Electrical cable for the aerospace field

Abstract

An insulated electrically conductive element (1) for the aerospace field has an elongate electrically conductive element surrounded by at least two layers, said two layers being an electrically insulating layer (4) surrounding the elongate electrically conductive element (2) and a first semiconductor layer (5) surrounding said electrically insulating layer (4), at least one of the layers having at least one fluoropolymer.

Claims

1. An insulated electrically conductive element for the aerospace field, comprising: an elongate electrically conductive element surrounded by at least two layers, said two layers being an electrically insulating layer surrounding the elongate electrically conductive element; and a first semiconductor layer surrounding said electrically insulating layer, at least one of said two layers comprising at least one fluoropolymer.

2. The element according to claim 1, wherein the two layers comprise at least one fluoropolymer.

3. The element according to claim 1, wherein said element further comprises a third layer, said third layer being a second semiconductor layer surrounding the elongate electrically conductive element and being surrounded by the insulating layer.

4. The element according to claim 1, wherein each of the three layers comprises at least one fluoropolymer, preferably the same fluoropolymer.

5. The element according to claim 1, wherein the fluoropolymer is chosen from polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) copolymers, perfluoroalkoxy alkane (PFA) copolymers, perfluoromethoxy alkane (MFA) copolymers, ethylene tetrafluoroethylene (ETFE), and one of the mixtures thereof.

6. The element according to claim 1, wherein the fluoropolymer is chosen from perfluoroalkoxy alkane (PFA) copolymers.

7. The element according to claim 3, wherein each of the three layers comprises at least one perfluoroalkoxy alkane (PFA) copolymer.

8. The element according to claim 1, wherein said element withstands temperatures ranging from −70° C. to 250° C.

9. The element according to claim 1, wherein said element withstands an electric field E ranging from 1 kV/mm to 30 kV/mm.

10. The element according to claim 1, wherein the insulating layer has a thickness e.sub.i, the value of said thickness e.sub.i being determined according to the operating voltage U of the insulated electrically conductive element and an inner diameter d.sub.1 of the electrically insulating layer.

11. The element according to claim 1, wherein the value of the thickness e.sub.i satisfies the following relationship:
ei≥e.sub.1

12. The element according to claim 1, wherein the value of the thickness e.sub.i satisfies the following relationship:
ei≥e.sub.1+e.sub.2

13. The element according to claim 1, wherein the minimum value of the thickness e.sub.i expressed in millimetres (mm) is determined according to a following relationship R1: $R1=\frac{U}{E_{\max }\times \frac{d_1}{2}}$

14. The element according to claim 1, wherein the maximum value of the thickness e.sub.i is determined according to a following relationship R2: $R2=\frac{3\times U}{E_{\max }\times \frac{d_1}{2}}$

15. An electrically conductive cable, said electrically conductive cable comprising: at least one insulated electrically conductive element according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The attached drawings illustrate the invention:

[0096] FIG. 1 shows a cross section of an insulated electrically conductive element according to one embodiment of the invention;

[0097] FIG. 2 shows a cross section of an electrically conductive cable according to a first embodiment of the invention;

[0098] FIG. 3 shows a cross section of an electrically conductive cable according to a second embodiment of the invention;

[0099] FIG. 4 is a graph showing the partial discharge inception voltage for various types of cables; and

[0100] FIG. 5 is a graph showing the partial discharge extinction voltage for various types of cables.

DESCRIPTION OF ONE OR MORE EMBODIMENTS

[0101] For reasons of clarity, only those elements that are essential to the understanding of the embodiments described below have been presented diagrammatically, without regard to scale.

[0102] As illustrated in FIG. 1, an insulated electrically conductive element 1 according to one embodiment of the invention comprises an elongate electrically conductive element 2, a second semiconductor layer (CSC) 3 surrounding the elongate electrically conductive element 2, an electrically insulating layer (CI) 4 surrounding the second semiconductor layer 3 and a first semiconductor layer (CSC) 5 surrounding said electrically insulating layer.

[0103] The second semiconductor layer 3 has a thickness e.sub.2 and the first semiconductor layer 5 has a thickness e.sub.1. The electrically insulating layer 4 has a thickness e.sub.i determined according to one embodiment of the invention which is greater than the sum: e.sub.1+e.sub.2.

[0104] In this embodiment, the second semiconductor layer 3, the electrically insulating layer 4 and the first semiconductor layer 5 constitute a trilayer 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 5 is in direct physical contact with the electrically insulating layer 4.

[0105] The elongate electrically conductive element 2 is formed by 37 strands made of copper covered with a layer of nickel and thus has a diameter of 12 AWG (American Wire Gauge).

[0106] The first and the second semiconductor layers 5 and 3 and the insulating layer 4 are formed by PFA.

[0107] FIG. 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 shield 16 of “braided” type made of nickel-plated copper. The metal shield 16 is surrounded by a protective sheath 17 which is the outermost layer of the cable 10 and which is based on PFA.

[0108] FIG. 3 shows 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 in the thickness of the semiconductor layers and the insulating layer.

[0109] The assembly formed by the three insulated electrically conductive elements 1, 1′ and 1″ is surrounded by a metal shield 16 of braided type. The metal shield 16 is surrounded by a protective sheath 17 which is the outermost layer of the cable 10 and is based on PFA. The electrically conductive cable 20 also comprises spaces 25 which comprise air.

EXEMPLARY EMBODIMENTS

Example 1

[0110] The electrically conductive cable 10 according to the first embodiment and without the protective sheath 17 of the invention is prepared by co-extrusion of the trilayer insulation system around the elongate electrically conductive element 2, the trilayer insulation system being formed by the first semiconductor layer 5, the electrically insulating layer 4 and the second semiconductor layer 3.

[0111] The metal shield 16 is then placed around the second semiconductor layer.

[0112] The elongate electrical conductor 2 is formed by 37 strands made of copper and covered with a layer of nickel according to the EN 2083 European standard.

[0113] The first semiconductor layer is formed from a polymeric mixture A comprising at least 60% by weight of perfluoroalkoxy alkane (PFA) copolymer in relation to the total weight of the polymeric mixture, sold under the reference S185.1 B by PolyOne.

[0114] The electrically insulating layer is formed from a second polymeric mixture B comprising at least 95% by weight of perfluoroalkoxy alkane (PFA) copolymer in relation to the total weight of the polymeric mixture, sold under the reference AP-210 by DAIKIN.

[0115] The second semiconductor layer is formed from a third polymeric mixture C comprising at least 60% by weight of perfluoroalkoxy alkane (PFA) copolymer in relation to the total weight of the polymeric mixture, sold under the reference S185.1 B by PolyOne.

[0116] The polymeric mixtures A, B and C were each introduced into one of the three extruders for the three-layer co-extrusion and extruded around the elongate 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 adjusted to between 5 and 100 rpm.

[0117] The cable 10 having the dimensions below is then formed: [0118] mean diameter of the conductor=2.15 mm (±10%); [0119] mean thickness e.sub.2=0.15 mm (±10%); [0120] mean outer diameter of the layer 3=2.45 mm (±10%); [0121] mean thickness e.sub.i=1.62 mm (±10%); [0122] mean outer diameter of the layer 4=5.70 mm (±10%); [0123] mean thickness e.sub.1=0.15 mm (±10%); [0124] mean outer diameter of the layer 5=6.00 mm (±10%); and [0125] mean thickness of the shield=0.2 mm (±10%).

[0126] In this exemplary embodiment, the cable 10 comprises a second semiconductor layer 3 which is in direct contact with the electrically insulating layer, and the inner diameter d.sub.1 of the electrically insulating layer is equal to the outer diameter of the second semiconductor layer 3.

[0127] The insulating layer 4 of the cable 10 exhibits the following features: [0128] feature 1: withstands temperatures ranging from −55° C. to 250° C.; [0129] feature 2: withstands an electric field E from 10 kV.sub.peak/mm, when this electric field is applied continuously for a duration that may last up to 90 000 hours (h); [0130] feature 3: a dielectric strength according to the ASTM D149 standard that is higher than 60 kV/mm; [0131] feature 4: a dielectric loss factor according to the ASTM D150 standard of 3×10.sup.−4 for a frequency of between 100 Hz and 100 kHz and at a temperature from 0 to 200° C.; [0132] feature 5: a dielectric permittivity according to the ASTM D150 standard of 2.0 for a frequency of between 100 Hz and 100 kHz and at a temperature from 0 to 200° C.; [0133] feature 6: a coefficient of linear thermal expansion according to the ASTM D696 standard of 12 K.sup.−1 at 23° C.; and [0134] feature 7: a limiting oxygen index (LOI) according to the ASTM D2863 standard of 90.

[0135] This cable is intended for an operating voltage of 10 kV.sub.peak.

Comparative Examples 2 to 6

[0136] The cable 10 of Example 1 will be compared with cables 2 to 6 in which the trilayer insulation system is replaced with the insulation given in Table 1, the electrically conductive element being identical to that of the cable 10.

TABLE-US-00001 TABLE 1 Thickness Diameter No Insulation Polymer (mm) (mm) 2 CI, overlaid ribbon PTFE 0.42 3.0 3 CI, edge-to-edge ribbon PTFE 0.42 3.0 4 CI, extruded PFA 0.42 3.0 5 CI1, extruded PFA 0.15 2.45 CI2, extruded PFA 1.62 5.70 6 CSC1, ribbon PFA.sup.(1) 0.12 2.39 CI, ribbon PFA 0.40 3.19 CSC2, ribbon PFA.sup.(1) 0.12 3.43 .sup.(1) Comprises electrically conductive fillers

[0137] The thickness e.sub.i of the electrically insulating layer 4 does indeed satisfy both of the following relationships applied for the values of the example:

[00010]$\begin{array}{cc}\frac{2,45}{2}\left[\exp \left(\frac{10}{10\times \frac{2,45}{2}}\right)-1\right]\le ei\le \frac{2,15}{2}\left[\exp \left(\frac{3\times 10}{10\times \frac{2,45}{2}}\right)-1\right]\text{=>}1.55\mathrm{mm}\le \mathrm{ei}\le 13.00\mathrm{mm}& \left[\mathrm{Math}.9\right]\\ \mathrm{ei}\ge 0,15+0,15& \left[\mathrm{Math}.10\right]\end{array}$

[0138] The cables of Examples 1 to 6 are then subjected to a partial discharge test according to the EN 3475-307 standard, Method B. In this test, the voltage is increased by steps of 50 V until discharges occur and the partial discharge inception voltage (PDIV) is noted. Next, the voltage is decreased until partial discharges stop occurring and the partial discharge extinction voltage (PDEV) is noted.

[0139] For this, 10 samples were prepared for each exemplary cable 1 to 6 and the experiment was performed 10 times on each of these cables. The results are given in Tables 2 and 3 and are illustrated in FIGS. 4 and 5, respectively:

TABLE-US-00002 TABLE 2 PDIV U mean (V) U min. (V) Umax. (V) Dev Std (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

TABLE-US-00003 TABLE 3 PDEV U mean (V) U min. (V) Umax. (V) Dev Std (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

[0140] These results show that: [0141] an extruded electrically insulating layer increases the voltage at which partial discharges occur (comparison of Example 4 with Examples 2 and 3); [0142] increasing the thickness of the insulation layer increases the voltage at which partial discharges occur (comparison of Example 5 with Example 4); and [0143] an extruded trilayer insulation system further increases the voltage at which partial discharges occur (comparison of Example 1 with Example 6).

[0144] 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 occurring.