Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B9/00—Power cables
  • H01B9/02—Power cables with screens or conductive layers, e.g. for avoiding large potential gradients
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
  • H01B7/2806—Protection against damage caused by corrosion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
  • H01B7/2813—Protection against damage caused by electrical, chemical or water tree deterioration
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
  • H01B7/282—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable
  • H01B7/285—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable
  • H01B7/288—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable using hygroscopic material or material swelling in the presence of liquid
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A30/00—Adapting or protecting infrastructure or their operation
  • Y02A30/14—Extreme weather resilient electric power supply systems, e.g. strengthening power lines or underground power cables

Definitions

• the present invention relates to electric power cables with solid extruded insulation and more specifically to power cables having an improved resistance to corrosion e.g. due to mechanical damage of the outer jacket or sheath as well as an improved resistance to formation of the so-called "water trees" which will be discussed more fully below.
• the invention further relates to a method for the manufactureing of such cables.
• a typical power cable which may be improved according to the invention comprises the following components:
• a conductor e.g. made from Cu or Al,
• An inner semiconductive layer (the conductor screen) e.g. made from a cross-linked polyethylene copolymer containing semi-conductive particles e.g. carbon black,
• An insulating layer e.g. made from a polyethylene compound, a cross-linked polyethylene compound, an ethylene-propylene rubber compound or a butyl rubber compound,
• thermoplastic or cross-linked semi conductive layer (the insulation screen) which may or may not be easily strippable from the insulating layer.
• semi-conductive particles e.g. graphite may be applied by some sort of brushing or rubbing or may be applied in the form of a lacquer or paint layer containing a suitable binder,
• a metallic screen e.g. made from Cu or Al in the form of wires of tapes,
• An outer jacket or sheath e.g. made from PE or PVC.
• One common embodiment is to include three conductors provided with layers 2)-4) and a common metal screen or separate metal screens in a common jacket. Also semi-conductive layers 2) and 4) may be excluded, especially in low voltage cables.
• a water-soluble electrolyte in part or in the whole of the insulation in an amount equal to 10 -7 -1% by weight of the plastic insulation, which can be composed of e.g. polyethylene, cross-linked polyethylene, ethylene-propylene rubber or butyl rubber.
• said electrolyte is a strong electrolyte, such as sodium chloride or sodium sulfate.
• this solution is defective in certain respects since it is difficult to obtain a homogeneous distribution of the electrolyte even in the form of microparticles, and it is difficult if not impossible to avoid the positioning of some of the particles in or near the insulation surface where they may form sites for water trees when they are dissolved and eventually leached out. If the particles are not homogeneo ⁇ sly distributed so that aggregates are present or if the concentration in parts of the cable exceeds the upper limit of 1% by weight the insulation characteristics are adversely affected and/or infiltration of water due to osmotic pressure may arise.
• one solution to the problem would be to provide the insulation layer with a water tight or impervious metal sheath, for example of extruded lead or aluminium or in the form of tapes which are folded and welded around the cable core.
• Said materials capable of reducing the relative humidity can be chosen from among:
• Non-volatile materials which when dissolved in water reduce the vapour pressure above the solution relatively to the vapour pressure of pure water at the same temperature. Suitable materials of this kind are water soluble salts.
• Salts forming stable hydrates such as CaCl 2 , MgCl 2 and Mg(ClO 4 ) 2 .
• Said humidity reducing materials placed in a layer outside and separated from the outer semi-conductive layer do not provide a water-tight barrier.
• the purpose of these materials is to reduce the relative humidity in the insulation to a predetermined percentage.
• the active material must be placed somewhere between the insulation and the cable surroundings.
• the layer containing the active material may be extruded as a fourth preferably insulating layer on top of the common outer semi-conductive layer or the material may be incorporated in or adsorbed onto said layer.
• annular, spaced blocking elements between the cable core and the jacket which block or impede the longitudinal penetration of the water.
• Other known remedies to prevent longitudinal water penetration is to fill the interstices in the cable with powders e.g. cellulose derivatives which in contact with water either swell or form a highly viscous phase and thus physically prevent the water penetration.
• the object of the invention is to provide such a solution.
• the cable according to the invention which may be of any of the general types referred to above thus comprising one or more, e.g. three, conductors provided with an insulating layer and optionally an inner and outer semi-conductive layer and a metal screen, and further comprising as the characteristic features at least one separating layer around the metal screen and at least one outer layer of a paste material having a high degree of water resistance and in which one or more humidity reducing materials are incorporated.
• said humidity reducing materials are chosen from among the abovementioned water soluble salts or salts forming stable hydrates.
• the most preferred compounds are CaCl 2 , MgCl 2 and LiCl.
• the separating layer must have sufficient barrier properties to prevent ingress of water possibly containing dissolved salts and thus to prevent corrosion of the subjacent metal screen. Further, it must resist oily materials and additives which are present in the paste material to secure satisfactory flow.properties, since their penetration would be detrimental to the subjacent semi-conductive and insulating layers.
• a suitable material for this separating layer from a barrier point of view is a polyester material which can be formed to a film such as a polyethylene terephthalate.
• the separating layer a material which besides having the necessary barrier properties also has self-sealing properties, or at least sealing properties under influence of heat.
• a material which besides having the necessary barrier properties also has self-sealing properties, or at least sealing properties under influence of heat it may not be necessary to provide a separate sealing treatment since the heat from the later hot applied paste layer will promote the sealing of the overlappings of the folded layer or of the individual windings and further cause a contraction of the separating layer giving the necessary pressure during the sealing process for preventing distortion of the wires in the metal screen under processing and handling of the cable.
• a particularly suitable material is a film of a polyester of the abovementioned type which is laminated on one or both sides with polyethylene.
• Such a laminated film advantageously combines the good mechanical strength and excellent barrier properties of the polyester material especially towards organic solvents with the good sealing properties of the polyethylene and thus permits a free choice among a great number of paste materials and additives.
• Suitable polyester films are marketed under the trade marks Hostaphan ® , Mylar ® and Melinex ® .
• a separating layer of an extrudable polymer material having the mentioned barrier properties may be extruded onto the metal screen thus giving the additional advantage of securing the underlying screen in place.
• the critical criteria are the flow properties at the application temperature as well as the temperature of use, the water resistance and the ability to contain sufficient amounts of humidity reducing additives while retaining the flow properties as water is absorbed by the additives.
• the additives should not adversely effect the flow properties of the paste material.
• the paste must have such properties, and the additive must be incorporated in such a manner that it will not be easily washed out of the paste.
• Suitable materials for the paste are e.g.
• Rubber-like copolymers of ethylene and aliphatic unsaturated esters e.g. vinyl acetate, methyl acrylate, methyl methacrylate containing appr. 30% by weight of the ester monomer.
• inert fillers e.g. calcium carbonate, calcium magnesium carbonate and clay in an amount of up to 300 parts by weight per 100 parts by weight of the materials and mixtures mentioned.
• the humidity reducing material or materials are incorporated and homogenized in said filled or unfilled paste materials or mixtures so that the amount of active material per cm 2 surface of the finished cable is preferably not less than
• the cable may be provided with two or more alternating separating layers and paste layers or with an inner semi-conductive paste layer without humidity reducing materials, a separating layer, and one or more outer paste layers.
• a powder with swelling properties of the type mentioned above may be applied between the separating layer and the metal screen.
• This has the advantage that an embedding of the metal screen preventing a contact with the subjacent semi-conductive layer over a certain length, which might be feared if an inner paste material is used, will not take place. Thus no influence on the electrical properties is imparted to the cable and the powder is easy to apply without any dirtying problems.
• the invention further relates to a method of manufacturing cables of the types described, said method being characterized in that a cable core consisting of one or more conductors which in a known manner has been provided with an insulating layer and optionally an inner and outersemi-conductive layer and a metal screen is provided with a separating layer around the metal screen and at least one layer of a paste material having a high degree of water resistance and having incorporated one or more humidity reducing materials around said separating layer whereupon an outer jacket is applied by extrusion in a known manner.
• the separating layer is applied by winding, folding or extrusion.
• fig. 1 shows a cross-section of an embodiment of a power cable according to the invention
• fig. 2 schematically illustrates the manufacture of a cable according to the invention.
• Fig. 1 shows a cross-section through an embodiment of a cable according to the invention, where items 1 to 5 and 8 are traditional parts of a power cable.
• the conductor 1 is surrounded by an inner semi-conductive layer 2, an insulating layer 3, an outer semi-conductive layer 4, and a metal screen 5, all being of any desired material and thickness.
• the separating layer 6 may be a folded, wound or extruded layer as explained above and it is surrounded by the paste layer 7 which contains the humidity reducing material. 8 represents the outer jacket.
• the paste layer 7 may consist of two layers of which only the inner layer contains humidity reducing material.
• a semi-conductive paste or a powder mayer with swelling properties may further be provided between semi-conductive layer 4 and separating layer 6, and also humidity reducing paste layer 7 may be surrounded by a further separating layer and a further paste layer.
• Fig. 2 schematically illustrates the manufacture of a cable according to the invention.
• the conductor or conductors are provided with the layers 2-5 shown on fig. 1 in any known manner and supplied from a reel 10.
• powder or semi-conductive paste is applied by means 11 whereafter a separating layer is applied by winding means 12 or by folding or extrusion means.
• the cable is then passed through a box 13 where hot paste is applied, preferably in the form of stream flowing downward onto the cable and spreading over its periphery.
• hot paste preferably in the form of stream flowing downward onto the cable and spreading over its periphery.
• the cable passes a stripper removing excessive paste and is directly introduced into the extruder 14 where the jacket is applied.
• the finished cable is collected on a take off reel 15.
• one or more further paste boxes and/or winding means may be arranged between box 13 and extruder 14.
• the cable delivered from the reel 10 may already be provided with the separating layer and optionally a subjacent layer of powder or semi-conductive paste.

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• Insulated Conductors (AREA)
• Manufacturing Of Electric Cables (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10500631

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (8)

Citations (8)

• 1978
  • 1978-10-27 GB GB7842185A patent/GB2032678B/en not_active Expired
• 1979
  • 1979-10-24 NO NO793406A patent/NO793406L/no unknown
  • 1979-10-25 WO PCT/DK1979/000040 patent/WO1980000895A1/en unknown
  • 1979-10-26 FI FI793363A patent/FI793363A/fi not_active Application Discontinuation
• 1980
  • 1980-06-25 SE SE8004671A patent/SE8004671L/sv unknown

Patent Citations (8)

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