induced circular currents. The number of segments may vary from 2 to about 30.

Such a segmentation of the circular sheets makes it possible to eliminate the induced circular current loops. Only then persist the eddy currents which are, for their part, greatly reduced thanks to the small thickness of the sheets.

Another solution for reducing the circular current loops induced in the circular sheets forming the cheeks of the magnetic core is shown in FIG. figure 6 . It consists in creating baffles by making radial notches (or slots) 148 in these circular sheets. As represented on this figure 6 , the current loop path (schematized by the line 150) is thus elongated.

Yet another solution (not shown in the figures) for reducing the circular current loops induced in the circular sheets is to wind the circular sheets in the form of a spiral so as to avoid the creation of rings.

Furthermore, in order to reduce the appearance of eddy currents in the circular sheets forming the flanges 144, 144 ', it is preferable to reduce to the maximum the input of the magnetic induction vector in a direction normal to the plane of the magnetic sheets. .

For this purpose, as shown on the figure 7 , it is advantageously provided to have shims of non-magnetic material 152 between the flanks of each stack of sheets forming the bars and the sides of the notches 146 of circular plate packets 144 in which are assembled the sheets forming the bars. Typically, these shims 152 may be made of composite material with a polymer matrix or a non-ferromagnetic metallic material (for example an aluminum alloy).

Alternatively, it could be envisaged to leave a gap between the sides of the stacks of sheets forming the bars and the sides of the notches of the circular plate packets, this empty space can be filled with resin.

Moreover, when the circular sheets of the circular plate packets forming the flanges 144, 144 'of the magnetic core are segmented (case of the figure 5 ), there is a risk that the frank contact between the stacks of plates forming the bars and the cheeks does not create an electrical contact between the different segments of the circular sheets, thus canceling the effect of the segmentation.

In order to avoid such a phenomenon, it is advantageously provided to dispose an insulating material 154 in the bottom of the notches 146 of circular plate packets 144 ( figure 7 ). For example, this insulating material 154 will be in the form of a very thin sheet (typically of the order of a few hundredths of a millimeter) made of fiberglass or in a polyimide or polyetheretherketone (PEEK) type polymer film. .

Alternatively, the insulating material may be a varnish or an adhesive adapted or made by creating a non-conductive space by placing stops preventing frank contact between the stacks of sheets forming the bars and cheeks.

According to yet another advantageous arrangement of the invention shown in the figure 8 , the circular sheets forming each cheek 144, 144 'of the core have recesses 156 in them.

Such recesses 156 provide a gain in mass, a reduction of leakage inductances and free a passage for possible electrical connections.

Claims (9)

1. A magnetic core (12, 14; 14') for a rotary transformer (10), the core comprising bars (142; 142') arranged along a longitudinal axis (16) of the core and at least two cheeks (144; 144') that are axially spaced apart from each other and that extend radially from the bars in order to cooperate with the bars to define at least one annular groove (22) for receiving a toroidal coil (24), each cheek being made up of a packet of circular magnetic laminations that are arranged radially, each bar being made up of a plurality of stacks of magnetic laminations, the stacks of laminations forming the bars being arranged axially and being assembled to the packets of circular laminations while being angularly spaced apart from one another around the longitudinal axis of the core, the core being characterized in that each circular lamination forming a cheek includes radial notches (148) forming internal baffles serving to lengthen the paths of current loops.
2. A core according to claim 1, the circular laminations forming each cheek are segmented.
3. A core according to claim 1 or claim 2, wherein the circular laminations forming each cheek present hollows (156).
4. A core according to any one of claims 1 to 3, wherein the laminations of the stacks (142) forming each bar (142) are stacked in radial directions.
5. A core according to any one of claims 1 to 3, wherein the laminations of the stacks (142') forming each bar (142') are stacked in tangential directions.
6. A core according to any one of claims 1 to 5, wherein the packets of circular laminations making up the cheeks (144; 144') have axial notches (146; 146') in which the stacks of laminations forming the bars are assembled.
7. A core according to claim 6, further comprising spacers made of non-magnetic material (152) arranged between the flanks of each stack of laminations forming the bars and the flanks of the notches in the packets of circular laminations.
8. A core according to claim 6 or claim 7, further comprising insulating material (154) arranged in bottoms of the notches in the packets of circular laminations.
9. A rotary transformer (10) comprising an inner annular core (12) and an outer annular core (14; 14') that are mounted coaxially around a common longitudinal axis (16) so that one of the cores can rotate relative to the other about said longitudinal axis, the transformer being characterized in that at least one of the cores is a core according to any one of claims 1 to 8.

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