High-frequency and high-voltage electric power cable

Abstract

The invention relates to an electric power cable (20) including: - a hybrid conductor (21) comprising: - a central Litz wire portion (22) including a plurality of electrically conductive strands (23) which are electrically insulated from one another; - a crown portion (25) including electrically conductive strands (26) which are not electrically insulated from one another, a thickness of the crown portion (25) being calculated so as to be less than or equal to a skin thickness (δ); and - an insulator (27) which is arranged around the hybrid conductor (21).

Description

DESCRIPTION TITLE: HIGH FREQUENCY AND HIGH VOLTAGE POWER ELECTRIC CABLE

[0001] The present invention relates to a high-frequency, high-voltage power electrical cable. The invention finds a particularly advantageous, but not exclusive, application in the field of aeronautics for the transmission of high-current, high-frequency, high-voltage electrical signals between electrical equipment of an aircraft.

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental impacts with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

[0006] The electrification and hybridization of the propulsion chain of future-generation aircraft require high electrical power to generate the thrust necessary for the aircraft to take off and maintain flight conditions. All types of aircraft may be concerned, namely vertical takeoff and landing (VTOL) aircraft, short takeoff and landing (STOL) aircraft or conventional takeoff and landing (CTOL) aircraft, commercial or military aircraft, helicopters or drones.

[0007] High electrical power is achieved by combining high voltages at high frequencies with high currents. For example, electrical equipment is subjected to alternating or Pulse Width Modulation (PWM) voltages of up to 1000V and currents of 300A at electrical frequencies of 1500Hz. Voltage extremes can reach 3000V, while current and frequency extremes can reach 1000A and 3000Hz, respectively.

[0008] The electrical wiring interconnection system known as "EWIS" (for "Electrical Wiring Interconnection System" in English terminology) must be capable of transmitting these high currents and high voltages in order to distribute them between the numerous electrical equipment such as generators, electronic power modules including inverters and rectifiers, electric motors, which are distributed throughout the aircraft. In addition to these constraints, the limitation in mass as well as the reduction of the available space for cable routing and the densification of the environment complicate the integration of cabling into the aircraft.

[0009] Some known technologies allow for reducing the mass and bulk of cables.

[0010] Figure 1 shows a cable 1 comprising an electrical conductor 2 of the Litz wire type formed by a plurality of conductive strands 3 electrically insulated from each other. For this purpose, each strand 3 is surrounded by an insulator 4. All of the strands 3 are surrounded by one or more insulating sheaths 5 of the cable.

[0011] This type of cable makes it possible to reduce, or even eliminate, the so-called "skin effect" and "proximity effect" phenomena which increase heating when passing a high-frequency alternating current or PWM.

[0012] It is recalled that the skin effect is an electromagnetic phenomenon linked to the frequency which causes the passage of current around the periphery of the conductor. The circulation of current over a reduced section increases the heating of the cable. The skin thickness 5 is equal to 5=1 / (iT.pof) 1 / 2 , p being the permeability, o being the conductivity of the material and f being the frequency of the current signal.

[0013] In Figure 2, the dark crown 6 represents the crown through which most of the current passes, the central zone 7 is the part with low current flow.

[0014] The thickness 5 of this crown 6 depends on the frequency, it is constant whatever the diameter of the conductor. There is therefore no skin effect when this thickness is less than the radius of the conductor, but the phenomenon is amplified when the diameter of the conductor increases.

[0015] A Litz wire type cable allows a higher current to flow with the same conductor size as a conventional conductor. The graph in Figure 3 shows that for a copper conductor, with the same cross-section, the same heating and for a frequency of 1500Hz, the Litz wire type conductor Litz (see curve C1) allows 50% more current to be carried than a conventional conductor (see curve C2).

[0016] Cables with coaxial structure insulation are also known, comprising a stack of semi-conductor layers and insulating layers. As illustrated in FIG. 4, such a cable 10 comprises a conductor 11 surrounded by an internal semi-conductor layer 12, an insulating layer 13 and an external semi-conductor layer 14. A shield 15 and an external insulating sheath 16 are also provided.

[0017] With a thickness equal to that of a conventional insulator, this assembly improves the resistance to partial discharges and space charges and increases the dielectric strength and the lifespan of the insulation. Such an assembly also allows for a saving in mass and size.

[0018] In order to eliminate air gaps and smooth the electric field, a coaxial structure cable requires an internal layer made of a semiconductor material (the semiconductor layer 12) at the same electrical potential as the conductor 11. The electrical contact between the two parts must therefore have a low resistance value, which is impossible with the electrically insulated strands of a Litz wire type conductor. Indeed, due to its design, a Litz wire type conductor is made of electrically insulated strands, so that there is no electrical contact between a strand and its environment. The person skilled in the art is therefore a priori dissuaded from combining these two incompatible technologies within the same electrical cable.

[0019] It is also possible to add to the assembly described above an external layer 14, made of a semiconducting material, directly in contact with the insulating layer 13 and electrically connected to a reference potential. In this case, the semiconducting layers 12 and 14 on either side of the insulator 13 make it possible to contain the electric field in the insulator 13, improving the insulation performance.

[0020] The invention aims to propose an electric power cable combining the advantages of Litz wire type conductors and cables with coaxial structure insulation.

[0021] To this end, the invention relates to an electric power cable comprising: - a hybrid driver including: - a central part of the Litz wire type comprising a plurality of electrically conductive strands electrically insulated from each other, - a crown part comprising electrically conductive strands not electrically insulated from each other, a thickness of the crown part being calculated so as to be less than or equal to a skin thickness for a given frequency, and - an insulator placed around the hybrid conductor.

[0022] The invention thus makes it possible to combine the advantages of cables with coaxial structure insulation for electrical insulation with those of Litz wire conductors for current flow. The invention further optimizes the use of Litz wire conductor technology by limiting it to a central zone in which it is beneficial. The invention allows a reduction in mass, size, and cost price by limiting the use of insulated strands only to the effective central zone of the cable. The crown portion of bare conductors also provides a heat shield function when the insulation is installed around the hybrid conductor.

[0023] According to one embodiment of the invention, the insulator is an insulator with a coaxial structure comprising at least one semi-conductor layer and one insulating layer.

[0024] According to one embodiment of the invention, the semiconductor layer being an internal semiconductor layer, the insulator with coaxial structure further comprises an external semiconductor layer, the internal semiconductor layer and the external semiconductor layer being separated from each other by the insulating layer.

[0025] According to one embodiment of the invention, said electrical power cable comprises a conductive element for connection to a reference potential of the external semiconductor layer.

[0026] According to one embodiment of the invention, said electric power cable further comprises an external protective sheath arranged around the conductive element.

[0027] According to one embodiment of the invention, the central part and the crown part of the hybrid conductor are sized to comply with a standardized conductor section.

[0028] According to one embodiment of the invention, the skin thickness is calculated as a function of a frequency of an electric current passing through the hybrid conductor.

[0029] According to one embodiment of the invention, the strands of the central Litz wire-type part are arranged in strands according to a predefined arrangement and / or a predefined twisting pitch.

[0030] According to one embodiment of the invention, the electrically conductive strands of the central part and the electrically conductive strands of the crown part are made of copper or aluminum or an alloy of different electrically conductive materials or any other conductive material suitable for the application.

[0031] The invention further relates to an aircraft comprising at least two electrical equipments and at least one electrical power cable as previously defined providing an electrical connection between the two electrical equipments.

[0032] According to one embodiment of the invention, the electrical power cable is configured to operate at a voltage between 230V and 3000V, a current between 100A and 1000A, and a frequency between 400Hz and 3000Hz.

[0033] The present invention will be better understood and other characteristics and advantages will become apparent upon reading the detailed description which follows, comprising embodiments given for illustrative purposes with reference to the appended figures, presented as non-limiting examples, which may serve to complete the understanding of the present invention and the description of its embodiment and, where appropriate, contribute to its definition, in which:

[0034] [Fig.1] Figure 1, already described, shows an electric power cable comprising an electric conductor of the Litz wire type according to the state of the art;

[0035] [Fig.2] Figure 2, already described, illustrates, for a given frequency of a current signal, the skin effect of the passage of current at the periphery of the conductor for different diameters of standard conductors;

[0036] [Fig. 3] Figure 3, already described, is a graphical representation illustrating the passage of current as a function of frequency for a heating of 60°C respectively inside a standard electrical conductor and inside a Litz wire electrical conductor;

[0037] [Fig. 4] Figure 4, already described, shows a side perspective view of a power cable with coaxial structure insulation according to the state of the art;

[0038] [Fig. 5] Figure 5 is a cross-sectional view of a power cable according to the invention provided with a single semi-conducting layer;

[0039] [Fig. 6] Figure 6 is a cross-sectional view of a power cable according to the invention provided with a double semi-conducting layer.

[0040] [Fig. 7] Figure 7 is a schematic representation of an aircraft comprising two electrical equipment items electrically connected to each other by an electrical power cable according to the invention.

[0041] It should be noted that, in Figures 5 and 6, the structural and / or functional elements common to the different embodiments may have the same references. Thus, unless otherwise stated, such elements have identical structural, dimensional and material properties.

[0042] Figures 5 and 6 show a power cable 20 comprising a hybrid conductor 21 comprising a central portion 22 of Litz wire type and a crown portion 25 arranged around the central portion 22.

[0043] More specifically, the central portion 22 of the Litz wire type comprises a plurality of electrically conductive strands 23 electrically insulated from one another. For this purpose, a strand 23 is surrounded by an insulator 24 made for example of enamel, varnish or any other electrically insulating material suitable for the application. A strand 23 may be made of an electrically conductive material, such as copper or aluminum or an alloy of different electrically conductive materials, or any other conductive material suitable for the application. A strand 23 may consist of an electric wire.

[0044] The strands 23 of the central part 22 of Litz wire type are arranged in strands according to a predefined arrangement and / or a predefined twisting pitch. In the example shown, the central part 22 comprises 7 strands 34, each strand 34 comprising 7 strands 23. Thus, in the section, a central strand 34 and six strands 34 arranged around the central strand can be distinguished. More generally, the central part 22 may comprise a central strand 34 and a plurality of strands arranged around the central strand 34. The strands 23 are twisted inside a given strand 34 and the strands 34 are twisted relative to each other. The strands 23 thus have a double twist (inside a strand 34 and between the strands 34). Strands 23 may further be arranged between the strands 34. Of course, the number of strands and their arrangement may vary depending on the diameter of the strands 23, that of the power cable 20, and the frequency of the current.

[0045] The crown portion 25 comprises electrically conductive strands 26 which are not electrically insulated from one another. In other words, the strands 26 of the crown portion 25 are devoid of individual insulators so as to be in electrical contact with one another. A strand 25 may be made of an electrically conductive material, such as copper or aluminum or an alloy of different electrically conductive materials or any other conductive material suitable for the application. A thickness of the crown portion 25 is calculated so as to be less than or equal to a skin thickness 5. The skin thickness 5 is calculated as a function of a frequency of an electric current passing through the hybrid conductor 21. The table below shows different skin thicknesses 5 depending on the frequency of an electric current for conventional copper or aluminum conductors:

[0046] The strands 26 of the crown portion 25 are arranged in strands 35 according to a predefined arrangement and / or a predefined twisting pitch. In the example shown, the crown portion 25 comprises 16 strands 35 arranged circumferentially around the central portion 22. Each strand 35 comprises 7 wires. Of course, the number of strands 35 and their arrangement can vary depending on the diameter of the strands 23 and that of the power cable 20.

[0047] Advantageously, the central part 22 and the crown part 25 of the hybrid conductor 21 are sized to comply with a standardized conductor section, in particular according to the standardized AWG (for "American Wire Gauge") system.

[0048] Furthermore, a coaxial structure insulator 27 is arranged around the hybrid conductor 21.

[0049] In the embodiment of Figure 5, the coaxial structure insulator 27 comprises a semiconducting layer 28.1 and an insulating layer 29. The semiconducting layer 28.1 is arranged between the hybrid conductor 21 and the insulating layer 29. The semiconducting layer 28.1 can for example be made from a material chosen from polymers of the PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene) type, silicones, fluorosilicones, rubbers, thermosets or thermoplastics of the PEEK (polyetheretherketone) type or others, bio-sourced materials containing additives which make it possible to modify their electrical properties, such as for example carbon black or metallic nanoparticles, to improve electrical conductivity.

[0050] It should be noted that only the bare external conductors of the crown part 25 are in contact with the semi-conducting material of the layer 28.1 (extruded during the installation of the cable insulation). The semi-conducting material does not enter the spaces between the strands of the crown part 25 and the central part 22. These spaces remain made up of air.

[0051] The insulating layer 29 may for example be made of a material chosen from polymers of the PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene) type, silicones, fluorosilicones, rubbers, thermosets or thermoplastics of the PEEK (polyetheretherketone) type or others, or bio-sourced materials free from the aforementioned additives in order to retain their intrinsic dielectric properties.

[0052] Thus, when moving radially from the center of the power cable 20 outwards, one successively encounters the central part 22 of the Litz wire type, the crown part 25, the semi-conducting layer 28.1 and the insulating layer 29. It should be noted that the crown part 25 makes it possible to establish direct electrical contact with the semi-conducting layer 28.1.

[0053] In the embodiment of Figure 6, the coaxial structure insulator 27 comprises an inner semiconductor layer 28.1 and an outer semiconductor layer 28.2. The inner semiconductor layer 28.1 and the outer semiconductor layer 28.2 are separated from each other by the insulating layer 29. The outer semiconductor layer 28.2 may be made of the same material or a different material than the inner semiconductor layer 28.1.

[0054] The power cable 20 further comprises a conductive element 31 for connection to a reference potential of the external semiconductor layer 28.2 and an external protective sheath 32 arranged around the conductive element 31.

[0055] The conductive element 31 may for example be made of a conductive material of the copper or aluminum type or of an alloy of electrically conductive materials or any other conductive material suitable for the application.

[0056] The conductive element 31 may be in the form of a braid made up of cylindrical or flat strands, a covering made up of cylindrical or flat strands, a strip, or an assembly of these different technologies.

[0057] The conductive element 31 can be sized to provide a protective screen function against electromagnetic interference and / or lightning.

[0058] The outer protective sheath 32 may for example be made of a material chosen from polymers of the PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene), PTFE (polytetrafluoroethylene) type, silicones, fluorosilicones, rubbers, thermosets or thermoplastics of the PEEK (polyetheretherketone) type or others, or bio-sourced materials free from the aforementioned additives in order to retain their intrinsic dielectric properties. The outer protective sheath 32 may also be made of materials used mainly for mechanical protection in the form of a braid, such as Kevlar (trade name), Nomex (trade name), glass fibers, aramid fibers, polyamide, or any other material suitable for the application.

[0059] Thus, when moving radially from the center of the power cable 20 outwards, we successively encounter the central part 22 of the Litz wire type, the crown part 25, the internal semi-conductor layer 28.1, the insulating layer 29, the external semiconducting layer 28.2, the conductive element 31 and the external protective sheath 32.

[0060] The crown portion 25 of bare conductors provides a heat shield function when laying the semi-conductor layers 28.1, 28.2 and insulating 29. This makes it possible to protect the insulation of the Litz strands 23 (enamel, varnish, or other) and to avoid degradation of the latter due to the high laying temperature of the different layers of the coaxial structure insulation 27.

[0061] The use of the outer protective sheath 32 is however optional. According to an alternative embodiment, the power cable 20 can therefore be without an outer protective sheath 32.

[0062] Alternatively, the hybrid conductor 21 can be used with an insulator of conventional structure, i.e. without the semi-conductor layers 28.1, 28.2. In this case, the hybrid conductor 21 is surrounded only by an insulating layer, such as the insulating layer 29.

[0063] Figure 7 shows an aircraft 40 comprising at least two electrical equipments 41.1, 41.2 and at least one electrical power cable 20 providing an electrical connection between the two electrical equipments 41.1, 41.2. The electrical equipments 41.1, 41.2 can be chosen in particular from a generator, an electronic power module such as an inverter or a rectifier, or an electric motor. The electrical power cable 20 is advantageously configured to operate under a voltage of between 230V and 3000V, a current of between 100A and 1000A, and a frequency of between 400Hz and 3000Hz.

[0064] Of course, the various features, variants and / or embodiments of the present invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

[0065] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms and other variants that may be envisaged by those skilled in the art within the framework of the present invention and in particular all combinations of the different operating modes described above, which may be taken separately or in association.

Claims

CLAIMS 1. Electric power cable (20) characterized in that it comprises: - a hybrid conductor (21) comprising: a central part (22) of Litz wire type comprising a plurality of electrically conductive strands (23) electrically insulated from one another, the strands (23) of the central part (22) are arranged in strands, the central part (22) comprising a central strand (34) and a plurality of peripheral strands (34) arranged around the central strand (34), - a crown part (25) comprising electrically conductive strands (26) not electrically insulated from each other, a thickness of the crown part (25) being less than or equal to a skin thickness (5) for a given frequency, and - an insulator (27) arranged around the hybrid conductor (21).

2. Electric power cable according to claim 1, characterized in that the insulator is an insulator with a coaxial structure (27) comprising at least one semi-conducting layer (28.1) and one insulating layer (29).

3. Electric power cable according to claim 2, characterized in that the semi-conductor layer (28.1) being an internal semi-conductor layer, the coaxial structure insulator (27) further comprises an external semi-conductor layer (28.2), the internal semi-conductor layer (28.1) and the external semi-conductor layer (28.2) being separated from each other by the insulating layer (29).

4. Electric power cable according to claim 3, characterized in that it comprises a conductive element (31) for connection to a reference potential of the external semiconductor layer (28.2).

5. Electric power cable according to claim 4, characterized in that it further comprises an external protective sheath (32) arranged around the conductive element (31).

6. Electric power cable according to any one of claims 1 to 6. 5, characterized in that the central part (22) and the crown part (25) of the hybrid conductor (21) are sized to comply with a standardized conductor section.

7. Electric power cable according to any one of claims 1 to 5. 6, characterized in that the skin thickness (5) is calculated as a function of a frequency of an electric current passing through the hybrid conductor (21).

8. Electric power cable according to any one of claims 1 to 5. 7, characterized in that the strands (23) of the central part (22) of Litz wire type are arranged in strands according to a predefined arrangement and / or a predefined twisting pitch.

9. Electric power cable according to any one of claims 1 to 5. 8, characterized in that the electrically conductive strands (23) of the central part and the electrically conductive strands (26) of the crown part (25) are made of copper or aluminum or an alloy of different electrically conductive materials or any other conductive material suitable for the application.

10. Aircraft (40) characterized in that it comprises at least two electrical equipments (41.1, 41.2) and at least one electrical power cable (20) defined according to any one of the preceding claims ensuring an electrical connection between the two electrical equipments.

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