GB2441565A

GB2441565A - Electric Cable

Info

Publication number: GB2441565A
Application number: GB0614745A
Authority: GB
Inventors: Mark Billows
Original assignee: LINKRANCH Ltd
Current assignee: LINKRANCH Ltd
Priority date: 2006-07-05
Filing date: 2006-07-25
Publication date: 2008-03-12
Also published as: GB2439756A; GB0614745D0; GB0613401D0

Abstract

An electrical cable 101 has a set of conductor wires 103, 104, 105 extending along its length. The respective conductor wires have a conductor core and a respective insulator sheath 107 about the conductor core. The conductor wires are spaced and held in a respective tube-form space provided in a cable jacket 102, preferably a thermoplastics material, which is tubed onto the conductor wire set such that a respective discrete tube-form boundary wall 109 is present for a respective conductor wire and an air gap (110, fig.1a) exists between the tube-form boundary wall and the respective insulator sheath of the conductor wire. Preferably a lubricant such as chalk or talk is disposed between the tube form boundary wall and the respective insulator sheaths. The cable may be constructed of distinctive lobes 106 wherein the wires are held. An extruder die is used to produce the cable with the air gap between cable jacket and conductor insulating sheath.

Description

lectrical Cable The present invention relates to electrical cables.

The invention will be applicable to energy cables but may also be applied to data cables, audio video power cables and other cables intended for other general or specialist applications.

W02005/027148 and W02003/075287 disclose electrical cables designed to have technical features addressing perceived problems with cables. a... a S *

An improved electrical cable and manufacturing technique and apparatus has now been devised. So *

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According to a first aspect, the present invention provides an **S.

electrical cable comprising a set of conductor wires extending along the length of the cable, the respective conductor wires comprising a conductor core and a respective insulator sheath about the conductor core, the conductor wires being spaced and held in a respective tube-form space provided in a cable jacket, the cable jacket being tubed onto the conductor wire set such that a respective discrete tube-form boundary wall is present for a respective conductor wire and an air gap exists between the tube-form boundary wall and the respective insulator sheath of the conductor wire.

Such a cable has reduced capacitance interaction between wires, resulting in improved energy transmission characteristics.

Beneficially, the cable jacket comprises an insulator material and may be a PVC based Thermoplastic material.

The insulator sheaths of the respective conductor wires are also Preferably of plastics material as used Conventionally in the art for insulator sheathing conductor cores.

The conductor cores of the respective wires may be solid cores or alternatively include a plurality of conductor strands wound to form a core. Typically for such wound cores 7 or more conductor strands may be wound to form a core.

For energy cables typically the conductor set will comprise between 2 and 5 conductor cores (or wires) . British Standards BS 6500 and BS 7919 give an indication of various cables for *S*.

ordinary and light duty energy supply uses. * * : In one embodiment, it is preferred that the respective tube: form spaces for holding the conductor wires are provided in lobes which extend outwardly from the axis of the cable jacket.

Beneficially, the lobes are formed (for example having waisted portions or other zones of relative weakness) enabling the respective lobes to be stripped apart from one another. This provides beneficial characteristics for electrical connection to appliances, sockets, plugs and so on.

Desirably, the cable jacket is provided with a an internal bore, Void-space or cavity. More Preferably the cable is provided with an axial bore extending longitudinally of the cable. The provision f such a technical feature reduces the capacitance of the cable significantly resulting in a reduction in the power requirement for a given cable to transmit a given amount of energy.

Such an arrangement is believed to be novel and inventive per se.

Accordingly, a second aspect of the invention provides a an electrical cable comprising a set of conductor wires extending along the length of the cable, the respective conductor wires being spaced and held in a respective tube-form space of a cable jacket, the cable jacket being tubed onto the conductor wire set; wherein the respective tube form spaces for holding the respective wires are provided in discrete lobes of the jacket, the discrete lobes being strippable to come apart from one another; and/or, * * * * .* the cable jacket is provided with a vacant internal bore, void-space or cavity. *..

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It is preferred that the tube-form boundary wall is a continuous boundary around the respective insulator sheath of a respective conductor wire. More Preferably, tube-form *S..

boundary wall is without steps, apexes or projections. ** A lubricant or separation layer or material is Preferably provided between the tube-form boundary wall of the cable jacket and the respective insulator sheath of the respective conductor wire. The lubricant or separation material may be provided in powder form. In a preferred embodiment, the lubricant or separation material comprises chalk or talc.

It is preferred that the cable, including the cable jacket, is helically twisted along its length.

In one embodiment there are three conductor wires (cores) spaced about the axis of the cable.

According to a second aspect of the invention, there is provided a method of manufacturing an electrical cable comprising a set of conductor wires extending along the length of the cable, the respective conductor wires comprising a conductor core and a respective insulator sheath about the Conductor core, the conductor wires being spaced and held in a s respective tube-form space provided in a cable jacket, wherein the cable jacket is tubed onto the conductor set such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall of the jacket and the respective insulator sheath of the respective conductor wire.

Beneficially, the tube-form boundary is already formed before tubing onto the respective insulator sheath of a respective conductor wire.

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It is preferred that the solid jacket is formed upstream of a ** point at which the cable jacket is tubed onto the respective insulator sheath of a respective conductor wire. *SSa S * * S. *

Typically the cable jacket will be formed by extrusion, typically of Thermoplasj5 material.

In one realisation, the conductor wires, already with their respective insulator sheaths, pass through extrusion apparatus and the cable jacket is extruded and tubed on around the wires.

Beneficially, a lubricant or separation layer or material (such as chalk or talc) is introduced between the tube-form boundary wall and the respective insulator sheath of a respective conductor wire. Following extrusion, the cable, including the cable jacket, is preferably helically twisted along its length.

The cable may then be wound for storage in a conventional manner.

According to a further aspect, the invention provides a method of manufacturing an electrical cable comprising, a set of conductor wires extending along the length of the cable, the respective conductor wires being spaced and held in a respective lobe of a cable jacket, wherein the cable jacket is formed by extrusion and tubed onto the conductor wire set, the extrusion of the jacket Providing a vacant bore, void-space or cavity internally of the jacket.

According to a further aspect, the invention provides extrusion apparatus for forming a cable, the apparatus including: I. * * . * ..

a die having a die aperture; an extruder body having: .:.

a Plurality of guide channels for guiding the passage of respective conductor wires and S... I * I. *

a surface for guiding flowable material which solidifies to form a jacket about the respective conductor wires; wherein the die aperture is provided substantially level with the end of the extruder body, such that a solid cable jacket is formed by the extruder body upstream of a point at which the cable jacket is tubed Onto the conductor wires.

The present invention will now be further described by way of example only, and with reference to the accompanying drawings, in which; Figure 1 is a schematic sectional view of an electric cable in accordance with the invention; Figure la is a detailed view of a part of the cable of figure 1; Figure 2 is a schematic sectional view of extrusion die apparatus for forming the cable of the invention; Figure 3 is facing view of the extrusion die point body of the apparatus of figure 2; and, Figure 4 is a side view of the die point body of figure 3.

Referring to the drawings and initially to figures 1 there is shown an electrical cable ioi comprising a cable jacket 102 formed about a set of three conductor wires 103, 104, 105.

Each of the conductor wires 103, 104, 105 comprises a respective conductor core lO3a, 104a, 105a, sheathed in a respective Thermoplastic insulator sheath 107. The cable jacket 102 is beneficially of flexible material enabling the tube to be twisted into a lay along its length and also give * flexibility to the cable as will be described in detail. A suitable material for the jacket 102 is a PVC based Thermoplastic material.

The jacket 102 includes respective lobes 106a, 106b, 106c within which the wires are held, and neck portions 131a, 131b, 131c extending toward a central zone. The central zone is provided with an axial air-space bore 185.

The embodiment Primarily described has a set of 3 conductor wires. However it is important to note that the invention has applicability where other numbers of conductor wires are present. Typically between 2 and 5 conductor wires will be present The conductor cores 103 of the respective wires may be solid cores (for example of Copper) or alternatively may include a plurality of conductor strands (as shown in figure la) wound to form a core. Typically for such wound cores 7 or more conductor strands may be wound to form a core.

For energy cables typically the conductor set will comprise between 2 and 5 conductor cores (or wires) . British Standards s BS 6500 and BS 7919 give an indication of various cables for ordinary and light duty energy Supply uses.

The invention is directed to minimise capacitance effects between the wires 103, 104, 105, and thereby provide enhanced energy delivery capability and characteristics the jacket 102 acts to space the wires 103, 104, 105 from one another. The optimum spacing of the wires will vary depending upon particular technical applications Generally the greater the spacing between cables, the greater the reduction in capacitance however this needs to be counterbalanced by a desire not to make the overall width of the cable Un-manageably large.

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An important feature of the invention is that in forming the jacket 102, a receiving tube for each of the respective conductor wires is formed, in such a fashion that the wires 103, 104, 105 are not embedded within the jacket 102. Rather that a discrete non fused tube boundary 109 and air gap iio exists between the cable ja'cket 102 and the respective insulator sheaths 107 of each conductor wire. This is shown most clearly in figure la.

This technical configuratj and arrangement is different to the arrangements described for example in W02005/027148 and W02003/075287 in which the conductors are embedded in the jacket by pressure type plastics injection moulding to embed the conductor in the jacket. In these prior art arrangemen5 described, there is no presence of a receiving tube for the Conductors These prior art disclosures do not disclose a discrete non fused tube boundary and gap existing between the cable jacket and the respective conductors In accordance with the present invention the desired result (the air gap 110 and separation boundary 109) may be achieved by a plastics moulding process in which the jacket is tubed on to the respective conductor wire, about the insulator sheath 107 of the respective wire. This will be described in greater detail. In addition a separator or lubricant substance or layer may be introduced at manufacturing to enhance the boundary and separation effect at the non fused tube boundary 109 and air gap 110 existing between the cable jacket 102 and the respective conductor sheaths 107 of each conductor wire.

In a technically realisable procedure chalk or talc powder or:.

dust may be utilised as the separator or lubricant. The tube boundary 109 of the tube formed in the jacket is Without steps, apexes or projections **. S

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The technical benefits realised by a cable construction according to the present invention, in which the conductor wires are not embedded within the jacket 102, but rather a discrete non fused tube boundary 109 and gap 110 exists between the cable jacket 102 and the respective conductor sheaths 107 of each conductor wire, include enhanced performance in terms of reduced capacitance and magnetic interaction between the separate conductor wires 103, 104, 105. This is believed to be due to the presence of the discrete separation boundary 109 at the interface between the cable jacket 102 and the insulator sheath 107.

The material of the insulator sheath preferably has a dielectric constant less than 50. This aids in reducing capacitance. The conductor wires are Preferably spaced equidistant from the two most closely adjacent conductor wires.

This would result in the wires being positioned at the apexes of an equilater triangle for a 3 wire cable (such as the cloverleaf' design shown in figure 1). Similarly, the wires would be Positioned at the corners of a square for a four wire cable, and at the apexes of a pentangle for a five wire cable.

s Additionally enhanced performan has been found using twisting of the cable (including the cable jacket) along its longitudinal axis into a relatively tight helical lay-form.

Cable having the separation air gap 110 (enhanced by lubrication) enables the twisting into lay-form to be Consistently achieved with reduced damage to the respective such as kinking, buckling or stretching, all of which can adversely affect performance This is because the wires are not fully embedded within the jacket 2, but able to rotate:* within the jacket to a degree. :.:;:.

Twisting cable having fully embedded wires such as described in w02005/027148 and W02003/O75287 will be prone to damaging **.*.

effects such as kinking, buckling or stretching The air gap shown in figure la is pronounced, Primarily for the *:* purposes of explanation. In reality the air gap produced will *.

more likely be 0.5mm or less and in fact may be no more than the inherent space between adjacent and abutting surfaces of the tube form bore of the sheath 102 and the external surface of the wire insulation sheath 107. The air gap, however small, exists because of the fact that there is a separate tube boundary io formed in the cable jacket 102.

The construction of the jacket having lobes 106 a, 106b, lOGc enables the wires to be stripped apart at the ends of the cable, whilst remaining in the jacket 102. In effect the respective lobes peel apart along their lOngitudinal connection to one another. This provides benefits in terms of connecting the cable to appliances, sockets, plugs etc. The presence of the neck portions enhances the strip-ability of the cable, as does the presence of the axial bore 185.

The axial air space bore 185 in the jacket 102 has also been shown to yet further improve the performance of the cable in terms of reduced capacitance and other electromagnetic effects making the cable yet further efficient it should however be understood that in its broadest sense the invention does not require the presence of this axial bore 185.

Referring to figures 2 to 4, there is shown extrusion apparatus for Producing cable according to the invention having the air gap uo and separation interface at the tube on boundary 109.

The apparatus comprises an extrusion die 114 having a die:.

aperture conforming to the external profile configuration of the cable jacket 102. In the case of the cable of figure 1, the external profile of the cable jacket 102 is in the form of ** a three lobed cloverleaf' shape. In this case the die 114 aperture is Correspondingly shaped in the form of a cloverleaf shape. *. .

An extruder point body 118 is positioned upstream of the extrusion die 114 and has respective bores 123, 124, 125 extending through the extruder point body 118 through which are fed respective conductor wires, already having their insulator sheaths 107 in place. In figure 2 only upper and lower bores 123 and 125 (for wires 103, 105) are shown, the conductor wires 103 105 being fed from the left hand side of the apparatus.

The insulated conductor wires pass out from the extruder point body 118 via respective Cylindrical pipes 133,134,135 which have their respective downstream ends approximately co-terminal with the die aperture of the die body 114.

The molten Thermoplas0 material to form the cable jacket 102 flows along a generally conical outer surface 143 of the -1 a-extruder point body 118 an over and around the pipes 133, 134, and out through the die aperture. The flow of material has a set rate through the extruder point body 118 and die 114 and is not restricted, or choked. Because the flow rate is uniform s through the die, the thickness of the jacket 112 can be maintained accurately via adjustments to the line feed speed.

The die aperture of the die 114 is large enough for the extruder point body 118 to be Positioned within its periphery.

the extruder point body 118 includes a solid pin projection 285 for forming the axial air space bore 185 in the jacket. If the axial air space bore is not to be present in the cable, the pin projection 285 does not need to be present.

The solid jacket is formed on the pipes 133, 134, 135, an the:.

pin projection 285 upstream of the point of insertion of the conductor into the jacket (via the ends of the pipes). In this way, the already formed jacket is tubed onto the insulation sheaths 107 of the wire conductors 103, 104, 105 of conductors ensuring that a discrete non fused tube boundary 109 and separation gap 110 exists between the cable jacket 102 and the respective conductor sheaths 107 of each conductor wire. The die 114 aperture is provided substantially level with the end of the extruder body 118, such that a solid cable jacket is formed on the extruder body upstream of a point at which the cable jacket is tubed onto the conductor wires.

This is Contrasted with the prior art techniques such as certain embodiments described in W02005/027148 and W02003/075287 in which the extrusion point is behind the die aperture and the flow of material is restricted causing pressure build up and the extruded material to form about the conductors and fully embedding integrally in the jacket.

Particularly beneficial results have been achieved with cable in accordance with the present invention that has a longitudjni twist laid during manufacture The lay twist is applied following forming of the jacket 102 and Positioning of the conductor in the respective tubes formed in the cable jacket 102, at a forming station provided downstream of the extrusion apparatus.

The capacitance reduction that can be achieved using cable of the present invention is signifjcan Tests have shown that a prior art 3 core cable of conductor area l.5mm2 can have a mutual capacitance of ll0pf/m. The Clover leaf' design of figure 1 has been shown to have a mutual capacitance of in the:*. ** region of 5Opf/m for the same core area wires.

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Claims

Claims: 1. An electrical cable comprising a set of conductor wires

extending along the length of the cable, the respective conductor wires comprising a conductor core and a respective insulator sheath about the conductor core, the Conductor wires being spaced and held in a respective tube-form space provided in a cable jacket, the cable jacket being tubed Onto the conductor wire set such that a respective discrete tube-form boundary wall is present for a respective Conductor wire and an air gap exists between the tube-form boundary wall and the respective insulator sheath of the Conductor wire.
2. A cable according to claim i, wherein the cable jacket comprises an insulator material
3. A cable according to claim 1 or claim 2, wherein the **S.

cable jacket comprises a Thermoplastics material. . :
4. A cable according to any Preceding claim, wherein the respective tube form spaces for holding the respective wires are provided in discrete lobes of the jacket.
5. A cable according to claim 4, wherein the discrete lobes are Strippable to come apart from one another.
6. A cable according to any Preceding claim, wherein the cable jacket is provided with an internal bore, void-space or cavity.
7. A cable according to claim 6, wherein the cable is provided with an axial bore extending longitudinally of the cable.
8. A cable according to any Preceding claim, wherein the tube-form boundary wall is a continuous boundary around the respective conductor wire.
9. A cable according to any preceding claim, wherein a lubricant or separation layer or material is provided between the tube-form boundary wall and the respective insulator sheath of the conductor wire.
10. A cable according to claim 9 wherein the lubricant or separation material is provided in powder form. a. * * * *
11. A cable according to claim 10, wherein the lubricant or separation material comprises chalk or talc.
12. A cable according to any preceding claim, wherein the cable, including the cable jacket, is helically twisted *SS.

along its length. .. :
13. A cable according to claim 12 wherein the lay length of the twisted cable jacket is in the range 75mm to 200mm.
14. A cable according to any Preceding claim wherein the conductor set comprises three conductor wires spaced about the axis of the cable.
15. An electrical cable comprising a set of conductor wires extending along the length of the cable, the respective conductor wires being spaced and held in a respective tube-form space of a cable jacket, the cable jacket being tubed Onto the Conductor wire set; wherein the respective tube form spaces for holding the respective wires are provided in discrete lobes of -is-the jacket, the discrete lobes being strippable to come apart from one another; and/or, the cable jacket is provided with a vacant internal bore, void-space or cavity.
16. A method of manufacturing an electrical cable comprising a set of conductor wires extending along the length of the cable, the respective conductor wires comprising a conductor core and a respective insulator sheath about the conductor core, the conductor wires being spaced and:..

held in a respective tube-form space provided in a cable jacket, wherein the cable jacket is tubed Onto the conductor set such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall of the jacket and the respective insulator sheath of the respective conductor wire. is... 5. 5*
17. A method according to claim 16, wherein the tube-form boundary is already formed before tubing onto the respective wire.
18. A method according to claim 16 or claim 17, wherein the solid cable jacket is formed upstream of a point at which the cable jacket is tubed onto the conductor wire.
19. A method according to any of claims 16 to 18, in which the cable jacket is extruded on to the conductor wire set.
20. A method according to claim 19 in which the insulator sheathed conductor wires pass through extrusion apparatus and the cable jacket is extruded and tubed on around the insulator sheathed conductor wires.
21. A method according to any of claims 16 to 20, wherein a lubricant or separation layer or material is introduced between the tube-form boundary wall and the respective insulator sheathed conductor wire.
22. A method according to claim 21, wherein the lubricant or separation material is chalk or talc.
23. A method according to any of claims 16 to 22, wherein the cable, including the cable jacket, iS helically twisted along its length, during the jacket extrusion process. * S * * ..
24. A method according to any of claims 16 to 23, wherein the * cable jacket is extruded to have a vacant internal bore, void-space or cavity. *5* *

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25. A method of manufacturing an electrical cable comprising, *.S.

a set of conductor wires extending along the length of *S*s the cable, the respective conductor wires being spaced.. : and held in a respective lobe of a cable jacket, wherein the cable jacket is formed by extrusion and tubed onto the conductor wire set, the extrusion of the jacket Providing a vacant bore, void-space or cavity internally of the jacket.
26. Extrusion apparatus for forming a cable, the apparatus including: a die having a die aperture; an extruder body having: a Plurality of guide channels for guiding the passage of respective conductor wires and a surface for guiding flowable material which Solidifies to form a jacket about the respective conductor wires; wherein the die aperture is provided substantially level with the of the end of the extruder body, such that a solid cable jacket is formed on the extruder body upstream of a point at which the cable jacket is tubed onto the conductor wires.
27. Extrusion apparatus according to claim 26, wherein the extruder body has a Plurality of projecting pipes defining the ends of the plurality of guide channels for *.

guiding the passage of respective of Conductor wires, the extruder body and die being so positioned to ensure formation of tube- form spaces in the jacket with the tube-form boundary walls being formed on the Projecting * pipes. ***. * * * S. *
28. Extrusion apparatus according to claim 26 or claim 27, wherein the extruder body has a formation for defining a vacant internal bore, void-space or cavity in the extruded cable jacket.