Classifications

• • 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
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
  • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
  • H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes

Definitions

• This invention relates to electric power cable insulated with a polyethylene composition having an improved resistance to water trees.
• a typical electric power cable generally comprises one or more conductors in a cable core that is surrounded by several layers of polymeric material that include a first semiconducting shield layer, an insulating layer, a second semiconducting shield layer, a metallic tape or wire shield, and a jacket.
• insulated cables are known to suffer from shortened life when installed in an environment where the insulation is exposed to water, e.g., underground or locations of high humidity.
• the shortened life has been attributed to the formation of water trees, which occur when an organic polymeric material is subjected to an electrical field over a long period of time in the presence of water in liquid or vapor form. The net result is a reduction in the dielectric strength of the insulation.
• An object of this invention is to provide an insulated cable which exhibits a much improved resistance to water trees.
• the cable comprises one or more electrical conductors, each, or a core of one or more electrical conductors, surrounded by an insulating composition comprising
• Homogeneous polyethylenes are copolymers of ethylene, one or more alpha-olefins, and, optionally, a diene.
• the alpha-olefins can have 3 to 12 carbon atoms, and preferably have 3 to 8 carbon atoms.
• Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. As noted above, they have a polydispersity (Mw/Mn) in the range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution.
• the homogeneous polyethylenes are characterized by single and relatively low DSC melting points.
• Heterogeneous polyethylenes (the more common of the two), on the other hand, have a polydispersity (Mw/Mn) greater than 3.5 and do not have a uniform comonomer distribution.
• Mw is defined as weight average molecular weight
• Mn is defined as number average molecular weight.
• the homogeneous polyethylenes can have a density in the range of 0.86 to 0.93 gram per cubic centimeter, and preferably have a density in the range of 0.87 to about 0.92 gram per cubic centimeter. They also can have a melt index in the range of about 0.5 to about 30 grams per 10 minutes, and preferably have a melt index in the range of about 0.5 to about 5 grams per 10 minutes.
• Homogeneous polyethylenes can be prepared, for example, with vanadium based catalysts such as those described in United States Patents 5,332,793 and 5,342,907, and they can also be prepared with single site metallocene catalysts such as those described in United States Patents 4,937,299 and 5,317,036.
• the polyethylene glycol is defined by its molecular weight, which can be in the range of about 1000 to about 30,000, and is preferably in the range of about 5000 to about 25,000. The optimum molecular weight is 20,000.
• Polyethylene glycol is a polar compound, which can be represented by the formulas HOCH 2 (CH 2 OCH 2 ) n CH 2 OH or HO(C 2 H 4 O) n H wherein , for example, n can be 225 to 680. This translates into a molecular weight in the range of about 10,000 to about 30,000.
• the amount of polyethylene glycol that can be in the insulating composition can be in the range of about 0.1 to about 20 parts weight based on 100 parts by weight of the polyethylene component, and is preferably in the range of about 0.1 to about 1 part by weight, and can even be as low as about 0.05 part by weight.
• additives which can be introduced into the polyethylene formulation, are exemplified by antioxidants, coupling agents, ultraviolet absorbers or stabilizers, antistatic agents, pigments, dyes, nucleating agents, reinforcing fillers or polymer additives, slip agents, plasticizers, processing aids, lubricants, viscosity control agents, tackifiers, anti-blocking agents, surfactants, extender oils, metal deactivators, voltage stabilizers, flame retardant fillers and additives, crosslinking agents, boosters, and catalysts, and smoke suppressants.
• Fillers and additives can be added in amounts ranging from less than about 0.1 to more than about 200 parts by weight for each 100 parts by weight of the base resin, in this case, polyethylene.
• antioxidants are: hindered phenols such as tetrakis[methylene(3,5-di-tert- butyl-4-hydroxyhydrocinnamate)]methane, bis[(beta-(3,5-ditert-butyl-4-hydroxybenzyl)-methylcarboxyethyl)]sulphide, 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(2-tert-butyl-5-methylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), and thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate; phosphites and phosphonites such as tris(2,4-di-tert-butylphenyl)phosphite and di-tert-butylphenyl-phosphonite; thio compounds such as dilaurylthiodipropionate,
• the resin can be crosslinked by adding a crosslinking agent to the composition or by making the resin hydrolyzable, which is accomplished by adding hydrolyzable groups such as -Si(OR) 3 wherein R is a hydrocarbyl radical to the resin structure through copolymerization or grafting.
• Suitable crosslinking agents are organic peroxides such as dicumyl peroxide; 2,5-dimethyl- 2,5-di(t-butylperoxy)hexane; t-butyl cumyl peroxide; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3. Dicumyl peroxide is preferred.
• Hydrolyzable groups can be added, for example, by copolymerizing ethylene with an ethylenically unsaturated compound having one or more -Si(OR) 3 groups such as vinyltrimethoxy- silane, vinyltriethoxysilane, and gamma-methacryloxypropyltrimethoxysilane or grafting these silane compounds to the resin in the presence of the aforementioned organic peroxides.
• the hydrolyzable resins are then crosslinked by moisture in the presence of a silanol condensation catalyst such as dibutyltin dilaurate, dioctyltin maleate, dibutyltin diacetate, stannous acetate, lead naphthenate, and zinc caprylate.
• Dibutyltin dilaurate is preferred.
• hydrolyzable copolymers and hydrolyzable grafted copolymers are ethylene/ vinyltrimethoxy silane copolymer, ethylene/gamma- methacryloxypropyltrimethoxy silane copolymer, vinyltrimethoxy silane grafted ethylene/ethyl acrylate copolymer, vinyltrimethoxy silane grafted linear low density ethylene/1-butene copolymer, and vinyltrimethoxy silane grafted low density polyethylene.
• the cable of the invention can be prepared in various types of extruders, e.g., single or twin screw types. Compounding can be effected in the extruder or prior to extrusion in a conventional mixer such as a Brabender TM mixer or a Banbury TM mixer. A description of a conventional extruder can be found in United States patent 4,857,600.
• a typical extruder has a hopper at its upstream end and a die at its downstream end. The hopper feeds into a barrel, which contains a screw. At the downstream end, between the end of the screw and the die, is a screen pack and a breaker plate.
• the screw portion of the extruder is considered to be divided up into three sections, the feed section, the compression section, and the metering section, and two zones, the back heat zone and the front heat zone, the sections and zones running from upstream to downstream.
• the length to diameter ratio of each barrel is in the range of about 15:1 to about 30:1.
• the die of the crosshead feeds directly into a heating zone, and this zone can be maintained at a temperature in the range of about 130°C to about 260°C, and preferably in the range of about 170°C to about 220°C.
• the advantage of the invention lies in the much improved water tree growth rate.
• WTGR water tree growth rate
• Parts are by weight.
• each of the polyethylenes described below 100 parts are compounded with 0.61 part of polyethylene glycol (PEG) having a molecular weight of 20,000 (if the PEG is used); 0.76 part of p-oriented styrenated diphenylamine; and 0.4 part of vinyl modified polydimethyl siloxane in a two roll mill operating at 24 revolutions per minute (rpm) on the front roll and 36 rpm on the back roll and a temperature of 125 to 130 degrees C on the two rolls for a period of time (minutes).
• PEG polyethylene glycol
• the procedure involves preheating the resin to 70 degrees C in an oven; fluxing the resin as quickly as possible on the two roll mill (about 3 to 4 minutes); adding all of the non-peroxide additives and fluxing for an additional 3 to 4 minutes; and then adding the peroxide and fluxing, peeling, and folding until well mixed.
• Sufficient dicumyl peroxide is introduced into each composition to provide an oscillating disk rheometer (5 degree arc at 360 degrees F) reading of 48 inch-pound.
• A a copolymer of ethylene and 1-octene having an Mw/Mn ratio of about 2; a narrow comonomer distribution; 9.5 percent by weight 1-octene; a melt index of 3.5 grams per 10 minutes; and a density of 0.910 gram per cubic centimeter.
• B a copolymer of ethylene and 1-octene having an Mw/Mn ratio of about 2; a narrow comonomer distribution; 12 percent by weight 1-octene; a melt index of 1 gram per 10 minutes; and a density of 0.902 gram per cubic centimeter.
• C a copolymer of ethylene and 1-octene having an Mw/Mn ratio of about 2; a narrow comonomer distribution; 24 percent by weight 1-octene; a melt index of 1 gram per 10 minutes; and a density of 0.870 gram per cubic centimeter.
• D a copolymer of ethylene and 1-octene having an Mw/Mn ratio of about 2; a narrow comonomer distribution; 24 percent by weight 1-octene; a melt index of 5 grams per 10 minutes; and a density of 0.870 gram per cubic centimeter.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Organic Insulating Materials (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Communication Cables (AREA)
• Insulated Conductors (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Flexible Shafts (AREA)

Applications Claiming Priority (2)

Publications (3)

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Cited By (15)

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Citations (3)

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• 1996
  • 1996-03-07 TW TW085102785A patent/TW403916B/zh not_active IP Right Cessation
  • 1996-03-15 AT AT96301806T patent/ATE181453T1/de not_active IP Right Cessation
  • 1996-03-15 ES ES96301806T patent/ES2135169T3/es not_active Expired - Lifetime
  • 1996-03-15 DE DE69602872T patent/DE69602872T2/de not_active Expired - Lifetime
  • 1996-03-15 DK DK96301806T patent/DK0735545T3/da active
  • 1996-03-15 EP EP96301806A patent/EP0735545B1/fr not_active Expired - Lifetime
  • 1996-03-26 KR KR1019960008291A patent/KR100271686B1/ko not_active IP Right Cessation
  • 1996-03-29 CA CA002173038A patent/CA2173038C/fr not_active Expired - Lifetime
  • 1996-03-29 AU AU50382/96A patent/AU708233B2/en not_active Ceased
  • 1996-03-29 BR BR9601205A patent/BR9601205A/pt not_active IP Right Cessation
• 1999
  • 1999-07-30 GR GR990401972T patent/GR3030891T3/el unknown

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