HIGH FREQUENCY AND HIGH VOLTAGE POWER CABLE

Abstract

The invention relates to a power cable (20) comprising: - a hybrid conductor (21) comprising: a central portion (22) of the Litz wire type having a plurality of electrically conductive strands (23) electrically insulated from each other, a crown portion (25) having electrically conductive strands (26) not electrically insulated from each other, the thickness of the crown portion (25) being calculated to be less than or equal to a skin thickness (δ), and - an insulator (27) disposed around the hybrid conductor (21). Figure for abbreviation: Figure 5

Description

Title of the invention: HIGH FREQUENCY AND HIGH VOLTAGE ELECTRIC POWER 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 restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those currently in circulation, requiring the implementation of technological solutions to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve 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 that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers new generations of aircraft engines, the lightening 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 essential complements 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 takeoff of the aircraft and to maintain it in flight condition. All types of aircraft can be concerned, namely takeoff and landing aircraft vertical (VTOL for "Vertical TakeOff-Landing" according to Anglo-Saxon terminology), short takeoff and landing (STOL for "Short TakeOff-Landing" according to Anglo-Saxon terminology) or conventional takeoff and landing (CTOL for "Conventional TakeOff-Landing" according to Anglo-Saxon terminology) aircraft, commercial or military aircraft, helicopters or drones.

[0007] High electrical power is obtained by combining high voltages at high frequencies and 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. Extreme voltage values ​​can reach 3000V, while extreme current and frequency values ​​can reach 1000A and 3000Hz, respectively.

[0008] The electrical wiring interconnection system known as "EWIS" (for "Electrical Wiring Interconnection System" according to 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 mass limitation as well as the reduction of the space available for routing the cables and the densification of the environment complicate the integration of the wiring in the aircraft.

[0009] Certain known technologies make it possible to reduce the mass and bulk of cables.

[0010] [Fig.l] 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 a high-frequency alternating current or PWM passes through it.

[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 heating of the cable. The skin thickness ô is equal to ô=l / (ir.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 [Fig.2], the dark crown 6 materializes the crown over which passes the bulk of the current, the central zone 7 is the part with low current flow.

[0014] The thickness ô of this crown 6 depends on the frequency, it is constant whatever 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 [Fig. 3] shows that for a copper conductor, with the same cross-section, the same heating, and a frequency of 1500 Hz, the Litz wire type conductor (see curve C1) can carry 50% more current 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] At the same thickness as conventional insulation, this assembly improves resistance to partial discharges and space charges, and increases dielectric strength and insulation lifespan. Such an assembly also allows for weight and size reduction.

[0018] In order to eliminate air gaps and smooth the electric field, a coaxial cable requires an inner 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 conductor. Indeed, due to its design, a Litz wire conductor consists of electrically insulated strands, so that there is no electrical contact between a strand and its surroundings. A person skilled in the art would therefore be discouraged 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 semi-conductor material, directly in contact with the insulating layer 13 and electrically connected to a reference potential. In this case, the semi-conductor 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 one another, - a crown part comprising electrically conductive strands not electrically insulated from one another, 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 coaxially insulated cables 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 where it is beneficial. The invention allows for a reduction in mass, size, and cost by limiting the use of insulated strands only to the effective central zone of the cable. The exposed conductor portion also provides a thermal shielding 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 semi-conductor layer being an internal semi-conductor layer, the insulator with coaxial structure further comprises an external semi-conductor layer, the internal semi-conductor layer and the external semi-conductor 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 electrical 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 the frequency of an electric current passing through the hybrid conductor.

[0029] According to one embodiment of the invention, the strands of the central part of the Litz wire type 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 power cable is configured to operate under 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 features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures, presented by way of non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which:

[0034] [Fig-1] Fig. 1, already described, shows a power electrical cable comprising an electrical conductor of the Litz wire type according to the prior art;

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

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

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

[0038] [Fig.5] [Fig.5] is a cross-sectional view of a power cable according to the invention provided with a simple semiconductor layer;

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

[0040] [Fig.7] [Fig.7] is a schematic representation of an aircraft comprising two electrical equipment electrically connected to each other by an electric 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 reference numerals. 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 including a central part 22 of the Litz wire type and a crown part 25 arranged around the central part 22.

[0043] More specifically, the central part 22 of the Litz wire type comprises a plurality of electrically conductive strands 23 electrically insulated from each other. 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.

[0044] The strands 23 of the central part 22 of the 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. Strands 23 may also 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 that are not electrically insulated from one another. In other words, the strands 26 of the crown portion 25 lack individual insulation so as to be in electrical contact with each other. 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. The thickness of the crown portion 25 is calculated to be less than or equal to a skin thickness θ. The skin thickness θ is calculated as a function of the frequency of an electric current flowing through the hybrid conductor 21. The table below shows different skin thicknesses ô depending on the frequency of an electric current for conventional copper or aluminum conductors: Frequent Skin Thickness S punished classic driver 1ÛG3 1503 IlilBlll sotxs iiiiiiiiiiii : :

[0046] The strands 26 of the crown portion 25 are arranged in strands 35 according to a predefined arrangement and / or a predefined twist 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 20 power cable.

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

[0049] In the embodiment of [Fig. 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 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, bio-sourced materials comprising additives which make it possible to modify their electrical properties, such as for example carbon black or metal nanoparticles, to improve the electrical conductivity.

[0050] The insulating layer 29 can for example be made of a material chosen from among polymers of the type PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene), silicones, fluorosilicones, rubbers, thermosetting or thermoplastics of type PEEK (polyetheretherketone) or others, or bio-based materials free from the aforementioned additives in order to retain their intrinsic dielectric properties.

[0051] 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.

[0052] In the embodiment of [Fig.6], the coaxial structure insulator 27 comprises an inner semiconducting layer 28.1 and an outer semiconducting layer 28.2. The inner semiconducting layer 28.1 and the outer semiconducting layer 28.2 are separated from each other by the insulating layer 29. The outer semiconducting layer 28.2 may be made of the same material or a different material from that of the inner semiconducting layer 28.1.

[0053] 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.

[0054] 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.

[0055] The conductive element 31 can 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.

[0056] The conductive element 31 can be dimensioned to provide a protective screen function against electromagnetic interference and / or lightning.

[0057] 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.

[0058] Thus, when moving radially from the center of the power cable 20 outward, one successively encounters 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 semi-conductor layer 28.2, the conductive element 31 and the external protective sheath 32.

[0059] The crown portion 25 of bare conductors provides a thermal shielding function during the placement of the semiconducting layers 28.1, 28.2 and insulating layer 29. This protects the insulation of the Litz strands 23 (enamel, varnish, or other) and prevents degradation of the latter due to the high placement temperature of the different layers of the coaxial structure insulator 27.

[0060] 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.

[0061] Alternatively, the hybrid conductor 21 can be used with an insulator with a conventional structure, i.e. without the semiconducting 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.

[0062] [Fig.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 20 power electrical cable is advantageously configured to operate under a voltage between 230V and 3000V, a current between 100A and 1000A, and a frequency between 400Hz and 3000Hz.

[0063] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0064] 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 a person skilled in the art may consider within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

Claims

1. Electrical 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, - a crown part (25) comprising electrically conductive strands (26) not electrically insulated from one another, a thickness of the crown part (25) being calculated so as to be less than or equal to a skin thickness (ô) 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 semiconducting layer (28.1) being an internal semiconducting layer, the coaxial structure insulator (27) further comprises an external semiconducting layer (28.2), the internal semiconducting layer (28.1) and the external semiconducting 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 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 6, characterized in that the skin thickness (ô) 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 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 twist pitch.

9. Electric power cable according to any one of claims 1 to 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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