Earthing conductor

Abstract

Electrical conductor for earthing, comprising at least one metal wire comprising an aluminium core, at least one copper layer cladding said core, at least one coating layer of a metal selected f rom tin, nickel, bronze, brass, zinc, chrome, coating the copper layer. Said at least one coating layer has a thickness of from 2 to 50 pm. Compared to copper, the earthing conductor according to the present invention provides protection against corrosion, is flexible, robust in processing, resistant to bending during installation, provides equivalent performance in terms of melting current and electrical resistance, is about 40% lighter, has lower costs, is equally recyclable but with a different working process that makes it more difficult to recover immediately, thus discouraging theft.

Description

[0001] EARTHING CONDUCTOR

[0002] The present invention relates to an earthing conductor, in particular for infrastructures such as components of electrical and electronic, industrial, railway, power generation, telecommunications installations .

[0003] Currently, the most commonly used earthing conductors are made of copper, which combines high electrical properties with good mechanical performance and durability even in hostile environments . However, the cost of copper is steadily increasing, making these conductors very expensive and often subj ect to getting stolen, generating not only direct economic damage, but also serious inconvenience due to indirect damage caused by the lack of reliability of the systems .

[0004] Alternatives are available such as bimetallic conductors made of copper-clad steel (CCS) , galvanised or zinc-plated steel, but they have the disadvantage of being heavier as they need a larger cross-sectional area to guarantee the same performance, and they have greater rigidity, which creates difficulties during installation. In other cases, aluminium is used for its good electrical properties, low cost and lightweight, but is often unusable in critical environmental conditions due to its poor corrosion resistance .

[0005] The obj ect of the present invention is to provide an earthing conductor alternative to copper that provides protection against corrosion, is flexible, withstands bending and machining during installation, provides performance equivalent to copper in terms of melting current and electrical resistivity, islightweight and resistant to external agents, has lower costs than copper, and is more complicated to recycle so as to hinder theft .

[0006] According to the invention, this purpose is achieved with an earthing conductor according to claim 1 .

[0007] Other features are provided in the dependent claims .

[0008] An electrical conductor for earthing according to the present invention comprises an aluminium core, wherein said core is coated with a copper layer ( cladding) and further protected with a coating layer ( coating) of a metal selected from tin, nickel, bronze, brass, zinc, chromium, said coating layer having a thickness of from 2 to 50 pm.

[0009] Preferably the coating layer is tin.

[0010] The electrical conductor for earthing is designed to advantageously combine mechanical and electrical properties of aluminium and copper, enhanced by a protective coating layer of metal selected from tin, nickel, bronze, brass, zinc, chrome .

[0011] The characteristics and the advantages of the present invention will become more evident from the following description, which is exemplary and not limiting .

[0012] Advantageously, the electrical conductor for earthing according to the present invention comprises a multilayer structure that guarantees high performance, corrosion protection, cost reduction and a more complex recyclability cycle .

[0013] The aluminium core is a predominant component of the electrical conductor for earthing.With predominant component it is meant that the aluminium core representing a weight percentage greater than or equal to 50% of the entire electrical conductor for earthing.

[0014] The copper layer, otherwise referred to as cladding, is an intermediate layer applied between the core and the coating layer of metal selected from tin, nickel, bronze, brass, zinc, chrome .

[0015] Advantageously, the cladding improves the adhesion between the core and the outer coating layer and ensures mechanical and thermal compatibility as it has a thermal expansion coefficient similar to that of the aluminium in the core, reduces the overall electrical resistance of the conductor, and protects against oxidation and mechanical stress, in particular by improving the resistance to fretting caused by the surface friction of conductors in contact with each other .

[0016] Preferably the electrical conductor according to the present invention comprises the aluminium core clad with at least one layer of copper, referred to as CCA (acronym for Copper Clad Aluminium) , even more preferably CCA 10%, referring to the volume of copper, 10%, with respect to the total volume of the conductor .

[0017] The CCA preferably provides a ratio of 73% by weight of aluminium to 27% by weight of copper .

[0018] The weight ratio of aluminium to copper may vary, but aluminium must be at least 50% by weight .

[0019] The earthing conductor of the present invention can be provided to work well with a ratio of 99% by weight of aluminium and 1% by weight of copper .

[0020] More preferably, the weight ratio is provided to be 50% aluminium and 50% copper .The cladding can be applied to the core by means of known techniques, such as : metal or electrochemical coating, plating, dipping, metal spraying, electrochemical extrusion, acid bath solution. For this application, the preferred technology is metallurgical cladding, where a copper strip is deposited on a suitably treated aluminium wire to improve its adhesion at the aluminium / copper interface, which ensures robustness during production processes and reliability under operating conditions .

[0021] Advantageously, the copper cladding on said aluminium core is obtained by means of deposition techniques, so as to ensure robustness during production processes and reliability under operating conditions .

[0022] The coating layer applied over the cladding is a coating layer of metal selected from tin, nickel, bronze, brass, zinc, chrome . In order to achieve due corrosion protection, the thickness of the coating layer is from 2 to 50 pm, preferably from 2 to 20 pm, more preferably from 3 to 10 pm.

[0023] Advantageously, the metal coating protects the earthing conductor from corrosion, making it suitable for harsh outdoor environments, such as industrial and marine ones .

[0024] The metal coating layer can be applied over the copper cladding by means of techniques widely used in industry, such as hot dipping for thin coatings (e . g. 1-2 pm) , or electroplating for thicker coatings (e . g. between 4 and 10 pm, preferably between 4 and 7 pm) .

[0025] Advantageously, hot dipping or electroplating techniques ensure that structural integrity of the layer is maintained even after machining processes such asdrawing and stranding, as well as mechanical strength required in installation operations .

[0026] The earthing conductor may consist of a single metal wire comprising an aluminium core clad with at least one layer of copper and further protected by at least one coating layer according to the present invention.

[0027] Alternatively, the earthing conductor may comprise several metal wires stranded together, with each individual wire being made of aluminium clad with at least one layer of copper and further protected by at least one coating layer according to the present invention .

[0028] Preferably, there is only one copper layer, but alternatively it is possible to provide for the aluminium core clad by a multiplicity of copper layers .

[0029] Preferably there is only one coating layer, but alternatively it is possible to provide for the aluminium core clad with at least one copper layer to be coated with a plurality of coating layers according to the present invention.

[0030] Advantageously, the earthing conductor is made according to the rules of the best state of the art in the field of class 2 cords, comprising several tinned CCA metal wires stranded together, and preferably comprising 19 metal wires, so that conductor crosssections are equivalent to those of a pure copper conductor . The 19 metal wires comprise a central metal wire surrounded by six metal wires in turn surrounded by 12 metal wires .

[0031] Preferably, metal wires can be drawn to reduce the diameter, e . g. from 2. 60 mm to 2.38 mm, ensuring more compact and manageable conductors .Advantageously, the earthing conductor according to the present invention has high corrosion resistance . The coating layer protects the conductor in aggressive environments, such as industrial or marine ones .

[0032] The earthing conductor according to the present invention provides for an important cost reduction; in fact, the combination of aluminium and copper significantly reduces costs compared to pure copper conductors, while maintaining equivalent performance .

[0033] Advantageously, the earthing conductor according to the present invention is lighter than pure copper, facilitating transport and installation.

[0034] Advantageously, the reduced copper content and the appearance of the earthing conductor according to the present invention make it less appealing in terms of theft .

[0035] Even more advantageously, the material of the earthing conductor of the present invention is fully recyclable, with low environmental impact, but the metal recovery cycle is more complex to implement and not feasible with traditional processes for recovering either copper or aluminium alone, thus disincentivising the recovery of the scrap in the traditional supply chain .

[0036] Advantageously, the conductor of the present invention meets the melting current and electrical resistivity requirements normally adopted for pure copper conductors, and also ensures adequate electrical conductivity (>60% TAGS) and good short-circuit current handling capability.

[0037] For example, the conductor according to the present invention with a diameter cross-section of 2. 60 mm hasan IACS percentage conductivity of 61.5%, a breaking load of 143 kg, and an elongation at break of 1.2% . The copper layer and tin coating layer have a weight percentage of 10.63% . The copper cladding has a thickness comprised between 63 and 80 pm and the protective tin coating has a thickness comprised between 3. 6 and 8.3 pm.

[0038] For example, the conductor according to the present invention with a diameter cross-section of 2.38 mm has an IACS percentage conductivity of 62.4%, a breaking load of 114 kg, and an elongation at break of 1. 6% . The copper layer and protective tin coating have a weight percentage of 10.89% . The copper cladding has a thickness comprised between 58 and 67 pm and the protective tin coating has a thickness comprised between 4.2 and 6.2 pm.

[0039] Advantageously, the earthing conductor of the present invention can be used for earthing electrical, industrial, outdoor and / or marine cable conductors intended for extreme environmental conditions with high corrosivity .

[0040] The earthing conductor of the present invention may optionally be covered with a sheath of polymer material, usually non-cross-linked . The polymer material can be based on polyolefins (especially polyethylene, polypropylene or mixtures thereof ) , or chlorinated polyolefins (e . g. polyvinyl chloride) . The polyolefins may possibly be supplemented with an anti-flame agent, e . g. a mineral filler such as aluminium hydroxide or magnesium hydroxide .

[0041] The following are two examples of the most common earthing conductor cross-sections according to thepresent invention.

[0042] The first example consists of an 82 mm2cross-sectional cord, constructed in class 2 with 19 stranded wires (construction 1+6+12 ) adapted to replace a 50 mm2cross-sectional copper conductor, constructed in class 2 with 7 stranded wires (construction 1+6) at the same electrical resistance (approx . 0.35 Ohm / km) . The 82 mm2cross-section tinned CCA earthing conductor consists of individual wires with a diameter of 2.38 mm as opposed to 3.00 mm for the 50 mm2cross-sectional copper . The final diameter of the tinned CCA conductor is 11.9 mm compared to 9.0 mm for the copper conductor . The weight of the copper conductor is 444 kg / km, while the weight of the tinned CCA conductor is 284 kg / km, which is about 35% lighter . The electrical resistance of the copper conductor is 0.36 Ohm / km, while that of the tinned CCA conductor is 0.34 Ohm / km. The short-circuit current of the 2 conductors is also very similar, 19.7 kA for the copper conductor, and 20.1 kA for the tinned CCA conductor according to the present invention. The breaking load is 248 N / mm2for the copper conductor and 138 N / mm2for the tinned CCA conductor .

[0043] A second example consists of a 100 mm2cross-sectional cord, produced in class 2 with 19 stranded wires (construction 1+6+12 ) adapted to replace a 65 mm2cross-sectional copper conductor, also produced in class 2 with 19 stranded wires (construction 1+6+12 ) at the same electrical resistance (approx. 0.27 Ohm / km) . The 100 mm2cross-section tinned CCA earthing conductor consists of individual wires with a diameter of 2. 60 mm as opposed to 2.10 mm for the 65 mm2cross-sectional copper . The final diameter of the tinned CCA conductoris 13.0 mm compared to 10.5 mm for the copper conductor . The weight of the copper conductor is 590 kg / km, while the weight of the tinned CCA conductor is 340 kg / km, which is about 42% lighter . The electrical resistance of the copper conductor is 0.27 Ohm / km, while that of the tinned CCA conductor is 0.28 Ohm / km. The short-circuit current of the two conductors is also very similar, 26 kA for the copper conductor, and 24 kA for the tinned CCA conductor according to the present invention. The breaking load is 240 N / mm2for the copper conductor and 140 N / mm2for the tinned CCA conductor .

[0044] Advantageously, the earthing conductor according to the present invention provides high electrical performance, corrosion resistance and cost reduction, representing an effective alternative to copper-only earthing conductors .

[0045] Advantageously, compared to copper, the earthing conductor according to the present invention provides protection against corrosion, is flexible, robust in processing, resistant to bending during installation, provides equivalent performance in terms of melting current and electrical resistance, is about 40% lighter, has lower costs, is equally recyclable but with a different working process that makes it more difficult to recover immediately, thus discouraging theft .

[0046] Figure 1 shows a graph with the results of an accelerated corrosion test conducted in a laboratory where two earthing conductors according to the present invention comprising an aluminium core coated with at least one copper layer and a tin coating with a thickness of 4 pm (sample C) or 7 pm (sample D) were compared. These conductors were tested against a conductor withoutexternal protection (sample A) and a conductor with a 1 pm thick tin coating (sample B) .

[0047] The test was conducted by immersing the different samples in a solution of demineralised water and 35 g / 1 sodium chloride for a period from 0 to 3500 hours . As an indicator of the corrosion resistance of the different conductors, the change in weight of the conductors themselves was determined by means of successive measurements over the period of time considered. As is clear from Figure 1, tinned CCA earthing conductors according to the present invention with a tin coating of 4 pm and 7 pm are highly resistant to corrosion, exhibiting weight losses of less than 0.050 g after 3000 hours . In contrast, the comparison conductors, made of CCA and tinned CCA with a thickness of 1 pm, are highly corroded already after 1, 500 hours, and the uncoated CCA conductor in particular is highly compromised after 3, 000 hours of testing.

[0048] The invention thus conceived is susceptible to numerous modifications and variations that fall within the exclusive scope of the claims . In practice, the materials used, as well as their dimensions, can be of any type according to the technical requirements .

Claims

CLAIMS1. Electrical conductor for earthing, comprising at least one metal wire comprising:an aluminium core,at least one copper layer cladding said core, at least one coating layer of a metal selected from tin, nickel, bronze, brass, zinc, chrome, coating said at least one copper layersaid at least one coating layer having a thickness of from 2 to 50 pm.

2. Electrical conductor according to claim 1, characterised in that said at least one coating layer is a tin coating layer .

3. Electrical conductor according to one or more of any one of claims 1 or 2, characterised in that said aluminium core represents a weight percentage comprised from 50% to 99% of the electrical conductor .

4. Electrical conductor according to one or more of any one of claims 1-3, characterised in that said aluminium core represents a weight percentage of 50% and said at least one copper layer represents a weight percentage of 50% .

5. Electrical conductor according to one or more of any one of the preceding claims, characterised in that said aluminium core represents a weight percentage of 73% and said at least one copper layer represents a weight percentage of 27% .

6. Electrical conductor according to one or more of any one of the preceding claims, characterised in that said at least one coating layer is applied to said at least one copper layer by a hot dipping or electroplating process .

7. Electrical conductor according to one or more of any one of the preceding claims, characterised in that said at least one coating layer represents a percentage by weight less than or equal to 0.5% of the electrical conductor .

8. Electrical conductor according to one or more of any one of the preceding claims, characterised in that said at least one coating layer has a thickness of from 2 to 20 pm.

9. Electrical conductor according to claim 8, characterised in that said at least one coating layer has a thickness of from 3 to 10 pm.

10. Electrical conductor according to one or more of any one of the preceding claims, characterised in that it comprises a plurality of metal wires stranded together, wherein each individual metal wire of said plurality of wires comprises said aluminium core, said at least one copper layer cladding said core and said at least one coating layer coating said at least one copper layer .

11. Electrical conductor according to claim 10, characterised in that it comprises nineteen of said metal wires stranded together .

12. Electrical conductor according to claim 11, characterised in that said nineteen metal wires comprise a central metal wire surrounded by six metal wires in turn surrounded by twelve metal wires .

13. Electrical conductor according to any one of the preceding claims, wherein said conductor is coated with a sheath of polymer material, usually non-cross-linked .

14. Use of an electrical conductor according to anyone of the preceding claims, for earthing infrastructures such as components of electrical and electronic, industrial, railway, power generation, telecommunications installations .

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