Electrical power harness for an aircraft

Abstract

The invention relates to an electrical power harness (10) for an aircraft, comprising a plurality of cables (11), each cable (11) comprising, radially from the inside outward: - a conductive core (12), - a first layer (13) of semi-conductive material, - an insulating layer (14), and - a second layer (15) of semi-conductive material, characterized in that the harness (10) further comprises a common shield (16, 16') disposed in electrical contact with the second layers (15) of semi-conductive material of each cable (11).

Description

[0001] DESCRIPTION

[0002] TITLE: Aircraft Power Electrical Harness

[0003] Technical field of the invention

[0004] The invention relates to the field of transmitting high electrical power on board an aircraft, particularly in the context of electric or hybrid propulsion. More specifically, the invention relates to an electrical harness for this transmission.

[0005] State of the prior art

[0006] The transmission of high electrical power in an aircraft requires the use of alternating current (AC) or modulated (or PWM) voltages between the aircraft's rotating machinery (engine and / or electrical generator) and other aircraft systems, such as power converters and distribution network nodes.

[0007] The transmission of these high voltages, combined with the constraints typical of aeronautics (low pressure, high temperatures, high temperature gradients, etc.), requires the use of power cables with a coaxial structure, in which an insulator is radially interposed between two layers of semiconducting material (generally an insulator loaded with conductive particles).

[0008] In all that follows, the terms longitudinal, transverse and radial refer to the principal direction of elongation of the cable or cable harness.

[0009] Figure 1 is a cutaway representation of such a power cable 1, comprising, radially from the center outwards, a conductive core 2, a first internal layer 3 of semiconducting material, a first layer of insulating material 4, a second external layer 5 of semiconducting material, a shielding layer 6 and a sheath 7 for mechanical and / or hermetic protection.

[0010] At least three such cables 1 assembled in strand form, joined together in a harness 10 shown in Figure 2, are required to transmit power in a three-phase AC or PWM system.

[0011] The harness 10 further comprises a connection system at each end of the harness, composed of elements ensuring electrical contact, electrical insulation, continuity of the shields and the recovery of the mechanical and / or hermetic protective sheath, as well as protection against electromagnetic waves, of the sheath or over-braiding type in the case of a harness for PWM voltages, and mechanical and / or hermetic protection of the sheath or over-braiding. However, testing of these cables assembled into a harness shows a significant flow of unwanted current in the shielding, resulting from electromagnetic coupling, during operation at high frequency (for example 1500 Hz). Indeed, the current induced in the shielding is proportional to the frequency, which makes this parameter much more critical for high-frequency applications than for a usual 50 Hz current.

[0012] The problem is that this current flow in the shielding causes Joule losses in addition to those generated by the current flowing through the cable core, which is the only useful current. This stray current also passes through the connectors, electrical interfaces, and equipment housing connected to the shielding, also causing additional Joule losses in these areas. These areas are also not designed for continuous current flow and can be damaged in the long term.

[0013] Presentation of the invention

[0014] The invention aims to overcome these drawbacks. To this end, the subject of the invention is an electrical power harness for an aircraft, comprising a plurality of cables, each cable comprising, radially from the inside to the outside:

[0015] - a conducting soul,

[0016] - a first layer of semiconductor material

[0017] - a layer of insulation, and

[0018] - a second layer of semiconductor material, characterized in that the harness further comprises a common shield arranged in electrical contact with the second layers of semiconductor material of each cable.

[0019] Such a harness makes it possible to significantly reduce the induced currents circulating in the shielding thanks to the addition of the phase-opposition currents induced by each of the cables in the common shielding, the result of which is very low or even zero.

[0020] The harness may further include a single protective sheath arranged radially around the common shielding.

[0021] Such a feature allows both good maintenance of electrical contact between the common shield and the second layers of the cables, as well as protection of the harness against external conditions.

[0022] The common shield may be arranged in electrical contact with the second layer of each cable over a substantially equal contact area for each of the cables.

[0023] Such a characteristic makes it possible to further reduce the amplitude of the resultant of the currents induced by each of the cables.

[0024] By substantially equal is meant that deviations less than or equal to 10% of the area value of said contact surface are tolerated. The common shield may comprise a single shield layer arranged radially around the harness cables.

[0025] Such a feature allows for common shielding of the cables in a simple and robust manner, without significantly increasing the mass of the harness.

[0026] Each cable may include an individual shielding layer, with the individual shielding layers being held in common electrical contact.

[0027] Such a feature ensures that for each cable, the outer semiconducting layer is in contact with the ground reference which is carried by the individual shielding over its entire outer surface.

[0028] Common electrical contact can be maintained by a tight protective sheath around the cables.

[0029] Common electrical contact may also be maintained by a common shielding layer in electrical contact with each of the individual shielding layers.

[0030] The cables may be arranged substantially parallel to each other, aligned in a direction perpendicular to their main direction of elongation, the common shield being woven in a crisscross manner around each of the cables.

[0031] Such a feature allows for a flattened harness to be placed in narrow passages.

[0032] An electrical resistance of the shielding between two ends of the harness may be between 0.1 mQ and 100 mQ, and preferably between 1 mQ and 20 mQ, and even more preferably between 3 mQ and 10 mQ.

[0033] Such a feature ensures equipotential in the direction of harness elongation.

[0034] The shielding resistance is measured, for example, using an ohmmeter connected to both ends of the harness. Remember that one milliohm is equal to 10 -3 Ohm.

[0035] The outer layers can be made of a semiconductor material having an electrical resistivity between 10 Qm and 100 Qm.

[0036] Such a feature helps to avoid the occurrence of radial potential differences in the cables.

[0037] At at least one end of the harness, each cable may include an individual shielding layer on an end section.

[0038] The end portion may have a short length, for example less than 500 mm. This feature makes it possible to restrict the formation of the induced current resulting from the individual shielding of the cables at said end portion, and thus to minimize the resulting impact. This makes a single-channel connection possible for cables with large diameters.

[0039] Brief Description of the Figures [Fig. 1] Figure 1 is a cutaway view of a state-of-the-art aircraft power cable,

[0040] [Fig. 2] Fig. 2 is a cross-sectional view of a power harness comprising three cables like that of Fig. 1,

[0041] [Fig. 3] Figure 3 is a cross-sectional view of a power harness according to the invention,

[0042] [Fig. 4] Figure 4 is a top view of one end of the harness of Figure 3 allowing a single-track type connection,

[0043] [Fig. 5] Figure 5 is a cross-sectional view of a harness laid flat according to a second embodiment of the invention

[0044] [Fig. 6] Figure 6 is a cross-sectional view of a harness according to a third embodiment of the invention, and

[0045] [Fig. 7] Figure 7 is a cross-sectional view of a harness according to a fourth embodiment of the invention.

[0046] Detailed description of the invention

[0047] A power harness 10 for an aircraft according to the invention is shown in Figure 3. The harness 10 comprises three cables 11 with a coaxial structure comprising, radially from the inside to the outside, a conductive core 12, an internal layer 13 of semi-conductor material, an insulating layer 14 and an external layer 15 of semi-conductor material. The cables 11 therefore do not comprise, unlike those of the prior art previously described, a shielding layer and an individual protective sheath.

[0048] The three cables 11 are assembled together in a twisted strand, making it easier to maintain the overall structure of the harness 10.

[0049] Alternatively, the cables may be untwisted and run substantially parallel to each other.

[0050] A single common shielding layer 16 is arranged around the three cables 11, in direct electrical contact with the outer layers 15 of the three cables 11.

[0051] This common shielding layer 16 ensures the ground connections of each of the external semiconductor layers 15.

[0052] The shielding layer 16 is sized to ensure this ground connection and, if necessary, to ensure the function of protecting electromagnetic waves, depending on the number of cables, their size, the braiding angle, the type of shielding and the type of semiconductor material of the outer layer 15. Such an arrangement with a common shielding layer makes it possible to add the induced currents generated by each of the cables in the harness and gives a resulting current of zero value for a balanced three-phase AC system.

[0053] In the case of a balanced three-phase PWM system, the resultant is the high-frequency current that is linked to the switching of the power switches and is intrinsic to the PWM system. Such a resulting induced current has a low amplitude and therefore has a greatly reduced impact compared to the state of the art.

[0054] In Figure 3, it can be seen that the outer layers 15 of semiconductors are not in contact with the shielding layer 16 over their entire circumference.

[0055] To reduce possible radial potential differences in the harness 10, it is therefore advantageous to choose a semiconductor material for the layers 15 having low electrical resistivity.

[0056] For example, the semiconductor material making up the external layers 15 has an electrical resistivity of between 10 Qm and 100 Qm.

[0057] To ensure equipotential bonding in the direction of elongation of the harness 10, it is advantageous to choose for the shielding layer 16 a thickness of material such that the electrical resistance of the shielding layer 16 is between 0.1 mQ and 100 mQ, and preferably between 1 mQ and 20 mQ, and more preferably between 3 mQ and 10 mQ (it is recalled that one milliohm mQ 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 harness 10 (mechanical protection, hermetic, temperature resistance, etc.).

[0060] The sheath 17 may, for example, be a sheath made of stainless steel or stainless steel microfilaments, a braided sheath made of textile or polymer material, a heat-shrinkable sheath, an extruded sheath, a taped sheath, an overmolded sheath and a combination of several of the aforementioned sheaths.

[0061] The arrangement of the cables 11 in strands allows, if the cables 11 are of small section, a connection to the equipment 20 of the multi-channel type.

[0062] For 11 cables with a section larger than AWG1, the use of single-channel connectors may be preferred.

[0063] Such a connection point of the harness 10 to a piece of equipment 20, of the Y termination type, is shown in FIG. 4.

[0064] The invention can also be applied to terminal type connectors in a similar manner.

[0065] In the case shown, each of the cables 11 comprises an individual shield 16' on a short end section 21, in the vicinity of the ends 22 of the harness 10. The losses generated in the Y termination by the individual shields will be limited because the corresponding end sections are short, for example less than 50 cm.

[0066] Optionally, it is possible to further reduce losses in the individual shields by increasing the radial thickness of said individual shield on the end sections only, to reduce its resistance and therefore the losses by Joule effect.

[0067] It is also possible to add an electrical and thermal drain connected to the structure of the equipment 20 to prevent current from passing through the connectors.

[0068] An embodiment of the harness 10 according to the invention is shown in Figure 5, identical to that previously described except for the following.

[0069] In the case of narrow passages, the harness 10 can be laid flat, over all or part of its length. The cables 11 are then arranged aligned in a transverse direction of the harness 10.

[0070] The single common shielding layer 16 is then woven in a crisscross manner around each of the cables 11 so as to present a substantially equal contact surface with each of the cables 11 of the harness 10. This makes it possible to maintain a symmetry of contact between the shielding layer 16 and each of the cables 11 and thus to minimize the intensity of the resulting induced current.

[0071] Such a shielding layer 16 is for example made from woven and / or braided conductive wires.

[0072] A third embodiment of the harness according to the invention is shown in Figure 6. This embodiment is identical to the first embodiment, except for the following. Each of the cables 11 of the harness 10 comprises an individual shielding layer 16', which is added to the common shielding layer 16. Said common shielding layer 16 is further arranged in electrical contact with the individual shielding layers 16', so as to ensure electrical continuity and thus minimize the induced currents as described above.

[0073] The harness 10 according to this third embodiment is more sensitive to vibrations (friction between the shields) and heavier, but allows electrical contact between the individual shielding layer 16' and the entire periphery of each cable 11 of the harness 10.

[0074] The individual shielding layer 16' of the cables can be made by a covering which makes it possible to limit the problems of wear by friction and forms a light shielding layer. This third embodiment can be generalized to the harnesses laid flat, with each cable 11 comprising an individual shielding layer 16' and the harness comprising a common shielding layer surrounding all the cables 11.

[0075] A fourth embodiment of the harness 10 according to the invention is shown in Figure 7. In this embodiment, each cable 11 comprises an individual shielding layer 16', the individual shielding layers 16' being arranged in permanent electrical contact with each other, so as to form a single shield from the electrical point of view.

[0076] Permanent electrical contact between the individual shielding layers 16' is ensured by a clamping exerted by the protective sheath 17, which is for example a textile or polymer braided type sheath, a heat-shrink sheath, an extruded sheath, a taped sheath or an overmolded sheath.

Claims

DEMANDS 1. Aircraft electrical power harness (10), comprising a plurality of cables (11), each cable (11) comprising, radially from the inside out: - a guiding soul (12), - a first layer (13) of semiconductor material - a layer of insulation (14), and - a second layer (15) of semiconductor material, characterized in that the harness (10) further comprises a common shield (16, 16') arranged in electrical contact with the second layers (15) of semiconductor material of each cable (11).

2. Harness (10) according to the preceding claim, wherein the harness (10) further comprises a single protective sheath (17) arranged radially clamped around the common shield (16, 16').

3. Harness (10) according to the preceding claim, in which the common shield (16, 16') is arranged in electrical contact with the second layer (15) of each cable (11) on a substantially equal contact surface for each of the cables (11).

4. Harness (10) according to the preceding claim, wherein the common shielding (16, 16') comprises a single shielding layer (16) arranged radially around the cables (11) of the harness (10).

5. Harness (10) according to any one of the preceding claims, wherein each cable (11) comprises an individual shielding layer (16'), the individual shielding layers (16') being kept in common electrical contact.

6. Harness (10) according to any one of the preceding claims, wherein the cables (11) are arranged substantially parallel to each other, aligned in a direction perpendicular to their principal elongation direction, the common shield (16, 16') being woven in an interlaced manner around each of the cables (11).

7. Harness (10) according to any one of the preceding claims, wherein an electrical resistance of the common shield (16, 16') between two ends of the harness (10) is between 0.1 mQ and 100 mQ, and preferably between 1 mQ and 20 mQ, and even more preferably between 3 mQ and 10 mQ. Harness (10) according to any one of the preceding claims, wherein the second layers (15) are made of a semiconductor material having an electrical resistivity between 10 Qm and 100 Qm. Harness (10) according to any one of the preceding claims, wherein, at at least one end (22) of the harness (10), each cable (11) comprises an individual shielding layer (16') on an end segment (21).

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