CAPACITIVE POWER TRANSMISSION CABLE

Abstract

An object of the instant application is to provide a capacitive power transmission cable comprising at least two sets of conductive strands, the sets of strands being insulated from each other and in capacitive relationship, the one with the other; wherein the conductive strands are laid at least substantially in a multiples of six layer structure, with substantially equal numbers of strands of both sets; and wherein each layer has strands of one set alternating with strands of the other set and the strands of the respective sets have different contrasting color.

Claims

1. A capacitive power transmission cable, comprising: at least two sets of conductive strands, the sets of strands being insulated from each other and in capacitive relationship, the one with the other; wherein: the conductive strands are laid at least substantially in a multiples 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 and the strands of the respective sets have different contrasting colour.

2. A capacitive power transmission cable as claimed in claim 1, wherein each layer is comprised of bare strands of one of the sets alternating with one or more insulated strand of one or more further set or sets.

3. A capacitive power transmission cable as claimed in claim 1, wherein all the strands of the at least two sets have insulation on them, whereby each strand is insulated from all other strands along the length of the cable.

4. A capacitive power transmission cable as claimed in claim 1, wherein the insulation on each strand is of enamel.

5. A capacitive power transmission cable as claimed in claim 1, wherein the strands of the respective sets have different contrasting colour.

6. A capacitive power transmission cable as claimed in claim 1, wherein the strands are laid with differing helical angles from one layer to the next.

7. A capacitive power transmission cable as claimed in claim 1, wherein, the strands of one layer have helical angles equal and opposite those of the next layer.

8. A capacitive power transmission cable as claimed in claim 1, wherein inter-layer insulation is provided in addition to individual strand insulation.

9. A capacitive power transmission cable as claimed in claim 8, wherein the inter-layer insulation is non-conductive without super-conductive material.

10. A capacitive power transmission cable as claimed in claim 8, wherein the inter-layer insulation is of the tape with a relative permittivity between 2 & 6 and a thickness of 50 to 250 μm.

11. A capacitive power transmission cable as claimed in claim 8, wherein the inter-layer insulation is of the tape with a relative permittivity between 6 & 10 and a thickness of 250 to 1000 μm.

12. A capacitive power transmission cable as claimed in claim 1, wherein there are equal numbers of strands in the sets.

13. A capacitive power transmission cable comprised of a plurality of connected lengths of cable as claimed in claim 1, in which to one end the number of strands of one set is reduced and the number of strands of the other set is increased.

14. A capacitive power transmission cable as claimed in claim 1, including the said two sets of strands and one or more other sets of conductive strands.

15. A capacitive power transmission cable as claimed in claim 14, wherein there are in outer layers there are a multiple of four strands, the four sets can be connected as two pairs to give equal capacitive plate size in middle lengths of a long cable, whilst end lengths can be connected as three times as many strands of one, mainly conducting set, as the other, i.e. with reduced cable end capacitance per unit length.

16. A capacitive power transmission cable as claimed in claim 1, wherein strands of four sets are laid in sequence 1-2-3-4-1-2-3-4 etc., with four different colours can be used for identification of the strands.

17. A capacitive power transmission cable as claimed in claim 14, wherein in layers having a number of strands not divisible by four, the strands can provided as adjacent numbers of strands with one number of two colours and an adjacent number of the other two colours.

18. A capacitive power transmission cable as claimed in claim 1, including a single central strand of the same metal as and insulated in the same manner as the other strands.

19. A capacitive power transmission cable as claimed in claim 1, wherein certain layers are provided with compensatory additional strands beyond their strict multiples of six layer structure number.

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. (canceled)

Description

[0045] To help understanding of the invention, two embodiments and a variant thereof will now be described by way of example and with reference to the accompanying drawings, in which:

[0046] FIG. 1 is FIG. 2 of U.S. Pat. No. 3,164,669;

[0047] FIG. 2 is FIG. 2 of Document 6150821;

[0048] FIG. 3 is FIG. 2 of the above referenced 2019 IEEE paper;

[0049] FIG. 4 is a view similar to FIG. 1 of a capacitive power transmission cable of the invention without external sheathing;

[0050] FIG. 5 is a scrap end view of the a central conductor two inner layers of conductors of the cable of FIG. 3;

[0051] FIG. 6 is a full end view of the cable of FIG. 3 with external sheathing;

[0052] FIG. 7 is end view of the conductors only of a variant of the cable of FIG. 3;

[0053] FIG. 8 is a diagrammatic view of a connection of middle to end lengths of the variant cable;

[0054] FIG. 9 is a similar diagrammatic view of another connection of middle to end lengths of the variant cable and

[0055] FIG. 10 is a view similar to FIG. 3 of another cable of the invention.

[0056] Referring to the drawings, a capacitive cable 1 comprises six layers 2,3,4,5,6,7 of two set of alternating copper strands 8,9.

[0057] The layers are laid around a single inner strand 10 of the same size, for example 13AWG-1.82 mmOD. This single strand, and each succeeding layer, is wound with soft insulation 11 which is displaces on winding maintain the relative positioning of the strands, squeezing into interstices between them. Typically this insulation is laid 40-45 mm thick of semi-conductive water blocking tape, typically including: polyester non-woven fabric, polypropylene super absorbent powder, semi-conductive carbon black, polyester non-woven fabric. Such tape being semi-conductive assists in electron distribution and thus enhances capacitance. However, we prefer to use fully insulating polyester or PET tape for interlayer insulation. The resultant capacitance per unit length of this cable is 45 nF/m.

[0058] The layer 2 has six strands 8,9, three of one set and three of the other set. Those of one set are of conventionally coloured, i.e. red/brown, magnetic wire enamel R. Those of the other set are of black coloured enamel B. The result of this colour contrast is that at and end of a cable length, with the strands exposed for respective connection, the sets of strands can be readily separated, with all the red/brown strands of one set being bundled for connection to one terminal 12 and all the black strands of the other set being collected for connection to another terminal 14 of a connector 16.

[0059] The layer 3 has six strands 8,9, six of one set and six of the other set. As with the layer 1, its strands of the two sets run parallel to each other and are therefore in good capacitive relation with each other. The strands of the two layers are at opposite helical angles α to each other. Whilst they cross like with like regularly, they also cross like with opposite equally regularly. Thus there is inter-layer capacitance between the sets of conductors as well as intra-layer capacitance. This contributes to the overall capacitance of the sets of strands within the cable when connected as above.

[0060] The successive layers 4-7 each have six more strands 8,9. There are always an even number and always strands of the two sets are interdigitated.

[0061] Normally there will be the six layers 2-7 plus the single central strand 10. The latter could be replaced by a steel strand or an inert polymeric strand. Outside the outer sixth layer, there will normally be the usual insulating, protective and outer layers 15 of underground power cable. There may be one or more fewer or additional layers of conductive strands for lesser or great power capacity.

[0062] As shown in FIG. 8 below in respect of a variant, the cable 1 can be supplied with its two sets of strands bundled together at both ends. The enamel can be removed from the very ends of the strands, typically by abrasion, and the respective bundled crimped together—ref 20 in FIG. 7. The cable can be supplied in this form or with the addition of a connector, having terminals for the crimped ends. Conveniently a connector can be provided at a single end only whereby in use, each cable length can be connected to a next one for assembly into a longer finished cable.

[0063] In end lengths of several connected lengths of the cable, the colouring of the strands may be varied, or indeed the colouring now described can be used throughout the cable. For connection, the strands of respective colours are exposed by cutting back of the outer sheath of the cable and the interlayer insulation. The exposed strands are bundled by colour, their enamelling exposed at extreme ends and the bundles secured by conductive metal crimps 120. This allows certain of the strands to be connected together as above, whilst others of the strands are differently connected. For instance, if the strands are coloured orange O, green G, brown Br, blue Bl and so on in that order, in the end length at one end, the green G strands can be connected at a connector 16 together with the orange O and brown Br strands, to reduce the capacitance with the blue Bl strands and increase the current capacity of the orange O and brown Br connected strands to be connected to a load. This connection is shown in FIG. 7. At the opposite end of the cable, the opposite connection is used. Thus the capacitor plate of the orange O and brown Br strands is in effect constant in plate area per unit length in the middle part of the cable, increased at the end to be connected to a load and reduced the supply end, where it is isolated. The green G/blue Bl plate is configured oppositely.

[0064] Where the connector 16 of FIG. 8 has straight through connections 17 from its respective terminals 12, 14 on either side, into which respective bundles of crimped wires as to be connected are inserted; the connector 116 of FIG. 8 has four respective terminals 118 for the differing colour strands and internal connections 117 for providing the desired grouping of the strands to provide end length conduction.

[0065] Again this colouring of the strands may be used throughout the thickness of the cable or at least in the layers having a multiple of four strands. If the order of the strands is orange, green, brown, blue and so on, the orange and brown strands can be connected together as if they were all one colour and the green and brown strands can be connected together as if they were all another colour. Thus cable is equivalent to that described above.

[0066] Turning now to FIG. 10, there is shown another cable of the invention (without outer sheathing). It has enamelled strands 208 in each of its layers, of which there are six, interdigitated with un-enamelled, bare strands 209. The enamelling of the strands 208 keeps them insulated from the bare strands 209, both within the layers and from one layer to the next. The bare strands may contact each other from one layer to the next, without effect on the capacitance between the sets of strands. However, interlayer insulation 211 is preferably provided.

[0067] Since the priority date of this application, we have now determined that the interlayer insulation is preferably of insulating only tape, without semi-conducting material. The latter is squeezed between respective opposite strands can provide a conductive path between them if each has a blemish in its enamel relatively close together. Local conductive paths between the cables conductors are possible in this way and are avoided by use of insulating tape only.

[0068] Where the relative permittivity of the tape is between 2 and 6, we prefer to use tape of 50 to 250 μm thickness. Where the relative permittivity of the tape is between 6 and 10, we prefer to use tape of 250 to 1000 μm thickness. We have found a suitable tape to use to be “Non-conductive water blocking tape— K3214, from Freudenberg Performance Materials SE & Co. KG, 69469 Germany. It comprises a non-conductive polyester nonwoven substrate with super absorbent powder, corrosion inhibitor and adhesive.