EP3965124A1 - Electric cable limiting partial discharges - Google Patents

Abstract

The invention relates to an insulated electrically conductive element (1) for the field of aeronautics, characterized in that it comprises an elongated electrically conductive element surrounded by at least two layers, said two layers being an electrically insulating layer (4) surrounding the elongated electrically conductive element (2) and a first semiconductor layer (5) surrounding said electrically insulating layer (4), at least one of the layers comprising at least one fluorinated polymer.

Description

The present invention relates to an insulated electrically conductive element limiting the occurrence of partial discharges as well as an electrically conductive cable comprising such an element.

Electric cables generally comprise at least one electrically conductive element surrounded by at least one layer of an insulating material and optionally one or more layer(s) of a semiconductor material.

During the operation of the cable, partial discharges can be generated. These partial discharges can appear on the surface of the insulation and/or in the insulation when air bubbles or cavities are present in the layer or layers surrounding the electrically conductive element or between a layer and the element (conductive or layer) that it surrounds. Such air cavities can in particular form when the cables are taped.

Moreover, in the field of aeronautics, the cables are subjected to high voltages which, associated with the conditions of humidity, high temperature and low pressure, can favor the appearance of partial discharges. Partial discharges, which are tiny electric arcs in the insulating material, cause, over time, a degradation of the electrically insulating material, in particular by slow erosion, which can lead to its dielectric breakdown. A solution to prevent partial discharges from appearing is often to increase the thickness of the insulating layer

The problem of partial discharges in electric cables is all the more important with the development of hybrid or electric propulsion systems, particularly in the field of aeronautics. Indeed, in such systems, the cables will have to carry increasingly high voltages and intensities to reach powers that can go up to several tens of megavolt-amperes (MVA).

Furthermore, in the electric chain of hybrid or electric propulsion systems, it is possible to use a width modulation system Pulse Width Modulation (PWM) to convert a DC voltage into a variable voltage in order to regulate the speed of electric motors.

The PWM is based on the generation of a square voltage with variable duty cycle. The rise time of the pulse being short (about 200ns), an overvoltage can be created (which can go as far as doubling the value of the voltage) which is due in particular to the reflections of the wave of tension at the ends of the cable. Such overvoltages favor the appearance of partial discharges. Furthermore, the high chopping frequency of a PWM system (of the order of several tens of kHz) can accelerate the erosion of the insulating layer in the event of the appearance of partial discharges.

At such high voltage values, the insulating layer should have a significant thickness to avoid the appearance of partial discharges which would make the cables too heavy and unsuitable for use in certain fields such as for example in aeronautics.

The object of the present invention is to remedy at least one of the drawbacks of the prior art by proposing an electric cable having an insulation system allowing it to be subjected to high voltages and intensities while limiting or even avoiding the appearance of partial discharges.

The first subject of the present invention is an insulated electrically conductive element limiting the appearance of partial discharges, characterized in that it comprises an elongated electrically conductive element surrounded by an insulation system comprising at least one electrically insulating layer surrounding the elongated electrically conductive element and a first semiconductor layer surrounding said electrically insulating layer, said insulated electrically conductive element being characterized in that the electrically insulating layer has a thickness e _i , the value of said thickness e _i being determined as a function of the operating voltage U of the insulated electrically conductive element and an internal diameter d1 of the electrically insulating layer.

Such an electrically conductive element makes it possible to limit or even avoid the phenomenon of the appearance of partial discharges, known as Partial Discharge Inception (PDI). In particular, the combination of the insulation system comprising at least two layers, namely an electrically insulating layer and a first semiconductor layer, and a thickness of the insulation layer determined according to the invention makes it possible to limit or even to avoid the appearance of partial discharges and/or to avoid dielectric breakdowns, and this, even at very high operating voltage values of the electrically conductive element.

Advantageously, the thickness of the insulation layer is reduced compared to the cables of the prior art seeking to avoid the appearance of partial discharges, which allows the electrically conductive element to be light and to be able to be used in fields requiring light electrical cables such as aeronautics.

According to a preferred embodiment, the determination of the thickness of the insulation layer may involve a calculation, for example a calculation implemented by computer. In particular, the calculation of the value of the thickness of the insulation layer is carried out using the value of the operating voltage U of the insulated electrically conductive element and the value of the internal diameter d1 of the electrically insulating layer. .

When the electrically insulating layer is placed in direct contact with the electrically conductive element, the diameter d1 also corresponds to the outer diameter of the electrically conductive element.

In a preferred embodiment, the insulated electrically conductive element may further comprise a third layer, said third layer being a second semiconductor layer surrounding the elongated electrically conductive element and being preferably placed between the elongated electrically conductive element and the electrically insulating layer. According to this embodiment, the first semiconductor layer, the electrically insulating layer and the second semiconductor layer can constitute a three-layer insulation system. In other words, the electrically insulating layer can be in direct physical contact with the first semiconductor layer, and the second semiconductor layer can be in direct physical contact with the electrically insulating layer.

When the electrically insulating layer is placed in direct contact with the second semiconductive layer, the second semiconductive layer being placed between the elongated electrically conductive element and the electrically insulating layer, the diameter d1 corresponds to the outer diameter of the second layer semiconductor.

The current can be single-phase or three-phase or more generally multi-phase. The voltage can be sinusoidal, continuous, chopped continuous (in the case where a PWM system is used) or have any other temporal form. The operating voltage U corresponds to the voltage that can be applied between the electrically conductive isolated element and the neutral (the phase-to-neutral voltage) or between two electrically conductive isolated elements (the phase-to-phase voltage) and which can depend on its use.

The voltage U can have a value of at least 540 V, preferably of at least 800 V, preferably of at least 1200 V, and particularly preferably of at least 3000 V. In the case of a DC voltage, these voltage values correspond to the potential difference between the two poles (plus and minus). In the case of a non-continuous voltage (for example in alternating current or in PWM systems) these voltage values are peak-to-peak values (known as “peak to peak”).

Electrically insulating layer

The thickness e _i of the electrically insulating layer can be determined as a function of a ratio between the operating voltage U and the diameter d1.

Preferably, when the electrically insulated conductor comprises two layers, namely the insulating layer and the first semiconductor layer of thickness e ₁ , the value of the thickness e _i satisfies the following relationship: $$\mathit{yes}>\mathrm{and}1$$

When the electrically insulated conductor further comprises a second semi-conducting layer of thickness e ₂ , the value of the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \mathrm{and}1+\mathrm{and}2$$

In the present invention, the thickness e of a layer is in particular an average thickness which can vary by ± 30%, preferably by ± 20%, and in a particularly preferred way by ± 10% with respect to the average thickness . This variation in thickness can be random and be due in particular to the method of applying said layer to the element or the layer that it surrounds.

• U étant exprimée en kilovolts (kV),
• E_max étant la valeur maximale du champ électrique pouvant être appliqué à la couche d'isolation, ou encore que le matériau formant la couche d'isolation peut supporter, et ce pendant la durée de vie requise de l'élément conducteur isolé dans son environnement d'utilisation, E_max étant exprimée en kilovolts/mm (kV/mm) et le diamètre d1 étant exprimé en millimètres (mm).

The minimum value of the thickness e _i expressed in millimeters (mm) can be determined according to a following ratio R1: $$\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}1=\frac{U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}$$

• U being expressed in kilovolts (kV),
• E _max being the maximum value of the electric field that can be applied to the insulation layer, or that the material forming the insulation layer can withstand, and this during the required lifetime of the insulated conductive element in its environment of use, E _max being expressed in kilovolts/mm (kV/mm) and the diameter d1 being expressed in millimeters (mm).

The value of the electric field E _max corresponds to the maximum value of the electric field that can be applied to the insulation layer of the insulated electrically conductive element without there being any degradation of said element leading to a dielectric breakdown of the insulation layer for the required cable life. The value of the electric field E _max can be at most 30 kV/mm, preferably at most 20 kV/mm, and particularly preferably at most 10 kV/mm.

Preferably, the minimum value of the thickness e _i is determined according to a following expression E1: $$\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">E</figure-callout>}1=\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1$$

Particularly preferably, the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left[\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1\right]$$

The maximum value of the thickness e _i can be determined according to a following ratio R2: $$R2=\frac{3\times U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}$$

Preferably, the maximum value of the thickness e _i can be determined according to a following expression E2: $$\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">E</figure-callout>}2=\mathrm{<figure-callout\; id="3"\; label="exp"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">exp</figure-callout>}\left(\frac{3\times U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1$$

Particularly preferably, the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left[\mathrm{<figure-callout\; id="3"\; label="exp"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">exp</figure-callout>}\left(\frac{3\times U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1\right]$$

According to a preferred embodiment, the thickness e _i satisfies the following relationship: $$\frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left[\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)\le \mathit{yes}\le \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left(\frac{3\times U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1\right]$$

et $$\mathit{ei}\ge e1+e2$$

According to a particularly preferred embodiment, the thickness e _i simultaneously satisfies the following two relationships: $$\mathit{yes}\ge \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left[\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}}\right)-1\right]$$

and $$\mathit{yes}\ge \mathrm{and}1+\mathrm{and}2$$

According to a particularly preferred embodiment, the value of the electric field Emax is 5 kV/mm and the thickness e _i then satisfies the following relationship: $$\mathit{yes}\ge \frac{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}{2}\left[\mathrm{<figure-callout\; id="2"\; label="exp\; U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}"><figure-callout\; id="5"\; label="exp\; U"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">exp</figure-callout></figure-callout>}\left(\frac{U}{}\right)\left(\frac{}{}\right)\left(\frac{}{2,5\times {\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}\right)-1\right]$$

The electrically insulating layer may comprise at least one olefin polymer selected from linear low density polyethylene (LLDPE); a very low density polyethylene (VLDPE); low density polyethylene (LDPE); a medium density polyethylene (MDPE); a high density polyethylene (HDPE); an elastomeric ethylene-propylene copolymer (EPM); an ethylene propylene diene monomer (EPDM) terpolymer; a copolymer of ethylene and vinyl ester such as a copolymer of ethylene and vinyl acetate (EVA); a copolymer of ethylene and acrylate such as a copolymer of ethylene and butyl acrylate (EBA) or a copolymer of ethylene and methyl acrylate (EMA); an ethylene-alpha-olefin copolymer such as an ethylene-octene copolymer (PEO) or an ethylene-butene copolymer (PEB); a fluorinated polymer, chosen in particular from copolymers obtained from tetrafluoroethylene monomer, and in particular from polytetrafluoroethylene (PTFE), copolymers of fluorinated ethylene and propylene (FEP) such as for example poly(tetrafluoroethylene-co-hexafluoropropylene ), perfluoroalkoxy (PFA) copolymers such as, for example, perfluoro(alkylvinylether)/tetrafluoroethylene copolymers, perfluoromethoxy (MFA) copolymers, and poly(ethylene-co-tetrafluoroethylene) (ETFE); and a mixture thereof.

Preferably, the electrically insulating layer may comprise at least one fluorinated polymer, in particular chosen from the copolymers obtained from tetrafluoroethylene monomer, and in particular from polytetrafluoroethylene (PTFE); copolymers of fluorinated ethylene and propylene (FEP) such as for example poly(tetrafluoroethylene-co-hexafluoropropylene); perfluoroalkoxy (PFA) copolymers such as for example perfluoro(alkylvinylether)/tetrafluoroethylene copolymers; perfluoro methoxy (MFA) copolymers; and poly(ethylene-co-tetrafluoroethylene) (ETFE); or a mixture thereof.

Particularly preferably, the electrically insulating layer may comprise one or more perfluoroalkoxy (PFA) copolymers.

Preferably, the electrically insulating layer can comprise the same polymeric composition as the first semiconductor layer. When the electrically insulated conductor comprises three layers, the electrically insulating layer may comprise the same polymeric composition as the second semiconductor layer. Particularly preferably, the electrically insulating layer may comprise the same polymeric composition as the first and the second semiconductor layers.

In the present invention, a polymeric composition corresponds to a composition comprising one or more polymers in a determined quantity, and in particular with determined percentages by weight of polymers. The polymeric composition essentially comprises one or more polymers, preferably only one or more polymers. Thus, a layer can be formed from a polymeric mixture comprising a polymeric composition to which can be added additional agents such as, for example, fillers, pigments, crosslinking agents, flame-retardant fillers, antioxidants, conductive fillers ...

Preferably, the electrically insulating layer may comprise the same polymeric composition as the first semiconductor layer, the polymeric composition comprising one or more perfluoroalkoxy (PFA) copolymers. Preferably, the electrically insulating layer can comprise the same polymeric composition as the second semi-conductive layer, the polymeric composition comprising one or more perfluoroalkoxy (PFA) copolymers. Particularly preferably, the electrically insulating layer may comprise the same polymer composition as the first and the second semi-conducting layers, the polymer composition comprising one or more perfluoroalkoxy (PFA) copolymers.

The electrically insulating layer may comprise at least 50% by weight of polymer(s), preferably at least 70% by weight of polymer(s), even more preferably at least 80% by weight of polymer(s), and even more preferably at least 90% by weight of polymer(s).

The electrically insulating layer of the invention can conventionally comprise additional agents such as, for example, fillers, pigments, crosslinking agents, flame retardant fillers, etc.

The electrically insulating layer may be a layer extruded around the electrically conductive element, or a layer in the form of a ribbon wound around the electrically conductive element, or a layer of varnish deposited around the electrically conductive element, or a combination thereof.

Preferably, the electrically insulating layer is extruded around the electrically conductive element. Particularly preferably, the electrically insulating layer is coextruded with the first semi-conducting layer and, when present, with the second semi-conducting layer, around the electrically conducting element.

According to one embodiment, the electrically insulating layer can be placed directly around the elongated electrically conductive element. When the electrically insulated conductor comprises three layers, the electrically insulating layer can be placed directly around the second semiconductor layer and therefore be in direct physical contact with said layer.

In the present invention, the term "electrically insulating layer" means a layer whose electrical conductivity is very low or even zero, in particular less than 10 ^-6 S/m, and preferably less than 10 ^-13 S/m, and this in the operating temperature range can go up to 260°C.

• caractéristique 1 : une résistance à des températures allant de -70°C à 260°C, de préférence allant de -65°C à 250°C, et de façon particulièrement préférée de -55°C à 180°C ;
• caractéristique 2 : une résistance à un champ électrique E allant de 1 kV/mm à 30kV/mm , de préférence allant de 3 kV/mm à 20 kV/mm, et de façon particulièrement préférée allant de 5 kV/mm à 20 kV/mm, en particulier lorsque ce champ électrique est appliqué de façon continue pour une durée pouvant aller jusqu'à 430 000 heures (h) de préférence jusqu'à 260 000 h, et de façon encore plus préférée jusqu'à 90 000 h, ces valeurs étant données pour une couche électriquement isolante en forme de plaque d'une épaisseur de 0,5 mm ;
• caractéristique 3: une rigidité diélectrique selon la norme ASTM D149 supérieure à 20 kV/mm, de préférence supérieure à 40 kV/mm, et de façon particulièrement préférée supérieure à 60 kV/mm, ces valeurs étant données pour une couche électriquement isolante en forme de plaque d'une épaisseur de 0,5 mm et étant obtenues par analyse statistique avec une distribution de Weibull avec deux paramètres (cf. norme IEC 62539) sur une population d'au moins dix plaques ; le factor de forme de ladite distribution entant supérieur à 20 ;
• caractéristique 4 : un « facteur de pertes diélectriques» selon la norme ASTM D150 inférieur à 10^-2, de préférence inférieur à 10^-3, et de façon particulièrement préférée inférieur à 3×10^-4, et ce, pour une fréquence comprise entre 100Hz et 100kHz et à une température de 0 à 200°C ;
• caractéristique 5 : une permittivité diélectrique selon la norme ASTM D150 inférieure à 2,3, de préférence inférieure à 2,2, et de façon particulièrement préférée inférieure à 2,1 ; et ce, pour une fréquence comprise entre 100Hz et 100kHz et à une température de 0 à 200°C ;
• caractéristique 6 : un coefficient d'expansion linéaire thermique selon la norme ASTM D696 inférieur à 25×10^-5 K^-1 à 23°C, de préférence inférieur à 20×10^-5 K^-1 à 23°C, et de façon particulièrement préférée inférieur à 15×10^-5 K^-1 à 23°C ;
• caractéristique 7 : un indice limite d'oxygène (ILO) selon la norme ASTM D2863 supérieur à 30, de préférence supérieur à 60, et de façon particulièrement préféré supérieur à 90.

Preferably, the electrically insulating layer of the electrically conductive element of the invention may have one or more of the following additional characteristics:

• characteristic 1: resistance to temperatures ranging from -70°C to 260°C, preferably ranging from -65°C to 250°C, and particularly preferably from -55°C to 180°C;
• characteristic 2: resistance to an electric field E ranging from 1 kV/mm to 30 kV/mm, preferably ranging from 3 kV/mm to 20 kV/mm, and particularly preferably ranging from 5 kV/mm to 20 kV/ mm, in particular when this electric field is applied continuously for a period of up to 430,000 hours (h), preferably up to 260,000 h, and even more preferably up to 90,000 h, these values given for an electrically insulating layer in the form of a plate with a thickness of 0.5 mm;
• characteristic 3: a dielectric strength according to the ASTM D149 standard greater than 20 kV/mm, preferably greater than 40 kV/mm, and so particularly preferred greater than 60 kV/mm, these values being given for an electrically insulating layer in the form of a plate with a thickness of 0.5 mm and being obtained by statistical analysis with a Weibull distribution with two parameters (cf. IEC standard 62539) on a population of at least ten plates; the shape factor of said distribution being greater than 20;
• characteristic 4: a "dielectric loss factor" according to the ASTM D150 standard of less than 10 ^-2 , preferably less than 10 ^-3 , and particularly preferably less than 3×10 ^-4 , and this, for a frequency between 100Hz and 100kHz and at a temperature of 0 to 200°C;
• characteristic 5: a dielectric permittivity according to the ASTM D150 standard of less than 2.3, preferably less than 2.2, and particularly preferably less than 2.1; and this, for a frequency between 100Hz and 100kHz and at a temperature of 0 to 200°C;
• characteristic 6: a thermal linear expansion coefficient according to the ASTM D696 standard of less than 25×10 ^-5 K ^-1 at 23°C, preferably less than 20×10 ^-5 K ^-1 at 23°C, and so particularly preferred less than 15×10 ^-5 K ^-1 at 23°C;
• characteristic 7: a limiting oxygen index (ILO) according to the ASTM D2863 standard greater than 30, preferably greater than 60, and particularly preferably greater than 90.

According to a preferred embodiment, the electrically conductive element can be used in the field of aeronautics. According to this embodiment, the electrically insulating layer of the insulated electrically conductive element can possess one or more of the characteristics 1 to 7. According to this preferred embodiment, the electrically insulating layer of the insulated electrically conductive element can possess at least characteristics 1 and 2.

According to a possible embodiment, the first and/or the second semiconductor layer can possess one or more of the characteristics 6 and 7.

electrically conductive element

The elongated electrically conductive element can be a one-piece conductor such as for example a metal wire or a multi-body conductor such as a plurality of twisted or untwisted metal wires, preferably a plurality of metal wires, twisted or not, so as to increase the flexibility of cable. When the insulated electrically conductive element comprises a plurality of metallic wires, some of the metallic wires in the center of the conductor can be replaced by non-metallic wires having at least characteristic 1.

The elongated electrically conductive member can be aluminum, aluminum alloy, copper, copper alloy, and a mixture thereof.

The elongated electrically conductive element may include one or more carbon nanotubes or with graphene to increase electrical conductivity, thermal conductivity and/or mechanical strength.

According to one possible embodiment, the electrically conductive element can be covered with a metal or an alloy different from the metal forming the conductor or different from the alloy forming the conductor, such as for example nickel, an alloy of nickel, tin, a tin alloy, silver, a silver alloy, or a mixture thereof. Such a covering, called plating, can make it possible to protect the conductor from corrosion and/or to improve its contact resistance.

The electrically conductive element formed from a metal or a metal alloy means that the electrically conductive element comprises at least 70%, preferably at 80%, and even more preferably at least 90% less of said metal or of said alloy .

The electrically conductive element may have a section ranging from 3 mm ² (AWG 12) to 107 mm ² (AWG 0000), preferably ranging from 14 mm ² (AWG 6) to 107 mm ² (AWG 0000), preferably ranging from 34 mm ² (AWG 2) to 107 mm ² (AWG 0000), and even more preferably ranging from 68 mm ² (AWG00) to 107 mm ² (AWG0000).

The electrically conductive element can have an outer diameter ranging from 2.0 mm to 20 mm, preferably ranging from 4.5 mm to 18 mm, preferably ranging from 7.0 mm to 16 mm, and even more preferably ranging from from 10mm to 15.2mm.

First semiconductor layer

The first semiconductor layer can include at least one olefin polymer selected from linear low density polyethylene (LLDPE); a very low density polyethylene (VLDPE); low density polyethylene (LDPE); a medium density polyethylene (MDPE); high density polyethylene (HDPE); an elastomeric ethylene-propylene copolymer (EPM); an ethylene propylene diene monomer (EPDM) terpolymer; a copolymer of ethylene and vinyl ester such as a copolymer of ethylene and vinyl acetate (EVA); a copolymer of ethylene and acrylate such as a copolymer of ethylene and butyl acrylate (EBA) or a copolymer of ethylene and methyl acrylate (EMA); an ethylene-alpha-olefin copolymer such as an ethylene-octene copolymer (PEO) or an ethylene-butene copolymer (PEB); a fluorinated polymer, chosen in particular from copolymers obtained from tetrafluoroethylene monomer, and in particular from polytetrafluoroethylene (PTFE), copolymers of fluorinated ethylene and propylene (FEP) such as for example poly(tetrafluoroethylene-co-hexafluoropropylene ), perfluoroalkoxy (PFA) copolymers such as, for example, perfluoro(alkylvinylether)/tetrafluoroethylene copolymers, perfluoromethoxy (MFA) copolymers, and poly(ethylene-co-tetrafluoroethylene) (ETFE); and a mixture thereof.

Preferably, the first semiconductor layer may comprise at least one fluorinated polymer, chosen in particular from polytetrafluoroethylene (PTFE); copolymers of fluorinated ethylene and propylene (FEP) such as for example poly(tetrafluoroethylene-co-hexafluoropropylene); perfluoroalkoxy (PFA) copolymers such as for example perfluoro(alkylvinylether)/tetrafluoroethylene copolymers; perfluoro methoxy (MFA) copolymers; and poly(ethylene-co-tetrafluoroethylene) (ETFE); or a mixture thereof.

Particularly preferably, the first semiconductor layer may comprise one or more perfluoroalkoxy (PFA) copolymers.

The first semiconductor layer may comprise at least 50% by weight of polymer(s), preferably at least 70% by weight of polymer(s), even more preferably at least 80% by weight of polymer(s) , and even more preferably at least 90% by weight of polymer(s).

The first semi-conductive layer of the invention may conventionally comprise electrically conductive fillers in an amount sufficient to render the first semi-conductive layer. By way of example, it can comprise from 0.1% to 40% by weight of electrically conductive fillers, such as for example carbon black, carbon nanotubes, etc.

The first semiconductor layer may be a layer extruded around the elongated electrically conductive element, or a layer in the form of a ribbon wound around the elongated electrically conductive element, or a layer of varnish deposited around the electrically conductive element. elongated conductor, or a combination thereof.

Preferably, the first semiconductor layer is extruded around the electrically insulating layer.

According to a preferred embodiment, the first semiconductor layer can be placed directly around the electrically insulating layer and therefore be in direct physical contact with said element.

The first semiconductor layer may have a thickness e ₁ ranging from 0.05 mm (millimeter) to 1.0 mm, preferably ranging from 0.07 mm to 0.8 mm, and particularly preferably a thickness ranging from 0.09mm to 0.5mm.

In the present invention, the term "semiconducting layer" means a layer whose volume resistivity is less than 10,000 Ω×m (Ohm meter) (at room temperature), preferably less than 1000 Ω×m, and in such a way particularly preferred less than 500 Ω×m.

Second semiconductor layer

The second semiconductor layer can comprise at least one polymer such as those described for the first semiconductor layer.

Preferably, the second semiconductor layer can comprise at least one fluorinated polymer such as those described for the first semiconductor layer.

The second semiconductor layer may comprise at least 50% by weight of polymer(s), preferably at least 70% by weight of polymer(s), of even more preferably at least 80% by weight of polymer(s), and even more preferably at least 90% by weight of polymer(s).

The second semiconductive layer may typically include electrically conductive fillers in an amount sufficient to render the first layer semiconductive. By way of example, it can comprise from 0.1% to 40% by weight of electrically conductive fillers, such as for example carbon black, carbon nanotubes, etc.

The second semiconductor layer may be a layer extruded around the electrically conductive element, or a layer in the form of a ribbon wound around the electrically conductive element, or a layer of varnish deposited around the electrically conductive element, or a combination thereof.

According to a preferred embodiment, the second semiconductor layer can be extruded around the electrically insulating layer.

According to a preferred embodiment, the second semiconductor layer can be placed directly around the electrically conductive element and therefore be in direct physical contact with said element. The first semiconductor layer thus makes it possible to smooth the electric field around the conductor.

The second semiconductor layer may have a thickness e ₂ ranging from 0.05 nm to 1.0 mm, preferably ranging from 0.07 mm to 0.8 mm, and particularly preferably a thickness ranging from 0.09 mm to 0.5mm.

The second semiconductor layer may have an outside diameter ranging from 0.3 mm to 22 mm, preferably ranging from 0.8 mm to 18 mm, preferably ranging from 1.0 mm to 15 mm, and in a particularly preferred way ranging from 1.2mm to 12mm.

Insulated electrically conductive element

The insulated electrically conductive element can be used at an intensity which can range from 35 A _RMS to 1000 A _RMS , preferably from 80 A _RMS to 600 A _RMS , particularly preferably from 190 A _RMS to 500 A _RMS , these values being indicated for a maximum temperature of the conductor in service of 260°C.

The insulated electrically conductive element can be used in direct current or in alternating current. When it is used in alternating current, the frequency of use can range from 10 Hz (Hertz) to 100 kHz (kilohertz), preferably from 10 Hz to 10 kHz, in a particularly preferred way from 10 Hz to 3 kHz. In a PWM system, frequency means the fundamental frequency of the current.

The insulated electrically conductive element can be used, in an aircraft in a pressurized and non-pressurized zone, at a power ranging from 8 kVA (kilovoltampere) to 3000 kVA, preferably from 100 kVA to 2000 kVA, and particularly preferably from 250 kVA to 1500 kVA.

electrically conductive cable

A second object of the invention relates to an electrically conductive cable comprising one or more insulated electrically conductive elements as previously described.

The voltage, current, power and frequency values described for the insulated electrically conductive element also apply for the electrically conductive cable.

The electrical cable may include a metal screen forming electromagnetic shielding. In the case where the cable comprises a single insulated electrically conductive element, the metallic screen can be placed around the second semi-conductive layer. In the case where the cable comprises several electrically conductive insulated elements, the metal screen can be placed around the second semi-conductive layer of each element and/or around all the electrically conductive insulated elements.

The metallic screen can be a so-called “wired” screen, composed of a set of conductors based on copper or aluminum, arranged around the second semi-conducting layer or around all the insulated electrically conducting elements; a so-called “taped” screen composed of one or more conductive metal tapes placed in a helix around the second semi-conductor layer or around all of the insulated electrically conductive elements; a so-called “sealed” screen of metal tube type surrounding the second semiconductor layer or all of the insulated electrically conductive elements; or a so-called “braided” screen forming a braid around the second semiconductor layer. The metal screen is preferably "braided", in particular to give the electrically conductive cable flexibility.

All types of metallic screen can play the role of earthing the electric cable and can thus carry fault currents, for example in the event of a short-circuit in the network concerned.

Further, the electrically conductive cable may include a protective sheath. When the cable includes a metal screen, the protective sheath may surround the metal screen. In the case where the cable does not include a metal screen, the protective sheath can surround the second semi-conductor layer when the cable comprises a single insulated electrically conductive element, or surround all of the insulated electrically conductive elements when the cable includes several.

The protective sheath can be a layer based on polymers such as those described for the electrically insulating layer. For an application in the field of aeronautics, the protective sheath can preferably be based on one or more fluorinated polymers (such as, for example, of the PTFE, FEP, PFA and/or ETFE type) and/or polyimide.

Preferably, the protective sheath can be the outermost layer of the cable.

The protective sheath can be in the form of a tape, an extrudate or a varnish.

Brief description of the drawings

• La figure 1 représente une vue en coupe transversale d'un élément électriquement conducteur isolé selon un mode de réalisation de l'invention ;
• La figure 2 représente une vue en coupe transversale d'un câble électriquement conducteur selon un premier mode de réalisation de l'invention ;
• La figure 3 représente une vue en coupe transversale d'un câble électriquement conducteur selon un deuxième mode de réalisation de l'invention ;
• La figure 4 est un graphique représentant la tension d'apparition de décharges partielles pour différents types de câbles ; et
• La figure 5 est un graphique représentant la tension d'extinction de décharges partielles pour différents types de câbles.

The accompanying drawings illustrate the invention:

• The figure 1 shows a cross-sectional view of an insulated electrically conductive element according to one embodiment of the invention;
• The picture 2 shows a cross-sectional view of an electrically conductive cable according to a first embodiment of the invention;
• The picture 3 shows a cross-sectional view of an electrically conductive cable according to a second embodiment of the invention;
• The figure 4 is a graph representing the partial discharge onset voltage for different types of cables; and
• The figure 5 is a graph representing the partial discharge extinction voltage for different types of cables.

Description of embodiment(s)

For reasons of clarity, only the essential elements for the understanding of the embodiments set out below have been represented schematically, and this without respecting the scale.

As illustrated on the figure 1 , an insulated electrically conductive element 1 according to one embodiment of the invention comprises an elongated electrically conductive element 2, a second semiconductor layer (CSC) 3 surrounding the elongated electrically conductive element 2, an electrically insulating layer (CI) 4 surrounding the first semiconductor layer 3 and a first semiconductor layer (CSC) 5 surrounding said electrically insulating layer.

The second semiconductor layer 3 has a thickness e ₂ and the first semiconductor layer 5 has a thickness e ₁ . The electrically insulating layer 3 has a thickness ei determined according to one embodiment of the invention and which is greater than the sum: e ₁ + e ₂ .

In this embodiment, the second semiconductor layer 3, the electrically insulating layer 4 and the first semiconductor layer 5 constitute a three-layer insulation system, which means that the electrically insulating layer 4 is in direct physical contact with the second semiconductor layer 3, and the first semiconductor layer 3 is in direct physical contact with the electrically insulating layer 4.

The elongated electrically conductive element 2 is formed by 37 copper strands covered with a layer of nickel and thus has a diameter of 12 AWG (“American Wire Gauge”).

The first and the second semiconductor layers 3 and 5 as well as the insulating layer 4 are formed by PFA.

The figure 2 shows an electrically conductive cable 10 according to a first embodiment of the invention comprising a single insulated electrically conductive element 1 surrounded by a metal screen 16 of the “braided” type made of nickel-plated copper. The metal screen 16 is surrounded by a protective sheath 17 which is the outermost layer of the cable 10 and which is based on PFA.

The picture 3 represents an electrically conductive cable 20 according to a first embodiment of the invention comprising three insulated electrically conductive elements 1, 1' and 1" according to the invention. In this embodiment, the three insulated electrically conductive elements are identical, however , according to another possible embodiment, they may be different.They may differ in particular by the thickness of the semiconducting layers and of the insulating layer.

The assembly formed by the three insulated electrically conductive elements 1, 1' and 1" is surrounded by a metal screen 16 of the braided type. The metal screen 16 is surrounded by a protective sheath 17 which is the outermost layer of the cable 10 and which is based on PFA The electrically conductive cable 20 also comprises spaces 25 which include air.

Examples of realization Example 1

The electrically conductive cable 10 according to the first embodiment and devoid of the protective sheath 17 of the invention is prepared by coextrusion of the three-layer insulation around the elongated electrically conductive element 2, the three-layer insulation system being formed by the first semiconductor layer 3, the electrically insulating layer 4 and the second semiconductor layer 5.

The metal screen 16 is then placed around the second semiconductor layer.

The electrically elongated conductor 2 is formed by 37 copper strands and covered with a layer of nickel according to European standard EN 2083.

The first semiconductor layer is formed from a polymer blend A comprising at least 60% by weight of copolymer perfluoroalkoxy (PFA) relative to the total weight of the polymer mixture, marketed under the reference S185.1 B by the company PolyOne.

The electrically insulating layer is formed from a second polymer blend B comprising at least 95% by weight of perfluoroalkoxy copolymer (PFA) relative to the total weight of the polymer blend, marketed under the reference AP-210 by the company DAIKIN.

The second semiconductor layer is formed from a third polymer blend C comprising 60% by weight of perfluoroalkoxy copolymer (PFA) relative to the total weight of the polymer blend, marketed under the reference S185.1 B by the company PolyOne.

The polymer mixtures A, B and C were each introduced into one of the three extruders of the three-layer coextrusion and extruded around the elongated electrically conductive element 2 with a temperature profile ranging from 320° C. to 380° C., the speed of rotation of the screws of these three extruders being regulated between 5 and 100 rotations per minute.

• diamètre moyen du conducteur = 2,15 mm (± 10%) ;
• épaisseur moyenne e₂ = 0,15 mm (± 10%) ;
• diamètre extérieur moyen de la couche 3 = 2,45 mm (± 10%) ;
• épaisseur moyenne ei = 1,62 mm (± 10%) ;
• diamètre extérieur moyen de la couche 4 = 5,70 mm (± 10%) ;
• épaisseur moyenne e₁ = 0,15 mm (± 10%) ;
• diamètre extérieur moyen de la couche 5 = 6,00 mm (± 10%) ; et
• épaisseur moyenne de l'écran = 0,2mm (± 10%).

The cable 10 having the dimensions below is then formed:

• average conductor diameter = 2.15 mm (± 10%);
• average thickness e ₂ = 0.15 mm (± 10%);
• average outer diameter of layer 3 = 2.45 mm (± 10%);
• average thickness ei = 1.62 mm (± 10%);
• average outer diameter of layer 4 = 5.70 mm (± 10%);
• average thickness e ₁ = 0.15 mm (± 10%);
• average outer diameter of layer 5 = 6.00 mm (± 10%); and
• average screen thickness = 0.2mm (± 10%).

In this exemplary embodiment, the cable 10 comprises a second semi-conducting layer which is in direct contact with the electrically insulating layer and the inside diameter d1 of the electrically insulating layer is therefore equal to the outside diameter of the second semi-conducting layer 3 .

• caractéristique 1 : une résistance à des températures allant de -55°C à 250°C ;
• caractéristique 2 : une résistance à un champ électrique E de 10 kV_crête/mm, lorsque ce champ électrique est appliqué de façon continue pour une durée pouvant aller jusqu'à 90000 heures (h);
• caractéristique 3: une rigidité diélectrique selon la norme ASTM D149 supérieure à 60 kV/mm ;
• caractéristique 4 : un facteur de pertes diélectriques selon la norme ASTM D150 de 3×10^-4 et ce, pour une fréquence comprise entre 100 Hz et 100 kHz et à une température de 0 à 200°C ;
• caractéristique 5 : une permittivité diélectrique selon la norme ASTM D150 de 2,0, et ce, pour une fréquence comprise entre 100 Hz et 100 kHz et à une température de 0 à 200°C ;
• caractéristique 6 : un coefficient d'expansion linéaire thermique selon la norme ASTM D696 de 12 K^-1 à 23°C ;
• caractéristique 7 : un indice limite d'oxygène (ILO) selon la norme ASTM D2863 de 90;

The insulating layer 4 of the cable 10 has the following characteristics:

• characteristic 1: resistance to temperatures ranging from -55°C to 250°C;
• characteristic 2: resistance to an electric field E of 10 kV _peak /mm, when this electric field is applied continuously for a duration up to 90000 hours (h);
• characteristic 3: a dielectric strength according to standard ASTM D149 greater than 60 kV/mm;
• characteristic 4: a dielectric loss factor according to the ASTM D150 standard of 3×10 ^-4 and this, for a frequency between 100 Hz and 100 kHz and at a temperature of 0 to 200°C;
• characteristic 5: a dielectric permittivity according to the ASTM D150 standard of 2.0, and this, for a frequency comprised between 100 Hz and 100 kHz and at a temperature of 0 to 200° C.;
• characteristic 6: a thermal linear expansion coefficient according to the ASTM D696 standard of 12 K ^-1 at 23° C.;
• characteristic 7: a limiting oxygen index (LOI) according to the ASTM D2863 standard of 90;

This cable is designed for an operating voltage of 10kV _peak .

Comparative Examples 2 to 6

Cable 10 of example 1 will be compared with cables 2 to 6 in which the three-layer insulation system is replaced by the insulation indicated in table 1, the electrically conductive element being identical to that of cable 10. <u>Table 1</u> No. Insulation Polymer Thickness (mm) Diameter (mm) 2 CI, banded superimposed PTFE 0.42 3.0 3 CI, banded edge to edge PTFE 0.42 3.0 4 CI, extruded AFP 0.42 3.0 5 CI1, extruded AFP 0.15 2.45 CI2, extruded AFP 1.62 5.70 6 CSC1, banded AFP ⁽¹⁾ 0.12 2.39 CI, banded AFP 0.40 3.19 CSC2, banded AFP ⁽¹⁾ 0.12 3.43 (1) Includes electrically conductive loads

$$\mathit{ei}\ge 0,15+0,15$$

The thickness ei of the electrically insulating layer 4 indeed satisfies the following two relationships applied to the values of the example: $$\begin{array}{c}\frac{2,45}{2}\left[\mathrm{<figure-callout\; id="10"\; label="exp"\; filenames="imgf0001.png"\; state="\{\{state\}\}">exp</figure-callout>}\left(\frac{10}{10\times \frac{2,45}{2}}\right)-1\right]\le \mathit{yes}\le \frac{2,45}{2}\left[\mathrm{<figure-callout\; id="3"\; label="exp"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">exp</figure-callout>}\left(\frac{3\times 10}{10\times \frac{2,45}{2}}\right)-1\right]\\ =>1,55\mathrm{mm}\le \mathit{yes}\le 13,00\mathrm{mm}\hfill \end{array}$$

$$\mathit{yes}\ge 0,15+0,15$$

The cables of examples 1 to 6 are then subjected to a partial discharge test according to standard EN 3475-307 Method B. During this test the voltage is increased in steps of 50V until the appearance of discharges and the partial discharge onset voltage (known as “Partial Discharge Inception Voltage” or PDIV). Then the voltage is reduced until partial discharges disappear and the partial discharge extinction voltage (known as “Partial Discharge Extinction Voltage” or PDEV) is noted.

For this, 10 samples were prepared for each cable example 1 to 6 and the experiment was carried out 10 times on each of these cables. The results are shown in Tables 2 and 3 and are illustrated respectively on the figure 4 and 5 : <u>Table 2</u> IVDP U avg. (V) U min. (V) Umax. (V) Std Dev (V) CV (%) 1 10000 10000 10000 0 0 2 1680 1526 1830 66 3.9 3 1687 1485 1901 96 5.7 4 1778 1622 1919 72 4.1 5 4221 3437 4670 267 6.3 6 3659 3295 3943 141 3.9 PDEV U avg. (V) U min. (V) Umax. (V) Std Dev (V) CV (%) 1 10000 10000 10000 0 0 2 1551 1410 1707 67 4.3 3 1584 1372 1779 95 6.0 4 1631 1427 1877 67 4.1 5 4021 3305 4369 233 5.8 6 3267 3007 3559 99 3.0

• une couche électriquement isolante extrudée augmente la tension à laquelle les décharges partielles apparaissent (comparaison de l'exemple 4 avec les exemples 2 et 3) ;
• augmenter l'épaisseur de l'isolation augmente la tension à laquelle les décharges partielles apparaissent (comparaison de l'exemple 5 avec l'exemple 4) ; et
• une isolation tricouche extrudée augmente encore la tension à laquelle les décharges partielles apparaissent (comparaison de l'exemple 1 avec l'exemple 6).

These results show that:

• an extruded electrically insulating layer increases the voltage at which partial discharges appear (comparison of example 4 with examples 2 and 3);
• increasing the thickness of the insulation increases the voltage at which partial discharges appear (comparison of example 5 with example 4); and
• an extruded three-layer insulation further increases the voltage at which partial discharges appear (comparison of example 1 with example 6).

The cable 10 according to the invention makes it possible to increase the voltage to a value of at least 10 kV without partial discharges appearing.

Claims (14)

Insulated electrically conductive element limiting the appearance of partial discharges, characterized in that it comprises an elongated electrically conductive element surrounded by an insulation system comprising at least one electrically insulating layer surrounding the elongated electrically conductive element and at least one first semiconductor layer surrounding said electrically insulating layer, said electrically conducting insulated element being characterized in that the electrically insulating layer has a thickness e _i , the value of said thickness e _i being determined as a function of the operating voltage U of the insulated electrically conductive element and an internal diameter d1 of the electrically insulating layer. Element according to Claim 1, characterized in that the thickness e _i of the insulating layer is determined as a function of a ratio between the operating voltage U and the diameter d1. Element according to Claim 1 or 2 , characterized in that the first semiconductor layer has a thickness e ₁ and in that the value of the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \mathrm{and}1$$

Element according to any one of the preceding claims, characterized in that the minimum value of the thickness e _i is determined according to a following ratio R1: $$R1=\frac{U}{E_{\mathit{max}}\times \frac{d_1}{2}}$$

U being expressed in kilovolts (kV), E _max being the maximum value of the electric field that can be applied to the insulation layer and being expressed in kilovolts/mm, and the diameter d1 being expressed in millimeters (mm). Element according to any one of the preceding claims, characterized in that the minimum value of the thickness e _i is determined according to a following expression E1: $$E1=\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{d_1}{2}}\right)-1$$

Element according to any one of the preceding claims, characterized in that the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \frac{d_1}{2}\left[\exp \left(\frac{U}{E_{\mathit{max}}\times \frac{d_1}{2}}\right)-1\right]$$

Element according to any one of the preceding claims, characterized in that the maximum value of the thickness e _i is determined as a function of a following ratio R2: $$R2=\frac{3\times U}{E_{\mathit{max}}\times \frac{d_1}{2}}$$

Element according to any one of the preceding claims, characterized in that the maximum value of the thickness e _i is determined according to a following expression E2: $$E2=\exp \left(\frac{3\times U}{E_{\mathit{max}}\times \frac{d_1}{2}}\right)-1$$

Element according to any one of the preceding claims, characterized in that the thickness e _i satisfies the following relationship: $$\mathit{yes}\ge \frac{d_1}{2}\left[\exp \left(\frac{3\times U}{E_{\mathit{max}}\times \frac{d_1}{2}}\right)-1\right]$$

Element according to any one of the preceding claims, characterized in that it further comprises a third layer, said third layer being a second semiconductor layer surrounding the elongated electrically conductive element and being placed between the elongated electrically conductive element and the electrically insulating layer. Element according to any one of the preceding claims, characterized in that the electrically insulating layer, the first semiconductor layer and/or the second semiconductor layer comprises at least one fluorinated polymer. Element according to any one of the preceding claims, characterized in that the electrically insulating layer, the first semi-conducting layer and the second semi-conducting layer comprise at least one fluorinated polymer. Element according to any one of Claims 10 to 12, characterized in that the fluorinated polymer can be chosen from polytetrafluoroethylene (PTFE); copolymers of fluorinated ethylene and propylene (FEP) such as for example poly(tetrafluoroethylene-co-hexafluoropropylene); perfluoroalkoxy (PFA) copolymers such as for example perfluoro(alkylvinylether)/tetrafluoroethylene copolymers; perfluoro methoxy (MFA) copolymers; and poly(ethylene-co-tetrafluoroethylene) (ETFE); or a mixture thereof. Electrically conductive cable, characterized in that it comprises at least one insulated electrically conductive element according to any one of Claims 1 to 13.

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