Stator with winding resistant to extreme conditions for electrical machines, and electrical machines incorporating such a stator

Abstract

The invention relates to an electrical machine stator (110) in which said stator is configured to cooperate at an air gap (150) with a moving element (120') or a moving element such as a rotor (120) to produce a mechanical force and / or an induced electrical voltage. The stator (110) comprises a stator yoke (113) and a winding having at least one winding. The winding is characterized in that the winding comprises at least one winding (111) of a cable (170) having an electrically conductive core (171), an electrically insulating layer (172) surrounding said core, and an outer metallic sheath (173) surrounding said electrically insulating layer. The invention also relates to an electrical machine, such as an electric motor, electric generator, resolver, rotating transformer, or brake. See Figure 3.

Description

Title of the invention: Stator with a winding resistant to extreme conditions for an electrical machine, and electrical machine comprising such a stator

[0001] The present invention relates to an electrical machine stator in which said stator is configured to cooperate, without a stator protection ring, at an air gap with a moving element in translational or rotational motion, to produce a mechanical force or an induced electrical voltage. The stator according to the invention is particularly suitable for applications in which said electrical machine operates at very low or very high temperatures, or is immersed in corrosive or flammable fluids such as propellants.

[0002] The present invention also relates to an electrical machine, of the type electric motor, electric generator, resolver, rotating transformer or brake comprising such a stator. State of the art

[0003] There are more and more areas in which electrical machines operate at very low or very high temperatures, or are immersed in corrosive or flammable fluids.

[0004] This is particularly true of cryogenic engines used in rockets, which operate on the basis of a fuel / oxidizer mixture, for example, comprising liquid oxygen (LOx) mixed with liquid hydrogen (LH2), generally referred to as propellants. To transfer these propellants from the tanks to the combustion chamber of the cryogenic engine, electric motors are used in pumping devices. To avoid having to manage dynamic seals, the electric motors used can be immersed in the propellants.

[0005] However, the windings of these machines are not always compatible with these extreme conditions.

[0006] In the case of electric motors with an air gap immersed in propellants used to drive pumps or operate valves, one solution is to confine the stator in a sealed area by placing a stator confinement ring in the air gap.

[0007] However, in the case where the fret is metallic or at least electrically conductive, this solution does not solve the problem of extreme temperatures on the one hand, and leads on the other hand to significant eddy current losses, which are all the more significant as the rotation speed of the electric motor is high, thus reducing its performance.

[0008] Indeed, the disadvantages of the stator confinement ring in the air gap are as follows:

[0009] - The stator no longer benefits as well from the cooling that the potential can offer fluid flow rate in the air gap,

[0010] - The presence of the stator fret implies an increase in the air gap magnetic field strength, and therefore a reduction in performance.

[0011] - If the stator fret is made of metal, the fret can be the site of induced currents during from the rotation of the rotor,

[0012] - If the stator fret is not made of metal, but for example of PTFE, it can suffer from a lack of mechanical resistance if there is a large pressure differential between the immersed air gap and the sealed area where the stator is located.

[0013] Other solutions consist of overmolding the face of the stator carrying the winding with a resin, for example in Polyurethane, Silicone or Epoxy and / or impregnating the winding with a protective varnish in Polyamide-imide, Polyester or Silicone.

[0014] However, the use of polymers is not always compatible with cryogenic temperatures and / or flammable conditions induced by propellants.

[0015] One object of the present invention is to remedy at least one of the drawbacks of the prior art.

[0016] Another object of the invention is to propose a solution to protect the stator winding of an electrical machine operating at very low or very high temperatures, or immersed in corrosive or flammable fluids, without impacting the performance of said electrical machine. Description of the invention

[0017] The invention proposes to achieve at least one of the aforementioned goals by means of an electrical machine stator in which said stator is configured to cooperate at the level of an air gap with an element in translational motion or in rotational motion such as a rotor, to produce a mechanical force and / or an induced electrical voltage, said stator comprising a stator yoke and a winding having at least one winding, characterized in that the winding comprises at least one winding of a cable having an electrically conductive core, an electrically insulating layer surrounding said core, and an external metallic sheath surrounding said electrically insulating layer.

[0018] Various embodiments of the invention are provided, incorporating, according to all their possible combinations, the different optional features set out below.

[0019] Preferably, the electrically conductive core is made of copper selected from the list defined by: • Copper Cu-al (Cu-ETP - Electrolytic Tough-Pitch - 99.9% copper min and 0.04% oxygen max), • Copper Cu-cl (Cu-OF - Oxygen Free - 99.95% copper min and 0.001% oxygen max), • Copper Cu-c2 (Cu-OFE - Oxygen Free Electronic grade - 99.99% copper min and 0.0005% oxygen max), • OFHC copper.

[0020] Also preferably, the outer metallic sheath is made of a metallic alloy whose magnetic permeability is less than 1.1 regardless of the temperature.

[0021] Even more preferably, the outer metallic sheath is made of a metallic alloy chosen from the list defined by: • 316L (AISI) stainless steel, • 304L (AISI) stainless steel, • Inconel 625 (UNS), • Inconel 718 (UNS).

[0022] Preferably, the electrically insulating layer comprises an oxide or a mixture of oxides selected from the list defined by: • Magnesium oxides (MgO), • Aluminum oxides A12O3, • Silicon dioxides SiO2.

[0023] Advantageously, the two ends of at least one winding of said cable are connected in a confined manner to connectors, for example by welding or brazing, so as to protect the electrically insulating layer and the electrically conductive core of said cable.

[0024] According to one aspect of the invention, the diameter of the cable is between 0.25 and 5 mm.

[0025] According to a certain configuration, the stator is a stator of cylindrical geometry having an internal bore intended to accommodate the element in translational motion or in rotational motion.

[0026] According to another configuration, the stator is a discoidal geometry stator of which at least one face is provided to be opposite the element in rotational motion.

[0027] According to yet another configuration, the winding consists of a plurality of toroidal cable windings around the stator yoke.

[0028] According to one variant, the stator is preferably without notches.

[0029] According to yet another configuration, the stator is a stator of planar geometry of which at least one face is provided to be opposite the element in translational motion.

[0030] The invention also relates to an electrical machine comprising: • A stator according to an embodiment of the invention, and • An element in translational motion or in rotational motion such as a rotor.

[0031] According to a first target use, the machine is configured for operation at temperatures between +400°C and +1000°C.

[0032] According to a second target use, the machine is configured for operation when the winding is immersed in a fluid included in the list defined by: • Cryogenic fluids, • Liquid oxygen (LOx), • Liquid hydrogen (LH2), • Liquid methane (LCH4), • Liquid nitrogen (LN2), • Liquid helium (LHe), • Liquefied natural gas (LNG), • Corrosive fluids.

[0033] According to different possible applications, said machine can be an electric motor, or an electric generator, or a resolver, a rotating transformer or a brake. Description of the figures and methods of realization

[0034] Other advantages and features will become apparent upon examination of the detailed description of non-limiting embodiments and the accompanying drawings, in which: - Fig. 1 is a schematic representation following a longitudinal section of an example of the realization of an electrical machine according to the state of the art; - Fig. 2 is a schematic representation following a cross-section of an example of the realization of an electrical machine according to the state of the art; - Fig. 3 is a schematic representation following a longitudinal section of an example of an embodiment of an electrical machine according to an embodiment of the invention; - Fig. 4 is a schematic representation following a cross-section of an example of an embodiment of an electrical machine according to an embodiment of the invention; - Fig. 5 is a schematic representation following a perspective view of a detail of an embodiment of the invention; - FIGURES 6 to 9 are schematic perspective representations of embodiments of the invention;

[0035] It is understood that the embodiments described below are in no way limiting. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0036] In particular, all the variants and all the embodiments described are combinable with each other if nothing prevents this combination from a technical point of view.

[0037] In the figures and in the rest of the description, elements common to several figures retain the same reference.

[0038] FIGURES 1 and 2 are schematic representations of an example of an embodiment of an electrical machine according to the prior art, respectively according to a longitudinal sectional view and according to a transverse sectional view.

[0039] The electrical machine 100 according to the prior art represented in FIGURES 1 and 2 can be an electric motor, an electric generator, a resolver or a brake.

[0040] The electric machine 100 comprises a stator 110 and a rotor 120.

[0041] In the example shown, the electric machine 100 comprises an external stator 110 in which the rotor 120 is disposed. In particular, the rotor 120 is disposed in a bore provided in the external stator 110. The yoke of the stator 113 can be a single piece or made of a stack of laminations in order to reduce the magnetic losses induced by eddy currents.

[0042] Of course, this example is given for illustrative purposes only and the invention is not limited to this electrical machine architecture.

[0043] The space between the stator 110 and the rotor 120 constitutes the air gap 150. The rotor 120 and the stator 110 each have a generally cylindrical shape and are substantially concentric. Thus, the face of the stator 110 opposite the rotor 120 is called the stator air gap face and corresponds to the face of the internal bore of the stator 110. Similarly, the rotor air gap face is formed by the outer circumferential surface of the rotor 120.

[0044] The rotor 120 can be of the type comprising N pairs of poles, each pair of magnetic poles being formed by two opposite magnetic poles. These pairs of poles can be buried or surface permanent magnets or a winding.

[0045] The rotor may also not include magnets but may have a magnetic circuit geometry that induces a circumferential variation of reluctance in the air gap. Thus, the rotor may have a geometry with alternating circumferential large teeth and notches, the reluctance variation then being generated by the alternation of teeth and notches. Similarly, the rotor may be synchronously reluctant with cavities acting as flux barriers.

[0046] The stator 110 further includes a winding for conducting electric current. This winding receives an electrical supply in the case where the electric machine is, for example, an electric motor or a brake, and collects the current generated in the electric machine 100, in the case where the electric machine 100 is, for example, an electric generator or a resolver.

[0047] In the example of FIGURES 1 and 2, without loss of generality, the stator 110 includes slots 115 provided in the vicinity of the air gap 150. The winding consists of one or more windings 111 of winding wire, arranged in the slots 115, and preferably not protruding from the slots 115. The winding wires used are enameled copper wires for electrical insulation, the winding being able to be impregnated with a varnish to stiffen the assembly, dissipate heat and improve electrical insulation. Each notch 115 is delimited on either side respectively by a first stator tooth 112 and a second stator tooth 112 protruding towards the rotor 120. Of course, this architecture is by no means limiting: indeed, in other embodiments, the stator 102 may not include notches 115, or stator teeth 112, and the winding may be arranged directly on the air gap face.

[0048] The stator 110 has, at its edges / ends, coil heads 114, visible in [Fig. 1]. The winding is electrically connected to the outside of the electric machine 100 by a connection 116, visible in [Fig. 1].

[0049] The assembly formed by the stator 110 and its elements, as well as the rotor 120, is arranged in a housing 140, closed on each side by flanges 130, visible in [Fig. 1]. The rotor 120 is connected to a drive shaft 122 passing through the flanges 130.

[0050] When the electric machine 100 is immersed in a corrosive or flammable fluid, said fluid circulates between the stator 110 and the rotor 120, thus leading to a risk of degradation of the winding and / or a risk of ignition upon contact with the winding.

[0051] Therefore, the electrical machine 100, according to the prior art shown in FIGURES 1 and 2, comprises a metallic stator collar 160 which confines the stator winding. This collar can be made of Inconel or stainless steel.

[0052] However, such protection introduced at the level of the air gap tends to induce magnetic losses induced by eddy currents.

[0053] Therefore, the machine according to the invention, as represented in FIGURES 3 and 4, does not have a stator ring and has protection against flammable and / or corrosive fluids, which is integrated directly into the winding.

[0054] According to the principle of the invention and as represented in FIGURES 3 and 4, the stator 110 is an electrical machine stator, which is configured to cooperate at the level of an air gap 150, with an element in translational motion or in rotational motion such as a rotor 120, to produce a mechanical force and / or an induced electrical voltage.

[0055] The stator 110 comprises a stator head 113 that is either a single piece or made of a stack of laminations. The winding comprises several windings 111 of an electrically conductive cable 170.

[0056] The stator 110 includes slots 115 provided in the vicinity of the air gap 150. The winding consists of several windings 111 arranged in the slots 115, and preferably not protruding from the slots 115. Each slot 115 is delimited on either side respectively by a first stator tooth 112 and a second stator tooth 112 projecting towards the rotor 120.

[0057] The space between the stator 110 and the rotor 120 constitutes the air gap 150. The rotor 120 and the stator 110 each have a generally cylindrical shape and are substantially concentric. Thus, the face of the stator 110 opposite the rotor 120 is called the stator air gap face and corresponds to the face of the internal bore of the stator 110. Similarly, the rotor air gap face is formed by the outer circumferential surface of the rotor 120.

[0058] The rotor 120 can be of the type comprising N pairs of poles, each pair of magnetic poles being formed by two opposite magnetic poles. These pairs of poles can be permanent magnets buried or on the surface or a winding similar to that of the stator.

[0059] The rotor may also not include magnets but may have a magnetic circuit geometry that induces a circumferential variation of reluctance in the air gap. Thus, the rotor may have a geometry with alternating circumferential large teeth and notches, the reluctance variation then being generated by the alternation of teeth and notches. Similarly, the rotor may be synchronously reluctant with cavities acting as flux barriers.

[0060] It is also possible in cylindrical geometry to position the stator said to be "in internal configuration" inside the rotor then said to be "in external configuration".

[0061] The stator 110 has, at its edges / ends, coil heads 114, visible in [Fig.3]. The winding is electrically connected to the outside of the electric machine 100 by a connection 116, visible in [Fig.3].

[0062] The assembly formed by the stator 110 and its components, as well as the rotor 120, is arranged in a housing 140, closed on each side by flanges 130, visible in [Fig. 3]. The rotor 120 is connected to a drive shaft 122 passing through the flanges 130.

[0063] As shown in [Fig.5], this cable 170 comprises an electrically conductive core 171, an electrically insulating layer 172 surrounding said core, and an external metallic sheath 173 surrounding said electrically insulating layer.

[0064] Preferably, the electrically conductive core 171 is made of copper selected from the list defined by:

[0065] - Copper Cu-al (Cu-ETP - Electrolytic Tough-Pitch - 99.9% copper min and (0.04% maximum oxygen),

[0066] - Copper Cu-cl (Cu-OF - Oxygen Free - 99.95% minimum copper and 0.001% maximum oxygen),

[0067] - Copper Cu-c2 (Cu-OFE - Oxygen Free Electronic grade - 99.99% copper (min and 0.0005% oxygen max),

[0068] - OFHC copper.

[0069] Cu-al (Cu-ETP) copper is used for the manufacture of wires, bars, sheets, boards, profiles and strips for electrical use; it is the most common grade. It is sensitive to heating in a reducing atmosphere, which implies certain restrictions during heat treatment and welding, particularly with a torch.

[0070] Copper (Cu-cl) or Cu OF (Oxygen Free) is a high-purity copper without oxygen. This copper, also known as Cu-cl, has high electrical conductivity. It is characterized above all by its minimum copper content of 99.95%. With such a high copper content, it is insensitive to reducing atmospheres. Thanks to its very low impurity level, it is ideal for use in the electronics industry. This copper possesses all the qualities of the other grades (Cu-a and Cu-b) but with greater electrical and thermal conductivity and improved weldability.

[0071] Cu-c2 or Cu-OFE copper is a high-purity, non-deoxidized, oxygen-free copper that contains no elements that evaporate under vacuum and has high electrical and thermal conductivity. In addition to excellent hot and cold machinability, this type of copper also exhibits good corrosion resistance, particularly to atmospheric corrosion (due to its well-adhered oxide layer) and water, and is practically insensitive to stress corrosion cracking. It withstands heat treatments in reducing atmospheres and welds and brazes very well.

[0072] Oxygen-free copper (OFC) or high thermal conductivity oxygen-free copper (OFHC) is a group of high-conductivity wrought copper alloys that have been electrolytically refined to reduce the oxygen level to 0.001% or less. Oxygen-free copper is a premium grade of copper that Copper has a high level of conductivity and is virtually oxygen-free. Oxygen content in copper affects its electrical properties and can reduce conductivity. It is particularly used in cryogenics.

[0073] The core can consist of one or more electrically conductive wires insulated from each other.

[0074] The outer metallic sheath 173 is preferably made of a metallic alloy whose magnetic permeability is less than 1.1 regardless of the temperature.

[0075] The metallic alloy ensuring low magnetic permeability is chosen from the list defined by:

[0076] - 316L (AISI) stainless steel,

[0077] - 304L (AISI) stainless steel,

[0078] - Inconel 625 (UNS),

[0079] - Inconel 718 (UNS).

[0080] Stainless steels and grades of Inconel do indeed exhibit very high resistance to corrosion and high temperatures.

[0081] The electrically insulating layer 172 comprises an oxide or a mixture of oxides selected from the list defined by:

[0082] - Magnesium oxides MgO,

[0083] - Aluminium oxides A12O3,

[0084] - Silicon dioxides SiO2.

[0085] Preferably, the two ends of the cable windings 111 of cable 170 are connected in a confined manner to connectors, for example by welding or brazing, so as to protect the electrically insulating layer 172 and the electrically conductive core 171 of said cable.

[0086] The diameter of the 170 cable can be between 0.25 and 5 mm.

[0087] As shown in FIGURES 3 and 4, the stator 110 is a stator of cylindrical geometry with an internal bore designed to accommodate a rotor 120.

[0088] As shown in [Fig.6], the stator 110 is a planar geometry stator, one face of which is intended to be opposite a translationally moving element 120'. The electrical machine thus constituted is a planar linear motor.

[0089] As shown in [Fig.7], the stator 110 is a stator of cylindrical geometry with an internal bore designed to accommodate a moving element 120'. The electrical machine thus formed is a tubular linear motor.

[0090] As represented in [Fig.8], the stator 110 is a stator of discoidal geometry, one face of which is provided to be opposite a rotating moving element 120.

[0091] As shown in [Fig. 9], the winding consists of a plurality of windings 111 of toroidal cables. The stator may have notches or It may well be slotless (a so-called "slotless" configuration). Figure 9 corresponds to a slotless, two-air-gap discoid version with an internal stator.

[0092] The stator 110 according to the invention can be integrated into an electrical machine to cooperate at the level of an air gap 150 with an element in translational motion 120' or in rotational motion such as a rotor 120, to produce a mechanical force and / or an induced electrical voltage.

[0093] This machine can be an electric motor, or an electric generator, or a resolver, or a brake, or a rotating transformer.

[0094] In the case where the machine is used as a resolver, the rotor and stator are composed of a bundle of laminations. The rotor may include the primary winding. The stator then includes the two secondary windings, which are out of phase, in the sense that the voltages induced in the two secondary windings are electrically out of phase by an angle of approximately plus or minus 90°.

[0095] Alternatively, the stator may comprise the primary winding and the two secondary windings, the rotor being simply made of laminations.

[0096] The resolver functions as a transformer whose coupling varies with the mechanical angle of the rotor. When the primary winding is energized with an alternating voltage, two alternating voltages are obtained on the secondary windings of the stator.

[0097] Because the cable, constituting the windings 111, has a layer of oxides and an external metallic sheath highly resistant to temperature, the stator according to the invention allows the electrical machine to operate at temperatures between +400°C and +1000°C.

[0098] Similarly, the stator according to the invention allows the electrical machine to operate when immersed in a cryogenic fluid of the liquid nitrogen (LN2) or liquid helium (LHe) type.

[0099] The stator according to the invention integrated into a machine also allows operation when the winding is immersed in a flammable fluid of the propellant type such as LOx or LH2 for example, or a corrosive fluid, because the cable constituting the windings 111 has a highly resistant metallic outer sheath.

[0100] In general, the invention is not limited to the examples just described, which are given by way of illustration only.

Claims

Demands

1. Stator (110) of an electrical machine in which said stator is configured to cooperate at the level of an air gap (150), with an element in translational motion (120') or in rotational motion such as a rotor (120), to produce a mechanical force and / or an induced electrical voltage, said stator (110) comprising a stator yoke (113) and a winding having at least one winding (111), characterized in that said winding is a winding of a cable (170) comprising an electrically conductive core (171), an electrically insulating layer (172) surrounding said core, and an outer metallic sheath (173) surrounding said electrically insulating layer.

2. Stator according to any one of the preceding claims, characterized in that the electrically conductive core (171) is made of copper selected from the list defined by: - ​​Cu-al copper (Cu-ETP - Electrolytic Tough-Pitch - 99.9% copper min and 0.04% oxygen max), - Cu-cl copper (Cu-OF - Oxygen Free - 99.95% copper min and 0.001% oxygen max), - Cu-c2 copper (Cu-OFE - Oxygen Free Electronic grade - 99.99% copper min and 0.0005% oxygen max), - OFHC copper.

3. Stator according to any one of the preceding claims, characterized in that the outer metallic sheath (173) is made of a metallic alloy whose magnetic permeability is less than 1.1 regardless of temperature.

4. Stator according to any one of the preceding claims, characterized in that the outer metallic sheath (173) is made of a metallic alloy selected from the list defined by: - ​​316L stainless steel (AISI), - 304L stainless steel (AISI), - Inconel 625 (UNS), - Inconel 718 (UNS).

5. Stator according to any one of the preceding claims, characterized in that the electrically insulating layer (172) comprises an oxide or a mixture of oxides selected from the list defined by: - Magnesium oxides MgO, - Aluminium oxides Al2O3, - Silicon oxides SiO2.

6. Stator according to any one of the preceding claims, characterized in that the two ends of at least one winding (111) of said cable (170) are connected in a confined manner to connectors, for example by welding or brazing, so as to protect the electrically insulating layer (172) and the electrically conductive core (171) of said cable.

7. Stator according to any one of the preceding claims, characterized in that the diameter of the cable (170) is between 0.25 and 5 mm.

8. Stator according to any one of the preceding claims, characterized in that the stator (110) is a stator of cylindrical geometry having an internal bore provided for receiving the element in translational motion (120') or in rotational motion (120).

9. Stator according to any one of claims 1 to 7, characterized in that the stator (110) is a stator of discoidal geometry of which at least one face is provided to be opposite the rotating moving element (120).

10. Stator according to any one of claims 1 to 7, characterized in that the stator (110) is a planar geometry stator of which one face is provided to be opposite the translationally moving element (120').

11. Stator according to any one of the preceding claims, characterized in that the winding consists of a plurality of windings (111) of toroidal cables.

12. Electric machine comprising: - a stator (110) according to any one of the preceding claims, and - an element in translational motion (120') or in rotational motion such as a rotor (120).

13. Electric machine according to claim 12, characterized in that the machine is configured for operation at temperatures between +400°C and +1000°C.

14. An electric machine according to claim 12, characterized in that the machine is configured for operation when the winding is immersed in a fluid included in the list defined by: - ​​Cryogenic fluids, - Liquid oxygen (LOx), - Liquid hydrogen (LH2), - Liquid methane (LCH4), - Liquid nitrogen (LN2), - Liquid helium (LHe), - Liquefied natural gas (LNG), - A corrosive fluid.

15. An electric machine according to any one of claims 12 to 14, characterized in that said machine is: - An electric motor, or - An electric generator, or - A resolver, or - A brake, or - A rotating transformer.

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