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 POWER CABLE

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

[0002] 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 various states. In particular, an ambitious standard applies to both new types of aircraft and those currently 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.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain less energy-intensive and 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 focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] The electrification and hybridization of the propulsion system of future-generation aircraft require high electrical power to generate the thrust necessary for takeoff and flight. All types of aircraft may be affected, namely aircraft with takeoff and vertical takeoff and landing (VTOL for "Vertical TakeOff-Landing" according to Anglo-Saxon terminology), short takeoff and landing (STOL for "Short TakeOff-Landing" according to Anglo-Saxon terminology) aircraft or conventional takeoff and landing (CTOL for "Conventional TakeOff-Landing" according to Anglo-Saxon terminology), 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" in Anglo-Saxon terminology), must be capable of transmitting these high currents and voltages in order to distribute them among the numerous electrical devices such as generators, power electronic modules including inverters and rectifiers, and electric motors, which are distributed throughout the aircraft. In addition to these constraints, weight limitations, reduced space for cable routing, and the increasing density of the environment complicate the integration of the wiring within the aircraft.

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

[0010] [Fig. 1] shows a cable 1 comprising an electrical conductor 2 of the Litz wire type formed by a plurality of conductor strands 3 electrically insulated from each other. To this end, each strand 3 is surrounded by an insulator 4. The entire set of strands 3 is 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 "effect" phenomena skin effect and proximity effect which increase heating when passing a high-frequency alternating current or PWM.

[0012] It is recalled that the skin effect is an electromagnetic phenomenon related to frequency that causes current to flow around the periphery of the conductor. The flow of current over a small cross-section increases the heating of the cable. The skin thickness θ is equal to θ = l / (npof)1 / 2, where p is the permeability, θ is the conductivity of the material, and f is the frequency of the current signal.

[0013] In [Fig.2], the dark ring 6 represents the ring over which passes the majority of the current, the central zone 7 is the part with low current flow.

[0014] The thickness θ of this ring 6 depends on the frequency and is constant regardless of the conductor diameter. Therefore, there is no skin effect when this thickness is less than the conductor radius, but the phenomenon is amplified as the conductor diameter 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 insulation comprising a stack of semiconductor and insulating layers are also known. As illustrated in [Fig. 4], such a cable 10 comprises a conductor 11 surrounded by an inner semiconductor layer 12, an insulating layer 13, and an outer semiconductor layer 14. It also includes a shield 15 and an outer insulating sheath 16.

[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 outer layer 14, made of a semiconductor material, in direct contact with the insulating layer 13 and electrically connected to a reference potential. In this case, the semiconductor layers 12 and 14 on either side of the insulator 13 make it possible to contain the electric field within the insulator 13, thus improving the insulation performance.

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

[0021] To this end, the invention relates to a power cable comprising: - a hybrid driver including: - a central Litz wire-type portion comprising a plurality of electrically conductive strands electrically insulated from each other, - a corona portion comprising electrically conductive strands not electrically insulated from each other, the thickness of the corona portion 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 a coaxial structure insulator comprising at least one semiconducting layer and one insulating layer.

[0024] According to one embodiment of the invention, the semiconductor layer being an internal semiconductor layer, the coaxial structure insulator 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 power electrical cable includes a conductive element for connection to a reference potential of the external semiconducting layer.

[0026] According to one embodiment of the invention, said power electrical cable further comprises an outer 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 dimensioned 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 twists 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 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 equipment and at least one power electrical cable as previously defined ensuring an electrical connection between the two electrical equipment.

[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 current flow around the periphery of the conductor for different diameters of standard conductors;

[0036] [Fig.3] The [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 equipped with a simple semiconductor layer;

[0039] [Fig.6] Fig.6 is a cross-sectional view of a power cable according to the invention equipped 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 a 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 Litz wire-type portion 22 comprises a plurality of electrically conductive strands 23 that are electrically insulated from one another. To this end, 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 portion 22 of the Litz wire type are arranged in twists according to a predefined arrangement and / or a predefined twist pitch. In the example shown, the central portion 22 comprises 7 twists 34, each twist 34 having 7 strands 23. Thus, a central twist 34 and six twists 34 arranged around the central twist are distinguished in the cross-section. Additional twists 23 may be arranged between the twists 34. Of course, the number of twists and their arrangement can vary depending on the diameter of the strands 23, that of the power cable 20, and the current frequency.

[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 indicates different skin thicknesses θ depending on the frequency of an electric current for conventional copper or aluminum conductors: F = 3? — O Skin thickness § {snm} for a cisic conductor IlOOëlilï iïw 2.07 150$ ll / llllli 2305 11 / 40111 3 <W

[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 of the power cable 20.

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

[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 disposed between the hybrid conductor 21 and the insulating layer 29. The semiconducting layer 28.1 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 the type PEEK (polyetheretherketone) or others, bio-based materials comprising additives which allow to modify their electrical properties, such as for example carbon black or metallic nanoparticles, to improve 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 semiconducting layer 28.1 and the insulating layer 29. It should be noted that the crown part 25 allows a direct electrical contact to be established with the semiconducting layer 28.1.

[0052] In the embodiment of [Fig. 6], the coaxial 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 semiconductor layer external 28.2 may be in the same material or in a different material than that of the internal semiconductor layer 28.1.

[0053] The power cable 20 further comprises a conductive element 31 for connection to a reference potential of the external semiconducting layer 28.2 and an external protective sheath 32 disposed around the conductive element 31.

[0054] The conductive element 31 can for example be made of a conductive material such as copper or aluminium 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 sized to provide a shielding function against electromagnetic interference and / or lightning.

[0057] The outer protective sheath 32 can, for example, be made of a material selected from polymers such as PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene), PTFE (polytetrafluoroethylene), silicones, fluorosilicones, rubbers, thermosetting or thermoplastic materials such as PEEK (polyetheretherketone) or others, or bio-based materials free from the aforementioned additives in order to retain their intrinsic dielectric properties. The outer protective sheath 32 can also be made of materials used primarily for mechanical protection in the form of braiding, 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 outwards, one successively encounters the central part 22 of the Litz wire type, the crown part 25, the internal semiconducting layer 28.1, the insulating layer 29, the external semiconducting layer 28.2, the conductive element 31 and the external protective sheath 32.

[0059] The ring 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 may therefore be without an outer protective sheath 32.

[0061] Alternatively, the hybrid conductor 21 can be used with an insulator having a conventional structure, i.e., lacking the semiconducting layers 28.1, 28.2. In this In this case, the hybrid conductor 21 is surrounded only by an insulating layer, such as the insulating layer 29.

[0062] Figure 7 shows an aircraft 40 comprising at least two electrical devices 41.1, 41.2 and at least one power cable 20 providing an electrical connection between the two electrical devices 41.1, 41.2. The electrical devices 41.1, 41.2 can be selected, in particular, from a generator, a power electronic module such as an inverter or rectifier, or an electric motor. The power cable 20 is advantageously configured to operate at 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

Demands

1. Power electrical cable (20) characterized in that it comprises: - a hybrid conductor (21) comprising: a central part (22) of the Litz wire type having a plurality of electrically conductive strands (23) electrically insulated from each other, the strands (23) of the central part (22) are arranged in strands, the central part (22) having a central strand (34) and a plurality of peripheral strands (34) arranged around the central strand (34), - a crown part (25) having 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 (θ) for a given frequency, and - an insulator (27) arranged around the hybrid conductor (21).

2. Power electrical cable according to claim 1, characterized in that the insulator is a coaxial structure insulator (27) comprising at least one semiconducting layer (28.1) and one insulating layer (29).

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

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

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

6. Power electrical 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 dimensioned to comply with a standardized conductor cross-section.

7. Power electrical cable according to any one of claims 1 to 6, characterized in that the skin thickness (θ) is calculated based on the frequency of an electric current passing through the hybrid conductor (21).

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

9. Power electrical 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 of 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 equipment (41.1, 41.2) and at least one power electrical cable (20) defined according to any one of the preceding claims ensuring an electrical connection between the two electrical equipment.

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