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Capacitive Power Transmission Cable

20210249156 · 2021-08-12

    Inventors

    Cpc classification

    International classification

    Abstract

    A capacitive power transmission cable (1) comprising at least two sets of conductive strands (2). The strands of the sets are distributed in a transverse cross-section of the cable, whereby the two sets are in capacitive relation to each other.

    Claims

    1-33. (canceled)

    34. A capacitive power transmission cable comprising: at least two sets (21,121; 22,122) of conductive strands (23,123; 24,124), the sets of strands being insulated from each other and in capacitive relationship, the one with the other and the strands of the sets being distributed in a transverse cross-section of the cable, whereby the two sets (21,121; 22,122) are in capacitive relation to each other; characterised in that: capacitance between the two or more sets of strands, when all strands of respective sets are electrically connected together, is at least 10 nF/m and the strands are laid in layers (L1, L2, L3, L4, L5, L6, L7) of opposite twist.

    35. A capacitive power transmission cable as claimed claim 34, wherein the capacitance between the sets of strands is within the range 10 to 170 nF/m for a 3.6 kV cable or 5.5 to 92.5 nF/m for a 72.5 kV cable or 14 to 235 nF/m for a 240V cable or 5 to 84 nF/m for 145 kV cable.

    36. A capacitive power transmission cable according to claim 34, wherein all of the strands of at least one of the sets having a respective insulation (25,125; 26,126) of dielectric strength to enable the sets of conductive strands to remain isolated.

    37. A capacitive power transmission cable according to claim 34, wherein the sets are insulated from each other by insulation which is at least 10 μm thick.

    38. A capacitive power transmission cable according to claim 34, wherein the sets are insulated from each other by insulation which is between 20 μm and 540 μm thick.

    39. A capacitive power transmission cable according to claim 34, wherein the sets are insulated from each other by insulation which is between 17 μm and 1079 μm thick.

    40. A capacitive power transmission cable according to claim 34, wherein the strands (23,123; 24,124) of the two, or more sets (21,121; 22,122), are alternated in their layers (L1, L2, L3, L4, L5, L6, L7).

    41. A capacitive power transmission cable according to claim 34, wherein the strands (23,123; 24,124) are laid in alternating layers (L1, L2, L3, L4, L5, L6, L7) of all one set (21; 121) and then all another set (22; 122).

    42. A capacitive power transmission cable according to claim 34, wherein at least one of the sets (21,121; 22,122) of conductive strands (23,123; 24,124) is uninsulated, with the insulation of the strands (25,125; 26,126) of the other set (21,121; 22,122) providing the insulation.

    43. A capacitive power transmission cable according to claim 34, including: insulation (27; 127) between layers (L1, L2, L3, L4, L5, L6, L7) of different sets (21,121; 22,122), whereby the at least two sets are in capacitive relation to each other.

    44. A capacitive power transmission cable according to claim 43, wherein the insulation is soft polymer insulation between each layer to fill interstices between individual strands.

    45. A capacitive power transmission cable according to claim 34, the insulation is of tape between 30 μm and 1.35 mm.

    46. A capacitive power transmission cable according to claim 43, the insulation is of tape between 25 μm and 2.7 mm thick.

    47. A capacitive power transmission cable according to claim 43, wherein one set of strands is coloured and the other is uncoloured.

    48. A capacitive power transmission cable according to claim 43, wherein one set of strands is coloured being of tinned strands and the other is uncoloured being of plain strands.

    49. A capacitive power transmission cable according to claim 34, wherein the insulation is by means of insulating coatings (25,125; 26,126) of enamel of the type used in so-called “magnet wire” or the insulating coatings are extruded, wound or woven.

    50. A capacitive power transmission cable according to claim 34, wherein all sets of strands have their own insulation and the respective insulations of the sets are differently coloured to allow their separation for connection at opposite ends of the cable.

    51. A capacitive power transmission cable according to claim 34, wherein all sets of strands have their own insulation and the respective insulations of the sets are of different colours of enamel between the sets to allow their separation for connection at opposite ends of the cable.

    52. A capacitive power transmission cable according to claim 34, wherein there are between 37 and 397 strands per set.

    53. A capacitive power transmission cable according to claim 34, wherein there are between 19 and 547 strands per set.

    54. A capacitive power transmission cable according to claim 34, wherein the strands are of copper or aluminium wire.

    55. A capacitive power transmission cable according to claim 34, wherein the strands are die compressed in their layers.

    56. A capacitive power transmission cable according to claim 34, wherein the layers are of single conductor diameter thickness when the layers are insulated from each other.

    57. A capacitive power transmission cable according to claim 34, wherein the layers comprise two sub-layers of conductors, laid one way and the other.

    58. A capacitive power transmission cable according to claim 57, wherein the sub-layers within each layer are preferably braidingly combined.

    59. A capacitive power transmission cable according to claim 34, including: insulation (7) around the capacitively connected sets of strands, and a grounding sheath (5) around the insulation, the grounding sheath being in capacitive connection with the capacitively connected sets of strands, with the insulation being sufficiently thick to act as a dielectric causing conductive strands to sheath capacitance to be substantially two orders of magnitude, or more, less than capacitance between the two sets of strands.

    60. A capacitive power transmission cable according to claim 59, wherein the sheath is of spirally laid steel wires for armouring and action as an earth conductor.

    61. A capacitive power transmission cable according to claim 34, wherein, for connection to a supply conductor or a load conductor, a connector block (1007,1008) is provided with terminals (1009) for a first and second set of conductors (1003,1004) at respective ends (1005,1006) of the cable.

    62. A capacitive power transmission cable according to claim 61, wherein the supply or load terminal is a bus-bar (1015,1016) permanently connected thereto and one terminal (1019) in each block is isolated without a supply or load connection terminal, whilst the other is provided with a supply or load terminal (1017,1018).

    63. A capacitive power transmission cable according to claim 34, including a parallel-connection connector comprising respective terminals (15381/2/3/4) for respective sets of conductors on both sides and with internal interconnections (15481/2), whereby the one conductor of one length is connected to the one conductor of the other length, and the other conductors are similarly connected.

    64. A capacitive power transmission cable according to claim 34, including a series-connection connector having a terminal (15391) on one side for one set connected internally to a terminal (15394) on the other side for one or other set of the other length, and isolated terminals (15392/3) on the respective sides of the connector for the remaining sets to be terminated in.

    65. A capacitive power transmission cable according to claim 34 in combination with at least two or more such cables, at least one parallel connector comprising respective terminals (15381/2/3/4) for respective sets of conductors on both sides and with internal interconnections (15481/2), whereby the one conductor of one length is connected to the one conductor of the other length, and the other conductors are similarly connected and at least one serial connector comprising a terminal (15391) on one side for one set connected internally to a terminal (15394) on the other side for one or other set of the other length, and isolated terminals (15392/3) on the respective sides of the connector for the remaining sets to be terminated in, the cables and the connectors being connected as a long cable of desired capacitance.

    66. A capacitive power transmission cable according to claim 34, the cable including at least one additional set of strands for choice of capacitance of the cable or for straight through connection.

    67. A capacitive, power transmission cable according to claim 34, wherein the strands of one or more adjacent layers being of all one set and then radially outwards the strands of one or more adjacent layers being of all another set, insulation between the layers of different sets, whereby the at least two sets are in capacitive relation to each other and the individual strands are not insulated and are preferably differently coloured between their sets, one set of strands normally being of tinned strands and the other normally being of plain strands.

    68. A capacitive power transmission cable according to claim 34, comprising strands of at least two sets in each layer.

    69. A capacitive power transmission cable according to claim 34, having all the strands of respective sets connected together, one set at one end and the other set at the other end.

    70. Use of a capacitive power transmission cable according to claim 34, for transmitting power with one set connected to an electrical power source at one end and with the set connected to a load at the other end.

    Description

    [0056] To help understanding of the invention, a various specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

    [0057] FIG. 1 is a side view of a short piece of partially stripped cable of the invention;

    [0058] FIG. 2 is a diagrammatic view of a transverse cross-sectional view of the conductor sets of a simple conductor of the invention, without an outer sheath;

    [0059] FIG. 3 is a view similar to FIG. 2 of a seven layer cable of the invention having conductor strands of two sets alternated with layers;

    [0060] FIG. 4 is another similar view of a five layer cable in which sets of strands alternate in layers;

    [0061] FIG. 5 is a variant of the cable of FIG. 4 with six layers;

    [0062] FIG. 6 is a diagram of the cable of FIG. 2 provided with similar connectors at both ends for parallel connection of the cable with other such cables;

    [0063] FIG. 7 is a diagram of the cable of FIG. 2 provided with bus-bar connectors at its end;

    [0064] FIG. 8 is a parallel connector for a pair of cables of the invention;

    [0065] FIG. 9 is a series connector for a pair of cables of the invention;

    [0066] FIG. 10 is a cable end connector for a cable of the invention;

    [0067] FIG. 11 is a chart of typical dielectric strength for a selection of common enamel coatings;

    [0068] FIG. 12 is a chart of typical strength for a selection of common films/tapes;

    [0069] FIG. 13 is a chart of the minimal enamel thickness in mm against voltage in kV;

    [0070] FIG. 14 is a chart of the preferred lower enamel thickness in mm against voltage in kV;

    [0071] FIG. 15 is a chart of the preferred upper enamel thickness in mm against voltage in kV;

    [0072] FIG. 16 is chart of the maximum enamel thickness in mm against voltage in kV;

    [0073] FIG. 17 is chart of the combination of FIGS. 13 to 16;

    [0074] FIG. 18 is a chart of the minimum capacitance in nF/m against voltage in kV;

    [0075] FIG. 19 is a chart of the preferred lower capacitance in nF/m against voltage in kV;

    [0076] FIG. 20 is a chart of the preferred upper capacitance in nF/m against voltage in kV;

    [0077] FIG. 21 is a chart of the maximum capacitance in nF/m against voltage in kV; and

    [0078] FIG. 22 is a chart of the combination of FIGS. 17 to 21.

    [0079] Referring to the drawings, a power transmission cable 1 has copper strands 2 within a sheath 3. The sheath is generally conventional, having an outer protective polymer layer 4, a steel/copper wire protective grounding layer 5, a semi-conductive layer 6 and an insulating layer 7 and a semi-conductive layer 8. The copper conductive strands are in accordance with the invention.

    [0080] Typically in a cable intended to operate at 33 kV with a cross section of typically 300 mm2, the copper strands 2 have a lay-up diameter 12 typically of 16 mm. The insulation layer is typically 8 mm thick giving a diameter 14 of 32 mm and a ratio of 2:1. With the conductive strands having a typical capacitance between their set of 120 nF/m and the capacitance to ground of the strands in tow typically being 0.3 nF/m, this gives a capacitance to ground of two orders of magnitude less than that between the two sets of strands.

    [0081] Further the insulation between the strands or layers thereof is typically 0.1-0.2 mm, giving a typical ratio of insulator to ground thickness to inter-strand insulator thickness of 40:1-80:1.

    [0082] There are two sets 21,22 of the copper strands. Within each set, the strands 23,24, have respectively differently coloured, typically red and green, insulating enamel 25,26, of the type used in production of so-called “magnet wire”, i.e. copper wire coated with insulating polymeric material to provide insulation between contiguous windings in an electromagnetic machine.

    [0083] The strands are typically laid up as follows: [0084] Layer 1: two red strands 23 & two green strands 24, twisted clockwise; [0085] Layer 2: five red strands 23 & five green strands 24, twisted anti-clockwise; [0086] Layer 3: eight red strands 23 & eight green strands 24, twisted clockwise; [0087] Layer 4: eleven red strands 23 & eleven green strands 24, twisted anti-clockwise; [0088] Layer 5: fourteen red strands 23 & fourteen green strands 24, twisted clockwise; [0089] Layer 6: seventeen red strands 23 & seventeen green strands 24, twisted anti-clockwise; [0090] Layer 7: twenty red strands 23 & twenty green strands 24, twisted clockwise.

    [0091] The layers are laid with a conventional cable winding machine, with the bobbins of red and green strands for the individual layers alternated. Between each layer is wound soft polymeric material 27. After each layer is laid, the strands of the last laid layer are squeezed against this material, to urge it to fill the interstices between the strands. Again this is an essentially conventional step save that the dies, through which the strands are passed for this compression, are marginally larger than would otherwise be the case to avoid damage to the enamel.

    [0092] The strands are in intimate contact with each other, separated only by the thickness of their enamel coatings, and the soft polymer filling the interstices of between them, as when three strands lie in equilateral triangular arrangement. With reference to FIG. 3, it should be noted that although the figure shows several strands aligned with others of the same set, this figure is a cross-section at a particular point along the cable. Due to the opposite twisting of adjoining layers, cross-sectional arrangement of the strands is different at different points along the cable. The arrangement provides that the strands of the two sets are in capacitive relationship with each other.

    [0093] Turning now to FIG. 4, the power transmission cable 101 there shown has two sets 121,122 of the copper strands 123,124, having respectively differently coloured insulating enamel, and inter layer insulation 127. The strands are laid in oppositely twisted layers of all one or the other set. A central polymeric former 131 is provided, which is hollow for accommodating data fibres, such as temperature sensing optical fibres (not shown). The strands are laid as follows: [0094] Layer 1: sixteen red strands 123; [0095] Layer 2: twenty two red strands 123; [0096] Layer 3: twenty eight green strands 124; [0097] Layer 4: thirty four red strands 123; [0098] Layer 5: forty green strands 124.

    [0099] In this cable, the capacitive relationship comes from the radial alternation strands of the two sets. The reason for the additional Layer 1 of strands of the same colour/set as the next Layer 2, is that without it the total count of red strands 123 would be considerably less than that of the green strands 124, with the result that former would be carrying considerably more current at the end of the cable having these strands connected as now described.

    [0100] A variant of the second transmission cable is shown in FIG. 5. In it, it is not the inside two layers that are of the same set, but the second and third layers. The number of strands per layer of the different strands is [0101] Layer 1: sixteen red strands 123; [0102] Layer 2: twenty two green strands 124; [0103] Layer 3: twenty eight green strands 124; [0104] Layer 4: thirty four red strands 123; [0105] Layer 5: forty green strands 124; [0106] Layer 6: forty six red strands 123.

    [0107] This cable has the further layer 6, increasing its power transmission capability.

    [0108] For choice of the capacitance per unit length of the cable, account is taken of the inductance of the cable and other components of the electrical supply system of which the cable is part, with a view to balancing this inductance with the capacitance of the cable. More specifically, the following steps are gone through: [0109] 1. Selecting an initial cable size in accordance with the voltage and current that the cable is to carry, in particular, the cross-sectional area of metal to be included in the core; and on a first iteration the number of enamelled wires and/or the number of layers; and the length (l): [0110] 2. Computing the design inductance of the cable (LD) and the resistance of the cable (R) using computer simulation and modelling and including in particular its inherent inductance and any mutual inductance that may result from its inclusion in a 3-phase system, as if it were a conventional cable if need be: [0111] 3. Noting that for the inductive reactance for the cable resulting from LD is given by the Inductive Reactance Equation:


    X.sub.L=2nfL.sub.D

    where f equals the operating frequency in Hz, normally 50 or 60 Hz; [0112] 4. Noting that for the capacitive reactance of the cable, for a capacitance C is given by the Capacitive Reactance Equation:


    X.sub.C=1/2nfC

    where f equals the operating frequency in Hz, normally 50 or 60 Hz; [0113] 5. Noting that for XL to be approximately equal but slightly larger than X.sub.C, the following range is recommended:


    0.4R>X.sub.L−X.sub.C>0;


    2nfL.sub.D−1/2nfC<0.4R


    2nfL.sub.D−1/2nfC>0; [0114] 6. Computing the desired cable capacitance (C) within this range:


    1/((2nf).sup.2L.sub.D−2nf(0.4R))>C>1/(2nf).sup.2L.sub.D; [0115] 7. Using the tables below, suitable cable parameters can be chosen, which may result in revision of the number of wires or number of layers, in which case the cable choice can be refined; [0116] 8. Should all of the inductance not be able to be balanced, a cable that can balance as much as possible of L.sub.D and carry its load is chosen; [0117] 9. If other elements of inductance are to be balanced. This can be taken account of by modifying the values of L.sub.D and thus X.sub.L; [0118] 10. The resulting design is then modelled in simulation to validate the original inductance computation L.sub.D and the resulting X.sub.L and X.sub.C which may suggest design revision. One or more further iterations may be required.

    [0119] In order of magnitude terms, for a 15 km cable, 120 nF/m can balance a cable inductance of 375 nH/m, which is typical for a 3 phase 33 kV cable laid in trefoil. That said, it should be noted that if a different length of cable is concerned the effect of its length must be taken into account.

    [0120] The above steps need to take account of the fact that even for magnet wire enamel, the withstand strength of a dielectric does not rise linearly with voltage, as shown in the Charts 1 to 6 (FIGS. 11 to 16).

    [0121] The tables referred to are:

    TABLE-US-00001 TABLE 1 Enamel Thickness in mm for Varying Maximum Voltage in kV Preferred Preferred Maximum Minimum Lower Upper Maximum Voltage - Thickness - Thickness - Thickness - Thickness - kV mm mm mm mm 3.6 0.024 0.026 0.105 0.202 7.2 0.034 0.037 0.148 0.242 12 0.040 0.043 0.172 0.247 17.5 0.040 0.043 0.172 0.247 24 0.040 0.043 0.172 0.247 36 0.040 0.043 0.172 0.247 52 0.041 0.045 0.179 0.251 72.5 0.044 0.047 0.190 0.262

    [0122] It will be noted that the Y-axis scale differs between the above charts and that the minimum and lower preferred plots are similar. To give an appreciation of their relative values, they can be combined as shown in Charts 7 to 12 (FIGS. 17 to 22), and in Tables 2 to 6 below.

    TABLE-US-00002 TABLE 2 Dielectric Tape Thickness in mm for Varying Maximum Voltage in kV Preferred Preferred Maximum Minimum Lower Upper Maximum Voltage - Thickness - Thickness - Thickness - Thickness - kV mm mm mm mm 3.6 0.027 0.040 0.211 0.404 7.2 0.038 0.055 0.295 0.485 12 0.059 0.065 0.344 0.495 17.5 0.059 0.065 0.344 0.495 24 0.059 0.065 0.344 0.495 36 0.059 0.065 0.344 0.495 52 0.062 0.067 0.358 0.503 72.5 0.065 0.071 0.379 0.523

    TABLE-US-00003 TABLE 3 Capacitance in nF/m for Varying Maximum Voltage in kV Preferred Preferred Minimum Lower Upper Maximum Maximum Capaci- Capaci- Capaci- Capaci- Voltage - tance - tance - tance - tance - kV nF/m nF/m nF/m nF/m 3.6 22.0 44.0 264.0 316.8 7.2 21.0 42.0 252.0 302.4 12 20.0 40.0 240.0 288.0 17.5 18.5 37.0 222.0 266.4 24 17.5 35.0 210.0 252.0 36 16.0 32.0 192.0 230.4 52 15.0 30.0 180.0 216.0 72.5 14.5 29.0 174.0 208.8

    TABLE-US-00004 TABLE 4 Individual Strand Diameter in mm for Varying Maximum Voltage in kV Preferred Preferred Minimum Lower Upper Maximum Maximum Strand Strand Strand Strand Voltage - Diameter - Diameter - Diameter - Diameter - kV mm mm mm mm 3.6 0.50 0.60 2.50 3.00 7.2 0.50 0.60 2.50 3.00 12 0.50 0.60 3.00 4.00 17.5 0.50 0.60 3.00 4.00 24 0.50 0.60 3.00 4.00 36 0.50 0.60 3.50 4.50 52 0.50 0.70 3.50 4.50 72.5 0.70 0.80 4.00 5.00

    TABLE-US-00005 TABLE 5 Number of Strands for Varying Maximum Voltage in kV Maximum Minimum Preferred Preferred Maximum Voltage - Number Lower Number Upper Number Number kV of Strands of Strands of Strands of Strands 3.6 19 37 271 397 7.2 19 37 271 397 12 19 37 397 547 17.5 19 37 397 547 24 19 37 397 547 36 19 37 397 547 52 19 37 397 547 72.5 19 37 397 547

    TABLE-US-00006 TABLE 6 Number of Layers for Varying Maximum Voltage in kV Maximum Minimum Preferred Preferred Maximum Voltage - Number Lower Number Upper Number Number kV of Layers of Layers of Layers of Layers 3.6 3 4 10 12 7.2 3 4 10 12 12 3 4 12 14 17.5 3 4 12 14 24 3 4 12 14 36 3 4 12 14 52 3 4 12 14 72.5 3 4 12 14

    [0123] The above tables and charts show values of variables for the most common power transmission voltages. The invention is not restricted to these voltages.

    [0124] Indeed, the following charts, which are based for the central portion of their graphs, show a wider range of voltages.

    [0125] Both above described cables, including the variants, are connected in essentially the same way in that the strands of the one set, typically the red set, are bundled and at both ends and the strands of the other set are bundled in a like manner.

    [0126] After division into respective bundles, the enamel is stripped from the ends of the strands. The stripped strands are inserted into respective terminal block and tightly clamped together, providing mechanical and more importantly electrical connection.

    [0127] Turning now to FIGS. 6 to 10, connectors for a cable 1001 of the invention will now be described. All the red wires 1003 are bundled together. All the green wires 1004 are similarly bundled. The wires are similarly bundled at the other end of the cable. The enamel is removed from the ends of the bundled wires, suitably by dipping in solvent. The bundled ends are brought together in respective connectors 1007,1008. These have double-ended sockets 1009 for the bundles. Each end of the sockets has bores 1010 with clamping screws 1012 for the bundles of the cable. The bundled wires are inserted in the bores 1010 and clamped. This arrangement allows for the cable 1001 to be connected in parallel to other such cables with their red wires connected by the connectors to the red wires of the cable 1001 and the green wires similarly connected. For this the sockets have other end bores 1011 and other end clamping screws 1014. The bores 1011 could be through bores with the bores 1010. Their arrangement with un-bored middles ensures that neither set of wires takes up spaces intended for the other.

    [0128] Where the cable is to be used as a single length between a supply and a load, the electrical connection of the cable is between the red wires and the green wires as an elongate capacitor, extending the length of the cable 1001. Respective supply and load cables/bus-bars 1015,1016 are clamped in the other bores 1011 of the red wire socket 1017 at one end of the cable and of the green wire socket 1018 at the other end. Thus the red wires 1003 are connected to the supply cable/bus-bar 1015 at the end 1005 and the green wires 1004 are connected to the load cable/bus-bar 1016 at the end 1006. There is no metal/metal contact between the supply cable/bus-bar 1015 and the load cable/bus-bar 1016.

    [0129] The connectors have other, insulated single-ended sockets 1019 with a single bore 1020 and a single clamping screw 1021. The other wires, i.e. green wires at the supply end and the red wires at the load end, are received and clamped in these sockets. These wires are not connected by the sockets and are clamped purely for mechanical reasons in ensuring that they remain insulated. They do not need to be stripped of their insulating enamel, indeed leaving them enamelled assists in their identification. These insulated ends play no part in power transmission.

    [0130] The connectors shown in FIGS. 4 and 5 are shown diagrammatically. FIGS. 8, 9 & 10 show more detail. They include a connector cover 1050 which is essentially conventional and filled in use with insulating material 1051. The actual connection arrangements comprise central blocks 1052 of insulating material having four sockets 1053, with bores and bolts for clamping the cable wires, extending from each end. There are three sockets in the case of FIG. 10.

    [0131] The sockets on one side are electrically connected internally to the sockets on the other side. This is by a short length of conventional cable 1054, between internal bores and bolts. The connections are made first and then the blocks are formed around the connections.

    [0132] In the case of FIG. 8, the four sockets are connected in pairs, socket 15381 to socket 15383 and socket 15382 to socket 15384, via two short cable lengths 15481,15482. This connector allows two cables of the invention to be connected in parallel, with for instance the red wires 1003 of the cables being connected by sockets 15381,15383 and cable 15481 and the green wires 1004 by the sockets 15382,15384 and cable 15482.

    [0133] In the case of FIG. 9, the four sockets are connected in one pair, socket 15391 to socket 15394 via a short cable length 15491; whilst the sockets 15392, 15393 are unconnected. This connector allows two cables of the invention to be connected in series, with for instance the red wire of the cable being connected at sockets 15391, 15392 by the cable 15491 to the green wires of the cable connected at sockets 15393, 15394. The green wires of the first cable and the red wires of the second cable are merely anchored by the connectors 15392, 15393. The cable 15491 crosses from top to bottom to allow the red wires and the green wires on opposite sides to be connected at the same relative positions.

    [0134] In the case of FIG. 10, three sockets are provided with one internal cable 154101. On one side are sockets 153101,153102 for the incoming cable and on the other side is socket 153103 for an outgoing conventional cable 155 to a supply or load. This allows both green wires of the incoming cables to be connected by the internal cable 154101 to the single socket 153103, with the red wires of the incoming cable to be anchored.

    [0135] Similar connectors for aerial cables, with the additional feature of mechanical connection to the tension core can be provided.

    [0136] If the capacitance of the combined lengths needs to be less, the connector can be a series connector as shown in FIG. 9. With a red (cable A) to green connection (cable B) between the two cables, the free ends capacitance is between the green wires of cable A and the red wires of cable B. The capacitance is in effect of a single length with double the dielectric gap. It is given by the formula for capacitances in series:

    [00001] Series ⁢ ⁢ Capacitances C total = 1 1 C 1 + 1 C 2 ¯ + .Math. ⁢ ⁢ 1 C n

    Where the two lengths are identical, the capacitance is halved.

    [0137] A feature of capacitances in series is that the voltage across individual ones is divided by the number of capacitances. This is useful in enabling a high voltage line to be comprised of three sections, each carrying ⅓ of the high voltage. This has further advantages in reducing the thickness of the dielectric coating or tape/paper between the conductors. Thus loss of capacitance by connection in series can be offset by higher capacitance per unit length in the first place.

    [0138] In respect of the connectors, details can be altered. For instance, the bundled ends of the conductor wires may be preliminarily crimped before insertion the sockets. Further the sockets themselves may be crimped as opposed to screwed, via oppositely arranged openings in the connector bodies which can be subsequently sealed closed.

    [0139] The invention is not intended to be restricted to the details of the above described embodiment. For instance, more or less conductive layers can be provided. They can be provided as an even number as above or an uneven number of conductive cylinders with the inner and outer most interconnected. At the centre of the cable, a steel core can be provided for strength of the cable. Alternatively, or additionally, a hollow conduit may be provided centrally, for accommodating other elongate elements such as optical fibres for data transmission and/or temperature monitoring.