CA2231829A1 - Grounding electrode - Google Patents
Grounding electrode Download PDFInfo
- Publication number
- CA2231829A1 CA2231829A1 CA002231829A CA2231829A CA2231829A1 CA 2231829 A1 CA2231829 A1 CA 2231829A1 CA 002231829 A CA002231829 A CA 002231829A CA 2231829 A CA2231829 A CA 2231829A CA 2231829 A1 CA2231829 A1 CA 2231829A1
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- CA
- Canada
- Prior art keywords
- conductive member
- jacket
- elongate
- elongate conductive
- article
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
- C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
- C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
- C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
- H01R4/00—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation
- H01R4/58—Electrically-conductive connections between two or more conductive members in direct contact, i.e. touching one another; Means for effecting or maintaining such contact; Electrically-conductive connections having two or more spaced connecting locations for conductors and using contact members penetrating insulation characterised by the form or material of the contacting members
- H01R4/66—Connections with the terrestrial mass, e.g. earth plate, earth pin
Abstract
An elongate conductive member, preferably suitable as a grounding electrode, and comprising (a) an elongate core comprising a material, (b) a conductive polymeric element that surrounds, and is in electrical contact with the core, (c) a jacket that surrounds the conductive polymeric element and is spaced therefrom, and (d) a carbon rich material between the jacket and the conductive polymeric element.
Description
W O 97/141~6 PCT/GB~ 2302 GROUNDING F~ FCTRODE
This invention relates to an elongate conductive member suitable for use as a grounding electrode. In particular it relates to an elongate conductive member comprisin~ an inner conductive core, a surrounding jacket, and a particulate carbon rich material contained between the jacket and the core. The invention also provides methods of eleckically grounding articles using the elongate conductive member.
An elongate conductive member having the construction described above is known, for use not as a grounding electrode, but as an impressed current corrosion protection anode. WO9302311 (RK463) and GB 9411787.6 (B265), for example, each describe an elongate member comprising (i) a continuous elongate core having a resistivity at 23~C of less than Sx10~ ohm cm, and a resi~t~n~e at 23~ of less than 0.03 ohm/m (usually a metal), (ii) an element which is comprised of a conductive polymer composition, which preferably has an elongation of at least 10% and surrounds and is in eleckical contact with the core, and is at least 500 microns thick, (iii) a polymeric fabric outer jacket, and (iv) contained with;n the polymeric jacket, a particulate carbon rich material such as coke. Preferred materials for the polymeric jacket of the anodes described in the earlier patent applications are said to be polymers, copolymers or blends of polyacrylonitrile, partially or wholly halogentated aliphatic polymers, particularly polyvinylidene chloride or fluoride polytetrafluoroethylene, poly(ethylene-tekafluoroethylene), poly(ethylene-chlol~llifluoroethylene), polyvinyl fluoride, polyvinylchloride and polyvinylacetate. Preferred materials based on polyacrylonikiles are Dralon (Bayer), Orlon (Dupont), Courtelle (Courtaulds), Acrilan (Monsanto), and Dolan (Hoechst). Especially preferred materials are modacrylic polymers, that is a material comprising between 35% and 85% polyacrylonikile, for example, Teklan (Courtaulds - which comprises 50/50 polyacrylonikile/polyvinylidene dichloride), Velicren (Enimont), SEF (Monsanto) and Kaneklon (a vinyl chloride based composition supplied by Kanegafuchi).
Another preferred mzlteri~l is Saran (PVDC copolymer from Dow Chemical).
SUBSTITUTE SltEEr IRULE 26) W 0 97/14196 PCT/~5CI~ 30Z
Another possible though less ~ler~ ed, m~teri~l is poly(butylene-terephth~l~te). The preferred polymeric materials are selected in the earlier references to be particularly acid and chlorine re~i~t~nt which was found to be important for good lifetime performance of the elongate conductive members in an illlplessed current corrosion protection system.
In the known illl~lessed current corrosion protection systems the elongate conductive member is cormected, via a power supply of constant sign, to the article to be protected from corrosion. Electrolyte, e.g. soil, is present between the article to be protected from corrosion and the elongate conductive member, therefore completing a circuit and an electrochemiGal cell. Electrical current flows from the electrode (which acts as an anode) to the article, which acts as a cathode, to protect the article from corrosion. Typically the current density of the protective current flowing from the anode surface is of the order of 50 mA/m. Although current density values are often given in units of A/m, for ~;ullc~ flowing from the surface of elongate electrodes it is common practice to quote current densities in units of A/m, this being the total current value per metre length of the elongate electrode. Elongate electrodes known in the art, and used in the present invention typically have an outer diameter in the range 10 to 40mm.
The entire disclosures of W 09302311 and GB 941 1787, and their corresponding US applications, are incorporated herein by reference.
We have now found that an elongate conductive member, having a similar construction to that described in W093023 1 1 and GB 941 1787, but with an outerconductive jacket in place of the polymeric jacket of the references can be used as an efficient electrical grounding member. This is surprising given that the elongate conductive member is acting in a different electrical fashion in a grounding application from in an impressed current corrosion protection system. In particular, it is surprising since the current densities at discharge in a grounding application are of SUBSTITUTE SHEEI (RULE 26) the order of about 300 to 2000 A/m, i.e. six to forty times as high as that involved in impressed current corrosion protection systems.
Accordingly the present invention provides an elongate conductive member comprising:
(i) an elongate core comprising a m~t.?ri~l having a resistivity at 23~C of less than 5xl0~ ohm cm and a reSict~n~e at 23~C of less than 0.03 ohm/meter;
(ii) a conductive polymer element that surrounds and is in electrical contact with the core;
(iii) a jacket that surrounds the conductive polymeric element and is spaced t~l&l~rl~lll; and (iv) a carbon rich material in particulate form contained within the jacket, between the jacket and the conductive polymeric element;
characterised in that the elongate conductive member is suitable for use as a grounding electrode, and that the jacket material is electrically conductive, having a resistivity of less than 100 ohm cm The resistivity of the jacket m~t~ri~l iS preferably less than S0 ohm cm; more preferably less than 30 ohm cm, especially less than 20 ohm cm, more especially less than 10 ohm cm, even less than 5 ohm cm, or less than 2 ohm cm. An especially pl~rt;ll~d material for the jacket is carbon fibre having a resistivity of about 1.4 ohm cm.
The present invention preferably also provides a method of electrically grounding an article comprising, SUBSTITUTE SHEEr (RULE 26 CA 0223l829 l998-03-l2 (i) providing an elongate conductive member according to the invention, and (ii) electrically connecting one end of the elongate conductive member to the article to be grounded.
The core of the elongate conductive member of the present invention is preferably a metal, for example copper. Preferably the core has a diameter in the range of 2 to 10 mm. The core may comprise one or more wires.
The conductive polymeric element that surrounds, and is in electrical contact with the core is preferably a layer having a thickness in the range 500xlO~~m to 20mm thick. The conductive polymeric element preferably has a resistivity in the range 0.1 to 105 ohm cm, preferably 0.1 to 104 ohm cm, preferably 0.1 to 103 ohm cm, particularly 1 to 100 ohm cm, especially 1 to 50 ohm cm.
As used herein, the term "conductive polymer" means a composition compri~ing a polymer component, and dispersed therein a particulate conductive filler, for example carbon black. The term "conductive polymer" includes those compositions in which the polymer composition is a thermoplastic, a rubber or a thermoplastic rubber. Examples of m~teri~l.c for the base polymer component include acrylate rubbers, butyl or nitrile rubbers, olefin homopolymers, and copolymers, and fluorinated or chlorinated polymers.
In a preferred embodiment according to the present invention, the electrically conductive jacket of the grounding electrode is in the form of a fabric. Examples of suitable fabric constructions include weaves, braids, knits, warp-inserted-weft knits (WIWK), and the like. A particularly pler~.led jacket is a fabric jacket comprising carbon fibre, or a fabric jacket compri~ing flexible conductive polymeric fibres.
Although a fabric jacket is preferred, non-fabric conductive jackets, for example a continuous conductive polymeric jacket, are also envisaged.
SUBSTITUTE SHEET (RULE 26) W O 97/141~6 PCT/GB96/02302 s The multi layer construction of the elongate conductive member of the present invention provides a balance of properties making it particularly effective as agrounding electrode. The inner (usually metal) highly conductive core ensures current is tr~n~mitte~ rapidly away from the article to be grounded. The conductive polymeric layer surrounding and in electrical contact with the inner core, protects the inner core from rusting. Also the conductive polymeric layer, since it has a higher radial re~i~t~nce than the inner core, acts to distribute the electrical current further along the length of the elongate conductive member, prior to discharge into the ground, than would be the case in the absence of the conductive polymeric layer. This may enhance the lifetime of the grounding member, and avoids overheating at points directly beneath the articles being electrically grounded. The carbon rich particulate material, e.g. coke, surrounding the conductive polymeric layer reduces the resi~t~nce to ground at any particular point along the conductive member, compared to the same electrode in the absence of coke. The reduction in the rÇsict~nce to ground is achieved primarily by the increase in surface area provided by the presence of the carbon rich particulate m~teri~l A similar effect could be achieved, for example, by using a much thicker conductive polymeric layer. However, this would be much more expensive.
The conductive jacket retains the coke, and facilitates h~n~llin?~ of the coke cont~inin~
electrode. The conductive nature of the jacket ensures the radial rç~i~t~nce to ground is minimi~ed.
I he elongate conductive members according to the invention may vary in length considerably. Preferred lengths range from 1 to 500 m. Different lengths are plc;r~,led for different applications. For example, for grounding an article to resist a lipht~ning pulse, which typically lasts for a period of the order of a few microseconds, lengths of about lm are pler~ d. For grounding an article such as switchgear, which may be subjected to ~ lL~ of the order of thousands of Amps for a period of about a second, longer lengths, of several hundred metres, e.g. 200m, 300m or even 500m may be plc;rellc~d. In general, the longer the time period in which current is p~c~in~, the longer the preferred length of the conductive member of the present invention.
The length preferred also varies according to the soil resistivity in which the SUBSTITIJTE SlrlEE~ (RULE 2~) CA 0223l829 l998-03-l2 W O 97/14196 PCT/~ 30Z
conductive member is used. Where the length of the conductive member required islonger than about 50m, this may be provided by a single elongate conductive member, or by joining several conductive members end to end.
Preferably an additional resistive member is used in conjunction with the elongate conductive member of the present invention. The additional member is preferably positioned to surround and to be in electrical contact with the end of the elongate conductive member that is connected in use to the article to be grounded.
The shape and the resistivity of the additional resistive member are arranged to reduce the flow of current from the elongate conductive member from the part thereof surrounded by the resistive member. For example the additional resistive member may be generally conical, the widest part of the cone being nearest the said end of the elongate conductive member. The purpose of this additional resistive member is to reduce the increased current density that would otherwise exit the elongate conductive member at its point of connection to the article to be grounded. This feature isdescribed in British Patent Application (our reference B302 GBl) which is filed contemporareously herewith. The entire disclosure of .. (B302 GBl), andany corresponding US application, is incorporated herein by reference.
The present invention preferably provides a kit of parts comprising an elongate conductive member according to the invention, in combination with an additional resistive member of the type described above, and a method of electrically grounding an article using such a kit of parts.
The jacket of the elongate conductive member is preferably flexible, and used in combination with tensioning wraps tensioned around the flexible jacket such that the compaction of the particulate carbon rich material is increased relative to their compaction in the absence of such wraps. The outer tensioning wraps may advantageously be in the form of a braid. The flexible jacket of the elongate conductive member is flexible to the extent that it can be deformed into different configurations by movement of the particulate carbon rich material within it, and/or SUE~5~ A _ _~L ~ L_ ~6) - W O 97/141~6 PCT/GB96/02302 by the action of the tensioning wraps. The tensioning wraps preferably do not add significantly to the overall radial resistance of the elongate conductive member.
Preferably the tensioning wraps comprise a material that has similar pl~f~ d resistivity values to those stated above as being ~lcr~lled for the jacket of the elongate conductive member.
In the event that a section of the jacket of the elongate conductive member is damaged, it can be conveniently repaired by carrying out the following plc;r~ledmethod steps:
(i) securing annular portions of the jacket close to the conductive polymeric element, on either side of the damaged section of jacket;
(ii) removing the damaged jacket section and particulate carbon rich m~teri~l between the secured annular portions, to expose a length of the conductive polymeric element;
(iii) positioning a repair sleeve (preferably wraparound) around, but spaced from the exposed length of conductive polymeric element;
(iv) securing a first end of the repair sleeve to the underlying jacket;
(v) filling the space between the repair sleeve and the core with a carbon rich particulate m~t~ri~l; then (vi) securing the other end of the repair sleeve to the underlying jacket The repair sleeve preferably has the same physical and electrical properties as the jacket of the elongate conductive member.
SUBSTITUTE SI~IEET (RULE 26) Particular applications of the present invention include the grounding of pipelines, high energy switch gear and buildings.
Embo~liment.e of the present invention are now described, by way of example, with reference to the acconlpallyillg drawings, wherein Figure 1 shows an eleckical grounding application in which the elongate grounding member of the present invention can be used, and Figure 2 shows in detail the elongate grounding member used in Figure 1.
Figure 1 shows an eleckical grounding application in which the elongate grounding member of the present invention can be used. A building 1 to be protected is conn~cte~l via an ine~ tc-l lead wire 3 to an elongate conductive member 5 buried in soil 7.
Figure 2 shows in detail the construction of the elongate conductive member 5.
The member 5 comprises a cylindrical copper core 7, a conductive polymeric element in the form of a layer 9 surrounding and in electrical contact with the core 7, an outer tubular carbon fibre woven jacket 11, and particulate coke 13 sandwiched between the woven jacket 11 and the conductive polymeric layer 9. The outer diameter measurement resistivity values of each of the components of the conductive member 5 are set out below in Table 1. The actual thickness of any particular layer may be calculated by subkaction of the relevant outer diameter values.
Table 1 Outer diameter in Resistivity in mm ohm.m at 20~c Core 7 (copper) 4.11.8 x 10-~
Conductive SUBSTITUTE SHEET (RULE 26) CA 0223l829 l998-03-l2 W O 97/14196 PCTI~D~5.~302 polymeric element 9 13.0 1.5 x 10-' Coke layer 13 37.0 1 x 10-~
Carbon fibre jacket 11 37.8 1.4x 10-2 Although the resistivity of the carbon fibre jacket is similar to that of the conductive polymeric jacket, it contributes far less to the overall resi~t~nce of the elongate conductive member, since it is much thinner than the conductive polymeric element ~. In other words, the conductive polymeric element is the most significant resistive member in the conductive member, and therefore controls the current flow along, and ~ut of the conductive member.
The resistance to ground of an elongate conductive member according to the invention, having the construction of Figure 2, was measured at 50 H~ in (i) soil haying a ground resistivity of 2850 ohm cm, and (ii) soil having a ground resistivity of 65000 ohm cm.
The resi~t~nce measurement was carried out by positioning the electrode according to Figure 2 and a counter elongate electrode in the soil, generally parallel to each other, but spaced apart, and applying a potential difference at 50Hz, between the two electrodes. A re~ t~nce measuring electrode, also elongate in construction, was positioned between the electrode according to the invention and the counter electrode.
As a colnl)~dLive control, an elongate conductive member having the same construction as that shown in Figure 2, but with the carbon fibre jacket replaced by a Velicren jacket was tested under the same conditions. Velicren in a polyacrylonitrile based material supplied by Enimont. The results are set out in Table 2 below.
SUBSTITUTE SHEE~ (RULE 26) CA 0223l829 l998-03-l2 W O 97/14196 PCT/GB9G~'~2~02 Table ?.
Resistance to ground ohms Resistance to ground in as measured in soil of ohms, as measured in soil resistivity 2850 ohm cm of resistivity 65000 ohm cm Figure 2 embodiment (carbon fibre jacket) 20 395 Figure 2 embodiment with carbon fibre jacket 9600 7300 replaced by a fabric poly , acrylonitrile-based jacket (comparative example) As can be seen the resi~t~nce to ground is drastically reduced using a conductive carbon fibre jacket co~ ~ed to the resistance to ground using a polyacrylonitrile based jacket.
SUBSTITUTE SHEET ff~ULE 26)
This invention relates to an elongate conductive member suitable for use as a grounding electrode. In particular it relates to an elongate conductive member comprisin~ an inner conductive core, a surrounding jacket, and a particulate carbon rich material contained between the jacket and the core. The invention also provides methods of eleckically grounding articles using the elongate conductive member.
An elongate conductive member having the construction described above is known, for use not as a grounding electrode, but as an impressed current corrosion protection anode. WO9302311 (RK463) and GB 9411787.6 (B265), for example, each describe an elongate member comprising (i) a continuous elongate core having a resistivity at 23~C of less than Sx10~ ohm cm, and a resi~t~n~e at 23~ of less than 0.03 ohm/m (usually a metal), (ii) an element which is comprised of a conductive polymer composition, which preferably has an elongation of at least 10% and surrounds and is in eleckical contact with the core, and is at least 500 microns thick, (iii) a polymeric fabric outer jacket, and (iv) contained with;n the polymeric jacket, a particulate carbon rich material such as coke. Preferred materials for the polymeric jacket of the anodes described in the earlier patent applications are said to be polymers, copolymers or blends of polyacrylonitrile, partially or wholly halogentated aliphatic polymers, particularly polyvinylidene chloride or fluoride polytetrafluoroethylene, poly(ethylene-tekafluoroethylene), poly(ethylene-chlol~llifluoroethylene), polyvinyl fluoride, polyvinylchloride and polyvinylacetate. Preferred materials based on polyacrylonikiles are Dralon (Bayer), Orlon (Dupont), Courtelle (Courtaulds), Acrilan (Monsanto), and Dolan (Hoechst). Especially preferred materials are modacrylic polymers, that is a material comprising between 35% and 85% polyacrylonikile, for example, Teklan (Courtaulds - which comprises 50/50 polyacrylonikile/polyvinylidene dichloride), Velicren (Enimont), SEF (Monsanto) and Kaneklon (a vinyl chloride based composition supplied by Kanegafuchi).
Another preferred mzlteri~l is Saran (PVDC copolymer from Dow Chemical).
SUBSTITUTE SltEEr IRULE 26) W 0 97/14196 PCT/~5CI~ 30Z
Another possible though less ~ler~ ed, m~teri~l is poly(butylene-terephth~l~te). The preferred polymeric materials are selected in the earlier references to be particularly acid and chlorine re~i~t~nt which was found to be important for good lifetime performance of the elongate conductive members in an illlplessed current corrosion protection system.
In the known illl~lessed current corrosion protection systems the elongate conductive member is cormected, via a power supply of constant sign, to the article to be protected from corrosion. Electrolyte, e.g. soil, is present between the article to be protected from corrosion and the elongate conductive member, therefore completing a circuit and an electrochemiGal cell. Electrical current flows from the electrode (which acts as an anode) to the article, which acts as a cathode, to protect the article from corrosion. Typically the current density of the protective current flowing from the anode surface is of the order of 50 mA/m. Although current density values are often given in units of A/m, for ~;ullc~ flowing from the surface of elongate electrodes it is common practice to quote current densities in units of A/m, this being the total current value per metre length of the elongate electrode. Elongate electrodes known in the art, and used in the present invention typically have an outer diameter in the range 10 to 40mm.
The entire disclosures of W 09302311 and GB 941 1787, and their corresponding US applications, are incorporated herein by reference.
We have now found that an elongate conductive member, having a similar construction to that described in W093023 1 1 and GB 941 1787, but with an outerconductive jacket in place of the polymeric jacket of the references can be used as an efficient electrical grounding member. This is surprising given that the elongate conductive member is acting in a different electrical fashion in a grounding application from in an impressed current corrosion protection system. In particular, it is surprising since the current densities at discharge in a grounding application are of SUBSTITUTE SHEEI (RULE 26) the order of about 300 to 2000 A/m, i.e. six to forty times as high as that involved in impressed current corrosion protection systems.
Accordingly the present invention provides an elongate conductive member comprising:
(i) an elongate core comprising a m~t.?ri~l having a resistivity at 23~C of less than 5xl0~ ohm cm and a reSict~n~e at 23~C of less than 0.03 ohm/meter;
(ii) a conductive polymer element that surrounds and is in electrical contact with the core;
(iii) a jacket that surrounds the conductive polymeric element and is spaced t~l&l~rl~lll; and (iv) a carbon rich material in particulate form contained within the jacket, between the jacket and the conductive polymeric element;
characterised in that the elongate conductive member is suitable for use as a grounding electrode, and that the jacket material is electrically conductive, having a resistivity of less than 100 ohm cm The resistivity of the jacket m~t~ri~l iS preferably less than S0 ohm cm; more preferably less than 30 ohm cm, especially less than 20 ohm cm, more especially less than 10 ohm cm, even less than 5 ohm cm, or less than 2 ohm cm. An especially pl~rt;ll~d material for the jacket is carbon fibre having a resistivity of about 1.4 ohm cm.
The present invention preferably also provides a method of electrically grounding an article comprising, SUBSTITUTE SHEEr (RULE 26 CA 0223l829 l998-03-l2 (i) providing an elongate conductive member according to the invention, and (ii) electrically connecting one end of the elongate conductive member to the article to be grounded.
The core of the elongate conductive member of the present invention is preferably a metal, for example copper. Preferably the core has a diameter in the range of 2 to 10 mm. The core may comprise one or more wires.
The conductive polymeric element that surrounds, and is in electrical contact with the core is preferably a layer having a thickness in the range 500xlO~~m to 20mm thick. The conductive polymeric element preferably has a resistivity in the range 0.1 to 105 ohm cm, preferably 0.1 to 104 ohm cm, preferably 0.1 to 103 ohm cm, particularly 1 to 100 ohm cm, especially 1 to 50 ohm cm.
As used herein, the term "conductive polymer" means a composition compri~ing a polymer component, and dispersed therein a particulate conductive filler, for example carbon black. The term "conductive polymer" includes those compositions in which the polymer composition is a thermoplastic, a rubber or a thermoplastic rubber. Examples of m~teri~l.c for the base polymer component include acrylate rubbers, butyl or nitrile rubbers, olefin homopolymers, and copolymers, and fluorinated or chlorinated polymers.
In a preferred embodiment according to the present invention, the electrically conductive jacket of the grounding electrode is in the form of a fabric. Examples of suitable fabric constructions include weaves, braids, knits, warp-inserted-weft knits (WIWK), and the like. A particularly pler~.led jacket is a fabric jacket comprising carbon fibre, or a fabric jacket compri~ing flexible conductive polymeric fibres.
Although a fabric jacket is preferred, non-fabric conductive jackets, for example a continuous conductive polymeric jacket, are also envisaged.
SUBSTITUTE SHEET (RULE 26) W O 97/141~6 PCT/GB96/02302 s The multi layer construction of the elongate conductive member of the present invention provides a balance of properties making it particularly effective as agrounding electrode. The inner (usually metal) highly conductive core ensures current is tr~n~mitte~ rapidly away from the article to be grounded. The conductive polymeric layer surrounding and in electrical contact with the inner core, protects the inner core from rusting. Also the conductive polymeric layer, since it has a higher radial re~i~t~nce than the inner core, acts to distribute the electrical current further along the length of the elongate conductive member, prior to discharge into the ground, than would be the case in the absence of the conductive polymeric layer. This may enhance the lifetime of the grounding member, and avoids overheating at points directly beneath the articles being electrically grounded. The carbon rich particulate material, e.g. coke, surrounding the conductive polymeric layer reduces the resi~t~nce to ground at any particular point along the conductive member, compared to the same electrode in the absence of coke. The reduction in the rÇsict~nce to ground is achieved primarily by the increase in surface area provided by the presence of the carbon rich particulate m~teri~l A similar effect could be achieved, for example, by using a much thicker conductive polymeric layer. However, this would be much more expensive.
The conductive jacket retains the coke, and facilitates h~n~llin?~ of the coke cont~inin~
electrode. The conductive nature of the jacket ensures the radial rç~i~t~nce to ground is minimi~ed.
I he elongate conductive members according to the invention may vary in length considerably. Preferred lengths range from 1 to 500 m. Different lengths are plc;r~,led for different applications. For example, for grounding an article to resist a lipht~ning pulse, which typically lasts for a period of the order of a few microseconds, lengths of about lm are pler~ d. For grounding an article such as switchgear, which may be subjected to ~ lL~ of the order of thousands of Amps for a period of about a second, longer lengths, of several hundred metres, e.g. 200m, 300m or even 500m may be plc;rellc~d. In general, the longer the time period in which current is p~c~in~, the longer the preferred length of the conductive member of the present invention.
The length preferred also varies according to the soil resistivity in which the SUBSTITIJTE SlrlEE~ (RULE 2~) CA 0223l829 l998-03-l2 W O 97/14196 PCT/~ 30Z
conductive member is used. Where the length of the conductive member required islonger than about 50m, this may be provided by a single elongate conductive member, or by joining several conductive members end to end.
Preferably an additional resistive member is used in conjunction with the elongate conductive member of the present invention. The additional member is preferably positioned to surround and to be in electrical contact with the end of the elongate conductive member that is connected in use to the article to be grounded.
The shape and the resistivity of the additional resistive member are arranged to reduce the flow of current from the elongate conductive member from the part thereof surrounded by the resistive member. For example the additional resistive member may be generally conical, the widest part of the cone being nearest the said end of the elongate conductive member. The purpose of this additional resistive member is to reduce the increased current density that would otherwise exit the elongate conductive member at its point of connection to the article to be grounded. This feature isdescribed in British Patent Application (our reference B302 GBl) which is filed contemporareously herewith. The entire disclosure of .. (B302 GBl), andany corresponding US application, is incorporated herein by reference.
The present invention preferably provides a kit of parts comprising an elongate conductive member according to the invention, in combination with an additional resistive member of the type described above, and a method of electrically grounding an article using such a kit of parts.
The jacket of the elongate conductive member is preferably flexible, and used in combination with tensioning wraps tensioned around the flexible jacket such that the compaction of the particulate carbon rich material is increased relative to their compaction in the absence of such wraps. The outer tensioning wraps may advantageously be in the form of a braid. The flexible jacket of the elongate conductive member is flexible to the extent that it can be deformed into different configurations by movement of the particulate carbon rich material within it, and/or SUE~5~ A _ _~L ~ L_ ~6) - W O 97/141~6 PCT/GB96/02302 by the action of the tensioning wraps. The tensioning wraps preferably do not add significantly to the overall radial resistance of the elongate conductive member.
Preferably the tensioning wraps comprise a material that has similar pl~f~ d resistivity values to those stated above as being ~lcr~lled for the jacket of the elongate conductive member.
In the event that a section of the jacket of the elongate conductive member is damaged, it can be conveniently repaired by carrying out the following plc;r~ledmethod steps:
(i) securing annular portions of the jacket close to the conductive polymeric element, on either side of the damaged section of jacket;
(ii) removing the damaged jacket section and particulate carbon rich m~teri~l between the secured annular portions, to expose a length of the conductive polymeric element;
(iii) positioning a repair sleeve (preferably wraparound) around, but spaced from the exposed length of conductive polymeric element;
(iv) securing a first end of the repair sleeve to the underlying jacket;
(v) filling the space between the repair sleeve and the core with a carbon rich particulate m~t~ri~l; then (vi) securing the other end of the repair sleeve to the underlying jacket The repair sleeve preferably has the same physical and electrical properties as the jacket of the elongate conductive member.
SUBSTITUTE SI~IEET (RULE 26) Particular applications of the present invention include the grounding of pipelines, high energy switch gear and buildings.
Embo~liment.e of the present invention are now described, by way of example, with reference to the acconlpallyillg drawings, wherein Figure 1 shows an eleckical grounding application in which the elongate grounding member of the present invention can be used, and Figure 2 shows in detail the elongate grounding member used in Figure 1.
Figure 1 shows an eleckical grounding application in which the elongate grounding member of the present invention can be used. A building 1 to be protected is conn~cte~l via an ine~ tc-l lead wire 3 to an elongate conductive member 5 buried in soil 7.
Figure 2 shows in detail the construction of the elongate conductive member 5.
The member 5 comprises a cylindrical copper core 7, a conductive polymeric element in the form of a layer 9 surrounding and in electrical contact with the core 7, an outer tubular carbon fibre woven jacket 11, and particulate coke 13 sandwiched between the woven jacket 11 and the conductive polymeric layer 9. The outer diameter measurement resistivity values of each of the components of the conductive member 5 are set out below in Table 1. The actual thickness of any particular layer may be calculated by subkaction of the relevant outer diameter values.
Table 1 Outer diameter in Resistivity in mm ohm.m at 20~c Core 7 (copper) 4.11.8 x 10-~
Conductive SUBSTITUTE SHEET (RULE 26) CA 0223l829 l998-03-l2 W O 97/14196 PCTI~D~5.~302 polymeric element 9 13.0 1.5 x 10-' Coke layer 13 37.0 1 x 10-~
Carbon fibre jacket 11 37.8 1.4x 10-2 Although the resistivity of the carbon fibre jacket is similar to that of the conductive polymeric jacket, it contributes far less to the overall resi~t~nce of the elongate conductive member, since it is much thinner than the conductive polymeric element ~. In other words, the conductive polymeric element is the most significant resistive member in the conductive member, and therefore controls the current flow along, and ~ut of the conductive member.
The resistance to ground of an elongate conductive member according to the invention, having the construction of Figure 2, was measured at 50 H~ in (i) soil haying a ground resistivity of 2850 ohm cm, and (ii) soil having a ground resistivity of 65000 ohm cm.
The resi~t~nce measurement was carried out by positioning the electrode according to Figure 2 and a counter elongate electrode in the soil, generally parallel to each other, but spaced apart, and applying a potential difference at 50Hz, between the two electrodes. A re~ t~nce measuring electrode, also elongate in construction, was positioned between the electrode according to the invention and the counter electrode.
As a colnl)~dLive control, an elongate conductive member having the same construction as that shown in Figure 2, but with the carbon fibre jacket replaced by a Velicren jacket was tested under the same conditions. Velicren in a polyacrylonitrile based material supplied by Enimont. The results are set out in Table 2 below.
SUBSTITUTE SHEE~ (RULE 26) CA 0223l829 l998-03-l2 W O 97/14196 PCT/GB9G~'~2~02 Table ?.
Resistance to ground ohms Resistance to ground in as measured in soil of ohms, as measured in soil resistivity 2850 ohm cm of resistivity 65000 ohm cm Figure 2 embodiment (carbon fibre jacket) 20 395 Figure 2 embodiment with carbon fibre jacket 9600 7300 replaced by a fabric poly , acrylonitrile-based jacket (comparative example) As can be seen the resi~t~nce to ground is drastically reduced using a conductive carbon fibre jacket co~ ~ed to the resistance to ground using a polyacrylonitrile based jacket.
SUBSTITUTE SHEET ff~ULE 26)
Claims (6)
1. An elongate conductive member comprising (i) an elongate core comprising a material having a resistivity at 23°C of less than 5x10-4 ohm cm and a resistance at 23°C of less than 0.03 ohm/meter;
(ii) a conductive polymeric element that surrounds, and is in electrical contact with the elongate core;
(iii) a jacket that surrounds the conductive polymeric element and is spaced therefrom, and (iv) a carbon rich material in particulate form contained within the jacket, between the jacket and the conductive polymeric element;
characterised in that the elongate conductive member is suitable for use as a grounding electrode, and that the jacket material is electrically conductive, having a resistivity of less than 100 ohm cm.
(ii) a conductive polymeric element that surrounds, and is in electrical contact with the elongate core;
(iii) a jacket that surrounds the conductive polymeric element and is spaced therefrom, and (iv) a carbon rich material in particulate form contained within the jacket, between the jacket and the conductive polymeric element;
characterised in that the elongate conductive member is suitable for use as a grounding electrode, and that the jacket material is electrically conductive, having a resistivity of less than 100 ohm cm.
2. An elongate conductive member according to claim 1, wherein the jacket comprises a fabric.
3. An elongate conductive member according to claim 1 or 2, wherein the jacket comprises carbon fibre.
4. A method of electrically grounding an article comprising (i) providing an elongate conductive member according to any preceding claim, and (ii) electrically connecting one end of the elongate conductive member to the article to be grounded.
5. A kit of parts comprising an elongate conductive member in accordance with any of claims 1 to 4, in combination with a resistive member that is positioned, in use, to surround, and to be in electrical contact with, the end of the elongate conductive member that is connected to the article to be grounded, the shape and resistivity of the resistive member being arranged to reduce the electrical current density flowing from that part of the elongate conductive member surrounded by the resistive member, relative to the current density that would flow from the elongate conductive member in the absence of the resistive member.
6. A method of electrically grounding an article using a kit of parts according to claim 5, comprising the step of positioning the additional resistive member around the said end of the elongate conductive member that is electrically connected to the article to be grounded.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9520587.8 | 1995-10-09 | ||
| GBGB9520587.8A GB9520587D0 (en) | 1995-10-09 | 1995-10-09 | Grounding electrode |
| PCT/GB1996/002302 WO1997014196A1 (en) | 1995-10-09 | 1996-09-20 | Grounding electrode |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2231829A1 true CA2231829A1 (en) | 1997-04-17 |
Family
ID=10782010
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002231829A Abandoned CA2231829A1 (en) | 1995-10-09 | 1996-09-20 | Grounding electrode |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPH11514488A (en) |
| CA (1) | CA2231829A1 (en) |
| GB (1) | GB9520587D0 (en) |
| WO (1) | WO1997014196A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE69708138D1 (en) | 1996-10-28 | 2001-12-13 | Abb Power Systems Ab Vaesteras | SEA ELECTRODE FOR HVDC SYSTEM |
| EP0934612B1 (en) | 1996-10-28 | 2001-11-07 | Abb Power Systems Ab | Land electrode for a high voltage direct current transmission system |
| AU4101601A (en) * | 1999-10-11 | 2001-05-30 | Ashok Tripathy | Safe earthing electrode |
| SE533434C2 (en) | 2009-04-27 | 2010-09-28 | Fredrik Dahl | Grounding device |
| CA2921415C (en) | 2013-08-16 | 2021-12-28 | Shore Acres Enterprises Inc. (D/B/A Sae Inc.) | Corrosion protection of buried metallic conductors |
| CA2988847A1 (en) | 2017-08-14 | 2019-02-14 | Shore Acres Enterprises Inc. | Corrosion-protective jacket for electrode |
| US11121482B2 (en) | 2017-10-04 | 2021-09-14 | Shore Acres Enterprises Inc. | Electrically-conductive corrosion-protective covering |
| CA3092850A1 (en) | 2019-12-18 | 2021-06-18 | Shore Acres Enterprises Inc. | Metallic structure with water impermeable and electrically conductive cementitious surround |
| CN111641096B (en) * | 2020-04-27 | 2021-11-09 | 国网辽宁省电力有限公司电力科学研究院 | Construction process of conductive polymer material grounding grid |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU533610B2 (en) * | 1979-05-16 | 1983-12-01 | John Derwent Slatter | Carbon or graphite fibre electrode |
| US4473450A (en) * | 1983-04-15 | 1984-09-25 | Raychem Corporation | Electrochemical method and apparatus |
| GB9116114D0 (en) * | 1991-07-25 | 1991-09-11 | Raychem Ltd | Corrosion protection system |
-
1995
- 1995-10-09 GB GBGB9520587.8A patent/GB9520587D0/en active Pending
-
1996
- 1996-09-20 JP JP9514796A patent/JPH11514488A/en active Pending
- 1996-09-20 WO PCT/GB1996/002302 patent/WO1997014196A1/en active Search and Examination
- 1996-09-20 CA CA002231829A patent/CA2231829A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11514488A (en) | 1999-12-07 |
| GB9520587D0 (en) | 1995-12-13 |
| WO1997014196A1 (en) | 1997-04-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |