FR3062748A1 - ELECTRICAL CABLE RESISTANT TO PARTIAL DISCHARGES - Google Patents

Abstract

The present invention relates to an electrical cable comprising an elongated electrically conductive member, an electrically insulating layer comprising polyimide (PI) surrounding said elongated electrically conductive member, and a fluorinated electrically insulating layer comprising a fluorinated polymer surrounding said electrically insulating layer comprising polyimide (PI), said layers having specific thicknesses according to the section of the elongated electrically conductive element.

Description

© Publication number: 3,062,748 (to be used only for reproduction orders) (© National registration number: 17 50942 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY

COURBEVOIE © IntCI ⁸

H 01 B 3/00 (2017.01), H 01 B 7/17

A1 PATENT APPLICATION

©) Date of filing: 03.02.17. © Applicant (s): NEXANS — FR and SAFRAN ELEC- (© Priority: TRICAL & POWER - FR. @ Inventor (s): HAEHNER THOMAS, RYBSKI PATRICK, MANENTI LAURENT, AUBERT EDDY and (43) Date of public availability of the KOLIATENE FLAVIEN. request: 10.08.18 Bulletin 18/32. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): NEXANS, SAFRAN ELECTRICAL & related: POWER. ©) Extension request (s): (© Agent (s): IPSILON Simplified joint-stock company.

ELECTRIC CABLE RESISTANT TO PARTIAL DISCHARGES.

FR 3 062 748 - A1

The present invention relates to an electric cable comprising an elongated electrically conductive element, an electrically insulating layer comprising polyimide (PI) surrounding said elongated electrically conductive element, and an electrically fluorinated insulating layer comprising a fluoropolymer surrounding said electrically insulating layer comprising polyimide (PI), said layers having specific thicknesses depending on the section of the elongated electrically conductive element.

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ELECTRICAL CABLE RESISTANT TO PARTIAL DISCHARGES

The present invention relates to an electric cable comprising an elongated electrically conductive element, an electrically insulating layer comprising polyimide (PI) surrounding said elongated electrically conductive element, and an electrically fluorinated insulating layer comprising a fluoropolymer surrounding said electrically insulating layer comprising polyimide (PI), said layers having specific thicknesses depending on the section of the elongated electrically conductive element.

The invention typically but not exclusively applies to electrical cables used in the aeronautical field, for example on board aircraft.

In the prior art, it is known to equip planes with wiring wires (eg more than 500 kilometers of cable in ΙΆ380), these wires comprising a conductive element surrounded by a first polyimide layer of 0.017 to 0.065 mm d thickness, itself surrounded by a layer of polytetrafluoroethylene PTFE with a thickness of 0.1 to 0.22 mm for nominal conductor sections ranging from 0.15 to 95 mm ² . However, for such wiring wires, the applied voltage is of the order of 115 V (between the phase and the neutral of the three-phase system). In order to reduce the section of cables to pass the same amount of current, the operating voltage of aircraft cables has been increased to 230 V (between phase and neutral of the three-phase system). By doubling the tension, the mass of the cables is divided by about two. However, the relatively high voltage, combined with constraints related to aeronautics, such as humidity, high temperature and low pressure, can generate partial discharges (PD) on electrical equipment, in particular on the surface and / or in faults in insulating electrical cables. However, partial discharges, which are tiny electric arcs, cause over time, degradation of the insulating material until the dielectric breaks, leading to the possible establishment of an electric arc.

In order to reduce partial discharges, EP 2 557 572 A1 has described an electric cable comprising a conductive element, a layer comprising polyimide (PI) surrounding said conductive element, and a fluorinated layer comprising a fluorinated compound surrounding said layer comprising polyimide ( PI), the total thickness of all the fluorinated layers being at least 0.4 mm. However, the dimensions of the cable are not optimized to minimize its bulk and / or its weight while guaranteeing optimal partial discharge resistance.

The present invention aims to provide a cable which avoids all or part of the aforementioned drawbacks. In particular, the present invention aims to provide a cable having a space requirement and / or a reduced weight, while guaranteeing good resistance to partial discharges, in particular when the cable is intended for the aeronautical field and undergoes during flight, high temperatures (around 150 ° C), low pressures (around 145 mbar) and high voltages, such as 230 V (between phase and neutral of the three-phase system) or 400 V between phases.

To this end, the present invention relates to an electric cable comprising:

- an elongated electrically conductive element having a cross section s (in mm ² ),

an electrically insulating layer comprising polyimide (PI) surrounding said elongated electrically conductive element and having a thickness ei (in mm), and

a fluorinated electrically insulating layer comprising a fluoropolymer, surrounding said electrically insulating layer comprising polyimide (PI), characterized in that the thickness e ₂ (in mm) of the fluorinated electrically insulating layer is less than 0.4000 mm, and the total thickness ei + e ₂ (in mm) is such that ei + e ₂ > -0.02140 x In (s) + 0.41613.

Thus, the thicknesses of the various layers of the cable of the invention are reduced, inducing a minimum weight and / or bulk as a function of the diameter (ie of the section) of the elongated electrically conductive element, while guaranteeing the absence of the conditions conducive to the occurrence of partial discharges.

In a preferred embodiment, s (in mm ² ) is such that 0.25 <s <85, and preferably 1 <s <68.

According to one embodiment of the invention, the total thickness e _t + e ₂ (in mm) is such that ei + e ₂ > s 'x 0.00482 + 0.33012, with s' being the cross section of the electrically conductive element elongated in AWG.

In the present invention, the expression “AWG” means “American Wire Gauge” and designates a unit of measurement making it possible to measure the diameter of an electric cable. A correspondence table available in the literature converts the section s to mm ² into the section s' to AWG (httD: //www.astm.orq/Standards/B258.htm, httD: //www.astm.orq/ Standards / B286.htmy

We prefer the correspondence tables which take into account the multi-strand nature of a conductor.

In a preferred embodiment, s' (in AWG) is such that -2 (ie AWG000) <s' <24 (ie AWG24), and preferably s' (in AWG) is such that -1 (ie AWG00) <s' <10 (ie AWG10).

The cable of the invention makes it possible to avoid partial discharges under conventional conditions of use. It therefore preferably has a threshold voltage for the appearance of partial discharges, peak value (also well known under Anglicism PDIV for “partial discharge inception voltage”) greater than or equal to 800 V at a pressure of 145 mbar and a temperature of 150 ° C.

It preferably has a threshold voltage for the appearance of partial discharges, a value in volts RMS (also well known by anglicism PDIV in V RMS for “partial discharge inception voltage in voltage root mean square”) greater than or equal to 566 V for a sinusoidal voltage, at a pressure of 145 mbar and a temperature of 150 ° C.

The elongated electrically conductive element is preferably central.

The fluoropolymer is preferably a polymer obtained by polymerization of monomers among which at least one of said monomers is tetrafluoroethylene or vinyl fluoride.

a

For example, the fluoropolymer can be a homopolymer or fluoropolymer, and preferably it is chosen from a polytetrafluoroethylene (PTFE), hexafluoropropylene) (FEP), a perfluoro (alkyvinylether) / tetrafluoroethylene tetrafluoroethylene) (ETFE) and a of their combinations.

poly (tetrafluoroethylene-coun copolymer (PFA), a poly (ethylene-co) Preferably, a layer is said to "comprise a fluoropolymer" when it comprises, by mass relative to the mass of said layer, at least about 50% of fluoropolymer (s), preferably at least about 70% of fluoropolymer (s), and even more preferably at least about 80% of fluoropolymer (s), and so even more preferred approximately 90% of fluoropolymer (s), such as in particular PTFE, PFA, ETFE, FEP or one of their combinations.

Advantageously, the fluoropolymer is PTFE.

Preferably, the thickness e ₂ (in mm) of the fluorinated electrically insulating layer comprising a fluorinated polymer, such as for example PTFE, PFA, ETFE, FEP or one of their combinations, is such that 0.2000 mm <e ₂ <0.4000 mm, preferably such that

0.2000 mm <e ₂ <0.3950 mm, and more preferably such that

0.2500 mm <e ₂ <0.3850 mm.

In the invention, the thickness e ₂ of the electrically insulating fluorinated layer is measured after sintering of said layer. In fact, during sintering, the fluoropolymer can lose volume. In particular, PTFE can lose about 25% in volume.

In the invention, the thickness ei + e ₂ is measured after sintering of said layers.

The electrically fluorinated insulating layer is preferably sintered.

According to the invention, the electrically fluorinated insulating layer can be tape and / or extruded, and preferably tape.

When banded, the electrically insulating fluorinated layer may correspond to the winding of one or more ribbons of fluoropolymer (s). It is then sintered to give it its mechanical properties.

Preferably, the electrically insulating fluorinated layer comprises one or more tapes of fluoropolymer (s), preferably one or more tapes of PTFE.

The cable may further comprise at least one fluorinated adhesive layer comprising a fluoropolymer, the fluoropolymer included in said adhesive layer being in particular identical or different from that included in the electrically insulating fluorinated layer.

According to a characteristic of the invention, the fluorinated adhesive layer or layers are composed of one or more fluorinated polymers. This is called a fluorinated adhesive layer.

In particular, the fluoropolymer (s) of the fluorinated adhesive layer are chosen from a poly (tetrafluoroethylene-cohexafluoropropylene) (FEP), a perfluoro (alkyvinyl ether) / tetrafluoroethylene (PFA) copolymer, a polytetrafluoroethylene (PTFE), a poly ( ethylene-co-tetrafluoroethylene) (ETFE) and one of their combinations, said fluorinated compounds mentioned above having adhesion properties.

Advantageously, at least one fluorinated adhesive layer is disposed on at least one of the two faces of the electrically insulating layer comprising polyimide. The function of an adhesive layer is to allow adhesion between the layers that it connects or between the elongated electrically conductive element and the layer that it connects.

The fluorinated adhesive layer is generally able to adhere the elongated electrically conducting element to the electrically insulating layer of PI or the electrically insulating layer of PI to the electrically insulating fluorinated layer (eg layer comprising PTFE, PFA, FEP, ETFE or one of their combinations). Indeed, the fluoropolymer (s) of the adhesive layer undergoes a treatment beforehand which gives them their adherent property, as is the case for the Kapton FN® product sold by Dupont.

According to one embodiment, the electrically insulating layer comprising a polyimide and the electrically fluorinated insulating layer (e.g. comprising PTFE) are separated by a fluorinated adhesive layer.

The electrically insulating layer comprising a polyimide can be covered on each of its faces with a fluorinated adhesive layer, and in particular with a coating of fluorinated ethylene propylene copolymer (FEP).

The thickness of the fluorinated adhesive layer (e.g. FEP) can range from 2 to 2.5 μm approximately before sintering.

The thickness of the electrically insulating layer comprising a polyimide can range from approximately 20 to 30 μm, and preferably from approximately 23 to 27 μm.

The electric cable of the invention may further comprise one or more electrically insulating layers comprising additional polyimide (PI), each of the electrically insulating layers comprising a polyimide which can be covered on each of its faces with a fluorinated adhesive layer, and in particular a coating of fluorinated ethylene propylene copolymer (FEP).

In this case, the thickness ei (in mm) as defined in the invention denotes the total thickness of the electrically insulating layers comprising polyimide (PI),

The Kapton FN® product is suitable for the present invention. It is in the form of a ribbon comprising an electrically insulating layer of polyimide (PI) covered on each of its faces with a layer of FEP (FEP / PI / FEP).

Two electrically insulating layers comprising a polyimide can thus be obtained by winding at least two thicknesses of said strip so that there is overlap, and a total thickness of electrically insulating layers of polyimide before sintering (or after sintering) of the film results. on the order of approximately 50 to 51 μm, and a total thickness of adhesive layers of FEP before sintering (or after sintering) of the order of approximately 9 to 10 μm. Thus, the thickness of the assembly: FEP / PI / FEP / FEP / PI / FEP before sintering (or after sintering) is of the order of 60 μm.

The elongated electrically conductive element suitable according to the invention is for example of the solid or multi-stranded type (“stranded”).

The elongated electrically conductive element may correspond to copper (Cu), a tinned Cu alloy, a silver Cu alloy, a nickel-plated Cu alloy, aluminum (Al), nickel-plated aluminum or copper-plated and nickel-plated aluminum (well known under the Anglicism "nickel plated copper clad aluminum").

The elongated electrically conductive element according to the invention is preferably multi-strand.

When the cable comprises other fluorinated layer (s) (ie other layer (s) comprising a fluoropolymer as defined in the invention), the thickness e ₂ (in mm) denotes the thickness of the fluorinated electrically insulating layer cumulated with the respective thicknesses of the other optional fluorinated layers, in particular comprising at least one homo- or fluorinated copolymer such as in particular PTFE, PFA, ETFE, FEP or one of their combinations.

In particular, when one or more fluorinated adhesive layers are present, the thickness e ₂ (in mm) denotes the thickness of the electrically insulating fluorinated layer cumulated with the thicknesses of the fluorinated adhesive layers.

According to a preferred embodiment of the invention, the electrically fluorinated insulating layer is the outermost fluorinated layer of the cable.

According to another preferred embodiment of the invention, the cable further comprises one or more other fluorinated layers (i.e. additional fluorinated layers).

In this embodiment, the cable can comprise at least one additional fluorinated layer, in particular chosen from a fluorinated semiconductor layer, another electrically insulating fluorinated layer and an external fluorinated layer (surface) capable of being marked (ie marking layer ), and preferably a fluorinated semiconductor layer.

The fluorinated semiconductor layer may comprise at least one fluorinated polymer, the fluorinated compound included in said semiconductor layer being in particular identical or different from that included in the electrically insulating fluorinated layer.

The fluorinated semiconductor layer may be in the form of a tape, an extrudate, a varnish, or one of their combinations.

According to the invention, it is more particularly considered that a layer is semiconductor when its electrical conductivity is at least 0.001 S.m ' ¹ (Siemens per meter).

In particular, when the fluorinated semiconductor layer is in the form of a ribbon or an extrudate, it can be composed of at least one fluorinated polymer or copolymer and from 0.1% to 40% by mass approximately. (electrically) conductive charge, relative to the total mass of said fluorinated semiconductor layer.

When the fluorinated semiconductor layer is in the form of a varnish, it can be composed of at least one fluoropolymer or copolymer, of the FEP, PFA or PTFE dispersions type, and from 0.1% to Approximately 40% by mass of (electrically) conductive charge, relative to the total mass of said fluorinated semiconductor layer.

Preferably, the fluorinated semiconductor layer comprises at least 10% by mass approximately of electrically conductive charge, and even more preferably at least 25% by mass approximately of electrically conductive charge, relative to the total mass of said semiconductor layer fluorinated.

The electrically conductive charge can advantageously be chosen from carbon blacks, carbon nanotubes and one of their mixtures.

According to a characteristic of the invention, the fluorinated semiconductor layer has a longitudinal resistivity of 0.04 to 100 Ohm.m, and preferably from 0.06 to 0.6 Ohm.m.

The outer (surface) layer capable of being marked can be in the form of a tape, an extrudate or a varnish. It can in particular comprise at least one fluorinated polymer or copolymer, such as for example PTFE, FEP, PFA, ETFE, and at least one pigment of metallic complex type.

As indicated above, when one or more other fluorinated layers are present, the thickness e ₂ (in mm) denotes the thickness of the electrically insulating fluorinated layer cumulated with the thicknesses of the other fluorinated layers such as those mentioned above (layer of fluorinated marking, fluorinated semiconductor layer, other electrically insulating fluorinated layer, etc.).

The other fluorinated layers of the cable of the invention, if they exist, are preferably sintered (e.g. fluorinated adhesive layer (s)).

The electrically insulating layer comprising polyimide can be produced by tape (winding of a polyimide tape), by coating with varnish (mixture of components polymerizing in situ) or by extrusion, according to techniques known to those skilled in the art.

The cable comprising the aforementioned characteristics is intended for use in the aeronautical field, in particular at 230 V (between the phase and the neutral of the three-phase system) and is in particular intended for equipping airplanes.

For a better understanding of the invention, the description will refer to the attached drawing, which is given for illustration only and is not limitative.

Figure 1 illustrates a cross-sectional view of an electrical cable at the insulation stage (without sheath) according to a preferred embodiment of the invention.

Example of realization:

For reasons of clarity, only the essential elements for understanding the invention have been shown schematically, and this without respecting the scale in FIG. 1.

According to a first embodiment, the wiring wire (hook up wire) or the power cable 1, represented in FIG. 1, comprises: an electrically conductive elongated central element 2, in particular of copper or aluminum, of the multi-strand type, and, successively and coaxially around this central elongated electrically conductive element 2, a first adhesive layer of FEP 5a, an electrically insulating layer of polyimide (PI) 3, a second adhesive layer of FEP 5b and an electrically insulating layer of PTFE 4, here representing the outer layer of the cable 1. The different layers are obtained by tape. The cable is then heat treated to sinter the outer layer of PTFE. For this, a temperature above 340 ° C is applied.

The FEP / PI / FEP assembly preferably corresponds to the Kapton FN® tape from Dupont comprising a layer of PI of 25.4 μm in thickness coated on each of its faces with a layer of FEP of 2.5 μm thick before sintering.

After laying (or taping) the electrically insulating layer of PTFE, the electric cable thus insulated is heat treated in an oven at a temperature above the melting temperature of PTFE, namely at a temperature above 340 ° C, to obtain sintering of PTFE and FEP layers. This single heat treatment step, which includes the polyimide heat sealing step and the sintering step of PTFE and FEP layers, ensures the adhesion of all thicknesses of tapes. Indeed, the heat treatment leads to the cohesion of the electrically insulating layer of PTFE on the electrically insulating layer of PI and to the bonding of the electrically insulating layer of PI on itself and on the elongated electrically conductive element.

In Table 1 below, two cables are illustrated in accordance with the invention and for comparison two cables as described in EP 2 557 572 A1, with for each of the cables the total thickness of the electrically insulating layers of PI after sintering , the thickness of the fluorinated layers after sintering (adhesive layers and electrically insulating fluorinated layer), their section in mm ² and in AWG (which corresponds closest to the section in mm ² for multi-strand conductors) and their voltage d appearance of PDIV discharges in V RMS. In this example, we used two thicknesses of Kapton FN® tape from Dupont so that there was overlap. There is therefore an electrically insulating fluorinated layer of PTFE, two electrically insulating polyimide (PI) layers and four adhesive layers of FEP according to the following arrangement from the outermost layer to the innermost layer: PTFE / FEP / PI / FEP / FEP / PI / FEP / elongated electrically conductive element.

The PDIV in V RMS was measured according to the latest edition (2015) of standard EN 3475-307, method B.

TABLE 1

Section (in mm ² ) Section (in AWG) Thickness of fluorinated layers (in mm) Thickness of the PI layer (in mm) PDIV (in V RMS) Cable 1 3 12 0.35 0.0508 > 566 Cable 2 42 1 0.30 0.0508 > 566 Cable 3 ⁽ * ^} 3 12 0.50 0.0508 > 700 Cable 4 ⁽ *> 42 1 0.50 0.0508 > 1050

(*) Cable not part of the invention

It appears that we obtain respectively a reduced weight of 4.9% for cable 1 and 4.4% for cable 2, compared to cables 3 and 4 of the prior art, while ensuring a sufficient level voltage of appearance of partial discharges.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these these are within the scope of the invention.

Claims (12)

1. Electric cable (1) comprising: - an elongated electrically conductive element (2) having a cross section s (in mm ² ), an electrically insulating layer comprising polyimide (PI) (3) surrounding said elongated electrically conductive element (2) and having a thickness ei (in mm), and - an electrically insulating fluorinated layer comprising a fluorinated polymer (4) surrounding said electrically insulating layer comprising polyimide (PI) (3), characterized in that the thickness e ₂ (in mm) of the electrically insulating fluorinated layer is less at 0.4000 mm, and the total thickness ei + e ₂ (in mm) is such that ei + e ₂ > -0.02140 x In (s) + 0.41613. 2. Electric cable according to claim 1, characterized in that s is such that 0.25 <s <85. 3. Electric cable according to any one of the preceding claims, characterized in that the fluoropolymer is chosen from a polytetrafluoroethylene (PTFE), a poly (tetrafluoroethylene-cohexafluoropropylene) (FEP), a perfluoro (alkyvinyl ether) / tetrafluoroethylene (PFA) copolymer ), a poly (ethylene-cotetrafluoroethylene) (ETFE) and one of their combinations. 4. Electric cable according to any one of the preceding claims, characterized in that the fluoropolymer is PTFE. 5. Electric cable according to any one of the preceding claims, characterized in that the thickness e ₂ of the fluorinated electrically insulating layer comprising a fluorinated polymer (4) is such that 0.2000 mm <e ₂ <0.3950 mm. 6. Electric cable according to any one of the preceding claims, characterized in that the electrically insulating fluorinated layer (4) is tape. 7. Electric cable according to any one of the preceding claims, characterized in that it further comprises, at least one fluorinated adhesive layer comprising a fluoropolymer (5a, 5b), the fluoropolymer included in said adhesive layer (5a, 5b) being identical to or different from that included in the electrically fluorinated insulating layer (4). 8. Electric cable according to any one of the preceding claims, characterized in that the electrically insulating layer comprising a polyimide (3) is covered on each of its faces with a fluorinated adhesive layer (5a, 5b). 9. Electric cable according to any one of the preceding claims, characterized in that the elongated electrically conductive element (2) corresponds to copper (Cu), a tinned Cu alloy, a silver Cu alloy, a Cu alloy nickel-plated, aluminum (Al), nickel-plated aluminum or copper-plated and nickel-plated aluminum. 10. Electric cable according to one of the preceding claims, characterized in that the electrically fluorinated insulating layer (4) is sintered. 11. Electric cable according to one of the preceding claims, characterized in that it further comprises at least one fluorinated semiconductor layer. 12. Electric cable according to claim 11, characterized in that the fluorinated semiconductor layer comprises at least one fluoropolymer, the fluorinated compound included in said semiconductor layer being identical or different from that included in the electrically insulating fluorinated layer ( 4). 1/1