High-frequency high-voltage power cable

Abstract

The invention relates to a power cable (20) comprising:-a hybrid conductor (21) comprising:-a central litz wire portion (22) comprising a plurality of electrically conductive strands (23) electrically insulated from each other; -an annular portion (25) comprising a plurality of electrically conductive strands (26) that are not electrically insulated from one another, the calculated thickness of the annular portion (25) being less than or equal to the skin thickness (delta); and-an insulator (27) arranged around the hybrid conductor (21).

Description

Technical Field

[0001] This invention relates to a high-frequency, high-voltage power cable. This invention has particularly advantageous, but not exclusive, applications in the aviation field for transmitting high-current, high-frequency, and high-voltage electrical signals between various electrical devices within an aircraft. Background Technology

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. In fact, countries have enacted, are enacting, or will enact various carbon emission limits. Specifically, a stringent standard applies to new aircraft types and those currently in operation, requiring the implementation of technological solutions to comply with current regulations. Civil aviation has been actively working to contribute to addressing climate change for many years.

[0003] Technical research has led to significant improvements in the environmental performance of aircraft. The applicant has considered factors influencing all stages of design and development to obtain energy-efficient and environmentally friendly aerospace components and products that, when integrated and used in civil aviation, have a moderate environmental impact, aiming to improve the energy efficiency of aircraft.

[0004] Therefore, the applicant is committed to reducing its climate impact by utilizing methods and operating benign development and manufacturing processes that minimize greenhouse gas emissions to reduce the environmental footprint of its activities.

[0005] This ongoing research and development work also involves next-generation aircraft engines, aircraft weight reduction, particularly due to the use of materials and lighter airborne equipment, the development of electric technology to provide propulsion and necessary supplements to technological progress, and aviation biofuels.

[0006] The electrification and hybridization of propulsion systems for future generations of aircraft will require high electrical power to generate the thrust needed for takeoff and flight. All types of aircraft are likely to be affected, namely vertical takeoff and landing (VTOL) aircraft or conventional takeoff and landing (CTOL) aircraft, including commercial or military aircraft, helicopters, and drones.

[0007] High electrical power is achieved by combining high voltage and high current at high frequencies. For example, electrical devices can withstand AC or pulse-width modulation (PWM) voltages of up to 1000V and currents of 300A at an electrical frequency 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,” must be able to carry these high currents and voltages to distribute them across numerous electrical components throughout the aircraft, such as generators, power electronics modules (including inverters and rectifiers), and motors. In addition to these limitations, there are weight constraints and reduced available space for cabling, and the increasing density of the environment complicates cable integration into the aircraft.

[0009] Some known technologies make it possible to reduce cable weight and bulk size.

[0010] Figure 1 A cable 1 is shown, comprising an electrical Litz-wire-like conductor 2 formed by multiple electrically insulated conductor strands 3. Each strand 3 is surrounded by an insulator 4. All strands 3 are surrounded by one or more insulating sheaths 5 of the cable.

[0011] This type of cable allows for the reduction or even elimination of the so-called "skin effect" and "proximity effect," which increase heat generation during high-frequency alternating current or PWM transmission.

[0012] It's important to remember that the skin effect is a frequency-dependent electromagnetic phenomenon that causes current to flow around the periphery of a conductor. Current flowing through a small cross-section increases cable heating. The skin thickness δ is equal to δ = 1 / (πµσf). 1 / 2 , where µ is the magnetic permeability, σ is the material conductivity, and f is the frequency of the current signal.

[0013] exist Figure 2 In the diagram, the dark ring 6 represents the ring through which most of the current flows, while the central region 7 is the part where the current flow is lower.

[0014] The thickness δ of ring 6 depends on the frequency; it is constant and independent of the conductor diameter. Therefore, there is no skin effect when the thickness is less than the conductor radius, but the phenomenon is amplified as the conductor diameter increases.

[0015] Litz-like cables allow for higher current flow with the same conductor size as conventional conductors. Figure 3 The graph shows that, for copper conductors, at the same cross-section, the same heat generation, and a frequency of 1500 Hz, a Litz-like conductor (see curve C1) allows 50% more current to be carried than a conventional conductor (see curve C2).

[0016] We are also familiar with cables with coaxial insulation that includes stacked semiconductors and insulating layers. For example... Figure 4 As shown, this cable 10 includes a conductor 11 surrounded by an inner semiconductor layer 12, an insulation layer 13, and an outer semiconductor layer 14. It also includes a sheath 15 and an outer insulating sheath 16.

[0017] With a thickness equal to that of conventional insulation, this component improves performance under partial discharge and space charge conditions and increases dielectric strength and insulation lifetime. This component also allows for weight reduction and size reduction.

[0018] To eliminate air gaps and smooth the electric field, coaxial cables require an inner layer (semiconductor layer 12) made of a semiconductor material with the same potential as conductor 11. Therefore, the electrical contact between the two components must have a low resistance value, which is impossible with the electrically insulated strands of a Litz-like conductor. In fact, due to its design, a Litz-like conductor consists of electrically insulated strands, resulting in no electrical contact between the strands and their surroundings. Therefore, those skilled in the art would be deterred from combining these two incompatible technologies in the same cable.

[0019] An outer layer 14 made of semiconductor material can also be added to the above-mentioned components. This outer layer is in direct contact with the insulating layer 13 and electrically connected to the reference potential. In this case, the semiconductor layers 12 and 14 on either side of the insulator 13 can confine the electric field within the insulator 13, thereby improving the insulation performance. Summary of the Invention

[0020] The purpose of this invention is to provide a power cable that combines the advantages of a Litz wire conductor and a cable with coaxial insulation.

[0021] Therefore, the present invention relates to a power cable comprising: - Hybrid conductors, which include: -The central section is a type of Lids wire, which consists of multiple electrically insulated conductive strands. - A ring-shaped portion comprising conductive strands that are not electrically insulated from each other, wherein the calculated thickness of the ring-shaped portion is less than or equal to the skin thickness at a given frequency, and - An insulator placed around a hybrid conductor.

[0022] Therefore, this invention allows for the combination of the advantages of cables with coaxial insulation structures for electrical insulation and the advantages of Litz-like conductors for current flow. Furthermore, this invention optimizes the utilization of the Litz-like conductor technology by confining it to its advantageous central region. This invention reduces mass, size, and cost by limiting the use of insulated strands to the effective central region of the cable. When the insulation is installed around the hybrid conductor, the exposed conductor portion also serves as thermal shielding.

[0023] According to one embodiment of the present invention, the insulator is an insulator having a coaxial structure comprising at least one semiconductor layer and an insulating layer.

[0024] According to one embodiment of the present invention, the semiconductor layer is an inner semiconductor layer, and the insulator having a coaxial structure further includes an outer semiconductor layer, the inner semiconductor layer and the outer semiconductor layer being separated from each other by the insulating layer.

[0025] According to one embodiment of the present invention, the power cable includes a conductive element for connection to a reference potential of an outer semiconductor layer.

[0026] According to one embodiment of the present invention, the power cable further includes an outer protective sheath surrounding the conductive element.

[0027] According to one embodiment of the invention, the dimensions of the central portion and the annular portion of the hybrid conductor are designed to conform to a standardized conductor cross-section.

[0028] According to one embodiment of the invention, the skin thickness is calculated based on the frequency of the current passing through the hybrid conductor.

[0029] According to one embodiment of the invention, the strands of the central Litz wire portion are bundled according to a predetermined arrangement and / or a predetermined twist pitch.

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

[0031] The present invention also relates to an aircraft comprising at least two electrical devices and at least one power cable as defined above to ensure an electrical connection between the two electrical devices.

[0032] According to one embodiment of the invention, the 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. Attached Figure Description

[0033] The invention will be better understood by reading the following detailed description, which includes embodiments given for illustrative purposes with reference to the accompanying drawings, which are presented by way of non-limiting example and can be used to complete the understanding of the description of the invention and its implementations and ultimately contribute to its definition, wherein:

[0034] Figure 1 : already described Figure 1 A power cable including an electrical type Litz wire conductor according to the prior art is shown;

[0035] Figure 2 : already described Figure 2The skin effect of current passing through the periphery of a standard conductor of different diameters at a given current signal frequency is shown.

[0036] Figure 3 : already described Figure 3 It is a graph showing the change of current with frequency for heating at 60°C in a standard electrical conductor and an electrical Litz wire conductor, respectively.

[0037] Figure 4 : already described Figure 4 A side perspective view of a power cable with a coaxial insulator according to the prior art is shown;

[0038] Figure 5 : Figure 5 This is a cross-sectional view of a power cable equipped with a single semiconductor layer according to the present invention;

[0039] Figure 6 : Figure 6 This is a cross-sectional view of a power cable equipped with a double semiconductor layer according to the present invention.

[0040] Figure 7 : Figure 7 This is a schematic diagram of an aircraft according to the present invention, which includes two electrical devices electrically connected to each other via a power cable.

[0041] It should be noted that in the appendix Figure 5 and attached Figure 6 In the drawings, structural and / or functional elements common to different embodiments are given the same reference numerals. Therefore, unless otherwise stated, these elements have the same structure, dimensions, and material properties. Detailed Implementation

[0042] Figure 5 and 6 A power cable 20 is shown, comprising a hybrid conductor 21, which includes a central Lids wire portion 22 and an annular portion 25 surrounding the central portion 22.

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

[0044] The strands 23 of the central Lids wire section 22 are bundled according to a predetermined arrangement and / or a predetermined twist pitch. In the example shown, the central section 22 includes seven bundles 34, each bundle 34 comprising seven strands 23. Thus, in this section, we distinguish between the central bundle 34 and the six bundles 34 surrounding the central bundle. More generally, the central section 22 may include the central bundle 34 and multiple bundles surrounding the central bundle 34. The strands 23 are twisted within a given bundle 34, and the bundles 34 are twisted relative to each other. Thus, the strands 23 exhibit double twisting (both within the bundle 34 and between the bundles 34). The strands 23 may also be arranged between the bundles 34. Of course, the number of bundles and their arrangement can vary depending on the diameter of the strands 23, the diameter of the power cable 20, and the frequency of the current.

[0045] The annular portion 25 comprises conductive strands 26 that are not electrically insulated from each other. In other words, the strands 26 of the annular portion 25 do not have individual insulators for electrical contact with each other. The strands 25 may be made of a conductive material, such as copper or aluminum, or an alloy of different conductive materials, or any other conductive material suitable for this application. The calculated thickness of the annular portion 25 is less than or equal to the skin thickness δ. The skin thickness δ is calculated based on the frequency of the current passing through the mixed conductor 21. The table below shows different values ​​for the skin thickness δ as a function of current frequency for conventional copper or aluminum conductors:

[0046] The strands 26 of the annular portion 25 are arranged into bundles 35 according to a predetermined arrangement and / or a predetermined twist pitch. In the example shown, the annular portion 25 has 16 bundles 35 arranged circumferentially around the central portion 22. Each bundle 35 has 7 conductors. Of course, the number of bundles 35 and their arrangement can vary depending on the diameter of the strands 23 and the diameter of the power cable 20.

[0047] Advantageously, the dimensions of the central portion 22 and the annular portion 25 of the hybrid conductor 21 are designed to meet the standardized conductor cross-section, particularly according to the standardized AWG (American Wire Gauge) system.

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

[0049] exist Figure 5In the illustrated embodiment, the coaxial insulator 27 includes a semiconductor layer 28.1 and an insulating layer 29. The semiconductor layer 28.1 is located between the hybrid conductor 21 and the insulating layer 29. The semiconductor layer 28.1 may be made, for example, of a material selected from PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene copolymer), ETFE (ethylene-tetrafluoroethylene copolymer), silicone, fluorosilicone, rubber, thermosetting or thermoplastic materials such as PEEK (polyether ether ketone), or other materials, bio-based materials containing additives that allow for changes in their electrical properties, such as carbon black or metal nanoparticles, to improve conductivity.

[0050] It should be noted that only the outer exposed conductor of the annular portion 25 comes into contact with the semiconductor material of layer 28.1 (which is compressed during the installation of the cable insulation). The semiconductor material does not enter the space between the strands of the annular portion 25 and the strands of the central portion 22. These spaces remain filled with air.

[0051] The insulating layer 29 may be made of, for example, a material selected from the following: polymers such as PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene copolymer), ETFE (ethylene-tetrafluoroethylene copolymer), silicone, fluorosilicone, rubber, thermosetting or thermoplastic materials such as PEEK (polyether ether ketone) or other materials, or bio-based materials without the aforementioned additives, in order to maintain their inherent dielectric properties.

[0052] Therefore, when moving radially outward from the center of the power cable 20, it sequentially encounters the central Litz wire portion 22, the loop portion 25, the semiconductor layer 28.1, and the insulating layer 29. It should be noted that the loop portion 25 allows direct electrical contact with the semiconductor layer 28.1.

[0053] exist Figure 6 In the illustrated embodiment, the coaxial insulator 27 includes 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 an insulating layer 29. The outer semiconductor layer 28.2 may be made of the same or different material as the inner semiconductor layer 28.1.

[0054] The power cable 20 also includes a conductive element 31 for connection to a reference potential of the outer semiconductor layer 28.2, and an outer protective sheath 32 surrounding the conductive element 31.

[0055] The conductive element 31 may be made of, for example, a conductive material, such as copper or aluminum or an alloy of 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 of cylindrical or flat strands, a cover made of cylindrical or flat strands, a strip, or a component of these different technologies.

[0057] The size of the conductive element 31 can be designed to provide shielding against electromagnetic interference and / or lightning.

[0058] The outer protective sleeve 32 may be made of, for example, a material selected from polymers such as PFA (perfluoroalkoxy), FEP (fluorinated ethylene propylene copolymer), ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), silicone, fluorosilicone, rubber, thermosetting or thermoplastic materials such as PEEK (polyether ether ketone), or other materials, or bio-based materials without the aforementioned additives, to maintain their inherent dielectric properties. The outer protective sleeve 32 may also be made of a woven material primarily used for mechanical protection, such as Kevlar (trade name), Nomex (trade name), glass fiber, aramid fiber, polyamide, or any other material suitable for this application.

[0059] Therefore, when moving radially outward from the center of the power cable 20, it sequentially encounters the central Litz wire portion 22, the ring portion 25, the inner semiconductor layer 28.1, the insulating layer 29, the outer semiconductor layer 28.2, the conductive element 31, and the outer protective sleeve 32.

[0060] The annular portion 25 of the exposed conductor provides thermal shielding during the mounting of the semiconductor layers 28.1, 28.2 and the insulating layer 29. This protects the insulation (enamel, varnish or other) of the Litz wire strands 23 and prevents it from degrading due to the high placement temperatures of the different layers of the coaxial insulator 27.

[0061] However, the use of the outer protective sleeve 32 is optional. According to an alternative embodiment, the power cable 20 may therefore not have any outer protective sleeve 32.

[0062] Alternatively, the hybrid conductor 21 can be used together with a conventional insulator, that is, without semiconductor layers 28.1, 28.2. In this case, the hybrid conductor 21 is only surrounded by an insulating layer, such as insulating layer 29.

[0063] Figure 7 An aircraft 40 is shown, comprising at least two electrical devices 41.1, 41.2 and at least one power cable 20 for electrical connection between the two electrical devices 41.1, 41.2. The electrical devices 41.1, 41.2 may be particularly selected from generators, power electronic modules such as inverters or rectifiers, or electric motors. The power cable 20 is advantageously configured to operate at voltages between 230V and 3000V, currents between 100A and 1000A, and frequencies between 400Hz and 3000Hz.

[0064] Of course, different features, variations and / or embodiments of the present invention can be associated with each other in various combinations, as long as they are compatible with each other or not mutually exclusive.

[0065] Furthermore, the present invention is not limited to the embodiments described above, and is provided by way of example only. The present invention encompasses various modifications, alternatives, and other variations that may be conceived by those skilled in the art within the context of the invention, and in particular, any combination of the various operating modes described above may be employed individually or in combination.

Claims

1. A power cable (20), characterized in that, include: - Hybrid conductor (21), including: The central Litz wire portion (22) comprises multiple electrically insulated conductive strands (23), the strands (23) of the central portion (22) are arranged in a bundle, the central portion (22) includes a central bundle (34) and multiple peripheral bundles (34) surrounding the central bundle (34). - Annular portion (25), said annular portion comprising conductive strands (26) that are not electrically insulated from each other, the thickness of the annular portion (25) being less than or equal to the skin thickness (δ) at a given frequency, and - Insulator (27), the insulator surrounding the hybrid conductor (21).

2. The power cable according to claim 1, wherein, The insulator is a coaxial structure insulator (27), and the insulator includes at least one semiconductor layer (28.1) and an insulating layer (29).

3. The power cable according to claim 2, characterized in that, The semiconductor layer (28.1) is an inner semiconductor layer, and the coaxial structure insulator (27) further includes 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).

4. The power cable according to claim 3, characterized in that, The power cable includes a conductive element (31) for connection to a reference potential of the outer semiconductor layer (28.2).

5. The power cable according to claim 4, characterized in that, The power cable also includes an outer protective sheath (32) surrounding the conductive element (31).

6. The power cable according to any one of claims 1 to 5, characterized in that, The dimensions of the central portion (22) and the annular portion (25) of the hybrid conductor (21) are set to conform to the standard conductor cross-section.

7. The power cable according to any one of claims 1 to 6, characterized in that, The skin thickness (δ) is calculated based on the frequency of the current passing through the hybrid conductor (21).

8. The power cable according to any one of claims 1 to 7, characterized in that, The strands (23) of the central Lids line section (22) are bundled according to a predetermined arrangement and / or a predetermined twist pitch.

9. The power cable according to any one of claims 1 to 8, characterized in that, The conductive strands (23) of the central portion and the conductive strands (26) of the annular portion (25) are made of copper, aluminum, alloys of different conductive materials, or any other conductive material suitable for the application.

10. An aircraft (40), characterized in that, The aircraft includes at least two electrical devices (41.1, 41.2) and at least one power cable (20) as defined in any of the preceding claims for an electrical connection between the two electrical devices.

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