WO2004102590A1 - An electrical cable - Google Patents

An electrical cable Download PDF

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Publication number
WO2004102590A1
WO2004102590A1 PCT/IB2004/001490 IB2004001490W WO2004102590A1 WO 2004102590 A1 WO2004102590 A1 WO 2004102590A1 IB 2004001490 W IB2004001490 W IB 2004001490W WO 2004102590 A1 WO2004102590 A1 WO 2004102590A1
Authority
WO
WIPO (PCT)
Prior art keywords
fuel
electrical cable
barrier layer
fuel barrier
layer
Prior art date
Application number
PCT/IB2004/001490
Other languages
French (fr)
Inventor
Georges Atoine Basile Marie Ghislain Boyazis
Victor Charles Hall
Original Assignee
Colvic Petroleum Products (Pty) Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Colvic Petroleum Products (Pty) Ltd filed Critical Colvic Petroleum Products (Pty) Ltd
Publication of WO2004102590A1 publication Critical patent/WO2004102590A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
    • H01B7/282—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable
    • H01B7/2825—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable using a water impermeable sheath
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A30/00—Adapting or protecting infrastructure or their operation
    • Y02A30/14—Extreme weather resilient electric power supply systems, e.g. strengthening power lines or underground power cables

Definitions

  • This invention relates to an electrical cable.
  • the cables have included a drawn copper core which is used to conduct electricity and which is covered with pigmented PVC for core identification. These cores are then embedded in a flexible PVC sheath followed by metal strand armouring and then a PVC outer sheath making up the cable.
  • the outer sheath may be formed from different materials such as a low density polyethylene or a cross linked polyethylene.
  • the outer sheath may be formed from another material which may give the cable a fire retardant characteristic.
  • an electrical cable comprising:
  • a core comprised of an electrical conducting material
  • the fuel barrier layer being formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough, wherein the fuel barrier layer is the outermost layer of the electrical cable.
  • the electrical cable may further comprise an armour layer which may be formed from a metal.
  • the at least one insulation layer may be formed from a pigmented PVC.
  • the fuel barrier layer is formed from a polyethylene or polypropylene material which has been fluorinated.
  • the fuel barrier layer may be formed from PolytetraFluoro Ethylene (PTFE) or Viton.
  • the fuel barrier layer may be formed from a nylon sheath.
  • the fuel barrier layer is not dissolved or otherwise broken down by liquid fuel
  • an electrical cable according to the present invention includes a core 10 comprised of an electrical conducting material, typically in the form of a drawn copper core.
  • a core 10 comprised of an electrical conducting material, typically in the form of a drawn copper core.
  • the cable in the accompanying drawing includes only one core 10, the cable could equally include a plurality of cores 10.
  • the core 10 is surrounded with at least one insulation layer in the form of a pigmented PVC layer 12 which is used for core identification.
  • the prototype of the present invention included a second insulation layer in the form of a flexible PVC sheath 14. Furthermore, the prototype of the present invention also included an armour layer 16 typically formed from metal strands surrounding the other layers to protect them. It will be appreciated that this layer may not be necessary.
  • the second insulation layer 12 and the armour layer 16 may not always be required and may be left out of the electrical cable for certain applications.
  • the electrical cable is surrounded by a fuel barrier layer 18 which is formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough and which is not dissolved in or otherwise broken down by liquid fuel.
  • the fuel barrier layer is the outermost layer of the electrical cable
  • the fuel barrier layer is preferably formed from a high density polyethylene which has been fluorinated as will be described in more detail below.
  • the fuel barrier layer 18 may also be formed from a low or medium density polyethylene which has been fluorinated or a polypropylene material which has been fluorinated.
  • Polypropylene is not preferred as it is more rigid and not as good a barrier as polyethylene.
  • a nylon sheet may also be used as the fuel barrier layer 18, but this is not preferred as it is relatively more expensive and is not as flexible.
  • the fuel barrier layer 18 may be made from other types of materials which are resistant to fuels and chemicals such as the fluoroelastomer onTM.
  • fluorination is a chemical substitution process where hydrogen atoms bonded on the carbon chains of the polymer are substituted with fluorine molecules introduced into the process as elemental fluorine in a mixture with nitrogen gas.
  • the process being one of chemical substitution induces chemical bonding of the carbon and fluorine atoms forming a PolytetraFluoro Ethylene molecule (PTFE) or better known as TeflonTM. Due to the substitution, the fluorine atoms are integrated into the matrix of the polymer and the change is thus permanent, and can not be delaminated as other methods used to reduce fuel permeation in polyethylene matrices. The process however only occurs on the surface of the polymer.
  • in-line and off-line fluorination There are two methods of fluorination, namely in-line and off-line fluorination.
  • the in-line process is only used when a blow moulding operation is active where the blowing gas (normally air) is replaced with a fluorine/nitrogen mixture.
  • the off-line or post fluorination process is utilized.
  • the process requires the cable to be coiled onto a rack, which is then placed into a heated vacuum chamber (autoclave) where the internal atmosphere is changed by removing atmospheric air by way of vacuum with the reaction gases comprising of a fluorine/nitrogen mixture.
  • the cable is left in this atmosphere for a period of time to allow the substitution to take place to the required calculated level.
  • the level of fluorination is calculated by working out the surface area of the product to be fluorinated. Once this is known, the amount of fluorine can be calculated by various analytical calculating methodologies and thus the correct mass of diluted fluorine is added into the reactor.
  • the standing time of the product in the gas mixture is determined using previous data obtained by comparing the substitution ratio of carbon/fluorine atoms to the amount of un-reacted carbon/hydrogen atoms on the surface using a Fourier Turner Infrared Spectrophotometer (FTIR) for the purpose. The ratio obtained is thus compared to existing results of control samples.
  • the permeation characteristics of the control samples have been subjected to various international accreditation, which determines the amount permeation over an area of the product. Permeation of any substance depends on four processes, namely wetting, compatibility, mobility (migration) and evaporation. If any of these steps can be stopped then permeation through the substance will not occur.
  • Wetting is the process whereby the solvent will wet the surface of the solid.
  • petrol wets the surface of polyethylene. This would mean that the solvent will penetrate the surface of the solid.
  • Compatibility means that if the solvent has the same polarity as the solid it will be able to be absorbed or the two will mix (polar solvent/polar solid or non-polar solvent/non-polar solid are compatible).
  • Mobility means that the molecules which are compatible must be able to move through the material, i.e. they should be small enough for them to pass in between the molecules of the solid.
  • Evaporation means that the solvent when it gets to the other side of the wall must be removed by a process e.g. evaporation, otherwise the polymer will become saturated and the process will stop
  • permeation By stopping or limiting any one of the above processes, permeation will be halted.
  • the first step In the case of fluorination of the surface, the first step is halted, namely wetting and thus the permeation is halted at the surface.
  • the present invention has a number of advantages. Firstly, no fuel is allowed to permeate into the substrate of the polymeric sheath.
  • the fluorination layer is chemically bonded into the PE substrate, and therefore cannot wear off, or be delaminated.
  • the sheath is a cost effective sheath.
  • the material is easy to handle during the manufacturing process and avoids any excess layers being added to the cable.
  • the cable meets the South African Bureau of Standards 1507 requirements.
  • the cable is fuel and chemical resistant.

Landscapes

  • Organic Insulating Materials (AREA)
  • Insulated Conductors (AREA)

Abstract

According to the present invention there is provided an electrical cable including a core comprised of an electrical conducting material and at least one insulation layer surrounding the core. A fuel barrier layer surrounds the insulation layer, the fuel barrier layer being formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough. The fuel barrier layer is the outermost layer of the electrical cable. The fuel barrier layer is preferably formed from a polyethylene or polypropylene material which has been fluorinated and is not dissolved or otherwise broken down by liquid fuel.

Description

AN ELECTRICAL CABLE
BACKGROUND OF THE INVENTION
This invention relates to an electrical cable.
Electrical cables to be used in fuel stations and storage depots have typically not been much different from electrical cables made for other applications.
The cables have included a drawn copper core which is used to conduct electricity and which is covered with pigmented PVC for core identification. These cores are then embedded in a flexible PVC sheath followed by metal strand armouring and then a PVC outer sheath making up the cable.
In certain instances, the outer sheath may be formed from different materials such as a low density polyethylene or a cross linked polyethylene. Alternatively, the outer sheath may be formed from another material which may give the cable a fire retardant characteristic.
It has been known for manufacturers to add an extra layer between the outer sheath and the metal armouring, namely a lead liner layer which results in a lead jacketed cable. Although the lead is fuel resistant, the outer sheath is open to attack by the fuel and tends to become brittle or dissolve in fuel.
Until recently, these kind of cables have been useful, but with the introduction of new additives in fuels such as toluene, xylene, acetone and MEK as well as new unleaded fuels, materials which have commonly been known to work in the fuel environment have been failing. Cables have started failing due to the additives dissolving the sheath and inner liners and exposing the copper core. Once exposed, the cores which carry electricity have been known to arc and create sparks which have caused fires.
The problems are compounded when the cables are used to supply current to submersible pumps in manholes above underground tanks where fuel fumes rich in lower flashpoint compounds accumulate. When the manhole is opened daily to dip the tanks, air is introduced into the mixtures and an explosive mixture is obtained. The spark from the cable is all that is needed to ignite the mixture and heavy manhole covers have been known to be shot up into the air several metres, for example.
It is an object of the present invention to address this.
SUMMARY OF THE INVENTION
According to the present invention there is provided an electrical cable comprising:
a core comprised of an electrical conducting material;
at least one insulation layer surrounding the core; and
a fuel barrier layer surrounding the insulation layer, the fuel barrier layer being formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough, wherein the fuel barrier layer is the outermost layer of the electrical cable.
The electrical cable may further comprise an armour layer which may be formed from a metal.
The at least one insulation layer may be formed from a pigmented PVC. Preferably, the fuel barrier layer is formed from a polyethylene or polypropylene material which has been fluorinated.
The fuel barrier layer may be formed from PolytetraFluoro Ethylene (PTFE) or Viton.
Alternatively, the fuel barrier layer may be formed from a nylon sheath.
Preferably, the fuel barrier layer is not dissolved or otherwise broken down by liquid fuel
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing is a schematic drawing of an electrical cable according to the present invention
DESCRIPTION OF AN EMBODIMENT
Referring to the accompanying drawing, an electrical cable according to the present invention includes a core 10 comprised of an electrical conducting material, typically in the form of a drawn copper core. Although the cable in the accompanying drawing includes only one core 10, the cable could equally include a plurality of cores 10.
The core 10 is surrounded with at least one insulation layer in the form of a pigmented PVC layer 12 which is used for core identification.
The prototype of the present invention included a second insulation layer in the form of a flexible PVC sheath 14. Furthermore, the prototype of the present invention also included an armour layer 16 typically formed from metal strands surrounding the other layers to protect them. It will be appreciated that this layer may not be necessary.
It is envisaged that the second insulation layer 12 and the armour layer 16 may not always be required and may be left out of the electrical cable for certain applications.
Finally, the electrical cable is surrounded by a fuel barrier layer 18 which is formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough and which is not dissolved in or otherwise broken down by liquid fuel. The fuel barrier layer is the outermost layer of the electrical cable
The fuel barrier layer is preferably formed from a high density polyethylene which has been fluorinated as will be described in more detail below.
It is envisaged that the fuel barrier layer 18 may also be formed from a low or medium density polyethylene which has been fluorinated or a polypropylene material which has been fluorinated.
Polypropylene is not preferred as it is more rigid and not as good a barrier as polyethylene.
A nylon sheet may also be used as the fuel barrier layer 18, but this is not preferred as it is relatively more expensive and is not as flexible.
Alternatively, the fuel barrier layer 18 may be made from other types of materials which are resistant to fuels and chemicals such as the fluoroelastomer on™.
The process known as fluorination is a chemical substitution process where hydrogen atoms bonded on the carbon chains of the polymer are substituted with fluorine molecules introduced into the process as elemental fluorine in a mixture with nitrogen gas. The process being one of chemical substitution induces chemical bonding of the carbon and fluorine atoms forming a PolytetraFluoro Ethylene molecule (PTFE) or better known as Teflon™. Due to the substitution, the fluorine atoms are integrated into the matrix of the polymer and the change is thus permanent, and can not be delaminated as other methods used to reduce fuel permeation in polyethylene matrices. The process however only occurs on the surface of the polymer.
There are two methods of fluorination, namely in-line and off-line fluorination. The in-line process is only used when a blow moulding operation is active where the blowing gas (normally air) is replaced with a fluorine/nitrogen mixture. As no blow moulding operation is undertaken in the manufacture of cable, the off-line or post fluorination process is utilized. The process requires the cable to be coiled onto a rack, which is then placed into a heated vacuum chamber (autoclave) where the internal atmosphere is changed by removing atmospheric air by way of vacuum with the reaction gases comprising of a fluorine/nitrogen mixture. The cable is left in this atmosphere for a period of time to allow the substitution to take place to the required calculated level. The level of fluorination is calculated by working out the surface area of the product to be fluorinated. Once this is known, the amount of fluorine can be calculated by various analytical calculating methodologies and thus the correct mass of diluted fluorine is added into the reactor. The standing time of the product in the gas mixture is determined using previous data obtained by comparing the substitution ratio of carbon/fluorine atoms to the amount of un-reacted carbon/hydrogen atoms on the surface using a Fourier Turner Infrared Spectrophotometer (FTIR) for the purpose. The ratio obtained is thus compared to existing results of control samples. The permeation characteristics of the control samples have been subjected to various international accreditation, which determines the amount permeation over an area of the product. Permeation of any substance depends on four processes, namely wetting, compatibility, mobility (migration) and evaporation. If any of these steps can be stopped then permeation through the substance will not occur.
Wetting is the process whereby the solvent will wet the surface of the solid. In the present case, petrol wets the surface of polyethylene. This would mean that the solvent will penetrate the surface of the solid.
Compatibility means that if the solvent has the same polarity as the solid it will be able to be absorbed or the two will mix (polar solvent/polar solid or non-polar solvent/non-polar solid are compatible).
Mobility means that the molecules which are compatible must be able to move through the material, i.e. they should be small enough for them to pass in between the molecules of the solid.
Evaporation means that the solvent when it gets to the other side of the wall must be removed by a process e.g. evaporation, otherwise the polymer will become saturated and the process will stop
By stopping or limiting any one of the above processes, permeation will be halted. In the case of fluorination of the surface, the first step is halted, namely wetting and thus the permeation is halted at the surface.
The present invention has a number of advantages. Firstly, no fuel is allowed to permeate into the substrate of the polymeric sheath.
The fluorination layer is chemically bonded into the PE substrate, and therefore cannot wear off, or be delaminated.
The sheath is a cost effective sheath.
The material is easy to handle during the manufacturing process and avoids any excess layers being added to the cable. The cable meets the South African Bureau of Standards 1507 requirements.
The cable is fuel and chemical resistant.

Claims

CLAIMS:
1. An electrical cable comprising:
a core comprised of an electrical conducting material;
at least one insulation layer surrounding the core; and
a fuel barrier layer surrounding the insulation layer, the fuel barrier layer being formed from a fuel barrier material which does not allow liquid fuel or fuel vapours to permeate therethrough, wherein the fuel barrier layer is the outermost layer of the electrical cable.
2. An electrical cable according to claim 1 further comprising an armour layer formed from a metal.
3. An electrical cable according to claim 1 or claim 2 wherein the at least one insulation layer is formed from pigmented PVC.
4. An electrical cable according to any preceding claim wherein the fuel barrier layer is formed from a polyethylene or polypropylene material which has been fluorinated.
5. An electrical cable according to claim 4 wherein the fuel barrier layer is formed from PolytetraFluoro Ethylene (PTFE) or Viton.
6. An electrical cable according to claim 4 wherein the fuel barrier layer is formed from a nylon sheath.
7. An electrical cable according to any preceding claim wherein the fuel barrier layer is not dissolved or otherwise broken down by liquid fuel.
8. An electrical cable substantially as herein described with reference to the accompanying drawing.
PCT/IB2004/001490 2003-05-16 2004-05-11 An electrical cable WO2004102590A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ZA200303815 2003-05-16
ZA2003/3815 2003-05-16

Publications (1)

Publication Number Publication Date
WO2004102590A1 true WO2004102590A1 (en) 2004-11-25

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Application Number Title Priority Date Filing Date
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ZA (1) ZA200509270B (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9002602A (en) * 1990-11-28 1992-06-16 Nkf Kabel Bv Electrical cable having good chemicals, oils and solvents resistance - contg core of electrical or fibre=optic conductors, thin polyester foil and wound metallic layer having synthetic resin layer on each side
FR2709592A1 (en) * 1993-09-02 1995-03-10 Pirelli Cables Cable resistant to chemical attack
DE19828501A1 (en) * 1998-06-26 2000-01-05 Eilentropp Kg High voltage electric cable, especially a detonation cable
WO2000074075A1 (en) * 1999-06-02 2000-12-07 Tyco Electronics Corporation Insulated electrical conductor

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9002602A (en) * 1990-11-28 1992-06-16 Nkf Kabel Bv Electrical cable having good chemicals, oils and solvents resistance - contg core of electrical or fibre=optic conductors, thin polyester foil and wound metallic layer having synthetic resin layer on each side
FR2709592A1 (en) * 1993-09-02 1995-03-10 Pirelli Cables Cable resistant to chemical attack
DE19828501A1 (en) * 1998-06-26 2000-01-05 Eilentropp Kg High voltage electric cable, especially a detonation cable
WO2000074075A1 (en) * 1999-06-02 2000-12-07 Tyco Electronics Corporation Insulated electrical conductor

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Publication number Publication date
ZA200509270B (en) 2007-01-31

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