Conductor for Bare Overhead Electric Lines, Especially for Middle-High Thermal Limit, and Low Expansion at High Electronic Loads

Abstract

A conductor for electric lines includes a load-bearing core on which conductors for electric energy transportation are arranged. The load-bearing core includes a plurality of aligned aramidic fibres defining one or more ropes wrapped in one or more sheaths.

Claims

1. An electric conductor configured for bare overhead electric lines, comprising a load-bearing core on which conducting means for electric energy transportation are arranged, wherein said load-bearing core comprises a plurality of aligned aramidic fibres defining one or more ropes wrapped in one or more sheaths, and wherein said conductor is adapted for applications at operating temperatures above 90 C., and with a thermal expansion coefficient lower than 18*10-6/ C.

2. The electric conductor according to claim 1, wherein said aramidic fibres are made of Kevlar or Twaron or Zylon.

3. The electric conductor according to claim 1, wherein said aramidic fibres have a diameter in the range of 1 to 100 microns.

4. The electric conductor according to claim 1, wherein said core has a diameter in the range of 1 to 100 millimetres.

5. The electric conductor according to claim 1, wherein said one or more sheaths are made of thermoplastic material.

6. The electric conductor according to claim 5, wherein said thermoplastic material is an elastomeric polymeric material, preferably Hytrel or TPU, thermoplastic polyurethane, blended with additives, pigments and stabilizers.

7. The electric conductor according to claim 6, wherein said stabilizers are hindered amine light stabilizers (HALS).

8. The electric conductor according to claim 1, wherein the conducting means comprise a plurality of circular or profiled conducting wires arranged over the core, said conducting wires defining at least one circular crown on said core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features and advantages of the invention will become more apparent in the light of the description of a preferred but non-limiting embodiment of the conductor according to the invention, provided herein by way of non-limiting example with reference to the annexed drawings, wherein:

[0036] FIGS. 1a and 1b show two variants of the cross-section of a conductor according to the present invention;

[0037] FIG. 2 shows a table indicating the chemical resistance of some fibrous and metallic materials and of Kevlar;

[0038] FIG. 3 shows comparative stress-strain graphs for composites based on carbon fibres, glass fibres, aluminum, and aramidic fibres;

[0039] FIGS. 4.1-4.4 show some comparative tables concerning the chemical resistance properties of Kevlar compared to substances such as acids (FIG. 4.1), bases (FIG. 4.2), saline solutions and other substances (FIG. 4.3), organic solvents (FIG. 4.4);

[0040] FIG. 5 shows an example of a coupling terminal for the conductor with a load-bearing core made from aramidic fibres;

[0041] FIG. 6 shows a comparative table concerning some properties of: wires of high-tensile steel, wires of ACI 20SA (Aluminum Clad Invar) and aramidic fibres.

[0042] In the drawings, the same reference numerals and letters identify the same items or components.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

[0043] The conductor for bare overhead electric lines according to the invention is characterized in that it adopts a fibrous reinforcement of aramidic nature, particularly for operating ranges up to 120 C. and peaks up to 150 C.

[0044] By way of non-limiting example, Kevlar aramidic fibres will be taken into account herein.

[0045] As can be understood from the table shown in FIG. 2, compared to other materials that can be used for reinforcing conductors for overhead electric lines, Kevlar fibres have a high specific breaking modulus (higher by 70% than that of carbon) and a high specific modulus of elasticity (more than three times that of steel). Compared to steel, which is a typical reinforcement material, Kevlar fibres are five times lighter and have a higher breaking load by more than 30%, and this determines a specific breaking modulus which is about seven times higher. When compared to the best aluminum alloys, also used as reinforcements for overhead conductors, aramidic fibres have an elastic modulus and a breaking load respectively higher by 86% and 450%, which, combined with their densities, provide a specific elastic modulus more than three times higher and a specific breaking modulus twice as high.

[0046] As it can be seen in FIG. 3, which shows comparative stress-strain graphs for composites based on carbon fibres, glass, aluminum and aramidic fibres, aramidic fibres (such as Kevlar, by way of non-limiting example) absorb much energy before breaking, compared to the other known materials used for reinforcing conductors for overhead electric lines, thus de facto making for a ductile reinforcement. If on the one hand graphite-based reinforcements have high elastic modulus and breaking load, on the other hand the fragile tensile behaviour requires much attention to be paid during both the storage and processing stages. The behaviour of aramidic reinforcements, on the contrary, is similar to that of metals in terms of breaking modalities, which ensures much ease of handling during processing.

[0047] Considering the behaviour of aramidic fibres under the action of a constant load (creep), it has been found that at 10% of the breaking load aramidic yarns do not suffer from humidity and maintain a very limited creep velocity, even at temperatures around 120 C.

[0048] Considering the reinforcement phases, carbon fibres may induce galvanic corrosion with aluminum, although they do not undergo any degradation, except for oxidation, at high temperatures beyond 600 C.

[0049] As listed in FIGS. 4.1 and 4.2, aramidic fibres do not suffer from exposition to chemicals, with which it is likely that a conductor will come in contact in the course of its life. It must be pointed out that they do not suffer from exposition to organic solvents (e.g. acetone and kerosene) and seawater. In particular, it can be seen that aramidic fibres do not suffer from contact with sulfuric acid at a concentration of 10% for 100 hours, and with sodium chloride at a concentration of 10% for 100 hours at 99 C.

[0050] Though it is known that aramidic fibres do not suffer from adverse environments in terms of temperature, humidity and corrosion, considering a service life of about 40 years, it is preferable to employ a protective sheath to be wrapped around the aramidic fibrous reinforcement.

[0051] In the long run, in fact, problems may arise as concerns susceptibility to UV radiations (which is typical of polymeric materials containing benzene rings), to exposition to strong acids and bases (acetic and benzoic acids at 100 C., hydrochloric acid, nitric acid, hydrobromic acid, phosphoric acid, sulfuric acid, caustic soda and bleach) and to some concentrated salts (copper sulfate, sodium phosphate and ferric chloride at 100 C., and sodium chloride above 120 C.).

[0052] Even if aramidic yarns are notoriously very resistant to shear and fatigue, their long service life and the dynamic loads, thermal loads and relative friction they are subjected to, may also damage the aramidic fibrous reinforcement yarn over time, fibre by fibre, unless adequately protected.

[0053] Consequently, the sheath performs the function of protecting the aramidic fibrous reinforcement yarn both chemically, against locally accumulated concentrations of solvents/acids/bases/salts coming from the atmosphere, and physically, by insulating the aramidic fibres from contact with the upper layers of the conductor. The sheath will also be useful as an element for keeping the yarns confined and compact, and for protecting the aramidic fibres against exposition to UV radiations.

[0054] It will be considered herein the use of a sheath made of elastomeric polymeric material, such as, by way of non-limiting example, Hytrel (thermoplastic elastomer polyester) or TPU (thermoplastic polyurethane), resistant to temperatures up to 150 C. When properly blended with additives, pigments and stabilizers, such as, by way of non-limiting example, hindered amine light stabilizers (HALS), it can resist the environmental aggression caused by ultraviolet radiations, humidity, organic solvents, polar solvents and diluted acidic and basic solutions.

[0055] With reference to FIGS. 1a, 1b, there is shown a conductor for electric lines, designated as a whole by reference numeral 1.

[0056] The conductor 1 comprises a load-bearing core 4, on which conductors 3 for electric energy transportation are arranged.

[0057] The core 2-4 is made out of one or more ropes 4 of wires of aramidic fibres wrapped in a thermoplastic sheath.

[0058] Preferably, the aramidic fibres have a diameter between 1 and 100 microns.

[0059] Preferably, the core has a diameter between 1 and 100 millimetres.

[0060] The aramidic fibres are assembled by means of a containment sheath capable of withstanding high temperatures for a time compatible with the life of a common conductor with a steel load-bearing element.

[0061] The thermoplastic sheath 2 that surrounds the rope 4 is applied by high-pressure plastic extrusion.

[0062] The thermoplastic sheath 2 is extruded on the rope 4 of aramidic fibres for containing them and also for preventing them from being damaged by UV solar rays, as previously described. Said sheath, which is made of, by way of non-limiting example, Hytrel or TPU, is resistant to temperature peaks of 150 C. and can work for up to 40 years at operating temperatures of 120 C.

[0063] Moreover, the conductor 1 comprises a plurality of conducting wires 3 laid (wound in a spiral pattern) over the core 2-4, so as to define a circular crown around the core 2-4.

[0064] In other examples, however, there may be more than one circular crown of conducting wires 3, arranged concentrically one over the other; advantageously, the overlapped circular crowns of conducting wires 3 may be as many as five.

[0065] The conducting wires 3 have a circular cross-section or may be shaped like a circular crown sector; as an alternative, they may have any other cross-section compatible with the application of the conductor 1 within the frame of electric energy transmission.

[0066] The conducting wires 3 are made of annealed aluminum with a purity higher than 99.5% or AlMgSi or AlMn or AlZr alloys or other aluminum alloys for electric use.

[0067] In a preferred but non-limiting embodiment, the aramidic fibres are made of Kevlar or Twaron or Zylon, the sheath 2a of the core 2 is made of Hytrel or TPU thermoplastic elastomer polyester, and the conducting skirt is formed by conducting wires 3 made of AlZr alloy.

[0068] The operation of the conductor 1 according to the invention is apparent in the light of the above description and of the annexed drawings, being substantially as follows.

[0069] When the conductor 1 is installed, the core 2-4 (comprising the rope 4 of aramidic fibres and the sheath 2) supports the conductor 1, while the conducting wires or 3 are particularly dedicated to energy transportation.

[0070] When in operation, after span installation, the temperature of the conductor rises and, beyond a certain predetermined value (stress transition point or knee-point), detachment will occur between the core (comprising the rope 4 and the sheath 2) and the crowns of conducting wires 3, due to their different thermal expansion.

[0071] Then, as temperature increases further, the conductor 1 will expand according to the expansion coefficient of the core (which is extremely small), and not according to the average expansion coefficient of the conductor 1 as a whole (including the conducting wires 3, which is much higher because of the higher percentage of aluminum or alloys thereof).

[0072] This will cause the span deflections to remain compatible with the safety regulations notwithstanding the high temperatures (>100 C.).

[0073] It is clear from the above description that the electric conductor of the present invention is suitable for applications at operating temperatures above 90 C., and with a thermal expansion coefficient lower than 18*10.sup.6/ C.

[0074] The conductor thus conceived for installation on current electric lines as a replacement for current conductors requires suitable terminal couplings. The optimal solutions is a configuration based on the friction developed on a conical insert.

[0075] The load is distributed evenly over the fibres thanks to the cone that presses against just one layer of fibres on the respective insert. Once in traction, the fibres will drag the cone by friction, thereby tightening the fibres by compression.

[0076] FIG. 5 shows an example of embodiment of a coupling terminal adapted to couple the terminal part of the electric conductor to the electric line pylon.

[0077] The coupling terminal essentially comprises the following elements: [0078] an end cap 51, comprising on one side a pin 52 to be coupled to the pylon, and on the other side a threaded opening 53; [0079] a hollow termination body 54 with a truncated-cone shape, having on its bigger side a thread 55 adapted to be screwed into the threaded opening 53; [0080] a tightening cone 56 adapted to be inserted into the hollow termination body 54, so as to tighten said plurality of aramidic fibres of the terminal part of the conductor into the hollow termination body 54; [0081] preferably, there is also a gasket 57 that seals the hollow termination body.

[0082] First of all, after removing the first part of the external gasket for a length equal to that of the tightening cone 56, the rope 58 will have to be inserted into the hollow termination body 54, preferably made of aluminum alloy (or steel). Then all the fibres released by the gasket will have to be arranged properly: in fact, the yarn will have to be open relative to the centre, and the fibres will have to be properly separated from one another and evenly distributed in just one layer. Finally, the cone 56 will have to be inserted with its tip towards the central part of the rope, so that the fibres will arrange themselves on its oblique surface.

[0083] The last operation prior to closing the terminal will be positioning the wedge 56 into its seat, by pushing the cone towards the inside of the terminal 54 with the help of a tool or a small hammer. Before use, some traction will have to be applied for two main reasons. The first reason is that the wedge-fibres connection must be made stable in order to avoid causing any undesired elongation in operation, due to settling. The second reason is that any possible misalignment of the fibres within the rope, caused by the curvature taken during storage as a coil, must be eliminated.

[0084] In order to ensure good insulation against humidity entering the rope by capillarity, flexible gaskets 57 can be used on the terminal, such as silicone-based sealants or vulcanized tape. The advantages deriving from the application of the present invention are apparent. Compared to classical conductors with a steel load-bearing element, aramidic fibres allow creating conductors that can, due to their lightness and high breaking load, work at operating temperatures above 100 C. with the same deflection.

[0085] The conductor allows for increased conductivity by approx. 20% over equivalent traditional conductors with a steel load-bearing rope; in practice, the conductors according to the present invention allow creating overhead lines that, the conductors' mass and size being equal, allow transporting 50-70% more electric power in relation to their operating temperature.

[0086] The wire of aramidic fibres can be used in conductors with medium-to-high thermal limit and reduced expansion at high electric loads as a replacement for ACI (Aluminum Clad Invar) wires, resulting in a considerable mass reduction, so that the difference can be utilized for increasing the mass of conducting material (aluminum or alloys thereof) without increasing the total mass of the conductor.

[0087] Thanks to the expansion coefficient close to zero of aramidic fibres, conductors for high thermal limit can be produced, with a deflection at 120 C. equal to or lower than that of wires with a steel or Invar (FeNi alloy) load-bearing element, thus eliminating the problems related to pylon overload and span deflection.

[0088] The above-described example of embodiment may be subject to variations without departing from the protection scope of the present invention, including all equivalent designs known to a man skilled in the art.

[0089] The elements and features shown in the various preferred embodiments may be combined together without however departing from the protection scope of the present invention.

[0090] From the above description, those skilled in the art will be able to produce the object of the invention without introducing any further construction details.