Power harness for aircraft

Abstract

A power harness (10) for an aircraft, comprising a plurality of cables (11), where each cable (11) comprises, from inside to outside radially:-an electrically conductive core (12); -a first layer (13) of semiconductor material; an insulating layer (14); and-a second layer (15) of semiconductor material; characterized in that the wire harness (10) further comprises a common shielding sleeve (16, 16 ') placed in electrical contact with the second layer (15) of semiconductor material of each cable (11).

Description

Technical Field

[0001] The present invention relates to the field of high power transmission on board aircraft, in particular in the context of electric propulsion or hybrid propulsion. More specifically, the present invention relates to an electrical wiring harness for such transmission. Background Art

[0002] High power transmission in aircraft requires the use of alternating current (AC, Alternating Current) or modulated (or PWM, Pulse Width Modulation) voltage between the aircraft's rotating machines (motors and / or generators) and other aircraft systems (such as power converters and distribution network nodes).

[0003] The transmission of these high voltages associated with typical aerospace constraints (low voltage, high temperature, high temperature gradients, etc.) requires the use of coaxial structured power cables in which an insulator is radially inserted between two layers of semiconducting material (usually an insulator filled with conductive particles).

[0004] In all that follows, the terms longitudinal, transverse and radial are to be understood relative to the main direction of extension of the cable or cable harness.

[0005] Figure 1 is a cross-sectional view of such a power cable 1, which radially comprises, from the center to the outside, a conductive core 2, a first inner layer 3 of a semiconductor material, a first layer of an insulating material 4, a second outer layer 5 of a semiconductor material and a shielding layer 6, and a sheath 7 for mechanical protection and / or air tightness.

[0006] Transmitting power in a three-phase AC or PWM system requires at least three such cables 1 assembled into strands that are gathered at Figure 2 In the wiring harness 10 shown in FIG.

[0007] The wiring harness 10 further includes a connection system at each end of the wiring harness, which is composed of elements that provide electrical contact, electrical insulation, shielding continuity, and occupy a mechanical and / or airtight protective sheath and, in the case of a wiring harness for PWM voltage, provide electromagnetic wave protection for the sheath type or outer braiding layer and mechanical and / or airtight protection for the sheath or outer braiding.

[0008] However, testing of these cables assembled in harnesses has shown that during operation at high frequencies (e.g., 1500 Hz), a large amount of unwanted current circulation occurs in the shield from electromagnetic coupling. In fact, the current induced in the shield is proportional to the frequency, which makes this parameter more critical for high frequency applications than for typical 50 Hz currents.

[0009] The problem is that this current circulation in the shield causes Joule effect losses in addition to the losses caused by the current circulating in the core of the cable (which is the only useful current). This parasitic current also passes through the connectors, electrical interfaces and equipment housings connected to the shield, causing additional Joule losses in these areas as well. These areas have not been designed for continuous circulation of current and may be damaged over the long term. Summary of the invention

[0010] The present invention aims to remedy these drawbacks. To this end, the object of the present invention is a power harness for an aircraft, said power harness comprising a plurality of cables, wherein each cable comprises radially from the inside to the outside:

[0011] - conductive core;

[0012] - a first layer of semiconductor material;

[0013] - an insulating layer; and

[0014] - a second layer of semiconductor material;

[0015] Characterized in that the wiring harness further comprises a common shielding sleeve placed in electrical contact with the second layer of semiconductor material of each cable.

[0016] Such a harness is used to significantly reduce the induced currents circulating in the common shield by adding the anti-phase currents induced by each cable to the common shield, resulting in very small or even zero currents.

[0017] The wiring harness may further include a protective sleeve arranged radially and tightly around the common shielding sleeve.

[0018] This property allows to well maintain the electrical contact between the common shielding sleeve and the second layer of the cable and also protects the harness from extreme conditions.

[0019] The common shielding sleeve may be arranged to make electrical contact with the second layer of each cable over a substantially equal contact surface of each cable.

[0020] This characteristic serves to further reduce the magnitude of the resultant current induced by each cable.

[0021] Substantially equal is understood to mean that differences of less than or equal to 10% of the value of the contact surface area are tolerated.

[0022] The common shield may include a single shield layer placed radially around the cables of the harness.

[0023] This feature allows to simply and robustly have a shielding jacket shared by the cables without significantly increasing the mass of the harness.

[0024] Each cable may include a separate shielding layer, wherein the separate shielding layers are in electrical contact with each other.

[0025] This property serves to ensure that, for each cable, the outer semiconductive layer is in contact with the ground reference carried by the individual shielding sleeves over their entire outer surface.

[0026] The common electrical contact may be maintained by a protective sheath fastened around the cable.

[0027] Common electrical contact may also be maintained by a common shielding layer that is in electrical contact with each individual shielding layer.

[0028] The cables may be arranged substantially parallel to each other, aligned along a direction perpendicular to their main direction of extension, with a common shielding sheath woven crosswise around each cable.

[0029] Taking advantage of this property, a flat harness for placement in narrow passages is possible.

[0030] The resistance of the shielding sleeve between the two ends of the harness may be comprised between 0.1 mΩ and 100 mΩ, and preferably between 1 mΩ and 20 mΩ, and even more preferably between 3 mΩ and 10 mΩ.

[0031] This feature is used to provide equipotentiality in the direction of extension of the wire harness.

[0032] The resistance of the shield is measured, for example, by an ohmmeter connected near the ends of the harness. Recall that a milliohm is equal to 10 -3 Ω.

[0033] The outer layer may be made of a semiconductor material having a resistivity comprised between 10 Ω·m and 100 Ω·m.

[0034] This feature is used to avoid radial potential differences in the cable.

[0035] Near at least one end of the harness, each cable may include a separate shielding layer on an end section.

[0036] The end portion may have a short length, for example less than 500 mm.

[0037] This property serves to limit the formation of resulting induced currents of the individual shielding jackets of the cables in the end section, thereby minimizing the resulting effects. This makes single-channel connections for cables of large diameter possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a cross-sectional view of the power cable of a state-of-the-art aircraft;

[0039] Figure 2 It includes three Figure 1A transverse cross-sectional view of a power harness of a cable similar to a cable;

[0040] Figure 3 is a transverse cross-sectional view of a power harness according to the present invention;

[0041] Figure 4 It allows single channel type connection Figure 3 A top view of one end of a wiring harness;

[0042] Figure 5 is a transverse sectional view of a flat wire harness according to a second embodiment of the present invention;

[0043] Figure 6 is a transverse sectional view of a wire harness according to a third embodiment of the present invention; and

[0044] Figure 7 is a transverse sectional view of a wire harness according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0045] Figure 3 1 shows a power harness 10 for an aircraft according to the present invention. The harness 10 comprises three cables 11 having a coaxial structure which radially from inside to outside comprises a conductive core 12, an inner layer 13 of a semiconductor material, an insulating layer 14 and an outer layer 15 of a semiconductor material.

[0046] Unlike the previously described prior art, the cable 11 therefore does not comprise a separate shielding layer and a protective sheath.

[0047] The three cables 11 are assembled into twisted strands, thereby making it easier to maintain the overall structure of the wiring harness 10 .

[0048] Alternatively, the cables may be untwisted and extend substantially parallel to each other.

[0049] A single common shielding layer 16 is placed around the three cables 11 , in direct electrical contact with the outer layers 15 of the three cables 11 .

[0050] This common shielding layer 16 serves to ensure that each of the outer layers 15 of the semiconductor is firmly grounded.

[0051] The shielding layer 16 is sized to ensure this fixed grounding and, if necessary, provide protection against electromagnetic waves depending on the number of cables, the size of their braiding angles, the shielding type and the type of semiconductor material of the outer layer 15 .

[0052] This arrangement with a common shield allows the induced currents produced by each cable of the harness to be summed and provide a zero value resulting current for a balanced three-phase AC system.

[0053] In the case of a balanced three-phase PWM system, the high frequency currents generated are associated with the switching of the power switches and are inherent to the PWM system. Such resulting induced currents have small amplitudes and therefore have a greatly reduced impact compared to the prior art.

[0054] exist Figure 3 It can be seen that the outer semiconductor layer 15 is not in contact with the shielding layer 16 over its entire circumference.

[0055] In order to reduce possible radial potential differences in the wiring harness 10 , it is therefore advantageous to choose a semiconductor material for the layer 15 that has a low resistivity.

[0056] For example, the semiconductor material constituting the outer layer 15 has a resistivity comprised between 10 Ω·m and 100 Ω·m.

[0057] In order to ensure equipotentiality in the extension direction of the wiring harness 10, it is advantageous to choose a material thickness for the shielding layer 16 such that the resistance of the shielding layer 16 is comprised between 0.1 mΩ and 100 mΩ, preferably between 1 mΩ and 20 mΩ, and more preferably between 3 mΩ and 10 mΩ (recall that one milliohm mΩ is equal to 10 -3 ohm).

[0058] Advantageously, a common mechanical protection sheath 17 radially surrounds the shielding layer 16 .

[0059] The type of protection provided by the sheath 17 depends on the conditions of use of the wiring harness 10 (mechanical protection, air tightness, temperature resistance, etc.).

[0060] The sheath 17 may be, for example, a stainless steel or stainless steel microfilament sheath, a sheath braided from textile or polymer material, a heat shrink sheath, an extruded sheath, a wrapped tape sheath, an overmolded sheath, or a combination of the above.

[0061] The arrangement of the cables 11 in strands allows a multi-channel type connection on the device 20 if the cables 11 have a small cross section.

[0062] For cables 11 having a cross-section larger than AWG 1, it may be preferred to use a single channel connector.

[0063] Figure 4 Such a connection point for connecting the wiring harness 10 to a device 20 having a Y-type terminal is shown in FIG.

[0064] The present invention can also be similarly applied to terminal type connectors.

[0065] In the case shown, each cable 11 comprises a separate shielding jacket 16 ′ over an end section 21 of short length, close to an end 22 of the harness 10 .

[0066] Since the corresponding end section has a short length, for example less than 50 cm, the losses generated by the separate shielding sleeve in the Y-type termination will be limited.

[0067] Optionally, the losses in the separate shielding sleeve may be further reduced by increasing the radial thickness of said separate shielding sleeve only at the end sections, in order to reduce its electrical resistance and thus reduce Joule effect losses.

[0068] Electrical and thermal drains connected to the device structure 20 may also be added to avoid current flow through the connector.

[0069] exist Figure 5 An embodiment of a wire harness 10 according to the present invention is shown in FIG. 8 , which is the same as the previously described wire harness except for the following.

[0070] In the case of a tight channel, the harness 10 can be made flat over all or part of its length. Then, the cables 11 are aligned and arranged along the transverse direction of the harness 10 .

[0071] A single common shield 16 is then woven crosswise around each cable 11 to have a substantially equal contact surface with each cable 11 in the harness 10. This serves to maintain symmetry of contact between the shield 16 and each cable 11, thereby minimizing the magnitude of the resulting induced current.

[0072] This shielding layer 16 is made, for example, of woven and / or braided wire.

[0073] Figure 6 A third embodiment of a wiring harness according to the present invention is shown. This embodiment is identical to the first embodiment except for the following. Each cable 11 of the wiring harness 10 comprises an individual shielding layer 16' joining a common shielding layer 16. The common shielding layer 16 is further placed in electrical contact with the individual shielding layers 16' in order to ensure electrical continuity, thus minimizing induced currents as described above.

[0074] The wiring harness 10 according to this third embodiment is more sensitive to vibrations (friction between shielding sleeves) and heavier, but allows electrical contact between the individual shielding layers 16 ′ and the entire periphery of each cable 11 of the wiring harness 10 .

[0075] The individual shielding 16 ′ of the cable can be realized by braiding, which allows limiting wear problems caused by friction and forms a light shield.

[0076] This third embodiment can be extended to make a flat harness, wherein each cable 11 comprises an individual shield 16 ′, and the harness comprises a common shield surrounding all cables 11 .

[0077] Figure 7A fourth embodiment of a wiring harness 10 according to the invention is shown. In this embodiment, each cable 11 comprises an individual shielding layer 16', wherein the individual shielding layers 16' are arranged in permanent electrical contact with each other so as to form a single shield from an electrical point of view.

[0078] Permanent electrical contact between the individual shielding layers 16 ′ is ensured by the fastening applied by a protective sheath 17 , for example a braided textile or polymer type sheath, a heat shrink sheath, an extruded sheath, a wound tape sheath or an overmolded sheath.

Claims

1. A power harness (10) for an aircraft, comprising a plurality of cables (11), wherein each cable (11) radially from the inside to the outside comprises: - a conductive core (12); - a first layer (13) of semiconductor material; - an insulating layer (14); and - a second layer (15) of semiconductor material; Characterized in that the wiring harness (10) further comprises a common shielding sleeve (16, 16') placed in electrical contact with the second layer (15) of the semiconducting material of each cable (11).

2. The wiring harness (10) according to the preceding claim, characterized in that The wiring harness (10) further comprises a protective sleeve (17) which is arranged radially and tightly around the common shielding sleeve (16, 16').

3. The wiring harness (10) according to the preceding claim, characterized in that The common shielding sleeve (16, 16') is arranged to be in electrical contact with the second layer (15) of each cable (11) over a contact surface that is substantially equal for each of the cables (11).

4. The wiring harness (10) according to the preceding claim, characterized in that The common shielding sleeve (16, 16') comprises a single shielding layer (16) radially placed around the cables (11) of the wiring harness (10).

5. The wiring harness (10) according to any one of the preceding claims, characterized in that Each cable (11) comprises individual shielding layers (16'), wherein the individual shielding layers (16') are in electrical contact with each other.

6. The wiring harness (10) according to any one of the preceding claims, characterized in that The cables (11) are arranged substantially parallel to each other, aligned in a direction perpendicular to their main extension direction, wherein the common shielding sheath (16, 16') is woven crosswise around each of the cables (11).

7. The wiring harness (10) according to any one of the preceding claims, characterized in that The resistance of the common shielding sleeve (16, 16') between the two ends of the wiring harness (10) is comprised between 0.1 mΩ and 100 mΩ, and preferably between 1 mΩ and 20 mΩ, and even more preferably between 3 mΩ and 10 mΩ.

8. The wiring harness (10) according to any one of the preceding claims, characterized in that The second layer (15) is made of a semiconductor material having a resistivity comprised between 10 Ω·m and 100 Ω·m.

9. The wiring harness (10) according to any one of the preceding claims, characterized in that Near at least one end (22) of the harness (10), each cable (11) comprises a separate shielding layer (16') on an end section (21).

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