EP4282059A1

EP4282059A1 - Protection for the coils of an electric machine

Info

Publication number: EP4282059A1
Application number: EP22704930.1A
Authority: EP
Inventors: Sabrina Siham AYAT; Rémi Luc Stéphane DORGET; Benjamin DAGUSE
Original assignee: Universite de Lorraine; Safran SA
Current assignee: Universite de Lorraine; Safran SA
Priority date: 2021-01-21
Filing date: 2022-01-18
Publication date: 2023-11-29
Also published as: FR3119042A1; WO2022157450A1; CN117280583A; US20240097548A1; FR3119042B1

Abstract

The present invention relates to a superconducting electric machine (1), for example an axial or radial flow electric machine, comprising an inductor (3) having superconducting pellets (7) circumferentially distributed about an axis (X) of the electric machine (1), and a flow barrier (12) comprising a superconducting material, said flow barrier (12) being centered on the axis of rotation (X) and extending radially inside the superconducting pellets (7).

Description

DESCRIPTION

TITLE: Protection of the coils of an electrical machine

FIELD OF THE INVENTION

The present invention relates to the field of electrical machines comprising superconducting pads which can in particular be used in aircraft. In particular, the invention applies to electrical machines comprising magnetized or non-magnetized pads, to electrical machines with superconducting magnets or superconducting flux barriers, to entirely superconducting machines (superconducting armature and inductor) or partially superconducting (armature or superconducting inductor) as well as radial or axial flux superconducting machines.

STATE OF THE ART

Part of engineering is concerned with future means of transportation by seeking to make systems more environmentally friendly. In the field of air transport, various projects and prototypes have already emerged, such as SOLAR IMPULSE or the Airbus E-FAN. Environmental concerns, the reduction of fuel consumption and noise are so many criteria that encourage the use of electric machines. To be able to supplant current technologies, aircraft manufacturers are working on increasing the specific power of these electric machines. Thus, a study is conducted on the gain that superconducting materials HTC (acronym for high critical temperature) would bring to on-board actuators.

A superconducting material is a material which, when cooled to a temperature below its critical temperature, has zero resistivity, thus offering the possibility of circulating direct currents without losses. From this, several phenomena ensue, such as the diamagnetic response for any variation of the magnetic field, making it possible to produce excellent magnetic shielding.

In a manner known per se, an electric machine comprises an inductor and an armature. The inductor comprises an HTC coil made with HTC wires which generates a magnetic field modulated by superconducting pads, which act as magnetic screens. The armature, on the other hand, comprises a three-phase copper winding system comprising an arrangement of coils which rest on a ferromagnetic or non-magnetic support. The rotation of the screens varies the magnetic field and induces, by Lenz's law, an electromotive force in the coils. The dimensioning of such a machine leads to an axial flow structure without a rotating supply system (ring/brush type). Maintenance and safety problems, brought about by a ring/rotating brush system, are therefore avoided. This electric machine is partially superconductive insofar as only the inductor is made of a superconductive material, as opposed to a totally superconductive machine in which all the active parts are designed with superconductive materials.

In what follows, the term “inductor” will denote the HTC coil and the superconducting pads configured to modulate the magnetic flux created by the HTC coil. It will be noted that, in a superconducting electric machine with flux barriers, the diamagnetic behavior of the superconducting pellets when they are cooled out of the field is used. The superconducting pads are in this case non-magnetized and form a screen (screening) which deflects the field lines when they are immersed in a magnetic field. The magnetic field is then concentrated and of high amplitude between the non-magnetized superconducting pads and low downstream of them. Alternatively, the superconducting pads can be magnetized and form superconducting magnets. We then speak of a machine with superconducting magnets.

Generally, the pellets are made of at least one of the following materials which have in particular very good screening characteristics: in YBCO (English acronym for Yttrium Barium Copper Oxide for mixed oxides of Barium, Copper and Yttrium), in GdBCO (acronym for Gadolinium-Barium-Copper-Oxygen), NbTi (for niobium-titanium), MgB2 (magnesium diboride) or any RE-Ba-Cu-0 or RE material can be any rare earth.

Pellets are generally obtained through the germ growth process. Reference may in particular be made to the article by M. Morita, H. Teshima, and H. Hirano, “Development of oxide superconductors”, Nippon Steel Technical Report, vol. 93, p. 18-23, 2006 for more details on this method. In particular, this type of process consists in forming a crystal by progressive solidification of material on the surface of a pre-existing seed. The pellets thus obtained are therefore generally of circular or rectangular shapes. As a variant, it has also been proposed to produce the pellets by sintering. However, the inter-grain connection associated with this manufacturing process tends to decrease pellet performance. Another method consists in using superconducting ribbons (or "tapes") for the manufacture of superconducting pellets. In this case, we speak of stacks of tapes. These pellets, whose superconducting core is reinforced by the matrix of the ribbons constituting them, have good mechanical strength. This good mechanical strength is particularly advantageous when the pellets are magnetized (machine with superconducting magnets).

However, the Applicant has noticed that the concentration of the magnetic flux on the coils of the armature was not optimal, which not only reduces the power density of electrical machines but also risks saturating the parts made of ferromagnetic material and causing the electrical machine to fail.

DISCLOSURE OF THE INVENTION

An object of the invention is to increase, in a simple and effective manner, the power density of superconducting machines.

Another object of the invention is to reduce the risks of failure of superconducting machines.

The invention applies to any type of superconducting machine, which include in particular partially superconducting or totally superconducting machines, with flux barriers or superconducting magnets, with axial or radial flux.

It is for this purpose proposed, according to a first aspect of the invention, a superconducting electrical machine, for example with axial flux or radial flux, comprising an inductor comprising superconducting pads distributed circumferentially around an axis of the electrical machine. The electric machine further comprises a flux barrier comprising a superconducting material, said flux barrier being centered on the axis of rotation and extending radially inside the superconducting pads.

Certain preferred but non-limiting characteristics of the electric machine according to the first aspect are the following, taken individually or in combination, the flux barrier comprises an annular band extending in a plane radial to the axis, said annular band being coaxial with the axis; the flux barrier includes an annular band extending circumferentially around the axis; the electric machine further comprises at least one face extending radially towards the axis from the annular band, preferably two opposite faces axially offset from each other; the electrical machine further includes a drive shaft configured to rotate the superconducting pads about the axis, the face of the flux barrier including a through hole and the drive shaft passing through the through hole whereby the flux barrier is mounted around the drive shaft; the electric machine further comprises a cooling assembly for the superconducting pads and/or ferrofluid seals mounted near the drive shaft through the through hole, so that the flux barrier is mounted around the cooling assembly and/or ferrofluid seals; the electrical machine further comprises an armature comprising distributed coils circumferentially around the axis, the flux barrier being integral in movement with the armature; the flux barrier is integral in movement with the superconducting pellets; the flow barrier is continuous over its entire periphery; the electrical machine has axial flux, the flux barrier extending between the superconducting pads and the armature so as to at least partially cover the radially inner edge of all or part of the coils of the armature; and/or each coil further has side edges extending radially from the radially inner edge, the flux barrier covering at most 10% of the side edges.

According to a second aspect, the invention proposes an aircraft comprising an electric machine according to the first aspect.

DESCRIPTION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

[Fig. 1] Figure 1 is a simplified sectional view of an electrical axial flux machine according to a first embodiment of the invention in which the flux barrier is attached to the superconducting pads;

[Fig. 2] Figure 2 is a simplified, exploded and perspective view of an axial flux electric machine according to a second embodiment of the invention in which the flux barrier is fixed to the coils of the armature;

[Fig. 3] Figure 3 is a simplified, exploded and perspective view of a radial flux electrical machine according to a third embodiment of the invention in which the flux barrier is fixed to the support structure of the superconducting pellets, the adiabatic enclosure having been omitted;

[Fig. 4] Figure 4 is a simplified, exploded and perspective view of an alternative embodiment of the radial flux electric machine of Figure 4, the adiabatic enclosure having been omitted;

[Fig. 5] Figure 5 is a partial perspective view of an embodiment of a flow barrier; and

[Fig. 6] Figure 6 is a schematic view of an aircraft comprising an electric machine according to the invention.

In all the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

In what follows, the invention will be described and illustrated in the case of a partially superconducting axial flux electric machine 1 with flux barriers with non-magnetized pellets. As has already been indicated above, this is however not limiting, the invention applying mutatis mutandis to electrical machines comprising magnetized pads, to electrical machines with superconducting magnets, to entirely superconducting electrical machines (induced and superconducting inductors) as well as radial flux electric machines.

In FIG. 1 is shown schematically a superconducting axial flux electric machine 1 with flux barriers according to one embodiment of the invention conventionally comprising a rotating part, or rotor, and a fixed part, or stator.

In the present application, the axis X of the rotor is referred to as its axis of rotation. The axial direction corresponds to the direction of the X axis and a radial direction is a direction perpendicular to this axis and passing through it. Furthermore, the circumferential (or lateral) direction corresponds to a direction perpendicular to the axis X and not passing through it. Unless otherwise specified, internal (respectively, interior) and external (respectively, exterior), respectively, are used with reference to a radial direction such that the internal part or face of an element is closer to the X axis than the external part or face of the same element.

In a manner known per se, the superconducting axial flux electrical machine 1 comprises an armature 2 and an inductor 3. The armature 2 comprises an arrangement 4 of non-superconducting electromagnetic coils 5, generally made of copper. The inductor 3 comprises a superconducting coil 6 coaxial with the arrangement 4 of the electromagnetic coils 5 of the armature 2 and superconducting pads 7 mounted on a carrier structure 8 which are arranged in the same plane orthogonal to the axis X and radially inside the superconducting coil 6. Optionally, the inductor 3 further comprises a stator yoke comprising an iron crown 8. Here, the rotor is formed by the superconducting pads 7 which are driven in rotation around an axis of rotation extending in the axial direction. The stator is formed by the arrangement 4 of electromagnetic coils 5 and the superconducting coil 6.

The superconducting pads 7 are made of superconducting material and are distributed equidistantly around the axis of rotation, which allows a spatial variation of the electromagnetic field in the air gap. Here, the superconducting pads 7 are non-magnetized. Alternatively, the superconducting pads 7 could be magnetized. For example, the pellets are made of YBCO (English acronym for Yttrium Barium Copper Oxide for Mixed Oxides of Barium, Copper and Yttrium), in GdBCO (English acronym for Gadolinium-Barium-Copper-Oxygen), NbTi (for niobium-titanium), MgB2 (magnesium diboride) or any RE-Ba-Cu-0 material where RE can be any rare earth.

The superconducting coil 6 of the inductor 3 is a static superconducting coil supplied with direct current. If necessary, when the electric machine 1 comprises a yoke 4, the latter ensures mechanical strength of the electromagnetic coils 5 of the armature 2. In other words, the inductor 2 is superconducting while the armature 3 is non-superconductive.

The superconducting pads 7 can have any suitable shape.

In a first embodiment, each superconducting pad 7 has, in a manner known per se, the shape of a full (solid) disk (as illustrated in FIG. 2).

In a second embodiment, the superconducting pad 7 can be hollow in order to adapt its shape to the penetration thickness of the magnetic field in the pad 7 (as illustrated in FIG. 1). Each superconducting pad 7 comprises for this purpose a circumferential wall which has:

- a first border,

- a second border opposite the first border

- an internal face connecting the first border and the second border

- an external face opposite the internal face and

- A cavity formed between the first edge, the second edge and delimited by the internal face of the circumferential wall.

The inner face extends radially inside the outer face. The superconducting pad 7 is therefore hollow in that it has a cavity which, as will be seen in what follows, can be emerging, passing through or enclosed in the superconducting pad 7. The cavity is preferably empty (devoid of material) .

Optionally, the superconducting pad 7 can comprise one or more additional walls dividing the cavity into several parts. If necessary, a through hole can be formed in all or part of the walls. Reference may be made to document FR3104804 in the name of the Applicant for more details on these different embodiments of superconducting pads 7 with cavity.

In a third embodiment illustrated in FIGS. 2, 4a and 5a, the shape of the superconducting pads 7 is adapted (optimized) so as to maximize the screening/mass ratio of the pads 7, that is to say that the shape of the superconducting pellets 7 is adapted so that the variation of the axial component of the induced magnetic field, and therefore the shielding of the magnetic flux, is maximum, while minimizing the mass of the superconducting pellets 7. It is thus possible to obtain an increase in the speed of rotation of the rotor and therefore of the power of the electric machine. For this purpose, the superconducting pellets 7 may have a polygonal shape having at least five sides. For example, patch 7 has a hexagonal shape, preferably that of a regular isometric hexagon. Alternatively, face 8 of each superconducting pad 7 has the geometry and dimensions of a ring sector. By ring sector, we will understand here the shape delimited on the one hand by two coaxial circles, of different diameters, and on the other hand by two line segments originating from the center of the circles. The ring sector thus comprises two opposite curved sides and two opposite straight sides.

Reference may be made to document FR3104803 in the name of the Applicant for more details on these different embodiments of superconducting pads 7.

The magnetic field is generated by the superconducting coil 6. Therefore, it is enough to turn off the superconducting coil 6 to cut off the magnetic field in the superconducting electric machine. This has an advantage insofar as superconducting pads 7 which are cooled in the presence of a magnetic field are not able to screen the magnetic field. Thus, it is necessary for the magnetic field to be screened to appear at a time after the cooling of the superconducting pads 7 to enable them to play their role as magnetic screens, which is made possible by the use of the superconducting coil 6. In the invention, the superconducting coil 6 can therefore be turned off when the superconducting pads 7 are hot and turned on once they have cooled.

The coils 5 of the armature 2 can also have any suitable shape. In a manner known per se, the coils 5 may in particular have the shape of a ring sector.

Whatever the shape of the coils 5 of the armature 2, each coil has a radially inner edge 10, a radially outer edge 9 and lateral edges 11 which connect the radially inner edge 10 and the radially outer edge 9. The radially outer edge inner 10 and the radially outer edge 9 extend in a circumferential direction with respect to the axis X while the side edges 11 are substantially radial.

In a manner known per se, the electrical machine 1 further comprises a drive shaft, coaxial with the X axis, configured to drive the rotor in rotation, that is to say here the support structure on which the superconducting pads 7, as well as a set for cooling the superconducting pads 7 and the seals, for example magnetic seals comprising ferrofluids. The part of the shaft passing through the armature 2 and the field 3, the cooling assembly and the seals are generally housed in an adiabatic enclosure 9. In the figures, only the adiabatic enclosure 9 is visible (FIG. 2). The adiabatic enclosure 9 extends radially inside with respect to the superconducting pads 7.

The cooling assembly generally comprises a cryostat comprising a rotating part and a fixed part housed in an enclosure. The seals are configured to ensure a seal between the rotating part and the fixed part of the cryostat.

In order to increase, in a simple and effective manner, the power density of the superconducting electrical machine 1, the electrical machine 1 further comprises a flux barrier 12, comprising a superconducting material, which is centered on the X axis of rotation and which extends radially inside the superconducting pads 7 and radially outside the adiabatic enclosure 9. The flux barrier 12 is therefore positioned at the center of the electrical machine 1 so as to mask the parts which do not not participate in the generation of the torque, such as the drive shaft, the cooling assembly or the seals. The flux barrier 12 therefore forms a screen for the parts housed in the adiabatic enclosure 9, which do not participate in the generation of the torque, which makes it possible to concentrate the magnetic flux at the level of the superconducting pads 7, and therefore to increase the power density of the electric machine 1.

In one embodiment, the flux barrier 12 is placed between the superconducting pads 7 and the X axis, around the parts housed in the adiabatic enclosure 9, and extends continuously along the entire internal periphery of the superconducting pads 7. The flux barrier 12 is also coaxial with the axis X. The magnetic flux is thus screened over 360° and the power density of the electrical machine 1 is maximized. Assuming that the magnetic field created by the superconducting coil 6 alone varies very little over its radius, half of the magnetic flux of this same coil 6 passes through the parts housed in the adiabatic enclosure 9. Therefore, the presence of the barrier of flux 12 makes it possible to recover 50% of the magnetic flux to increase the induction in the useful part, and therefore to increase the power density of the electric machine 1 by approximately 30%.

In addition, the parts of the electrical machine 1 which include ferromagnetic materials, such as the seals if these include ferromagnetic parts, are then protected from the magnetic field. Indeed, in the absence of a flux barrier 12, there is a risk of saturating these ferromagnetic materials and therefore of causing the cooling assembly, and therefore the electrical machine 1, to fail.

The flux barrier 12 can be made of any of the superconducting materials envisaged for the superconducting pads 7 listed above. If necessary, the flux barrier 12 can be made of the same superconducting material as the pellets 7. The flux barrier 12 can also be cooled analogously to the superconducting pellets 7.

The flux barrier 12 can be fixed on the rotor or the stator of the electric machine 1.

In a first embodiment illustrated in FIG. 1, the flux barrier 12 is fixed on the rotor of the electric machine 1, for example on the superconducting pads 7 and/or on the support structure 8 on which the superconducting pads are mounted. 7. This configuration makes it possible to use a flux barrier 12 having a greater thickness (of the order of ten to twenty millimeters in thickness) and therefore to improve the shielding of the magnetic field. Indeed, when the flux barrier 12 is fixed at the level of the rotor, it can be made in one piece with the superconducting pads 7 used for the modulation of the flux. These pads 7 are typically thicker than the flux barrier 12 used for protection (a good quality of screening being required for the modulation of the field). However, when the flux barrier 12 and the pellets 7 are in one piece, for simplicity of production, they may have the same thickness. A consequence is then the improved screening for the ‘protective’ flux barrier 12.

The flux barrier 12 can for example be fixed on a radially internal edge of the superconducting pads 7 (that is to say the edge of the superconducting pads 7 which is closest to the axis X).

Alternatively, as illustrated in Figure 2, the flux barrier 12 can be mounted on the stator of the electric machine 1, for example on the coils 5 of the armature 2. In this case, the thickness of the barrier of flux 12 can be less than one millimeter so as not to interfere with the operation of the electric machine 1. Indeed, when the flux barrier 12 is mounted on the coils 5 of the armature 2, it is then at the level of the air gap of the electric machine 1. However, this air gap must be as small as possible because it is directly proportional to the torque of the electric machine 1 (and therefore to its power). This is why in this configuration, it is preferable to limit the thickness of the flux barrier 12.

Preferably, an external radius of the flux barrier 12 is less than or equal to an internal radius of the superconducting pads 7 so as not to disturb the screening of the magnetic field by the superconducting pads 7. By external radius of the flux barrier 12 , we understand here the maximum radius of the flux barrier 12, measured from the X axis of rotation. By internal radius of the superconducting pads 7, it will be understood here the minimum radius of said pads 7, measured from the X axis of rotation.

Thus, when flux barrier 12 is attached to superconducting pads 7 and/or to their supporting structure, said flux barrier 12 does not extend radially beyond superconducting pads 7. A radial length (that is to say along an axis radial to the X axis) of the flux barrier 12 is less than the air gap between the adiabatic enclosure 9 and the internal radius of the superconducting pads 7.

The flux barrier 12 extends substantially continuously around the X axis to ensure the development of current loops in the flux barrier 12 which channel the magnetic flux and thus improve the redirection of the flux towards the active parts. of the electrical machine 1. Thus, the flux barrier 12 does not comprise several sections glued to each other in the circumferential direction, but a single piece continues around its circumference.

In one embodiment (illustrated for example in Figure 2), the height of the flux barrier 12 is such that said barrier 12 extends in front of a radially inner edge 10 of all or part of the coils 5 of the armature, preferably all the coils 5, so as to at least partially cover their edge 10. Preferably, the flux barrier covers the entire radially internal edge 10 of the coils 5, covering between 0% and 10% of the side edges 11 . For maximum power density, the flux barrier 12 does not cover the side edges 11. This configuration then makes it possible to reduce the risks of deformation of the coils 5 of the armature 2 while improving the power density of the electric machine 1 Indeed, the forces at the level of the radially inner edge 10 of the coils 5 do not produce torque but are liable to deform the coils 5. Thanks to the flux barrier 12, the magnetic field is then screened at the level of the edge. radially internal 10 of the coils 5 and redirected from the armature 2 towards the active regions of the electric machine 1, that is to say radially in the direction of the lateral edges 11 and of the radially external edge 9 of the coils 5, which makes it possible to increase the power density of the electric machine 1 .

The flux barrier 12 can be generally annular in shape and centered on the X axis.

In a first embodiment, as illustrated in FIGS. 1 and 2, the flow barrier 12 may have the shape of a disk in which a through hole is made so as to obtain an annular strip 13 extending in a plane radial to the X axis. The adiabatic enclosure 9 (which houses the drive shaft, the cooling assembly and the ferrofluid seals) is thus placed with respect to the flux barrier 12 so as to extend to through the through hole of the annular strip 13. The flux barrier 12 is therefore mounted around these parts of the electrical machine.

In a second embodiment illustrated in FIG. 5, the flux barrier 12 comprises an annular strip 13 extending circumferentially around the axis X so as to to form a cylinder of revolution centered on the X axis. Here again, the drive shaft, the cooling assembly and the ferrofluid seals are thus placed relative to the flux barrier 12 so as to through the internal space delimited by the annular strip 13. Optionally, the flux barrier 12 further comprises at least one face 14 extending radially towards the axis X from the annular edge, preferably two opposite faces 14 axially offset l each other. Each face 14 then comprises a through hole 15 allowing passage in particular of the drive shaft, so that the drive shaft, the cooling assembly and the seals are housed at least partially within the annular strip 13 of flux barrier 12.

Whatever the configuration (radial or circumferential) of the annular band 13, said annular band 13 is preferably substantially continuous in the circumferential direction. In the case where the annular strip 13 is formed integrally and in a single piece with the superconducting pads 7, the thickness of the annular strip 13 can be substantially equal to that of the pads 7 to simplify the manufacture of this part of the rotor.

Manufacturing process

The flux barrier 12 can be obtained by growth of germs or by stacking of ribbons.

When the flow barrier 12 is obtained by growth of germs, the manufacturing process comprises the following steps:

- production of a conventional pellet-type part in the shape of a disc by growth of germs;

- machining of the part thus obtained so as to obtain the final shape of the flow barrier 12.

In the case of a flow barrier 12 of the annular band 13 type (radial or circumferential), the part obtained by seed growth preferably has the shape of a disk and the machining step consists in making a central orifice 15 crossing in the disc so as to obtain the annular band 13.

When the flow barrier 12 is obtained by stacking tapes, the manufacturing process comprises the following steps: precutting the tapes so as to obtain the annular strip 13 of the flow barrier 12; stacking of the ribbons thus precut in a conventional manner to obtain the flow barrier 12; and optionally, machining the superconducting pad 7 thus obtained. If necessary, when the flux barrier 12 is attached to the superconducting pads 7, the flux barrier 12 and the superconducting pads 7 can be formed integrally and in one piece. In other words, the flux barrier 12 and the superconducting pads 7 can be fabricated simultaneously by seed growth or by stacking ribbons. For this, the superconducting pellets 7 and the flux barrier 12 can be obtained by producing a disk-shaped pellet 7 whose external radius is equal to that of the superconducting pellets 7, then by machining this pellet 7 in order to form the orifice central 15 of the flux barrier 12 as well as the spaces between the pads 7. The thickness of the flux barrier 12 is then equal to the thickness of the superconducting pads 7 (generally, of the order of ten to twenty millimeters) .

It will be noted that, when the flux barrier 12 is fixed on the stator, the flux barrier 12 is preferably produced by stacking tapes in order to be able to obtain thicknesses of less than one millimeter.

Application to radial flux electric machines

In the case of a radial flux superconducting machine (see for example FIGS. 3 and 4), the inductor 3 comprises a front superconducting coil 6 and a rear superconducting coil 6' which are annular and coaxial with the axis X of rotation and superconducting pads 7 mounted on a support structure which are arranged circumferentially with respect to the axis X. The superconducting coils 6 generate the magnetic field. The pellets 7 are for example of rectangular shape. The armature 2 for its part comprises an arrangement of coils 5 arranged circumferentially with respect to the axis X, radially outside the superconducting pads 7.

The coils 5 of the armature 2 can each have a substantially rectangular shape, one larger side of which extends parallel to the axis X of the rotor. The coils 5 are assembled edge to edge along their longest side so as to define a substantially cylindrical assembly around the axis X of rotation.

The invention described above then applies mutatis mutandis to the electric machine 1 with radial flux. Preferably, the flux barrier 12 comprises an annular band 13 extending circumferentially around the axis X so as to form a cylinder of revolution centered on the axis X (see FIGS. 3 and 4). An axial length of the annular strip 13 (measured along the X axis) is substantially equal, to within 10%, to an axial length of the superconducting pads 7 in order to ensure effective screening of the magnetic flux. Where appropriate, the flux barrier 12 may further comprise at least one face 14, typically two opposite faces 14 extending from the annular band 13 (FIG. 4) to an area adjacent to the drive shaft. The characteristics of the flux barrier 12 described above in relation to the axial flux electrical machine are found mutatis mutandis in the flux barrier of a radial flux electrical machine. In particular, the flux barrier 12 can be placed radially inside the superconducting pads 7 so as to at least partially mask the drive shaft, the cooling assembly and/or the ferrofluid seals. Furthermore, the flux barrier 12 can be fixed on the armature 2 or on the rotor, that is to say mounted radially inside the coils 5 of the armature 2 or on their support structure 8.

On the other hand, in a radial flux electric machine 1, the flux barrier 12 is mounted on the support structure 8 (and not on the superconducting pads 7 or the armature 2 since they extend radially with respect to the axis X).

The electric machine 1 can in particular be used in an aircraft 100.

Claims

1. Superconducting electric machine (1), for example axial flux or radial flux, comprising an inductor (3) comprising a superconducting coil (6) configured to generate a magnetic field and superconducting pads (7) distributed circumferentially around an axis (X) of the electric machine (1), the electric machine (1) being characterized in that it further comprises a flux barrier (12) comprising a superconducting material, said flux barrier (12) being centered on the axis (X) of rotation and extending radially inside the superconducting pads (7).

2. Electrical machine (1) according to claim 1, wherein the flux barrier (12) comprises an annular band (13) extending in a plane radial to the axis (X), said annular band (13) being coaxial with the axis (X).

3. Electrical machine (1) according to claim 1, wherein the flux barrier (12) comprises an annular band (13) extending circumferentially around the axis (X).

4. Electrical machine (1) according to claim 3, further comprising at least one face (14) extending radially towards the axis (X) from the annular band (13), preferably two faces (14) opposite offset axially from each other.

5. Electrical machine (1) according to claim 4, further comprising a drive shaft configured to rotate the superconducting pads (7) about the axis (X), the face (14) of the flux barrier (12) comprising a through hole (15) and the drive shaft passing through the through hole (15) so that the flux barrier (12) is mounted around the drive shaft.

6. Electrical machine (1) according to claim 5, further comprising a cooling assembly of the superconducting pads (7) and / or ferrofluid seals mounted near the drive shaft through the through hole (15) , such that the flux barrier (12) is mounted around the cooling assembly and/or ferrofluid seals.

7. Electrical machine (1) according to one of claims 1 to 6, further comprising an armature (2) comprising coils (5) distributed circumferentially around the axis (X), the flux barrier (12) being integral in movement with the armature (2).

8. Electrical machine (1) according to one of claims 1 to 7, wherein the flux barrier (12) is integral in movement with the superconducting pads (7).

9. Electrical machine (1) according to one of claims 1 to 8, wherein the flux barrier (12) is continuous over its entire periphery.

10. Electrical machine (1) according to one of claims 1 to 9, said electrical machine being axial flux, the flux barrier (12) extending between the superconducting pads (7) and the armature (2) of so as to at least partially cover the radially inner edge (10) of all or part of the coils (5) of the armature (2).

11. Electrical machine (1) according to claim 10, wherein each coil (5) further has lateral edges (11) extending radially from the radially inner edge (10), the flux barrier (12) covering at plus 10% of side borders (11).

12. Aircraft (100) comprising an electrical machine (1) according to one of claims