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(11) | EP 1 821 318 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | conductor cable for electrical lines |
| (57) The conductor cable (1) for electrical lines comprises, for transporting electrical
energy, a support core (2) comprising a plurality of composite carbon fibre wires
(4) defining a cord (2a) embedded in a matrix (2b) of aluminium or its alloys.
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[0001] The present invention relates to a conductor cable for electrical lines; specific reference will be made hereinafter to bare overhead electrical lines, preferably for high limiting temperature and low expansion at high electrical loads.
[0002] Electrical lines of the indicated type are currently formed using conductor cables provided with a steel cord on which a plurality of usually aluminium electric wires are disposed, the steel cord being specifically used to support the cable when installed, and the aluminium wires being intended for energy transport.
[0003] It has however been found that cables of the described type are able to transport only relatively limited electrical powers, in which respect the electroconductive characteristics of steel are fairly poor and hence contribute to the electrical energy transport only to a limited extent; the result is that the cross-section actually used for the electrical energy transport is merely the cross-section of the aluminium wires.
[0004] The technical aim of the present invention is therefore to provide a conductor cable for electrical lines by which the stated technical drawbacks of the known art are eliminated.
[0005] Within the scope of this technical aim an object of the invention is to provide a cable which enables a very high electrical power to be transported, in particular in relation to traditional cables of the same dimensions (in the sense of their outer diameter) and overall mass.
[0006] The technical aim, together with this and other objects are attained according to the present invention by a conductor cable for electrical lines in accordance with claim 1.
[0008] Further characteristics and advantages of the invention will be more apparent from the description of a preferred but non-exclusive embodiment of the cable according to the invention, illustrated by way of non-limiting example in the accompanying drawings, in which:
Figure 1 shows a cross-section through a cable of the present invention;
Figure 2 shows a dimensioned example of a cable according to the invention;
Figure 3 is a comparative table showing the properties of: high-strength steel wires, ACI 20SA (aluminium-clad invar) wires, composite carbon fibre wires; and
Figure 4 shows a different embodiment of the cable according to the invention.
[0009] With reference to said figures, these show a conductor cable for electrical lines indicated overall by the reference numeral 1.
[0010] The cable 1 comprises a support core 2 on which the conductor means 3 for transporting the electrical energy are disposed.
[0011] The core 2 is in the form of a cord 2a of composite carbon fibre wires embedded in a matrix 2b of aluminium or aluminium alloys.
[0012] Using resins, the carbon fibres are assembled into composite wires 4 (from 1 to 36 wires for each cord) possibly joined together as a spiral to form the cord 2a of the core 2; the resins are of a type able to withstand temperatures up to 180°C and preferably up to 240°C for 40 years.
[0013] The composite wires 4 each comprise between 12,000 and more than 100,000 elemental carbon fibres; the composite wires 4 have a diameter comprised between 0.1-10.0 millimetres and preferably comprised between 1.5-4.5 millimetres, the carbon fibres having a diameter less than 20 micron, preferably less than 10 micron, more preferably comprised between 3-20 micron, and still more preferably comprised between 6-8 micron. In the illustrated example, the carbon fibres have a diameter of 7 micron; composite wires with these characteristics are produced for example by the Soficar company of Abidos (France).
[0014] The aluminium or aluminium alloy matrix 2b surrounding the cord 2a is applied (onto the composite wires 4) by high pressure plastic extrusion, in order to at least partially co-penetrate the stellar areas 6 of the cord 2a.
[0015] If the material of the matrix 2b is aluminium, it consists of annealed aluminium of greater than 99.5% purity, whereas if the material of the matrix 2b consists of aluminium alloys, these are Al-Mg or AI-Mn or Al-Zr or AI-Mg-Si alloys.
[0016] Preferably, each individual composite wire 4 of carbon fibres is surrounded by a first protective sheath 7 to prevent possible contact between the aluminium and the carbon fibres, which could lead to aluminium corrosion.
[0017] In this respect, the composite wires 4 are surrounded by a protective sheath 7 of thermoresistant material from 100 to 260°C, preferably from from 130°C to 240°C, such as PEEK (polyetherechetone), PPS, PPSU, PTFE, PET, TEFZEL, KAPTON, MYLAR, NOMEX, IMIDE POLYESTER, AMIDE IMIDE; the protective sheath 7 has a load deformation strength of at least 46 N/mm2 up to 200°C, good corrosion resistance and a working utilization temperature of 260°C.
[0018] The wires 4 are also surrounded by a second sheath 8, superposed on the sheath 7, made for exemple of self-hardening polyamide or produced by binding tape of a material suitable for maintaining the wires held tightly together before extrusion, such as for exemple PTFE, PET, KAPTON, PPS, TEFZEL, PPSU MYLAR, NOMEX, IMIDE POLYESTER, AMIDE IMIDE.
[0019] The sheath 8 has a thickness of about 10 micron, its purpose being to compact the constituent carbon fibre wires 4 of the cord during its formation and to hold the wires in position before applying the matrix 2b.
[0020] The cable 1 also comprises a plurality of conductor wires or segments 9 (representing the conductor means 3) which are superposed (possibly spiral-wound) on the core 2 to define a circular ring disposed about the core 2.
[0021] However, in other examples, the circular rings of conductor wires or segments 9 can be more than one in number and can be disposed concentrically one on the other; advantageously the superposed circular rings of conductor wires or segments 9 can be up to five in number.
[0022] The conductor wires or segments 9 are shaped as a circular ring sector, with a cross-section comprised between 1-25 mm2 and preferably 5-25 mm2; alternatively the conductor wires or segments 9 can be shaped as circular wires of cross-section comprised between 1-25 mm2 placed in one or more concentric layers.
[0023] These conductor wires or segments 9 are made of annealed aluminium of greater than 99.5% purity or of AI-Mg or Al-Mn or AI-Zr or Al-Mg-Si alloys.
[0024] In a preferred embodiment the matrix 2b of the core 2 is of aluminium and the conductor wires or segments 9 are of AI-Zr alloy.
[0025] The operation of the cable of the invention is apparent from that described and illustrated, and is substantially as follows.
[0026] When the cable 1 is installed the core 2 (comprising the carbon fibre cord 2a and the matrix 2b) supports the cable 1, whereas the conductor wires or segments 9 transport energy.
[0027] The cable 1 enables an increase in conductivity compared with equivalent traditional cables with a steel cord of the order of 30% to be achieved, together with a decrease in transmitted power losses of the same order; in practice the cables of the invention enable overhead lines to be installed which, for equal cable mass and dimensions, enable from 3% to 7% more electrical power to be transported, depending on operating temperature.
[0028] Because of their low density and very high ultimate tensile stress, the composite carbon fibre wires 4 enable cables 1 with a carbon fibre cord 2a to be produced for operating temperatures of 70-90°C, and the carbon fibre wires can also be used in high limiting temperature cables with low expansion at high electrical loads instead of ACI (aluminium-clad invar) wires, with a considerable mass reduction, so enabling the difference to be used for increasing the mass of conductor material (aluminium or its alloys) without increasing the total cable mass.
[0029] Moreover, because of the low expansion coefficient of carbon fibres, high limiting temperature cables can be produced with a sag at 180°C equal to or less than that of cords with Invar (Fe-Ni alloy) carriers, so eliminating problems of excess weight on the trestles and of span sagging.
[0030] The electrical conductivity of carbon fibres is 2-3 times less than that of steel or Fe-Ni alloys (Invar), however this does not influence the overall cable conductivity because other traditional materials used for making the support cord (steel or Invar) also have very low conductivity.
[0031] The aluminium or aluminium alloy matrix 2b is extruded over the cord 2a of carbon wires to prevent longitudinal moisture infiltration.
[0032] The cable of Figure 2 can continuously transport a current of 800 A at low, medium or high voltage at a temperature of 150°C for 40 years.
[0033] These values can be exceeded by suitably dimensioning the diameter of the wires 4 and of the layer 3 and/or increasing the number of conductor wires 9 or the number of rings or the cross-section of the conductor wires or segments 9.
[0034] The structure composed of the cord 2a and of the matrix 2b extruded over it behaves as a compact indivisible element.
[0035] The total cross-section of the carbon fibres in the core is less than 50% of the total cross-section of the core 2.
[0036] The traction force in operation must be applied to the entire core (i.e. the clamps must grip the aluminium layer); in this manner the core is able to be subjected to very high transverse compression stresses which are much higher than those applicable to the individual composite wires.
[0037] During operation, after its spanned installation, the cable temperature rises and, beyond a certain predetermined value (stress transition point or knee point), the core 2 (comprising the cord 2a and the matrix 2b) becomes detached from the rings of conductor wires 9 because of their different thermal expansion.
[0038] Then, as the temperature further increases, the cable 1 expands in accordance with the expansion coefficient of the core (very small) rather than the mean expansion coefficient of the cable 1 overall (including the conductor wires or segments 9, this being much higher because of the greater percentage of aluminium or its alloys).
[0039] This means that notwithstanding the high temperature (150-180°C), the span sags remain compatible with safety regulations.
[0040] In a different embodiment (Figure 4), the cable 1 of the invention has a structure defined only by the core 2, which comprises the plurality of composite carbon fibre wires 4 defining the cord 2a embedded in the matrix 2b of aluminium or its alloys.
[0041] The characteristics of the constituent elements of this cable are those already specified with reference to the other described embodiment.
[0042] The conductor cable for electrical lines conceived in this manner is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept; moreover all details can be replaced by technically equivalent elements.
In practice the materials used and the dimensions can be chosen at will in accordance with requirements and the state of the art.
1. A conductor cable (1) for electrical lines, comprising a support core (2) for transporting
electrical energy, characterised in that said core (2) comprises a plurality of composite carbon fibre wires (4) defining
a cord (2a) embedded in a matrix (2b) of aluminium or its alloys.
2. A cable (1) as claimed in the preceding claim, characterised by comprising, for transporting electrical energy, conductor means (3) disposed on said
core (2).
3. A cable (1) as claimed in one or more of the preceding claims, characterised in that each of said composite wires (4) comprises between 12000 and more than 100000 carbon
fibres.
4. A cable (1) as claimed in one or more of the preceding claims, characterised in that said composite wires (4) have a diameter comprised between 0.1-10.0 millimetres and
preferably comprised between 1.5-4.5 millimetres.
5. A cable (1) as claimed in one or more of the preceding claims, characterised in that said carbon fibres have a diameter less than 20 micron, preferably less than 10 micron,
more preferably comprised between 3-20 micron, and still more preferably comprised
between 6-8 micron.
6. A cable (1) as claimed in one or more of the preceding claims, characterised in that said aluminium or aluminium alloy matrix (2b) is applied onto the composite wires
(4) by high pressure plastic extrusion.
7. A cable (1) as claimed in one or more of the preceding claims, characterised in that the aluminium of the matrix (2b) consists of annealed aluminium of greater than 99.5%
purity, whereas the aluminium alloys of the matrix (2b) consist of AI-Mg or AI-Mn
or Al-Zr or AI-Mg-Si alloys.
8. A cable (1) as claimed in one or more of the preceding claims, characterised in that each composite carbon fibre wire (4) is surrounded by a first protective sheath (7)
made of thermoresistant material from 100 to 260°C, preferably from 130°C to 240°C,
such as for exemple PEEK, PPS, PPSU, PTFE, PET, TEFZEL, KAPTON. MYLAR, NOMEX, IMIDE
POLYESTER, AMIDE IMIDE.
9. A cable (1) as claimed in one or more of the preceding claims, characterised in that the first protective sheath (7) has a load deformation strength of at least 46 N/mm2 up to 200°C, good corrosion resistance and a working utilization temperature of 260°C.
10. A cable (1) as claimed in one or more of the preceding claims, characterised in that each composite carbon fibre wire (4) is surrounded by a second protective sheath
(8) made for exemple of self-hardening polyamide or produced by binding tape for exemple
of PTFE, PET, KAPTON, PPS, TEFZEL, PPSU, MYLAR, NOMEX, IMIDE POLYESTER, AMIDE IMIDE.
11. A cable (1) as claimed in one or more of the preceding claims, characterised in that the composite wires (4) have the first sheath (7) and, superposed on the first sheath
(7), they have the second sheath (8).
12. A cable (1) as claimed in one or more of the preceding claims, characterised in that the conductor means (3) comprise a plurality of conductor wires or segments (9) superposed
on the core (2).
13. A cable (1) as claimed in one or more of the preceding claims, characterised in that said conductor wires or segments (9) define at least one circular ring disposed on
said core (2).
14. A cable (1) as claimed in one or more of the preceding claims, characterised in that said conductor wires or segments (9) are shaped as a circular ring sector.
15. A cable (1) as claimed in one or more of the preceding claims, characterised in that said circular ring sectors have a cross-section comprised between 1-25 mm2 and preferably 5-25 mm2.
16. A cable (1) as claimed in one or more of the preceding claims, characterised in that said conductor wires or segments (9) are shaped as circular wires and are placed
in one or more concentric layers.
17. A cable (1) as claimed in one or more of the preceding claims, characterised in that the conductor wires or segments (9) are made of annealed aluminium of greater than
99.5% purity or of AI-Mg or AI-Mn or AI-Zr or AI-Mg-Si alloys.
18. A cable (1) as claimed in one or more of the preceding claims, characterised in that the total cross-section of the carbon fibres in the core (2) is less than 50% of
the total cross-section of the core (2).