Capacitive power transmission cable

Abstract

To provide an improved capacitive power transmission cable using a multiple-of-six layer structure.SOLUTION: A capacitive power transmission cable consists of a plurality of connected lengths of cable. The lengths of cable comprise at least two sets of conductive strands, where the sets of strands are insulated from and in capacitive relationship with each other. The conductive strands are laid at least substantially in a multiple-of-six layer structure, with substantially equal numbers of strands of both sets. Each layer has strands of one set alternating with strands of the other set. To one end, the number of strands of one set is reduced and the number of strands of the other set is increased.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a capacitive power transmission cable. [Background technology]

[0002] U.S. Patent No. 1,825,624 describes and claims: "1. An electric power transmission system comprising: an AC source; a receiving circuit; a transmission circuit for interconnecting said AC source and said receiving circuit; and a distributed capacitance inserted in series with said transmission circuit and having a value sufficient to substantially neutralize an inductive reactance of said transmission circuit to increase the ultimate power of the system."

[0003] The abstract of U.S. Pat. No. 4,204,129 is as follows: "The present invention relates to the transmission of electrical power, and in particular to an electrical power transmission system that provides vector control, reduced voltage drop, and reduced power losses by including a capacitance in the cable in series between the generator and the load by utilizing a conductor, or coupling link, that has a distributed capacitance along the length of the cable. Such capacitance is achieved by splitting the conductor into two portions separated by a dielectric material, such that the two conductor portions are in a capacitive relationship along the length of the cable, connecting one conductor portion to the generator and the other conductor portion to the load, such that the distributed capacitance is in series with the generator and the load."

[0004] In its Abstract, WO 2010 / 026380 states the following with reference to FIG. 1: "The charge transfer zero loss power and signal transmission cable comprises eight conductive layers (18) stacked one on top of the other in a row, each of which can be electrically coupled to form any desired length. Each conductive layer is separated from the other by alternating layers of dielectric material (19). The conductive layers (10-17) are formed into a closed folded loop (20) for charging and a closed folded loop (21) for discharging, and the apexes of the pleats (22) of each of the oppositely oriented closed folded loops form the ends of the cable, and the conductive layers are in capacitive contact with each other by the dielectric material (19), which is a means for transferring charge from the charging loop to the discharging loop, thereby transmitting alternating current from a power source to a transmission point with substantially zero resistance through the two charging and discharging loops, thereby transmitting power from a power source to a transmission point over a given distance with zero power loss."

[0005] It is surprising that such a capacitive cable can transmit data and / or power over long distances with low, if not completely zero, losses, and this has been confirmed in tests carried out by the inventors.

[0006] This cable teaches that looping is essential. The inventors believe that looping is not essential.

[0007] Litz wire and split conductors are known, each consisting of a thin and a thicker strand, usually bound together by twisting, insulated from each other by a so-called "enamel", typically based on a polymer such as that used for magnet wire. They reduce the skin effect, which reduces the conductive capacity of a round, solid conductor with the same amount of conductive material per unit length. In split conductors, the wires are not necessarily insulated from each other, especially when they are arranged in six mutually insulated segments. The usual degree of insulation between the wires in split conductors is "light". 1 . 1http: / / www.electropedia.org / iev / iev.nsf / display?openform&ievref=461-01-15

[0008] Therefore, litz wire and split conductors are not preferred, as the former is suitable for light loads and the split conductors only have light insulation.

[0009] U.S. Patent No. 3,164,669 describes a similar cable in which the strands are semi-hard copper wires for pulling into the tube. Selected strands / wires are enamel coated to reduce the overall skin effect in the cable. The described construction is as follows: "Therefore, for a conductor consisting of 127 strands, the following structure is considered effective. Center line-bare line 6 layers - all enameled wire 12 layers - alternating bare and enameled wires 18 layers - fully enameled wire 24 layers - alternating bare and enameled wires 30 layers - fully enameled wire 36 layers - alternating bare and enameled wires"

[0010] Figure 1 attached hereto is Figure 2 of this US patent. The patent emphasizes that: "Polyurethane enamel has the important advantage that it can be baked at a temperature lower than that for annealing individual wires, and that it decomposes when exposed to temperatures similar to those of molten solder (about 600°C), and the decomposition products have a fluxing effect. For this reason, concentrically stranded enamel conductors can be easily connected, and solder joints can be made with ordinary equipment."

[0011] Apart from the feature that the strands / wires are partly bare and partly enamelled, we refer to layered structures with 6, 12, 18, 24, 30 and 36 wires as "multiple of six" structures, i.e. each layer has a multiple of six strands, with each successive radially outer layer having six more strands.

[0012] A May 15, 2018 article in the Modern Power Systems journal titled “Capacitative transfer promises significant reduction in losses” (available at https: / / www.modernpowersystems.com / features / featurecapacitative-transfer-promises-significant-reduction-in-losses-6150871 / ) states: "Figure 2. Cross-section of a Type III cable. Each individual bundle contains six upstream electrodes (connected to the power source) and six downstream electrodes (connected to the load). Each bundle is made of twisted insulated wires, which are twisted together as a group to form a cable and which is sheathed in accordance with the appropriate international standard." This "Figure 2" is reproduced as FIG. 2 attached hereto. In FIG. 2, the numbering is 1 to 12 for each wire bundle. This document is hereinafter referred to as "6150821 document."

[0013] In our international application PCT / GB2019 / 051593, which is unpublished at the priority date of this application, we described and claimed: "A capacitive power cable having at least two pairs of conductive strands insulated from one another and in a capacitive relationship with one another."

[0014] A paper titled "Capacitive Transfer Cable and Its Performance in Comparison with Conventional Solid Insulated Cable" presented by Dr. Yang Yang and Dr. Darwish at the IEEE conference in Calgary in June 2019 states: "CTS cables have been developed for various models, but the function of series capacitance compensation is the same. The main difference between CTS cables and conventional cables is the dielectric inside the cable. There are two types of dielectric materials used in CTS cables. One is the same insulation material as conventional cables. The other dielectric layer is applied between the strands to compensate the inductive reactance of the main conductor and lower the line impedance. Figure 2 shows the cross section of an enamel-type CTS cable. The gray strand is the input wire, the yellow strand is the output wire, and... The layers other than the conductor are the same as conventional cables." The Figure 2 referred to here is Figure 3 of the accompanying drawings, in which the name annotation has been replaced with the following: Outer sheath: A Metal sheath: B Semiconductive layer:C Insulation: D Semiconductive layer: E Input wire conductor: F Dielectric / enamel layer: G Output wire conductor: H Summary of the Invention [Problem to be solved by the invention]

[0015] It is an object of the present invention to provide an improved capacitive power transmission cable utilizing the multiple of six layer structure described above. [Means for solving the problem]

[0016] According to a first aspect of the present invention, A capacitive power transmission cable comprising at least two pairs of conductive strands insulated from one another and in a capacitive relationship with one another, The conductive strands are arranged in a layer structure of at least substantially a multiple of six, and the number of strands in each set is substantially equal; In each layer, the wires of one set are alternated with the wires of the other set, There is provided a capacitive power transmission cable, wherein the strands of each set have different contrasting colours.

[0017] While it is envisioned that each layer may have a set of bare strands interleaved with one or more further sets of one or more insulated strands, the preferred embodiment has insulation on all of the strands so that each strand is insulated from every other strand, at least away from the ends of the cable, i.e., along the length of the cable. Bare strands, if present, can be identified by this.

[0018] Preferably the insulation on each strand comprises so-called enamel, of the kind typically used for so-called "magnet wire."To facilitate identification of which strands belong to which set for capacitive connection, it is convenient for the strands of each set to be coated with enamel of a different contrasting color.

[0019] The two sets of strands may be wound with different helix angles from one layer to the next, but it is preferred that the helix angle of one layer be equal and opposite to the helix angle of the next layer.

[0020] In particular, where a cable is provided with bare wires, the layers may be insulated from one another by wrapping insulation between successive layers. Typically, interlayer insulation is provided when insulation is provided on all of the wires.

[0021] Typically, there will be an equal number of strands in one set and another set, but it is nevertheless envisaged that a length of cable may be constructed as a series of connected cables with fewer strands in one set and more strands in the other set towards one end, in order to absorb most of the current flowing through one of the capacitively related sets of conductive strands at each end of the length of cable.

[0022] It is also envisaged that one or more other pairs of conductive strands may be included in addition to the two pairs. For example, the four pairs, especially in the outer layers where there are a multiple of four strands, may be connected as two pairs in order to equalize the capacitive plate size in the middle cables of a long cable, and the end cables may be connected with one pair of strands that mainly conducts, with three times as many strands as the other pair, i.e., reducing the capacitance per unit length at the cable end. The strands in a layer may be arranged in the order 1-2-3-4-1-2-3-4... etc. For this purpose, four different colours of enamel may be used to identify the strands. In layers with a number of strands not divisible by four, such as the fifth layer, the strands may be arranged in a slightly uneven number, such as seven strands of two colours and eight strands of the other two colours. This arrangement allows biasing of conductive strands to be provided in layers other than those where the number of strands is strictly divisible by four.

[0023] Typically, the multiple-of-six plies are arranged around a single central strand. This central strand may be made of a reinforcing material such as steel, while the other strands are made of copper or aluminum. However, the central strand is usually made of the same metal as the other strands and is insulated in the same way. The central strand may be connected to the strands of either set.

[0024] In certain layers, the multiple of six construction may result in slight gaps in the wires. This is because, without interlayer insulation, the perimeter of the layers increases with their diameter, but with interlayer insulation, the increase in diameter from one layer to the next is proportional to the wire diameter plus the insulation thickness, but the perimeter is taken up only by the wire diameter. To accommodate this, compensating extra strands may be provided in certain layers beyond their strict multiple of six construction. This is expected to make only a small difference to the capacitance per unit length of the cable.

[0025] According to a second aspect of the present invention, A capacitive power transmission cable comprising at least two pairs of conductive strands insulated from each other and in a capacitive relationship with each other, At each end of the cable, all the wires of one pair are bundled together, At each end of the cable, all the wires of one separate pair are bundled together, There is provided a capacitive power transmission cable, wherein all the wires of said two or more sets remain insulated from each other along the length of the cable and also at each end of the cable.

[0026] Preferably, the bundling electrically connects the respective strands. Conveniently, the bundling is performed by crimping the respective strands together. Crimping makes it easier to attach connectors between or at the ends of the cables when installing the cables in muddy trenches, etc.

[0027] Alternatively, the ends of the cables may be inserted into and clamped by their respective connectors. In an advantageous embodiment, the cable has a set of crimped wires at both ends and a connector at only one end, and the connector can receive and clamp the crimped wire ends of the next cable, at least when, as is usually the case, the cables are provided as multiple cables shorter than the full length cable to be installed, and the crimped ends of that cable can be received and clamped by the connector of the previous cable.

[0028] In a preferred embodiment of the second aspect of the present invention, The conductive strands are arranged in a layer structure of at least a multiple of six, and the number of strands in each set is substantially equal; In each layer, the wires of one set alternate with the wires of the other set.

[0029] In order to facilitate an understanding of the invention, two embodiments and variants thereof will now be described, by way of example, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is FIG. 2 of U.S. Pat. No. 3,164,669. [Diagram 2] Figure 2 is Figure 2 from document 6150821. [Diagram 3] Figure 3 is Figure 2 from the 2019 IEEE paper referenced above. [Figure 4] FIG. 4 shows a view similar to FIG. 1 of a capacitive power transmission cable according to the invention without its outer sheath. [Diagram 5] FIG. 5 is a cutaway cross-sectional view of the center conductor and two inner conductor layers of the cable of FIG. [Figure 6] FIG. 6 is a general end view of the cable of FIG. 3 with the outer sheath. [Figure 7] FIG. 7 is a conductor-only end view of a variation of the cable of FIG. [Figure 8]FIG. 8 is a diagram showing a connection part for connecting a middle cable of the modified cable to a cable at an end part. [Figure 9] FIG. 9 is a similar diagram showing another connector for connecting an intermediate cable to an end cable of the modified cable. [Figure 10] FIG. 10 is a view similar to FIG. 3 showing another cable of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] With reference to the drawings, the capacitive cable 1 comprises six layers 2, 3, 4, 5, 6 and 7 of two pairs of alternating copper strands 8 and 9.

[0032] These layers are arranged around a single inner strand 10 of the same size, e.g., 13AWG-1.82mmOD. This single strand and each subsequent layer are wrapped with soft insulation 11, which is arranged to maintain the relative position of the strands as they are wound and is forced into the gaps between the strands. Typically, this insulation is a semiconductive waterproof tape, typically containing polyester nonwoven, polypropylene superabsorbent powder, semiconductive carbon black, and polyester nonwoven, applied to a thickness of 40-45mm. Such a tape, being semiconductive, aids in electron distribution and thus improves capacitance. However, it is preferable to use fully insulating polyester or PET tape for the interlayer insulation. The cable has a combined capacitance per unit length of 45nF / m.

[0033] Layer 2 has six wires 8 and 9, three in one set and three in the other set. The wires in one set are of conventional color, i.e., red / brown magnetic wire enamel R. The wires in the other set are of black enamel B. This color contrast allows the sets of wires to be easily separated at one end of a cable, with the wires exposed for their respective connections, and the red / brown wires of one set all bundled together for connection to one terminal 12 and the black wires of the other set all bundled together for connection to another terminal 14 of the connector 16.

[0034] Layer 3 has six strands 8 and 9, six in one set and six in the other. As with layer 1, the two sets of strands in layer 3 run parallel to each other and are therefore in good capacitive relationship with each other. The strands in these two layers have opposite helix angles α. While the same type of strands cross over each other regularly, the different types of strands cross over each other equally regularly. Thus, there is an intra-layer capacitance as well as an inter-layer capacitance between the conductor sets. This contributes to the overall capacitance of the strand sets in the cable when connected as above.

[0035] Each successive layer 4 to 7 has six more strands 8 and 9. The number of strands is always an even number, and the two sets of strands are always interdigitated.

[0036] Typically, in addition to the six layers 2-7 above, there is a single central strand 10. The latter may be replaced with steel strands or inert polymer strands. Outside the outer sixth layer, there is typically the usual insulating layer 15, protective layer 15, and outer layer 15 of an underground power cable. For smaller or larger power capacities, there may be one or more fewer or one or more additional conductive strand layers.

[0037] Regarding a modification example, as shown in FIG. 8 below, the cable 1 can be supplied with its two sets of strands bundled at both ends. The enamel can be removed from the tips of the strands, typically by abrasion, and the respective bundles can be crimped together (see 20 in FIG. 7). The cable can be supplied in this form, or a connector having terminals for the crimped ends can be added and supplied. Conveniently, the connector can be provided only at one end, so that in use, each cable can be connected to the next cable and assembled into a longer finished cable.

[0038] For the end cables among several connected cables, the color of the strands may be changed, but in fact, it is also possible to use the coloring described below for the entire cable. To connect, the outer sheath and the interlayer insulator of the cable are trimmed to expose the strands of each color. The exposed strands are bundled by color, their enamel coatings are exposed at the tips, and the bundles are fixed by a crimping fitting 120 made of a conductive metal. As a result, some of the strands are connected as described above, and the other strands are connected in a different way. For example, when the strands are colored in the order of orange O, green G, brown Br, blue Bl, etc., at one end of the cable, the green G strands are connected with the orange O and brown Br strands by the connector 16, the capacitance with the blue Bl strands is reduced, and the current capacity of the orange O and brown Br connecting strands connected to the load can be increased. This connection is shown in FIG. 7. At the opposite end of the cable, the reverse connection is adopted. Therefore, the capacitor plates of the orange O and brown Br strands have a substantially constant plate area per unit length in the middle part of the cable, increase at the connection end to the load, and decrease at the insulated supply end. The green G / blue Bl plates are configured conversely.

[0039] Whereas connector 16 of FIG. 8 has straight feed-through connections 17 on either side from respective terminals 12 and 14 into which respective crimped wire bundles to be connected are inserted, connector 116 of FIG. 8 has four respective terminals 118 for wires of different colors and internal connections 117 to provide the desired grouping of wires to achieve continuity of the end cable.

[0040] Again, this coloring of the strands may be used throughout the thickness of the cable, or at least in layers having strands that are a multiple of 4. If the strands are ordered orange, green, brown, blue, etc., the orange and brown strands can be connected as if they were all one color, and the green and blue strands can be connected as if they were all another color. Thus, the cable is equivalent to the above.

[0041] 10, another cable of the present invention is shown (without the outer sheath). This cable has enamel-coated wires 208 in each of six layers, interlaced with bare wires 209 that are not enamel-coated. The wires 208 are enamel-coated to maintain insulation from the bare wires 209 within each layer and between one layer and the next. The bare wires may touch each other between one layer and the next, but this does not affect the capacitance between pairs of wires. However, interlayer insulation 211 is preferably provided.

[0042] Since the priority date of this application, the inventors have determined that the interlayer insulation preferably consists of insulating-only tape, without any semiconductive material. The semiconductive material pressed between each of the dissimilar strands could provide a conductive path between the strands if each strand had relatively close defects in its enamel. Local conductive paths between cable conductors could thus result, but are avoided by using only insulating tape.

[0043] If the dielectric constant of the tape is between 2 and 6, it is preferable to use a tape having a thickness of 50 to 250 μm. If the dielectric constant of the tape is between 6 and 10, it is preferable to use a tape having a thickness of 250 to 1000 μm. The inventors have found that a suitable tape to use is "Non-conductive Water Blocking Tape-K3214 from Freudenberg Performance Materials SE & Co KG, 69469 Germany". This tape comprises a non-conductive polyester non-woven substrate, a superabsorbent powder, a corrosion inhibitor, and an adhesive.

Claims

1. 1. A capacitive power transmission cable consisting of a plurality of connected cable lengths, The cable length is - at least two pairs of conductive strands insulated from each other and in a capacitive relationship with each other; The conductive strands are arranged in a layer structure of at least substantially a multiple of six, with the number of strands in both sets being substantially equal; In each layer, the wires of one set alternate with the wires of the other set; A capacitive power transmission cable, in which towards one end the number of strands in one set decreases and the number of strands in the other set increases.

2. 2. The capacitive power transmission cable of claim 1, wherein each layer is constructed with bare strands of one of the sets interleaved with one or more insulated strands of one or more further sets.

3. 2. The capacitive power transmission cable of claim 1 having insulation on all strands of the at least two sets, whereby each strand is insulated from every other strand along the length of the cable.

4. 4. The capacitive power transmission cable of claim 3, wherein the insulation on each strand comprises enamel.

5. 5. A capacitive power transmission cable according to any one of claims 1 to 4, wherein the insulation of each of the sets has a different contrasting colour.

6. 6. A capacitive power transmission cable according to any one of claims 1 to 5, wherein the strands are arranged at a different helix angle from one layer to the next.

7. 6. A capacitive power transmission cable as claimed in any one of claims 1 to 5, wherein the strands of one layer have equal and opposite helix angles to the strands of the next layer.

8. 8. A capacitive power transmission cable according to claim 1, wherein an interlayer insulation is provided in addition to the insulation of the individual strands.

9. 9. The capacitive power transmission cable of claim 8, wherein the interlayer insulation is non-conductive and does not include superconducting material.

10. 10. A capacitive power transmission cable according to claim 8 or 9, wherein the interlayer insulation consists of a tape with a relative dielectric constant of 2 to 6 and a thickness of 50 to 250 μm.

11. 10. A capacitive power transmission cable according to claim 8 or 9, wherein the interlayer insulation consists of a tape with a relative dielectric constant of 6 to 10 and a thickness of 250 to 1000 μm.

12. 12. A capacitive power transmission cable according to any one of claims 1 to 11, comprising the two sets of strands and one or more other sets of conductive strands.

13. 13. A capacitive power transmission cable (1) according to claim 12, comprising the two sets of strands (8, 9) and one other set of conductive strands.

14. 13. A capacitive power transmission cable (1) according to claim 12, comprising the two sets of strands (8, 9) and two other sets of conductive strands.

15. 15. A capacitive power transmission cable as claimed in claim 12 or 14 depending on claim 12, wherein in the outer layers where there are multiples of four strands, the four sets can be connected as two pairs to equalize the capacitive plate sizes in the middle cables of a long cable length, and the end cables can be connected with three times the number of strands in one predominantly conducting set as the other set.

16. 16. The capacitive power transmission cable of claim 15, wherein the cable has reduced capacitance per unit length at the cable ends.

17. 17. A capacitive power transmission cable according to any one of claims 1 to 16, wherein the four sets of strands are arranged in a repeating 1-2-3-4-1-2-3-4 order and four different colours can be used to identify the strands.

18. 13. A capacitive power transmission cable as claimed in claim 12, wherein in a layer having a number of strands not divisible by four, the strands are arranged in a number of adjacent strands of two colours and adjacent strands of the other two colours.

19. 19. A capacitive power transmission cable according to any one of the preceding claims, comprising a single central strand made of the same metal and insulated in the same way as the other strands.

20. 20. A capacitive power transmission cable according to any one of claims 1 to 19, wherein certain layers are provided with compensatory extra strands beyond the number of strands in a strict multiple of six layer construction.

21. A capacitive power transmission cable, comprising: - at least two pairs of conductive strands insulated from each other and in a capacitive relationship with each other; At each end of the cable, all the wires of one set are bundled together; At each end of the cable, all the strands of a different set are bundled together; all wires of the two or more sets remain insulated from one another along the length of the cable and at each end of the cable; A capacitive power transmission cable, wherein the number of strands in one set decreases and the number of strands in the other set increases towards one end of the capacitive power transmission cable.

22. 22. The capacitive power transmission cable of claim 21, wherein the bundling provides an electrical connection of the respective strands.

23. 23. The capacitive power transmission cable of claim 22, wherein the electrical connection of each of the strands is made by crimping the respective strands together.

24. 22. The capacitive power transmission cable of claim 21, wherein ends of the bundled strands are inserted into and clamped in respective connectors.

25. 22. The capacitive power transmission cable of claim 21, wherein the cable comprises a set of crimped strands at both ends thereof and a connector at only one end.

26. The conductive strands are arranged in a layer structure of at least substantially a multiple of six, and the number of strands in both sets is substantially equal; 22. A capacitive power transmission cable as claimed in claim 21, wherein in each layer, the strands of one set alternate with the strands of the other set.

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