ELECTRICAL CABLE AND MANUFACTURING THEREOF

Abstract

Low-loss lightweight high-power kilohertz alternating-current high-voltage electrical cables 1 usable in low pressure having a bundle 2 of metallic wires 3 being separated from each other by non-conductor layers 4 provided on the individual metallic wires, wherein the metallic wires 3 alternate between outer positions 5 and inner positions 6 in the bundle along a longitudinal extension 7 of the electrical cable in order to counteract skin effect in the electrical cable bundle 2, as well as enabling counteraction of proximity effect, when in use, an inner semi-conductive layer 8 of broad range temperature rated polymeric material surrounding said bundle 2 of metallic wires 3, and an insulating layer 9 of broad range temperature rated polymeric material surrounding and bonded to the inner semi-conductive layer 5, at least one of the metallic wires 3 being in electric contact with the inner semi-conductive layer 8 as well as a manufacturing method.

Claims

1. A single-phase lightweight high-power kilohertz alternating-current high-voltage electrical cable, comprising: a bundle of metallic wires; the metallic wires being separated from each other by non-conductor layers provided on at least a majority of the individual metallic wires; the metallic wires being woven in a configuration such that each of the metallic wires alternates between outer positions and inner positions in the bundle along a longitudinal extension of the electrical cable in order to counteract skin effect in the bundle of metallic wires, when in use; an inner semi-conductive layer of broad range temperature rated polymeric material surrounding the bundle of metallic wires; an insulating layer of broad range temperature rated polymeric material surrounding and bonded to the inner semi-conductive layer; at least one of the metallic wires being in electric contact with the inner semi-conductive layer.

2. The electrical cable of claim 1, wherein the configuration is such that each of the metallic wires alternates between lateral positions on opposed sides of the bundle along the longitudinal extension of the electrical cable to enable counteraction of proximity effect.

3. The electrical cable of claim 2, comprising wherein the configuration is such that each of the metallic wires alternates between the lateral positions on opposed sides of a center of the bundle, so as to form a diametrically even distribution of the metallic wires relative to the center of the bundle.

4. The electrical cable of claim 1, wherein: the bundle is made up of multiple groups of the metallic wires; the metallic wires of each group are mutually twisted; and the groups are mutually twisted.

5. The electrical cable of claim 4, wherein at least one of the metallic wires of each of at least two groups is in electric contact with the inner semi-conductive layer.

6. The electrical cable of claim 1, wherein the electric contact between at least one of the metallic wires and the inner semi-conductive layer is provided by the non-conductor layer being electrically insulating and exhibiting openings in the non-conductor layer at a physical interface between an inner surface of the inner semi-conductive layer and metallic wires of the bundle.

7. The electrical cable of claim 1, wherein the electric contact between at least one of the metallic wires and the inner semi-conductive layer is provided by the non-conductor layer exhibiting semi-conductive properties at a physical interface between an inner surface of the inner semi-conductive layer and metallic wires of the bundle.

8. The electrical cable of claim 1, wherein the broad range temperature rated polymeric material of the insulating layer is selected from among fluoropolymer, PAEK-family materials, and silicone.

9. The electrical cable of claim 1, wherein the broad range temperature rated polymeric material of the inner semi-conductive layer is selected from among semi-conductivity-prepared fluoropolymer, PAEK-family materials, and silicone.

10. The electrical cable of claim 1, wherein the insulating layer is surrounded by and bonded to an outer semi-conductive layer of broad range temperature rated polymeric material.

11. The electrical cable of claim 10, wherein the outer semi-conductive layer contains broad range temperature rated polymeric material selected from among fluoropolymer, PAEK-family materials, and silicone.

12. The electrical cable of claim 1, wherein each of the metallic wires is made of copper or aluminum alloy; and wherein each of the non-conductor layers is made of an insulating material having an additive of non-insulating material.

13. The electrical cable of claim 1, wherein each of the metallic wires is made of aluminum alloy; and wherein each of the non-conductor layers is made of aluminum oxide.

14. The electrical cable of claim 1, wherein each of the metallic is made up of multiple metallic strands.

15. The electrical cable of claim 14, wherein each of the multiple metallic strands is made of copper, or copper alloy, and is plated with a material selected from among tin, silver, and nickel.

16. The electrical cable of claim 1, comprising: a central non-conductive core inside the bundle of metallic wires.

17. At least a first electrical cable and a second electrical cable, each according to claim 1, and provided within a common protective jacket, constituting a multi-phase electrical cable.

18. The first and the second electrical cables of claim 17, wherein the metallic wires of each of the first and the second electrical cables alternating between lateral positions on opposed sides of the respective bundle, to counteract proximity effect in each one of the first and the second electrical cables, when in use.

19. The electrical cable of claim 1, wherein, when in use, each metallic wire has a diameter less than a factor times a skin depth for the alternating current; wherein the factor is selected as K/(N{circumflex over ()}0.25); wherein 2<K<3; and wherein N is the total number of metallic wires in the bundle.

20. A method for manufacturing an electrical cable according to claim 1, the method comprising: selecting a wire material for the metallic wires; selecting an operational frequency of alternating current to be conveyed by the electrical cable; based on the selected material and the selected operational frequency, selecting a nominal maximum diameter of the metallic wires, when in use, being less than a factor times a skin depth for the alternating current in the metallic wires at the operational frequency for the wire material, the factor being selected as K/(N{circumflex over ()}0.25), wherein 2<K<3 and N is the total number of metallic wires in the bundle; and preparing the electrical cable.

21. The electrical cable of claim 1, wherein the electric contact between at least one metallic wire and the inner semi-conductive layer is provided in operation by a majority of the non-conductor layers being made of electrically insulating material and exhibiting thicknesses small enough to render larger a first capacitance collectively formed between the majority of the metallic wires and the inner semi-conductive layer than a second capacitance formed between the inner semi-conductive layer and an outside of the insulating layer of the electrical cable.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] FIG. 1 shows a perspective view of a single-phase cable according to the invention, which has a bundle of mutually insulated metallic (conductive) wires grouped five by five around a non-conductive (insulator) core and a semi-conductive layer, an insulating layer, and another semi-conductive layer surrounding the bundle. There is also an indication of a longitudinal direction of the cable.

[0036] FIGS. 2a and 2b, respectively, are explanatory of the twisting of the metallic wires (an individual one being identified by a letter) and show cross-sectional views of the single-phase cable according to the invention, at separated locations along the longitudinal direction, with the layers surrounding the metallic wires having fixed rotational positions between FIGS. 2a and 2b (that is, only the wires have moved/rotated when comparing the views of FIGS. 2a and 2b). Rotations are visualized of the groups of metallic wires as well as of the metallic wires within each group.

[0037] FIG. 3a shows again the cross-sectional view of FIG. 2a, but with an indication of how each group (only shown explicitly for group A-B-C-D-E in FIG. 2a) of five metallic wires each having a non-conductor coating and being made up of five separate strands. For simplicity, all five metallic wires of group A-B-C-D-E are shown as having identical non-conductor coatings although this will not be the case in all variants of the invention.

[0038] FIGS. 3b-3d show some variants for a single wire of group A-B-C-D-E of FIG. 3a including metal-plated (plating generally being too thin to be visible in cross-sectional drawings) metallic strands without (FIG. 3b), partially with (FIG. 3c) and wholly with (FIG. 3d, corresponding to what is indicated in FIG. 3a) the non-conductor coating.

[0039] FIG. 4 shows a cross-sectional view of a multi-phase electrical cable according to the invention, in which two single-phase electrical cables according the invention are combined within a common insulating protective jacket.

[0040] FIG. 5 shows in the group A-B-C-D-E a diameter of a single metallic wire and an indication of a skin depth of electric current in a single wire when the electric cable is in use.

[0041] FIG. 6 shows a perspective view of a short section of the single-phase electric cable according to the invention marked with an identifier of electric properties of the cable.

[0042] FIG. 7 shows a flow chart for the manufacturing of a cable according to the invention.

[0043] FIG. 8 shows a perspective view of a single-phase cable, which is according to the invention but different to that of FIG. 1 in that it lacks a non-conductive cable core.

DETAILED DESCRIPTION OF INVENTION

[0044] With reference to FIGS. 1, 2a, 2b, and 3a, the invention, that is, a single-phase lightweight high-power kilohertz alternating current electrical cable 1 suitable for high voltage and high (as well as low) temperature applications and normal and low-pressure environments includes a bundle 2 of metallic wires 3. These metallic wires 3 are separated from each other by non-conductor layers 4 (FIG. 3c and FIG. 3d) provided on or around at least a majority of the individual metallic wires, which are woven in a configuration such that each of the metallic wires 3 alternates between outer positions 5 and inner positions 6 in the bundle along a longitudinal extension 7 of the electrical cable 1 in order to counteract skin effect in the bundle 2, when in use. Rotation of wires around the cable center will counteract proximity effect, when in use in combination with at least one more cable (conductor) to form an electrical circuit.

[0045] Further, an inner semi-conductive layer 8 of broad range temperature rated polymeric material surrounds said bundle 2 of metallic wires 3. When possible, it is preferred to use the same type of insulating (or non-conductor or semi-conductive) material throughout all relevant layers of the cable 1 and along essentially the full length thereof (note that layers may exhibit openings or may be partially removed as explained herein). There is also an insulating layer 9 of broad range temperature rated polymeric material surrounding and bonded to the inner semi-conductive layer 8. The insulating layer 9 is surrounded by an outer semi-conductive layer 19, also made of broad range temperature rated polymeric material and bonded to the insulation. When referring to a broad range temperature rated polymeric material in this description, it should be understood to preferably include fluoropolymers (fluorinated-polymers or -copolymers: including but not limited to: PTFE, FEP, PFA, and ETFE), also Polyaryle-Ether-Ketones (PAEK) family materials (including, but not limited to PEEK), and/or also silicone materials (including also fluoro-silicones). Further, a semi-conductive property of the broad range temperature rated polymeric material is preferably created by addition of a non-insulating material. The non-insulating material is favorably selected as carbon-based particles, including but not limited to: carbon black, carbon nanotubes, and graphene.

[0046] The bundle 2 of the electrical cable 1 is made up of multiple groups, wherein the metallic wires 3 of one of the groups are indicated by 15. The metallic wires 3 of each group 15 are mutually twisted, which is a way of counteracting skin effect in the cable 1. Further, each individual group 15 is mutually twisted around the cable core 21 along the extension 7 of the cable 1, which is a way of counteracting proximity effect. As the skilled person would appreciate, exactly how this should be done will depend on the other conductor(s)/cable(s) (both design and excitation), such as a return cable (refer to cable 22 in FIG. 4), with which the cable 1 forms an electric circuit. On average along the extension 7 of the cable 1, all the metallic wires 3 must be at an essentially equal distance from the other conductor(s)/cable(s).

[0047] As part of the elimination of partial discharges in the cable 1, at least one of the metallic wires 3, preferably at least one wire of every group 15 of wires should be in electric contact with the inner semi-conductive layer 8. Seen from an individual wire 3, this contact will be intermittent along the extension 7 of the cable 1, since the wire 3 is twisted together with the other wires. However, this will be enough for bringing the semi-conductive layer 8 to essentially the same electric potential as a periphery of the bundle 2.

[0048] Specifically, the metallic wires 3 are woven in a configuration such that each of the metallic wires 3 alternates between lateral positions 11 on opposed sides 12, 13 of the bundle 2 along the longitudinal extension 7 of the electrical cable 1. The configuration is such that each of the metallic wires 3 alternates between the lateral positions 11 on opposed sides 12, 13 of a center 14 of the bundle 2, so as to form a diametrically even distribution of the metallic wires 3 relative to the center 14 of the bundle 2. FIGS. 2a and 2b indicate how, for instance, a group of wires marked A-B-C-D-E at one longitudinal position along the cable 1 (FIG. 2a) has reached a different rotational position (about 72 degrees clockwise) as a group at a different longitudinal position along the cable 1 (FIG. 2b). As can be seen, the group of wires marked A-B-C-D-E has also rotated around its own center between these longitudinal positions (about 216 degrees clockwise). It is highly preferable that a rotational pitch of the one of these two rotations should not be an even multiple of a rotational pitch of the other, since it is important to avoid systematically upsetting the respective average distributions between inner/outer positions (relating to skin effect) and opposed lateral positions (relating to proximity effect). The depicted electrical cable 1 has a central non-conductive core 21 inside said bundle of metallic wires 3, which may be preferable to achieve an efficient and lightweight design. As mentioned above the non-conductive core 21 could provide a path in it (not shown explicitly) for a cooling agent to pass through it to enhance dissipation of heat caused by resistive losses.

[0049] FIG. 4 shows the cable 1 in combination with another, identical cable 22, within a common protective jacket 23, constituting a multi-phase electrical cable 24. Combining cables 1 and second cable 22 into a multi-phase cable 24 will generally give better control over twisting or weaving for optimal performance in relation to counteracting proximity effect. For such a multi-phase electric cable 24, counteraction of proximity effect, caused by a different conductor in a proximity of the multi-phase electrical cable 24, could potentially be improved by mutual twisting of both (or all) of the combined single-phase cables 1, 22 along a central axis of the common protective jacket 23 to suppress losses due to proximity effect caused externally. To further explain this: if one of the single-phase cables 1, 22 is always closer to, for instance, a metallic wall along the multi-phase electrical cable's extension and both (or all) single-phase electric cables 1, 22 are completely straight, this phase will have higher losses. Twisting of both (or all) single-phase electric cables 1, 22 along the central axis of the multi-phase electrical cable 24 would instead equalize (distribute equally) the losses to both (or all) single-phase electrical cables 1, 22.

[0050] With reference to FIGS. 3b and 3a, one way of establishing electric contact at electric contact point 10 between at least one of the metallic wires 3 and the inner semi-conductive layer 8 would be by omitting the non-conductor layer 4 on one electric wire in each group and thus achieve electric contacts at respective physical interfaces 17 between an inner surface 18 (of FIG. 3a) of said inner semi-conductive layer 8 and metallic wires 3 of said bundle 2. Note that the wire of each groups making this contact will most preferably be insulated in relation to the other wires of that group and in relation to wires of neighboring groups of wires.

[0051] With reference to FIGS. 3c and 3a, one way of establishing electric contact at electric contact point 10 between at least one of the metallic wires 3 and the inner semi-conductive layer 8 would be by letting the non-conductor layer 4 be electrically insulating and exhibit openings 16 in the non-conductor layer at respective physical interfaces 17 between an inner surface 18 of said inner semi-conductive layer 8 and metallic wires 3 of said bundle 2. In manufacturing of the cable 1, such openings 16 could be made by removing non-conductor material once the twisting or weaving of the wires 3 is completed, for instance, through grinding, etching, or melting.

[0052] With reference to FIGS. 3d and 3a, one way of establishing electric contact at electric contact point 10 between at least one of the metallic wires 3 and the inner semi-conductive layer 8 would be by letting the non-conductor layer 4 exhibit semi-conductive properties at a physical interface 17 between said inner surface 18 of said inner semi-conductive layer 8 and metallic wires 3 of said bundle 2. For practical purposes, the whole layer 4 would preferably be of the same material.

[0053] This means that the material must be insulating enough between the wires and conductive enough to reduce a difference in the electric potential between the wires and the inner semi-conductive layer.

[0054] In FIGS. 3b-3d, as a preferred example, each wire 3 is made of copper (or copper alloy) strands 20 with tin plating 28. Alternatively, each copper strand could have an individual silver or nickel plating (not shown). Another possible wire material is aluminum alloy, in which case the non-conductor layer 4 could be prepared as aluminum oxide either by oxidization in air or further treatment. In both cases, the non-conductor layer 4 could be made of an insulating material, such as a resin. In case semi-conduction is desirable the insulating material could contain an additive of non-insulating (that is, more or less conducting) material.

[0055] FIG. 5 shows wires 3 of a group 15 of wires. Marked in one of the wires 3 are diameter 25 and skin depth 26 when the electric cable is in use. The metallic wires have a diameter (25) less than a factor times a skin depth (26) for the alternating current. This factor F is selected as F=K/(N{circumflex over ()}0.25), wherein 2<K<3 and N is the total number of metallic wires 3 in the bundle 2. The denotation used to express the factor means K divided by the divisor N raised to the power of 0.25. Skin effect in a multi-wire conductor (N>1) will cause extra losses of up to about 10% to that of operating at zero frequency (DC), where skin and proximity effects are absent, if K is equal to 2.0, which is generally preferable in an optimized cable according to the invention. K being equal to 3.0 will give losses of up to about 50% but at the same time will require fewer total strands for a given cross section.

[0056] These are illustrating examples in the case of K=2:1 metallic wire in the bundle gives wire diameter=2skin depth; 16 metallic wires in the bundle gives wire diameter=1skin depth; 256 metallic wires in the bundle gives wire diameter=0.5skin depth. The two latter examples are within the scope of the invention, while the first example is not.

[0057] With reference to FIG. 6, showing a segment of the cable, and FIG. 7 showing a flow chart, the invention also includes a method of manufacturing of the inventive electrical cable discussed above, comprising the following steps: selecting 101 a wire material for the conductive wires; selecting 102 an operational frequency of alternating current to be conveyed by said electrical cable; based on the selected material and the selected operational frequency, selecting 103 a nominal maximum diameter of said conductive wires being less than the skin depth related factor F times the skin depth for the alternating current in the conductive wires at the operational frequency for the wire material; preparing 104 said electrical cable; optionally, applying 105 an identifier 27 to the electrical cable being an indicator, externally of said electrical cable, of said operational frequency. The removal of a non-conductor layer 4 (reference is made to FIG. 3c and related description) is another potentially essential method step in the method of manufacturing of the inventive cable. A way of twisting or weaving the electric wires is inherently part of the method.

[0058] For ease of explicability and depictability, cables of only 25 (55) metallic wires are shown in the drawings. However, a preferable order of magnitude for the number of metallic wires is 100 to 1000, in view of the technical applications discussed herein.

[0059] Inequalities expressed herein by the sign < should be understood to include is less than or equal to.

[0060] It is currently anticipated that an inventive cable of the type disclosed herein could have a total cross-sectional conductor area of up to about 150 square millimeters when operated at up to 5 kHz due to practical limitations during manufacturing in handling thousands of metallic wires simultaneously.

[0061] In foreseen uses of the inventive electrical cable, such as in a variable frequency drive for an electric motor for propelling an aircraft or similar, it is anticipated that electrical properties relating to skin and/or proximity effects the electrical cable 1 should be optimized for conveying AC power within a frequency band defined as from 0.4 kHz and/or up to its (highest) operational frequency of 5 kHz. It is believed that a so optimized electrical cable design, and any use thereof, would even further distinguish from the prior art the present invention as defined in any of the appended claims directed towards electrical cable(s).

[0062] Referring to FIG. 8, it should be noted that the central non-conductive cable core 21 is by no means regarded as a necessity in the inventive cables disclosed herein. It may even be the case that the cable core 21 should be omitted to attain the most advantageous embodiments of the invention. This means that the bundle 2 och metallic wires 3 could be disposed essentially as shown in FIG. 1, but without a central non-conductive cable core 21. However, after twisting or weaving of the bundle 2, it is then anticipated that any process of making the bundle 2 more compact (which is common practice) would result in an electrical cable 1 of somewhat different cross-sectional layout of the metallic wires 3 compared to an electrical cable 1 having the central non-conductive cable core 21, although their electrical properties relating to skin and/or proximity effects could be rather similar. Also, it is seen as fully possible for multiple similar non-conductive cores (intermixed among the wires), although not all in a central cable location, to form part of the inventive electrical cable 1.

[0063] List of parts electrical cable 1; [0064] bundle 2;

[0065] metallic wires 3;

[0066] non-conductor layers 4;

[0067] outer positions 5 (of metallic wires 3 in bundle 2);

[0068] inner positions 6 (of metallic wires 3 in bundle 2);

[0069] longitudinal extension 7 (of electrical cable 1);

[0070] inner semi-conductive layer 8;

[0071] insulating layer 9;

[0072] electric contact point 10 (between metallic wire 3 and inner semi-conductive layer 8);

[0073] lateral positions 11 (of metallic wire 3) opposed sides 12, 13 (of cross section 2);

[0074] center 14 (of bundle 2);

[0075] group 15 (of metallic wires 3);

[0076] openings 16 (in non-conductor layers 4) physical interface 17 (between inner surface 18 of inner semi-conductive layer 8 and metallic wires 3) outer semi-conductive layer 19; [0077] metallic strands 20 (forming metallic wires 3); [0078] central non-conductive core 21 (inside bundle of metallic wires 3); second electrical cable 22 common protective jacket 23 (of first and second electrical cables); multi-phase electrical cable 24; [0079] metallic wire diameter 25; [0080] skin depth 26 (of alternating current); [0081] external identifier 27 (of electrical cable indicating operational frequency) tin plating 28.