Conductive element with improved heat dissipation

Abstract

Disclosed is a conductive element (10, 100, 200, 300), in particular of an electric machine or a switching apparatus, comprising at least one structure for limiting the heating of same caused by the current routed via this element, the conductive element comprising at least one hollow conductive portion (12B), the hollow conductive portion being formed by a conductive shell (120) defining and extending around a closed cavity (129), the cavity being partially filled with a fluid, in particular a liquid, and placed under vacuum.

Description

[0001] CONDUCTIVE ELEMENT WITH IMPROVED THERMAL DRAINAGE

[0002] DESCRIPTION

[0003] TECHNICAL FIELD AND PREVIOUS ART

[0004] This application relates to the field of electrical conductors and in particular to those of direct current or alternating current electrical machines, in particular electrical machines enabling the generation and / or motorization of certain electrical components of an aircraft, as well as to conductors of switching devices such as contactors and circuit breakers, and in particular those used in an aircraft.

[0005] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by different countries. In particular, an ambitious standard applies to both new types of aircraft and those already in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change. Technological research efforts have already led to significant improvements in the environmental performance of aircraft.The Applicant takes into account the factors impacting all phases of design and development to obtain less energy-intensive and more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving aircraft energy efficiency. This sustained research and development work focuses in particular on new generations of hybrid thermal and electric aircraft engines. One of the Applicant's objectives is to develop aircraft incorporating a high-power electrical generation system. This would increase the proportion of electrical equipment on board in order to reduce fuel consumption.In this context, and in many electrotechnical applications, electrical conductors pass through electrically insulating materials that are poor thermal conductors and do not easily dissipate Joule losses associated with the current flow. These Joule losses can then lead to heating of the conductor, with the formation of localized hot spots within it. An increase in temperature within the conductor can affect its electrical resistivity. This increase in resistivity can, in turn, lead to an increase in Joule losses and therefore, again, in temperature, which can result in thermal runaway and, in particular, degradation of the material in which the conductor is embedded, if the current flowing through the conductor cannot be limited to a certain value.

[0006] The structure and dimensioning of an electrical machine are guided by its thermal resistance and this is mainly a function of the amplitude of the electric currents it supports within its conductive windings.

[0007] For example, some electrical machines for aircraft, and in particular electrical machines intended to provide propulsion and / or electrical lift to the aircraft, produce electrical currents of high intensity, in particular exceeding several hundred amperes.

[0008] To cool a conductive element of an electrical machine, it is known to use natural or forced convection.

[0009] Such a solution is not entirely satisfactory. Furthermore, it is not applicable to a portion of a conductive element located in, or embedded within, a material with poor thermal conductivity.

[0010] To cool such a section, thermal drainage towards its ends is attempted. However, this cooling method is inefficient when the conductive section has a small cross-section and a significant length.

[0011] Another solution for cooling a conductive element is liquid forced convection cooling, using a device to circulate a fluid. Such a system may require the addition of a pump and a heat exchanger, which makes it complex to implement, can increase its overall mass and size, and makes it susceptible to leaks or failures.

[0012] In view of the above, the problem arises of improving the cooling of electrical conductors subject to significant losses by Joule effect, particularly when they are embedded in a thermally insulating material or a poor thermal conductor.

[0013] DESCRIPTION OF THE INVENTION

[0014] It is therefore an object of the present invention to provide an electrical current-conducting element comprising at least one structure to limit its heating due to the transmission of current through this element, the conducting element comprising a conductive envelope defining and extending around a closed cavity, the cavity being partially filled with at least one fluid, in particular a liquid, the conducting envelope comprising a conductive portion arranged so that when said high-intensity current passes through the conductive portion, heating of this conductive portion is capable of causing at least partial evaporation of said liquid to limit the heating of said conducting element through which said current passes.

[0015] Such a cavity provides a simple, space-saving means of limiting the appearance of hot spots, without necessarily requiring the circulation of fluid.

[0016] The liquid is chosen, particularly in terms of vaporization temperature, so that the passage of a high-intensity current through the conductive portion of the conductive element is likely to cause the liquid to vaporize, thereby enabling heat absorption.

[0017] To improve heat drainage and cooling of the electrically conductive element extending from the hollow conductive portion, the casing includes an "end" region located at the end of the hollow conductive portion. This region incorporates at least one cooling structure or is coupled to a cooling device. The vaporized liquid, transformed into steam, can then be condensed back into liquid, thereby enabling heat absorption.

[0018] Thus, one embodiment provides: a conductive element for carrying a high intensity current, in particular greater than 10 Amperes, the conductive element comprising a conductive envelope defining and extending around a closed cavity, the cavity being partially filled with a liquid, the conductive envelope comprising a hollow conductive portion through which the current is intended to pass and further comprising at least one hollow "end" region inside which the cavity extends and which is located in an extension of the hollow conductive portion, this at least one so-called end region comprising a cooling structure, in particular formed of fins on its external surface, and / or being coupled to an external cooling device, in particular having a fluidic circuit.

[0019] Preferably, the cavity partially filled with liquid is closed and placed under vacuum, in particular a primary vacuum, i.e. at a pressure typically less than 1 mbar and which can be between 10 -3 mbar and 1 mbar. This allows the vaporization temperature of the liquid to be lowered. In a specific embodiment where the liquid in the cavity is water, this water can then evaporate at a temperature below 100°C.

[0020] According to a particular embodiment, the hollow electrically conductive portion passes through and is surrounded by a so-called "heat-insulating" material which is electrically and thermally insulating or electrically insulating and weakly thermally conductive, in particular with a thermal conductivity of at least less than 20 W / m. K. The "end" region and in particular its cooling structure or cooling device is advantageously located outside the heat-insulating material in which it is not always possible or easy to integrate a cooling function.

[0021] Advantageously, the cooling structure can be a finned structure, known as "external" finned structure, over which an airflow can be directed.

[0022] In the case of an external cooling device, this device may be equipped with a fluidic circuit in which a fluid or liquid is circulated. According to a particular embodiment, the hollow conductive portion extends primarily in a first direction, particularly horizontally, while the hollow end region extends primarily in a second direction, particularly vertically. This second direction forms a non-zero angle with the first direction, typically 90° or substantially equal to 90°. The hollow end region preferably extends in a non-horizontal direction. This allows, where appropriate, for condensation generated in the hollow end region to flow back down by gravity to the hollow conductive portion, thereby improving the cooling of the hollow conductive portion.

[0023] Advantageously, the hollow conductive portion passing through the insulating material can be provided with several changes of direction.

[0024] One particular embodiment involves integrating a porous material into the cavity. This can, in particular, improve the capture of condensate at the conductive portion and contributes to improved cooling.

[0025] One embodiment provides a conductive envelope having an internal surface comprising internal fins that extend into the closed cavity.

[0026] According to a particular embodiment, the hollow conductive portion is a first hollow conductive portion and the cavity is a first cavity, the electrically conductive element comprising, in the extension of the first hollow conductive portion, at least a second hollow conductive portion, this second hollow conductive portion being electrically connected in series with the first hollow conductive portion and comprising a second closed cavity, said second cavity partially filled with fluid or liquid, for example the same working fluid as that of the first cavity, the second cavity being distinct from the first cavity and separated from the first cavity without fluidic communication with the first cavity.

[0027] Advantageously, the first cavity and the second cavity are separated from each other by a conductive wall formed by a region of said conductive envelope. This conductive wall may include an internal cooling device or be coupled to a cooling structure.

[0028] According to a particular embodiment, a solid conductive region configured to carry the current between the first hollow conductive section and the second hollow conductive section may be provided between them. This solid conductive region is preferably located outside the insulating material.

[0029] Advantageously, the conducting element can be provided with a solid conductive area entirely made of conductive material in contact with the hollow conductive portion to carry the current to the hollow conductive part.

[0030] The conductive element can also be provided with a solid conductive area entirely made of conductive material in contact with the hollow conductive portion for current output.

[0031] Alternatively, the conducting element can form a closed conducting circuit, the electric current passing through it being in this case an induced electric current.

[0032] The present invention also relates to a winding, in particular of a rotating machine or of a transformer comprising at least one conductive element as defined above.

[0033] The present invention also relates to an electrical machine squirrel cage comprising one or more conductive elements as defined above.

[0034] According to another aspect, the present invention relates to an electrical machine, in particular an aircraft machine, comprising one or more conductive elements as defined above.

[0035] According to another aspect, the present invention relates to the use of hollow conductive element(s) as defined above in an aircraft.

[0036] In another aspect, the present invention relates to the use of an electrical machine with hollow conductor(s) as defined above for the propulsion and / or electrical levitation of an aircraft. In another aspect, the present invention relates to an electrical switching device, in particular a circuit breaker or contactor, comprising:

[0037] - a first conducting element as defined above,

[0038] - a second conductive element, at least one of said first conductive element and second conductive element being movable and configured to move reversibly between at least one position called "contact", in which the hollow conductive portion is electrically connected with said second conductive element, and at least one other position, called "disconnection", in which the hollow conductive portion is at a distance and electrically isolated from said second conductive element.

[0039] Advantageously, the second conducting element comprises a hollow conducting portion having internally a closed enclosure, in particular filled with a liquid, the hollow conducting portion of the second conducting element being electrically connected with the hollow conducting portion of the first conducting element in said connection position.

[0040] Preferably, the hollow conductive part includes a region equipped with a cooling structure.

[0041] According to one possible implementation of the switching device, this device may further include a third conductive element, the third conductor being provided with a hollow conductive portion, the first conductive element being arranged between the second conductive element and the third conductive element and in which, in the "contact" position, the hollow conductive portion of the first conductive element is electrically connected with the hollow conductive portion of the second conductive element and with the hollow conductive portion of the third conductive element, in the disconnection position the hollow conductive portion is at a distance and electrically isolated from said second conductive element and the third conductive element.

[0042] In another aspect, the present invention relates to an electrical switching device as defined above for an aircraft electrical system. BRIEF DESCRIPTION OF DRAWINGS

[0043] The present invention will be better understood on the basis of the following description and the accompanying drawings, in which:

[0044] Figure 1 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a first embodiment of the present invention.

[0045] Figure 2 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a second embodiment, including a vertical hollow conductive part.

[0046] Figure 3 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a third embodiment, notably with a hollow end region forming an angle with a main hollow conductive portion.

[0047] Figure 4 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a fourth embodiment, including a non-straight hollow main conductive portion.

[0048] Figure 5 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a fifth embodiment, including the conductive portions connected in series through a solid conductive zone.

[0049] Figure 6 is a longitudinal cross-sectional representation of a hollow electrically conductive element according to a sixth embodiment, including a hollow conductive portion internally comprising a cavity incorporating a liquid and a porous material in that cavity.

[0050] Figure 7 is a cross-sectional representation of a hollow electrically conductive element according to a seventh embodiment, including a hollow conductive portion forming a closed conductive circuit in which an induced current is made to flow.

[0051] Figure 8 is a cross-sectional representation of a hollow electrically conductive element according to an eighth embodiment, including a hollow conductive portion forming a closed conductive circuit and extended by a hollow end region coupled to a cooling device.

[0052] Figure 9 is a cross-sectional representation of a hollow electrically conductive element according to a ninth embodiment, notably with the addition of successive hollow conductive portions forming several internal cavities not communicating with each other.

[0053] Figure 10 is a longitudinal cross-sectional representation of a switching device with hollow electrically conductive elements.

[0054] Figure 11 is a perspective representation of a squirrel cage structure for an electrical machine and formed of hollow conductive elements.

[0055] Figure 12 is a perspective representation of an electrical machine winding made of hollow conductive elements.

[0056] Figure 13 is a schematic representation of the winding with hollow conductive elements and whose end is coupled to a cooling device.

[0057] Figure 14 is a schematic representation of a cross-section of a hollow conductor with fins on an inner wall.

[0058] Figure 15 is a schematic representation of a hollow conductor with a porous material on an inner wall.

[0059] Figure 16 is a schematic representation of a connection between a hollow conductor and a cooling structure via connecting portions made of electrically insulating and thermally conductive material.

[0060] DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0061] We first refer to Figure 1, which provides an initial example of a conductive element 10 for carrying an electric current. This element is equipped, in particular, with at least one structure to limit its heating when an electric current, especially a high-intensity electric current, passes through it. "High intensity" here refers specifically to an intensity greater than 10 Amperes and typically between 10 and 500 Amperes, for example, between 100 and 200 Amperes.

[0062] The current supply and output I are achieved in this example respectively by means of solid conductive zones 101, 102, that is to say, entirely made of electrically conductive material, for example copper or aluminum. These conductive zones 101, 102 extend here along the same x-axis (of an orthogonal coordinate system [O; x; y; z] given in Figure 1) as a portion 12B of a conductive part 12 of a particular configuration.

[0063] Unlike zones 101 and 102, a conductive part 12 is hollow and formed by a casing 120, arranged around and delimiting a closed cavity 129. The casing 120 is made of an electrically conductive material, typically a metallic material, for example, aluminum- or copper-based, or an aluminum-copper alloy. This cavity 129 contains a certain quantity of a liquid called the "working fluid." This fluid is disposed of, preferably under vacuum, inside the hollow electrical conductor. A primary vacuum between 10 mbar and 10 -3 mbar is specifically implemented.

[0064] The liquid partially fills cavity 129. The liquid is chosen so that it can vaporize by absorbing the heat released by the Joule effect from the sheath of the hollow conductor through which the current flows. The liquid is preferably chosen based on its evaporation temperature. The working liquid is preferably chemically compatible with the sheath of the hollow conductor so as not to damage it. For example, to avoid corrosion, a liquid other than water is used in the case of an aluminum conductor.

[0065] On the portion 12B of length L (dimension measured parallel to the x-axis), the hollow conductive part 12 is surrounded by a material 25 called "heat insulation". The heat insulation material 25 here forms a sheath in contact with the conductive casing 120.

[0066] The heat-insulating material 25 can be both a thermal insulator or a very low thermal conductor, and an electrical insulator, such as PVC or rubber, glass, ceramic, or Teflon (PTFE). The heat-insulating material 25 can also be a material with low thermal and electrical conductivity, such as magnetic sheet metal, with very low thermal conductivity.

[0067] By "very low thermal conductor", we mean here and throughout the description a thermal conductivity strictly less than 1 W / (mK).

[0068] By "low thermal conductor", we mean here and throughout the description a thermal conductivity of less than 20 W / (mK).

[0069] Portion 12B can have a cylindrical shape, in particular a cylinder of revolution with an external diameter Dext (dimension measured parallel to the z-axis in Figure 1). For example, when the length L of portion 12B is between 100 mm and 500 mm, Dext / 2 can be, for example, between 1 mm and 5 mm, and the envelope has a thickness e which can be, for example, between 0.25 mm and 2 mm.

[0070] The external outer diameter Dext of the hollow conductor, determined according to the current to be carried, can range, for example, from several millimeters to several tens of millimeters. Typically, the larger the diameter Dext of the hollow section 12B, the greater its length L.

[0071] According to a first example of embodiment, a hollow conductive portion 12B can be provided with an outer diameter Dext of 5 mm, an inner diameter Dint (dimension measured parallel to the z-axis in Figure 1) of 3 mm, with a length of portion 12B of 200 mm.

[0072] According to a second embodiment example, a hollow conductive portion 12B can be provided with an outside diameter Dext of 10 mm, an internal diameter Dint of 6 mm and a length L of the portion 12B of 500 mm.

[0073] According to a third embodiment example, we can provide for a hollow conductive portion 12B with an outside diameter Dext of 2 mm, an internal diameter Dint of 1 mm and a length L of the portion 12B of 100 mm.

[0074] In the embodiment shown in Figure 1, the solid conductive zones 101 and 102 located on either side of and extending from section 12B have, for example, a cylindrical shape with an outside diameter that may be identical to that of the hollow conductive section 12. Alternatively, however, it is possible to provide solid conductive zones with cross-sections different from that of the central section 12B.

[0075] In this particular embodiment, the cavity 129 also extends inside several hollow regions 12A, 12C of the envelope 120.

[0076] Preferably, the hollow regions 12A, 12C are configured and / or arranged so that they do not conduct the current carried by the conductive portion 12B.

[0077] In this example, these hollow regions 12A, 12C extend out of the heat-insulating material 25 on either side of the portion 12B. These so-called "end" regions 12A, 12C, arranged as extensions of the conductive portion 12B, advantageously extend in a direction forming a non-zero angle, and here in particular 90°, with the principal direction of this portion 12B. The regions 12A, 12C have a length L' (measured parallel to the y-axis), typically less than or equal to L. Preferably, the length of the conductive portion 12B is not too great compared to those of the hollow regions 12A and 12C, or is of the same order of magnitude as that of the hollow regions 12A and 12C. For example, for a portion 12B of a given length L, we can foresee regions 12A and 12C of length L' between L / 4 and L / 3. The length of the conductive portion 12B can be of the same order of magnitude as the length of regions 12A and 12C.

[0078] The end regions 12A and 12C are advantageously each provided with a structure 50 for cooling the conductive element 10. In this example, the cooling structure 50 has so-called "external" fins 52 located at the ends of the hollow conductive portion, over which a natural or forced airflow FA can be directed. Such an airflow can be provided, for example, by ventilation. The external fins 52 can also be cooled by a device through which a liquid, for example, such as water or oil, is circulated.

[0079] The hollow structure allows for better drainage of Joule losses at the level of the portion 12B surrounded by heat-insulating material 25, from this hollow portion 12B to the end regions 12A and 12C. The end regions 12A and 12C artificially increase the longitudinal thermal conductivity of the conductor while preserving its electrical properties, in order to limit hot spots in the center of the conductor. One operating mode of the device is as follows: A current I, introduced by a conductive zone 101, flows primarily through the conductive portion 12B and exits through the conductive zone 102. Because the current I follows the path of least resistance, it essentially flows through portion 12B of the casing 120 along the shortest path. Under the Joule effect generated by the high-intensity current flowing through the hollow conductive portion 12B, the liquid 13 in the cavity 129 vaporizes, at least partially.The vapor is then transported to the end regions 12A, 12C and in particular their cold ends where this vapor will tend to condense, then return to the portion 12B of the hollow conductor.

[0080] This return of liquid towards the interior of the hollow conductive portion 12B is favored here, under the effect of gravity, due to the "non-horizontal" arrangement of regions 12A and 12C. Regions 12A and 12C extend here preferably in a direction forming a non-zero angle with a horizontal direction (i.e., a direction parallel to the x-axis) and preferably vertical (i.e., a direction parallel to the z-axis) or substantially vertical, that is to say, parallel or substantially parallel to the gravity vector. Cooling of the conductive portion 12B, surrounded by heat-insulating material 25, is thus achieved. By "non-horizontal" arrangement, we mean that when portion 12B is arranged parallel to a horizontal x-axis, regions 12A and 12C form a non-zero angle of at least 10° with this axis.

[0081] Due to their arrangement, and in particular because they are on a longer conductive path than that of section 12B between conductive zones 101, 102, the hollow regions 12A, 12B are not crossed by the current I.

[0082] The hollow portion 12B of the conducting element 10 can have a different orientation. Thus, in another embodiment shown in Figure 2, the hollow conducting part 12 of the conducting element 10, and in particular the conducting portion 12B surrounded by heat-insulating material 25, is this time oriented in a vertical or substantially vertical direction (in other words, parallel or substantially parallel to the gravity vector g and to the z-axis of the orthogonal frame [O; x; y; z]), while the solid conducting areas 101, 102 respectively for current supply and output I, arranged on either side of the portion 12B surrounded by heat-insulating material 25, here make a non-zero angle with this hollow conducting portion 12B and can in particular be oriented orthogonally to this portion 12B.The current supply can be made for example through a conductive zone 101 located here under the region of heat-insulating material 25, while the current output I is made at the level of the conductive zone 102 located above the region of heat-insulating material 25.

[0083] The hollow conductive portion 12 extends out of the insulating material 25 into an end region 12A of the casing 120 located above. In this example, as in the previous one, the end region is sized and arranged so that little or no current flows through it. This region 12A also includes an external cooling structure 50, for example, equipped with fins 52. This hollow end region 12A is preferably oriented vertically or substantially vertically.

[0084] Thus, here again, an operation of the type described previously can be implemented. A high-intensity current passing through the portion 12B located between the solid conductive zones 101 and 102 of the hollow conductor is likely to cause significant heating. This hollow conductor contains a liquid, which is prone to vaporization. The end region 12A, equipped with the cooling structure 50, then tends to cause condensation of the vapor resulting from this vaporization, which then falls back to the surface as a liquid, causing the conductor to cool.

[0085] Another example of this arrangement is shown in Figure 3. The hollow conductive portion 12 here has an 'L'-shaped arrangement, different from the 'U'-shaped arrangement in Figure 1, and extends out of the insulating material 25 into a single non-horizontal hollow end region 12C, which is in this case vertical or substantially vertical. The hollow end region 12C may also be equipped with a cooling structure 50. Heat dissipation occurs mainly on one side of the hollow conductive portion 12B, for example, here on the side where the current exits through the conductive zone 102.

[0086] In another example of a configuration illustrated in Figure 4, the hollow conductive portion 12B through which the current I flows is this time formed of successive sections extending in different directions relative to the previous one. The path of the current I in the insulating material 25 is not rectilinear here.

[0087] The hollow conductive portion 12B has, in particular in this example, a U-shaped form with two vertical sections 12B1, 12B3 on either side of a horizontal section 12B2. Here again, the casing 120 may include one or more end regions 12A, 12C which extend out of the heat-insulating material 25 and are coupled to, or fitted with, a cooling structure 50, for example of the finned type described previously or a different one.

[0088] An example of a cooling device 150, different from the finned structure 50 described previously, is schematically represented in the embodiment shown in Figure 5. It consists of a fluidic system in which a fluid or cooling liquid is circulated, or a heat pipe system containing a specific liquid. Preferably, an electrically insulating liquid such as deionized water is chosen.

[0089] For this variant, the conductive element 10 comprises two structures of the type shown in Figure 4, connected in series. The conductive element 10 thus formed has a first hollow conductive portion 12 situated between two solid conductive zones 101, 103. This first conductive portion 12 is formed, as in the embodiment shown in Figure 5, of a U-shaped conductive portion 12B in the insulating material 25 and is connected in series with a second conductive portion 22 of similar configuration and provided with a cavity 229. The second hollow conductive portion 22 is arranged between the solid conductive zone 103 and another solid conductive zone 102.

[0090] The conductive parts 12, 22 extend out of the heat-insulating material 25 respectively into hollow end regions 12A, 12C and 22A, 22C against which the cooling device 150 is arranged to maintain a given temperature T0 at the level of the hollow end regions 12A, 12C, and 22A, 22C.

[0091] According to one possible application of the conductive element illustrated in Figure 5, it can form two hollow turns of a stator or rotor winding of an electrical machine, connected in series. The heat-insulating material 25 could correspond, for example, to the magnetic circuit, such as a silicon iron or cobalt iron alloy, which is a weak thermal and electrical conductor.

[0092] In the case of a hollow copper conductor placed inside a magnetic circuit, the copper losses are evacuated from portion 12B to portion 12A by means of the fluid placed inside portion 12B of the hollow conductor and the losses inside the magnetic circuit (iron losses) are drained by thermal conduction to the hollow conductor placed closest to the magnetic circuit.

[0093] In either of the described embodiment examples, end zones 12A, 12C are provided, preferably forming a non-zero angle and advantageously of 90° with the portion 12B embedded in the heat-insulating material 25, in particular to allow a return of liquid from condensation.

[0094] In an alternative embodiment illustrated in Figure 6, the conductive element comprises a horizontal or substantially horizontal hollow conductive portion 12B surrounded by heat-insulating material 25 and extending into at least one end region 12C outside the heat-insulating material 25, which is itself horizontal or substantially horizontal. This end region 12C is coupled to a cooling device or comprises a cooling structure 50.

[0095] In this case, to facilitate the recovery of liquid from condensation in region 12C at the conductive portion 12B, a layer or zones of porous material 127 can be provided in the cavity 129, and in particular lining the internal walls of a conductive envelope 120 forming the conductive portion 12B. The porous material 127 can, for example, be in the form of a woven wick and / or a porous metallic material such as porous sintered copper or nickel.

[0096] In either of the embodiments described above, a hollow conductive portion is provided between two solid conductive zones 101 and 102, respectively intended to supply current to the conductive element and to collect the current that has passed through the conductive element. Alternatively, the cooling principle presented above can be applied to a conductive element forming a closed conductive circuit and capable of carrying an induced current.

[0097] Thus, in an example of an embodiment illustrated in Figure 7, the hollow conductive portion 12B surrounded by heat-insulating material 25 forms a closed conductive circuit 128 through which an induced current can flow. This current can be, in particular, the result of a change in the intensity of a magnetic field or of the relative motion between the conductive portion 12B and a magnetic field. The hollow conductive portion extends into a medium different from the heat-insulating material 25 in a hollow end region 12A. This end region 12A, which extends vertically, allows the Joule losses generated in the coil to be dissipated to a cooling structure 50.

[0098] In the particular example of Figure 7, the hollow conductive portion 12B has a spiral or circular ring shape, but other shapes may be provided.

[0099] Thus, in the example of figure 8, the conductive portion 12B creates a conductive circuit 128 of polygonal shape and in particular rectangular or square in the heat-insulating material 25.

[0100] As with either of the examples described previously, the finned structure can be combined with or replaced by another cooling device, for example, one in which a liquid is circulated. This type of electrical conductor configuration short-circuited on itself can be adapted and integrated into various devices such as an eddy current disk, an electric machine squirrel cage, a phase-shifting ring (also called a "Frager loop"), or a Thomson effect device, and in particular a Thomson effect actuator. In such an actuator, a capacitor is discharged through a coil. Under the effect of a rapidly increasing current intensity, eddy currents can be induced in a disk or ring placed near the coil. These currents result in a strong repulsive Laplace force exerted by the coil on the disk or ring.Such Thomson effect actuators can be used for example in a crimping or rapid stamping device.

[0101] In an example of an embodiment illustrated in Figure 9, a series of hollow conductive sections 12i, 122, 12s, 124, 12s are arranged side-by-side and joined together between a solid current-supplying conductive zone 101 and a solid current-supplying conductive zone 102. Each of these hollow conductive sections 12i, 122, 12s, 124, 12s internally defines a cavity 129i (or 1292, 129s, 1294, 129s, respectively). A series of closed and separated cavities 129i, 1292, 129s, 1294, 129s is thus provided. A cooling structure or device can be provided at a partition wall 95 between adjacent cavities 129i, 1292.

[0102] Thus, in the illustrated embodiment example, several cooling devices 250i, 2502, 250s, 2504, 250s represented schematically are arranged along the hollow conductor and each located at the level of a separation wall.

[0103] Alternatively, the hollow conductive partitions 12i, 122, 12s, 124, 12s can each be provided with an end region comprising a cooling structure 50 as described previously, for example in connection with figures 1 to 4.

[0104] To allow optimal operation, the length L of each conductive portion is appropriately chosen according to the internal cross-section (section taken parallel to the plane [O;y;z] in figure 9) of the cavity.

[0105] According to a particular implementation of one or the other of the examples of embodiments described above, rather than having a smooth inner wall, the conductive envelope 120 defining the internal cavity of a conductor can be provided on its inner wall with elements such as internal grooves and / or fins 152 participating in cooling.

[0106] An example of an internal fin structure 152 is shown, for instance, in the cross-sectional view of Figure 14. This structure increases the contact between the liquid and the conductive shell 120, thus improving cooling. In the embodiment illustrated in Figure 15, the conductive shell 120, which defines the internal cavity of a cylindrical conductor, is this time coated on its inner wall with a porous material 127, as previously described.

[0107] A conductive element with hollow conductive portion(s) as described above has numerous applications and can be integrated, for example, into a conductive structure or buried electrical device, a conductive structure or electrical device passing through an insulating wall, a transformer coil or winding, a rotating electrical machine winding (whether in the stator or rotor), an induction motor squirrel cage, a DC motor brush commutator, a current limiter, a battery connection, a capacitor connection, or a fixed and / or moving part of a circuit breaker or contactor. A conductive element with hollow conductive portion(s) as described above is particularly useful in the implementation of electrical machines or aircraft electrical equipment.

[0108] A hollow conductive element of a type such as described above can also be adapted for the implementation of an improved switching device, in particular of the circuit breaker or contactor type.

[0109] A specific example of an electrical switching device for a circuit breaker or contactor is shown in Figure 10. It has a movable, hollow conductive element 100, formed of a conductive portion 12B, this portion having an internal cavity 129 advantageously containing a liquid. The conductive portion 12B is bridge-shaped and extends between a first conductive contact 191 and a second conductive contact 192. Advantageously, the hollow conductive element 100 may have a hollow end region 12C, continuous with the bridge-shaped hollow conductive portion 12B, and which is provided with a cooling structure 50, for example, a finned structure.

[0110] The conductive element 100 is here arranged between two other conductive elements 200, 300 advantageously also hollow conductive elements and is intended to alternately ensure an electrical connection or break the electrical connection between these conductive elements 200, 300. The conductive element 100 is capable of moving between at least one position called the "contact" position in which this element 100 is electrically connected to the hollow conductive elements 200, 300 and at least one position, called the "disconnection" position, in which the conductive element 100 is arranged at a distance and electrically isolated from the hollow conductive elements 200, 300.

[0111] In the contact position, the contacts 191, 192 are arranged against respectively a conductive contact 291 of the hollow conductive element 200 and a conductive contact 392 of the other hollow conductive element 300, to allow a current to be carried for example from a solid conductive area 1001 of the hollow conductive element 200 to a solid conductive area 1002 of the hollow conductive element 300.

[0112] To promote thermal drainage, the hollow conducting elements 200, 300 arranged on either side of the conducting element 100 in a bridge can also each be provided with a hollow end region with a cooling structure 50, for example equipped with fins.

[0113] Such a switching device can form a double-break contactor.

[0114] According to a variant (not shown) of such a device, it is also possible to provide the mobile conductive element 10 forming a double break contactor between two solid conductive elements or between a solid conductive element and a hollow conductive element.

[0115] According to another variant, it is also possible to integrate such a structure of mobile conductive element 10 to form a single break contactor with another conductive element, solid or hollow.

[0116] Another embodiment, as in either of the previously described examples, involves replacing the finned cooling structures with at least one cooling device, for example, a liquid circulation system. Another specific application example is shown in Figure 11, with n conductive elements 110i, 1102, 1103, 110 n 110 n-i hollows each forming a bar of a squirrel cage, in particular of a rotor.

[0117] The conductive elements 110i, IIO2, IIO3, ..., 110 n 110 n -i hollow, can be made of, for example, aluminium or copper.

[0118] The conductive bars extend here between two hollow conductive sections 70, 80, each forming a short-circuit ring. The conductive bars, connected at each end by a conductive ring, thus create a cage-like structure.

[0119] At least one, and advantageously both, of the short-circuit rings 70 and 80 are fitted with cooling fins 92. The respective internal cavities (not visible in Figure 11) of the conducting elements 110i, 1102, 1103, ..., 110 n 110 n -i are preferably filled with liquid, for example water or ethanol. The conductive elements 110i, IIO2, IIO3, ..., 110 n 110 n-i are thus capable of forming a set of heat pipes. The internal cavities of the conducting elements 110i, IIO2, IIO3, ..., 110 n 110 n - 1 communicate with each other and with rings 70 and 80, allowing fluid exchange, advantageously between each bar and the other bars and / or between each bar and ring(s) 70 and 80. An improved thermal drainage squirrel cage is thus implemented. The internal fluid-filled cavity(ies) preferably extend into the fins 92.

[0120] According to one example of implementation, the manufacture of the cage may include the production of the bars by casting and the assembly of these bars to the 70, 80 short-circuit rings for example by brazing.

[0121] In another example, such a cage can be manufactured using 3D printing or additive manufacturing, for example, powder bed fusion. Once assembled or manufactured, the cage can be equipped with one or more filling ports communicating with the internal cavity(es). If all the cavities are interconnected to form a single enclosure, a single filling port is advantageous. A certain quantity of liquid is introduced into the cavity through this filling port, and then the cavity is evacuated. The same port used to introduce the liquid or a separate port can be used for the evacuation.

[0122] Another application example involves a plurality of hollow conductive elements 210 assembled to form a winding, for example, that of a wound rotor. In the specific embodiment shown in Figure 12, the hollow conductive elements 210 of the winding are each in the form of a hollow conductive bar, for example, made of copper or aluminum, in a V-shape or a hairpin shape. Such a winding allows for better heat dissipation compared to a conventional winding. The presence of a cavity (not shown in Figure 12) in each hollow conductive element 210 further enhances cooling.

[0123] The cavities communicate advantageously with each other and form a closed enclosure advantageously filled with liquid, for example, water for a copper conductor or ethanol for an aluminum conductor. When a high current flows through the winding, to further improve heat dissipation, the winding can be coupled to a cooling device 150 as in the embodiment schematically represented in Figure 13. Such a device 150 is here arranged at one end of the hollow conductor bars.

[0124] The hollow conductive elements 210 of the winding can be linked or connected together and form a solid assembly, by means of connection zones 233 made for example by welding.

[0125] Such a type of winding with hollow hairpin conductive bars can alternatively be used to form a stator of a rotating electrical machine.

[0126] A squirrel cage structure and a winding with hairpin conductors as described above are particularly suited to electrical machines dedicated to the propulsion and / or electric lift of an aircraft.

[0127] Depending on a specific implementation of one or more of the previously described examples, it is possible to thermally connect the end region(s) 12A, 12C to a cooling structure or device without bringing this structure or device to the same electrical potential as the rest of the conductive element. For this purpose, an electrically insulating material that is a good thermal conductor, such as aluminum nitride (AIN), can be used as the connection between the cooling structure and the conductive sheath. A welded joint between a copper conductive sheath and such a material can be achieved. A copper-dysprosium alloy can be used to create a Cu / AIN joint with high thermal conductivity.

[0128] Thus, in the particular embodiment shown in Figure 16, the cooling structure 50 formed of fins 52 is fixed to the external surface of an end region 12A of the conducting element by means of connecting portions 167 of electrically insulating and thermally conductive material 168 such as, for example, AIN.

Claims

DEMANDS 1. Current-conducting element (10, 100, 200, 300) comprising a conductive envelope (120) defining and extending around a closed cavity (129, 229), said cavity (129) being partially filled with a liquid (13), said conductive envelope (120) comprising a hollow conductive portion (12B) for carrying a high-intensity current, in particular exceeding 10 Amperes, said envelope further comprising at least one hollow "end" region (12A, 12C) within which the cavity (129) extends and located in an extension of said hollow conductive portion (12B), said at least one "end" region (12A, 12C) comprising a cooling structure (50), in particular formed of external fins (52) on its external surface, and / or being coupled to an external device (150) cooling system, in particular equipped with a fluidic circuit,so that when the high-intensity current passes through said hollow conductive portion (12B) and generates a heating of this hollow conductive portion (12B) enabling at least partial evaporation of said liquid (13), a vapor generated by this evaporation is capable of recondensing at said end region (12A, 12C).

2. Conductive element according to claim 1, in which the hollow conductive portion (12B) passes through and is surrounded by a material (25) said to be "heat-insulating" electrically and thermally insulating or electrically insulating and weakly thermally conductive in particular with a thermal conductivity of at least less than 20 W / mk, said "end" region (12A, 12C) extending out of said heat-insulating material (25).

3. Conductive element according to the preceding claim, said hollow conductive portion (12B) passing through the heat-insulating material (25) having several changes of direction.

4. Conducting element according to one of claims 2 or 3, said cavity (129) being placed under vacuum, in particular a primary vacuum.

5. Conductive element according to any one of the preceding claims, wherein said hollow conductive portion (12B) extends mainly in a first direction, in particular horizontal, said end region (12A, 12C) extending mainly in a second direction, in particular vertical, the second direction making a non-zero angle with the first direction, typically of 90° or substantially equal to 90° with respect to the first direction.

6. Conductive element according to any one of the preceding claims, in which the conductive envelope (120) is provided with an internal surface comprising internal fins (152) which extend into said closed cavity (129).

7. Conducting element according to any one of the preceding claims, wherein said hollow conducting portion (12B, 12i) is a first hollow conducting portion and said cavity (129, 129i) is a first cavity, the electrically conducting element comprising, in the extension of said first hollow conducting portion, at least a second hollow conducting portion (22B, 122), the second hollow conducting portion being electrically connected in series with the first hollow conducting portion and comprising a second closed cavity (229, 1292), said second cavity being partially filled with liquid, the second cavity being distinct from the first cavity and separated from the first cavity without fluidic communication with the first cavity.

8. Conductive element according to claim 7, in which said first cavity and second cavity are separated from each other by a conductive wall (95) formed by a region of said conductive envelope, said conductive wall comprising a cooling device (250i, 25Û2, 250s, 25Û4, 250s) or a cooling structure (50).

9. Conducting element according to claim 7, comprising between the first hollow conducting portion (12B) and the second hollow conducting portion (22B), a solid conducting area (103) configured to carry the current between the first hollow conducting portion and the second hollow conducting portion.

10. Conductive element according to any one of the preceding claims, further comprising a solid conductive zone (101, 102, 103, 1001, 1002) entirely made of conductive material in contact with the hollow conductive portion (12B) to bring said current to the hollow conductive portion or to draw said current from the hollow conductive portion (12B).

11. Conducting element according to claim 10, wherein the solid conductive zone (101) is a first solid conductive zone (101) located outside the heat-insulating material (25) and is configured to carry the current to the hollow conductive portion, the conducting element further comprising a second solid conductive zone (102) located outside the thermally insulating material (25) and configured to draw the current.

12. Conducting element according to any one of the preceding claims in which the hollow "end" region (12A, 12C) is arranged relative to said hollow conducting portion (12B) so as not to conduct said high intensity current.

13. Conductive element according to any one of the preceding claims wherein the cooling structure is connected to the conductive envelope via portions (167) of electrically insulating and thermally conductive material (168) such as AIN.

14. Coil, in particular of a rotating machine or transformer comprising at least one conductive element according to any one of claims 1 to 13.

14. Electrical machine squirrel cage comprising one or more conductive elements according to any one of claims 1 to 13.

15. Electrical machine, in particular aircraft, comprising one or more conductive elements according to any one of claims 1 to 13.

16. Electrical switching device, in particular a circuit breaker or contactor, comprising: - a first conductive element (100) according to any one of claims 1 to 13, - a second conductive element (200), at least one of said first conductive element and second conductive element being movable and configured to move reversibly between at least one position called "contact", in which the hollow conductive portion is electrically connected with said second conductive element, and at least one other position, called "disconnection", in which the hollow conductive portion is at a distance and electrically isolated from said second conductive element.

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