EP0360836B1 - Elektrischer draht - Google Patents

Elektrischer draht Download PDF

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Publication number
EP0360836B1
EP0360836B1 EP88905962A EP88905962A EP0360836B1 EP 0360836 B1 EP0360836 B1 EP 0360836B1 EP 88905962 A EP88905962 A EP 88905962A EP 88905962 A EP88905962 A EP 88905962A EP 0360836 B1 EP0360836 B1 EP 0360836B1
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Prior art keywords
wire
polymer
control layer
aromatic
layer
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English (en)
French (fr)
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EP0360836A1 (de
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Richard John Penneck
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Raychem Ltd
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Raychem Ltd
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    • 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
    • H01B3/303—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups H01B3/38 or H01B3/302
    • H01B3/306—Polyimides or polyesterimides
    • 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
    • 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
    • H01B3/42—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 polyesters; polyethers; polyacetals
    • H01B3/421—Polyesters
    • H01B3/422—Linear saturated polyesters derived from dicarboxylic acids and dihydroxy compounds
    • H01B3/423—Linear aromatic polyesters
    • 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
    • H01B3/42—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 polyesters; polyethers; polyacetals
    • H01B3/427—Polyethers

Definitions

  • This invention relates to electrical wires, and especially to wires that employ electrical insulation based on aromatic polymers.
  • aromatic polymer insulation have been used for many years in numerous applications.
  • wires that employ polyimide wraps or tapes usually bonded with fluoropolymer adhesive layers have been used extensively as aircraft wire, for both civil and military applications.
  • Other examples of aromatic insulation that have been used for equipment wire or "hook-up" wire, air frame wire and in wire harnesses include aromatic polyether ketones, polyether ether ketones, modified polyphenylene oxide, and polyimide amides.
  • Highly aromatic polymers have been used successfully in many applications because they have a range of desirable properties especially high strength and toughness, abrasion resistance, temperature resistance, dielectric strength and are often inherently highly flame-retarded.
  • a catastrophic cascade failure can result from a fault to a single wire if adjacent wires that are at a different electrical potential are also susceptible to tracking or if the bundle is in contact with a grounded structure. Tracking can occur at low voltages e.g. 100V a.c. or less but becomes less likely as the voltage is reduced.
  • a related phenomenon, to which these polymers are also highly susceptible, is that of breakdown due to arcing.
  • a potential difference between two conductors, or between a conductor in which the insulation has been mechanically damaged, and ground, can result in the formation of an arc between the conductors or between the conductor and ground.
  • the high temperature of the arc causes the polymer to degrade extremely rapidly and form an electrically conductive carbonaceous deposit which can extend rapidly, as with wet tracking, and lead to catastrophic failure in which many or all of the wires in a bundle are destroyed.
  • Arcing can occur at very low voltages, for example 24V d.c. or lower, and since, unlike tracking, no electrolyte or moisture is involved, it is a particularly hazardous phenomenon.
  • Arcs may also be struck by drawing apart two conductors between which a current is passing as described for example by J.M. Somerville "The Electric Arc", Methuen 1959.
  • insulating material is removed by a vaporization process originated by an electrical discharge without the formation of electrically conductive deposits so that failure of the insulation will not occur until complete puncture of the insulation occurs.
  • One electrical wire that has a resistance to electrical arcing is described in FR-A-2555799.
  • This wire may comprise a conductor and an insulation comprising a thermoplastic having a glass transition temperature below 250°C, an aromatic polyimide layer and a thin layer of varnish or lacquer.
  • wires are disclosed in EP-A-132,343 which comprise a thin inorganic layer deposited on the conductor followed by a polymeric insulation which may be dual wall insulation having a fluoropolymer outer layer.
  • an electrical wire which comprises an elongate electrical conductor, an inorganic arc-control layer surrounding the conductor, an insulating layer which surrounds the arc-control layer and comprises an aromatic polymer and a secondary tracking control layer surrounding the insulating layer, the secondary tracking control layer having a comparative tracking index of at least 300V.
  • the "comparative tracking index" (C.T.I.) of a polymer is defined below.
  • the aromatic polymer will normally have a carbonaceous char residue of at least 25%, preferably at least 30%, some polymers having a char residue of at least 40% and even at least 50%. This does not mean to say that a high char value is desired for its own sake, but simply that good mechanical and physical properties of these aromatic polymers including temperature stability and fire retardancy, are usually associated with high char residues.
  • the char residue of the polymer components in the electrical wire according to the invention can be measured by the method known as thermogravimetric analysis, or TGA, in which a sample of the polymer is heated in nitrogen or other inert atmosphere at a defined rate, e.g. 10°C per minute to a defined temperature and the residual weight, which is composed of char, is recorded.
  • TGA thermogravimetric analysis
  • the char residue is simply the quantity of this residual char expressed as a percentage of the initial polymer after having taken into account any non polymeric volatile or non-volatile components.
  • the char residue values quoted herein are defined as having been measured at 850°C and at a heating rate of 10°C per minute.
  • Such polymers include polyketones, polyether ketones, polyether ether ketones, polyether sulphones, polyether ketone/sulphone copolymers, polyether imides and polyphenylene oxides. Blends of different polymers can be used.
  • the polymers may be wholly aromatic or they may include one or more aliphatic moieties which may comprise pendant alkyl groups or may comprise alkylene groups in the polymer backbone. Preferably the or each aliphatic moiety has not more than 4, and more preferably not more than 3 carbon atoms.
  • each group is most preferably a methyl group, while in the case of alkylene groups each group preferably has not more than 3 carbon atoms, and especially only one carbon atom, in the chain backbone, for example a methylene or isopropylidine group.
  • Preferred aromatic polymers are polymers with a melting or softening point of at least 250°C, particularly at least 300°C and which may be crystalline or amorphous. Softening points of amorphous polymers may conveniently be measured by thermomechanical analysis (TMA), in which case the softening point refers to the temperature at which the probe has reached 60% penetration.
  • TMA thermomechanical analysis
  • the polymer comprises, and preferably consists essentially of, units of the formula -Ar-Q- the units being the same or different, wherein Ar represents an unsubstituted or substituted divalent aromatic radical and Q represents -O-, -S-, -SO2-, -CO-, -NH-CO- or -COO-, or Ar represents a polyvalent radical and Q represents each bond of the Q radical preferably being bonded directly to an aromatic carbon atom.
  • One preferred class of polymer comprises the polyphenylene oxides of the repeating unit in which the groups R1, which may be the same or different, each represents a hydrogen or halogen atom or a hydrocarbon atom having no tertiary alpha carbon atom.
  • the aromatic polymer is a crystalline polyarylene ether comprising recurring units of the formula -O-E-O-E'- where E is the residue of a dihydric phenol and E' is the residue of an aromatic compound having an electron withdrawing group in at least one of the positions ortho and para to the valence bonds, the E and E' radicals being linked to the -O- radicals through aromatic carbon atoms.
  • E is a radical of the formula wherein R2 is a divalent radical; x is 0 or 1; Y is a radical selected from halogen atoms, alkyl radicals containing 1 to 4 carbon atoms and alkoxy radicals containing 1 to 4 carbon atoms; y is 0, 1, 2, 3 or 4; Y' is a radical selected from halogen atoms, alkyl radicals containing 1 to 4 carbon atoms and alkoxy radicals containing 1 to 4 carbon atoms; z is 0, 1, 2, 3 or 4, and E' is a radical of the formula wherein R3 is a sulphone, carbonyl, vinyl, sulphoxide, azo, saturated fluorocarbon, organic phosphine oxide or ethylidene radical.
  • polysulphones are those in which y and z are 0, x is 1, R3 is a sulphone radical and R2 is a radical of the formula wherein each of R4 is independently selected from the group consisting of hydrogen; alkyl radicals containing 1 to 4 carbon atoms; halogen-substituted alkyl radical containing 1 to 4 carbon atoms; aryl, alkaryl and aralkyl radicals containing 6 to 10 carbon atoms; and halogen-substituted aryl alkaryl and aralkyl radicals containing 6 to 10 carbon atoms.
  • the polymer is a polyether imide or polysulphone imide which comprises recurring units of the formula where Q is -O- or -SO2-, Z is a trivalent aromatic radical, R5 is a divalent aromatic radical and R6 is a divalent organic radical.
  • the aromatic polymer has the general repeat unit in which D represents a group of the formula: and R' represents an arylene group.
  • polyetherketones that have repeating groups comprising aromatic ether and aromatic ketone groups together with an imide, amide, ester, benzoxazole or benzothiazole group.
  • examples of such polymers are those having repeating units of the formula: where R7 represents an imide, amide or ester group.
  • polyarylates that may be used include those that are derived from dihydric phenols and at least one aromatic dicarboxylic acid.
  • examples of such polymers include those derived from a dihydric phenol of the general formula in which the groups Y, which may be the same or different, each represent a hydrogen atom, a C1 to C4 alkyl group, or a chlorine or bromine atom; b is 0 ir an integer from 1 to 4;
  • R8 represents a divalent saturated or unsaturated hydrocarbon group, e.g. an alkylene, alkylidine, cycloalkylene or cycloalkylidine group, an oxygen or sulphur atom or a carbonyl or sulphonyl group; and c is 0 or 1.
  • Preferred aromatic polymers consist essentially of repeating units having one of the following formulae wherein each of x, m and n is 0 or 1, with n being 0 when x is 1, p is an integer from 1 to 4, with m being 1 and x being 0 when p is greater than 1, e.g., or in which units derived wholly from isophthalic acid or terephthalic acid or a mixture of both are present.
  • polymers having aromatic moieties e.g. poly 1,12-dodecamethylene pyromellitimide or 1,13-tridecamethylene pyromellitimide, as described in U.S. patent No. 3,551,200, may be used.
  • Blends of any two or more of the above polymers may be employed as may copolymers based on any two or more of these polymers.
  • the preferred aromatic polymers will usually have a molar C:H ratio of at least 1.0, preferably at least 1.2, more preferably at least 1.3 and especially at least 1.4.
  • the toughest polymers such as the polyaryl ether ketones, which are associated with high char residues, will have C:H ratios greater than 1.5.
  • the insulating layer may, in some cases, have an inner surface that has a C.T.I. of at least 250V.
  • the C.T.I. of the inner surface of the principal insulating layer is at least 300V and most especially at least 500V.
  • Such values for the C.T.I. will normally be associated with carbonaceous char levels of not more than 10% by weight preferably not more than 5% by weight more preferably not more than 2% and especially 0%.
  • the C.T.I. of the inner surface of the insulating layer may be achieved in certain cases by selection of the appropriate aromatic polymer. Alternatively it may be appropriate to blend the aromatic polymer with an aliphatic polymer in order to reduce the char level or increase the C.T.I. of the layer.
  • the insulating layer may be in the form of two or more layers, the outermost layer comprising the aromatic polymer, either alone or as a blend with one or more other polymers, and the inner layer comprising a polymer having a low char residue, e.g. not more than 10% by weight.
  • the inner layer may, and preferably does, comprise one or more of the aliphatic polymers mentioned below.
  • the total thickness of the insulating layer will usually be in the range of from 50 to 250 micrometres, and especially from 75 to 200 micrometres.
  • the inner layer will normally have a thickness of from 75 to 125 micrometres
  • the outer layer will normally have a thickness of up to 150 micrometres, preferably up to 100 micrometres, and especially up to 75 micrometres.
  • the purpose of the arc-control layer is to control the growth of the arc roots which, according to the invention, is achieved by controlling the arc diameter through the provision of a refractory, preferably adherent, layer on the electrical conductor, which will aid quick conductor melting and severence before more extensive wire or bundle damage can occur.
  • a layer of alumina, silica, silicon nitride, aluminium nitride, magnesium oxide, and titanium dioxide may be applied by any appropriate means, for example a vapour deposition method. Examples of such methods includes sputtering, chemical vapour deposition, flame spraying, plasma ashing, reactive ion plating, electron beam evaporation or by other techniques.
  • refractory coatings and methods of forming them on a conductor are described in our patent application No. GB-2,144,260A (US 818,854), the disclosure of which is incorporated herein by reference.
  • a weathered mica coating may be employed, for example as described in our copending International applications Nos. WO 89/00762 and WO 89/00764, the disclosures of which are also incorporated herein by reference.
  • the thickness of the arc-control layer will depend on, amongst other things, the material from which it is formed. In the case of refractory layers, the thickness will normally be in the range of from 0.1 to 10 micrometres preferably 5 to 10 micrometres, and the layer will preferably adhere to the electrical conductor for example by provision of a metallic or refractory interlayer. For other materials, thicknesses up to 100 micrometres may be used.
  • the secondary tracking control layer has a C.T.I. of at least 300V. Preferably it has a C.T.I. of at least 400V, more preferably at least 500V and especially at least 600V. This normally will mean that the material from which the secondary tracking control layer is formed will have a carbonaceous char residue of not more than 10%, more preferably not more than 5%, most preferably not more than 2% and especially 0% by weight.
  • the secondary tracking control layer preferably comprises an aliphatic polymer or blend of aliphatic polymers, although it is possible for the aliphatic polymer to include one or more aromatic moieties in addition to its aliphatic moieties, and indeed a number of preferred polymers do so.
  • polymer should have sufficient aliphatic nature that its molar C:H ratio is not more than 1.
  • aliphatic polymers and polymers containing aliphatic moieties include olefin homopolymers and copolymers of olefins with other olefins and with other monomers e.g. vinyl esters, alkyl acrylates and alkyl alkacrylates, e.g.
  • low, medium and high density polyethylene low, medium and high density polyethylene, linear low density polyethylene and ethylene alpha-olefin copolymers, ethylene/propylene rubber, butyl rubber, ethylene vinyl acetate, ethylene ethyl acrylate and ethylene acrylic acid copolymers, and linear or radial styrene diene di- or tri-block copolymers e.g.
  • polystyrene/butadiene styrene/isoprene copolymers
  • styrene/butadiene/styrene and styrene/isoprene/styrene hydrogenated versions of these block copolymers especially styrene ethylene/butylene/styrene block copolymers.
  • a particularly preferred class of low charring polymers is the polyamides.
  • Preferred polyamides include the nylons e.g.
  • nylon 46, nylon 6, nylon 7, nylon 66, nylon 610, nylon 611, nylon 612, nylon 11, nylon 12, nylon 1212, and aliphatic/aromatic polyamides polyamides based on the condensation of terephthalic acid with trimethylhexamethylene diamine (preferably containing a mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diamine isomers), polyamides formed from the condensation of one or more bisaminomethylnorbornane isomers with one or more aliphatic, cycloaliphatic or aromatic dicarboxylic acids e.g. terephthalic acid and optionally including one or more amino acid or lactam e.g.
  • ⁇ -caprolactam comonomers polyamides based on units derived from laurinlactam, isophthalic acid and bis-(4-amino-3-methylcyclohexyl) methane, polyamides based on the condensation of 2,2-bis-(p-aminocyclohexyl) propane with adipic and azeleic acids, and polyamides based on the condensation of trans cyclohexane-1,4-dicarboxylic acid with the trimethylhexamethylene diamine isomers mentioned above.
  • Other aliphatic polymers that may be used include polyesters e.g.
  • Preferred aliphatic polymers include the polyamides mentioned above, polyethylene, polybutylene terephthalate, ionomers based on metal salts of methacrylated polyethylene, acrylic elastomers e.g.
  • G is a divalent radical remaining after the removal of terminal hydroxyl groups from a polyalkylene oxide) glycol, preferably a poly (C2 to C4 alkylene oxide) having a molecular weight of about 600 to 6000;
  • R is a divalent radical remaining after removal of carboxyl groups from at least one dicarboxylic acid having a molecular weight of less than about 300; and
  • D is a divalent radical remaining after removal of hydroxyl groups from at least one diol having a molecular weight less than 250.
  • polyether-ester amide block copolymers include those based on polyether and polyamide blocks, especially the so called a "polyether-ester amide block copolymers" of repeating unit: wherein A represents a polyamide sequence of average molecular weight in the range of from 300 to 15,000, preferably from 800 to 5000; and a represents a linear or branched polyoxyalkylene sequence of average molecular weight in the range of from 200 to 6000, preferably from 400 to 3000.
  • the polyamide sequence is formed from alpha,omega-aminocarboxylic acids, lactams or diamine/dicarboxylic acid combinations that include C4 to C14 alkylene carbon chains, and the polyoxyalkylene sequence is based on ethylene glycol, propylene glycol and/or tetramethylene glycol, and the polyoxyalkylene sequence constitutes from 5 to 85%, especially from 10 to 50% of the total block copolymer by weight.
  • these polymers and their preparation are described in UK Patent Specifications Nos. 1,473,972, 1,532,930, 1,555,644, 2,005,283A and 2,011,450A.
  • the aliphatic polymer preferably has a C:H ratio of not more than 0.9, more preferably not more than 0.75, most preferably not more than 0.65 and especially not more than 0.55.
  • the aliphatic polymer may be unsubstituted or substituted.
  • One class of aliphatic polymer that is particularly useful is the fluorinated polymers, preferably those containing at least 10%, more preferably at least 25% fluorine by weight.
  • the fluorinated polymer may be a single fluorine containing polymer or a mixture of polymers one or more of which contains fluorine.
  • the fluorinated polymers are usually homo-or copolymers of one or more fluorinated, often perfluorinated, olefinically unsaturated monomers or copolymers of such a comonomer with a non-fluorinated olefin.
  • the fluorinated polymer preferably has a melting point of at least 150°C, often at least 250°C and often up to 350°C, and a viscosity (before any crosslinking) of less than 104 Pa.s at a temperature of not more than 60°C above its melting point.
  • Preferred fluorinated polymers are homo- or copolymers of tetrafluoroethylene, vinylidine fluoride or hexafluoropropylene, and especially ethylene/tetrafluoroethylene copolymers e.g.
  • the secondary tracking control layer may have a thickness of up to 100 micrometres, e.g. from 50 to 100 micrometres in the case of a polymeric layer. Thinner secondary tracking control layers may be provided by other means.
  • the polymeric insulation of the wire is preferably cross-linked.
  • the aromatic polymers will exhibit a lower degree of crosslinking than the aliphatic polymers, and in many cases the aliphatic polymers may be highly crosslinked while the aromatic polymers remain substantially uncrosslinked.
  • the polymeric composition may be cross-linked, for example, by exposure to high energy radiation.
  • Radiation cross-linking may be effected by exposure to high energy irradiation such as an electron beam or gamma-rays. Radiation dosages in the range 20 to 800 kGy, preferably 20 to 500 kGy, e.g. 20 to 200 kGy and particularly 40 to 120 kGy are in general appropriate depending on the characteristics of the polymer in question.
  • a prorad such as a polyfunctional vinyl or allyl compound, for example triallyl cyanurate, triallyl isocyanurate (TAIC), methylene bis acrylamide, metaphenylene diamine bis maleimide or other crosslinking agents, for example as described in U.S. patents Nos. 4,121,001 and 4,176,027, are incorporated into the composition prior to irradiaton.
  • the polymers used for the various layers may include additional additives, for example reinforcing or non-reinforcing fillers, stabilisers such as ultraviolet stabilisers, antioxidants, acid acceptors and anti-hydrolysis stabilisers, pigments, processing aids such as plasticizers, halogenated or non-halogenated flame retardants, hydrated metal oxides such as alumina trihydrate and magnesium hydroxide, or decabromodiphenyl ether or combinations thereof, fungicides and the like.
  • stabilisers such as ultraviolet stabilisers, antioxidants, acid acceptors and anti-hydrolysis stabilisers
  • pigments processing aids such as plasticizers, halogenated or non-halogenated flame retardants, hydrated metal oxides such as alumina trihydrate and magnesium hydroxide, or decabromodiphenyl ether or combinations thereof, fungicides and the like.
  • the wires and cables according to the invention may be formed by conventional techniques.
  • the polymers may be blended together if necessary in a mixer, together with any additional components, pelletised, and then extruded onto a wire conductor.
  • Other non-preferred wires may be formed by a tape-wrapping method.
  • a polyamide e.g. trimethylhexamethylene terephthalamide may be dissolved in a solution of a polyamic acid and, after the solvent has been evaporated, the aromatic polymer may be imidized by heat and cut into tapes which can then be wrapped around the conductor and underlying layers.
  • the wires may be used individually as equipment or "hook-up" wires, or airframe wires, or in bundles and harnesses, both jacketted and unjacketted, and may be used in multiconductor cables.
  • the wires, harnesses or cables may be unscreened or they may be provided with a screen to protect them from electromagnetic interference, as well known in the art.
  • flat cables may be formed using the insulation materials according to the invention, either employing flat conductors or round conductors.
  • an electrical wire comprises a conductor 11 which may be solid or stranded as shown and is optionally tinned.
  • a 10 micrometre thick silica or alumina layer 12 is formed on the conductor by a vacuum deposition process, e.g. by sputtering, 5 micrometre intermediate layer formed from for example aluminium optionally being provided in order to improve adhesion of the layer 12 to the conductor 11.
  • a 100 to 200 micrometre thick aromatic polymer insulation 13 is then extruded onto the coated conductor followed by a 100 micrometre thick tracking control layer 14 formed e.g. from an ethylene-tetrafluoroethylene copolymer. After both layers have been extruded, the insulation is irradiated by high energy electrons, to a dose of about 120 kGy to crosslink the tracking control layer 14 and optionally also the aromatic polymer layer (depending on the aromatic layer).
  • This test is designed to simulate the condition occuring when a damaged wire bundle comes into contact with an electrolyte.
  • the electrolyte may be moisture containing dust particles or other ionic contaminant. Damage to the bundle may occur through a number of reasons e.g. abrasion, hydrolysis of the insulation, aging, etc.
  • Current flow through the electrolyte results in heating and evaporation of the solution. This causes one or more dry bands to appear across which the test voltage is dropped, resulting in small, often intense, scintillations which damage the insulation.
  • FIG. 2 shows the sample set-up.
  • a wire bundle 1 is prepared from seven 14cm lengths 2 of 22AWG tinned-copper or nickel-plated copper conductor coated with a layer of the wire insulation under test.
  • the bundle 1 is arranged with six wires around one central wire and is held together using tie wraps 3 so that the wires are not twisted.
  • Two adjacent wires are notched circumferentially to expose 0.5mm bare conductor on each wire.
  • the notches 4 are arranged such that they are 5mm apart with the tie wraps 5mm either side of them.
  • One end of each wire is stripped to enable connections to be made to the power supply via insulated crocodile clips.
  • the sample is held at an angle of 30 degrees to the horizontal using a simple clamp made of an electrically insulating resin so that the damaged wires are uppermost and the stripped ends are at the upper end of the bundle.
  • a piece of filter paper 5 20 x 10mm wide is wrapped around the bundle approximately 2mm above the upper notch; this is best held in place with the upper tie wrap.
  • a peristaltic pump conveys the electrolyte from the reservoir to the sample via a dropping pipette 6, and a power supply is provided to energise the bundle.
  • the electrolyte used is 2% sodium chloride and 0.02% sodium dodecyl sulphate surfactant in distilled or deionised water.
  • the pump is set to deliver this solution at a rate of approximately 60mg per minute through the pipette 6 which is positioned 10mm vertically above the filter paper 5.
  • the power is supplied by a 3-phase 400Hz 115/200V generator of at least 5kVA capacity or a single phase 50Hz 115V transformer of at least 3kVA capacity.
  • a device for recording time to failure is provided which records the time when either a wire goes open circuit, or when a circuit breaker comes out. Leakage currents can be followed with the use of current clamps surrounding the wires and connected to a suitable oscilloscope.
  • Wire insulations exhibiting "failures" due to (b) or (c) may be considered to be good non wet-tracking insulation if no more than two of the originally undamaged wires become open circuit.
  • This test is designed to simulate what happens when a fault in a wire bundle causes arcing under dry conditions.
  • a graphite rod is used to initiate the arc which causes thermal degradation of the insulation.
  • Continuation of the fault current can only occur through the wire bundle under test due to shorting across adjacent phases through a conductive char, or direct conductor-conductor contact such as might occur if the insulation is totally removed by the duration of the arc.
  • FIG. 3 shows the sample set-up.
  • a wire bundle 21 is prepared from seven 10cm lengths 22 of 22AWG tinned-copper or nickel-plated copper conductor coated with a layer of the wire insulation under test.
  • the bundle 22 is arranged with six wires around one central wire and held together with tie wraps spaced about 5cm apart.
  • One of the outer wires is notched circumferentially between the tie wraps to expose 0.5mm bare conductor and one end of each wire is stripped to enable connections to be made via insulating crocodile clips.
  • a rod 23 is provided which is made of a spectrographically pure graphite, diameter 4.6mm, with an impurity level not more than 20ppm. It is prepared before each test by sharpening one end using a conventional pencil sharpener of European design to give an angle of 10 degrees off vertical with a tip diameter of 0.4 ⁇ 0.1mm.
  • a 100g weight 24 is clamped onto the top of the rod 23 to maintain contact during the arc initiation and also acts as a device to limit the depth of penetration of the rod by restricting its downward travel.
  • the rod passes through a PTFE bush which allows it to slide freely up and down.
  • levers enables precise positioning of the rod 23 on the wire bundle 21 which is held securely in place by means of a simple clamp 25 made of an electrically insulating resin and mounted on a block 26 made of the same material.
  • the power source can be either:
  • the fault current is detected by means of current clamps surrounding the connecting leads and the voltage at failure is measured using a 10:1 voltage probe.
  • the transducer signals are fed into a multi-channel digital storage oscilloscope where they can be displayed and manipulated to obtain power curves (voltage x current) and energy (integration of power curve).
  • the wire bundle 21 is positioned in the clamp 25 so that the notched wire is uppermost. Adjacent wires of the bundle are connected to different phases of the supply through 7.5A aircraft type circuit breakers, and the central wire is connected directly to neutral. In the case of single phase or d.c. supplies, alternate wires are connected to neutral or the negative terminal, with the remaining wires, including the central wire, connected through circuit breakers to live or the postive terminal.
  • the carbon rod is also connected to neutral or the negative terminal and positioned so that the point is in contact with the exposed conductor.
  • the gap between the 100g weight and the PTFE bush is adjusted to the diameter of the insulated wire under test, using a suitable spacer to limit the penetration of the rod into the sample.
  • a voltage probe is connected across the damaged wire and the rod, and current clamps positioned on each of the three phases, or on the wires connected to the live side of the supply.
  • a protective screen is placed in front of the test set-up and the power switched on. A material is deemed to pass this test if:
  • non-tracking materials will have relatively few spikes in the current trace with a correspondingly low total energy consumed.
  • Tracking materials show many spikes usually on all three phases, which are accompanied by violent crepitation and large energy consumption.
  • This method is a modification of IEC 112 which measures the low voltage track resistance (up to 600V) as Comparative Tracking Index (CTI) of materials in the presence of an aqueous contaminant.
  • CTI Comparative Tracking Index
  • each polymeric layer is prepared by either compression or injection moulding plaques with minimum thickness of 3mm and with sufficient area to ensure that during the test no liquid flows over the edge of the sample. Before testing, the surface of the sample is cleaned with methanol to remove any surface contamination.
  • the test apparatus is as described in IEC 112. It consists of two platinum electrodes, each with one end chisel-shaped to an angle of 30 degrees. The electrodes are symmetrically arranged such that the opposing chisel faces are vertical and 4.0 ⁇ 0.1mm apart when placed on the surface of the specimen.
  • the power supply consists of a 0.5kVA transformer capable of supplying an a.c. voltage in the range 100-600V at 50Hz.
  • a rheostat is incorporated into the circuit so that the short circuit current may be adjusted to give 1.0 ⁇ 0.1 amp.
  • An over-current relay is provided which shuts off the HV supply when a current of at least 0.5 amps flows for 2 seconds, the criteria for failure.
  • a device for dropping electrolyte solution between the electrodes is provided.
  • This consists of a peristaltic pump which draws liquid from a reservoir and pumps it out of a needle situated at height of 30-40mm above and between the electrodes.
  • the dropping rate is set to 1 drop every 30 ⁇ 5 seconds with a drop volume of 20 ⁇ 3 mm3.
  • the needle is cleaned and purged with several drops of electrolyte to ensure the correct concentration of reagent is used.
  • the electrolyte solution used in these tests is 0.1 ⁇ 0.002% ammonium chloride and 0.01% sodium dodecyl sulphate surfactant in deionised water and has a resistivity of 405 ⁇ 5 ohm.cm at 23°C.
  • the specimen is put into position and the electrodes lowered on to the surface. A suitable voltage is chosen and the short circuit current adjusted accordingly. The electrolyte is then allowed to drop between the electrodes until either
  • CTI comparative tracking index
  • CTI is then quoted as >600 and the erosion of the sample is measured by preweighing a plaque of the material, running the test at 400V for 101 drops of electrolyte, and then reweighing the sample after removing any loose surface debris. The erosion is quoted as mg of material lost.
  • the following wire constructions were prepared by use of a 20mm Baughan extruder for the polymeric layers and by sputtering for the inorganic layers. In the cases where a blend has been used, it has been prepared using a Baker Perkins twin screw extruder. The conductor was 22 AWG nickel plated copper unless otherwise stated. The results for the wet and dry tracking tests are shown in the table.
  • a 10 ⁇ m silica arc control layer on top of a 5 ⁇ m aluminium interlayer was coated with 160 ⁇ m of polyaryletheretherketone as the primary insulation layer and 75 ⁇ m crosslinked ethylenetetrafluoroethylene as the secondary tracking control layer.
  • a 6-7 ⁇ m alumina arc control layer on top of a 7 um aluminium interlayer was coated with 125 ⁇ m of polyaryletheretherketone as the primary insulation layer and 125 ⁇ m of a blend of polytetramethylene terephthalate and a poly(ether-ester) block copolymer comprising approximately 57% by weight polybutylene terephthalate hard blocks and approximately 43% by weight poly(butylene glycol polyether terephthalate) soft blocks in the ratio of 70:30 as the secondary tracking control layer. (22 AWG copper conductor).
  • a 6 ⁇ m silica arc control layer on top of a 5.7 ⁇ m aluminium interlayer was coated with 125 ⁇ m of polyaryletheretherketone as the primary insulation layer and 125 ⁇ m of a blend of polytetramethylene terephthalate and a poly(ether-ester) block copolymer comprising approximately 57% by weight polybutylene terephthalate hard blocks and approximately 43% by weight poly(butylene glycol polyether terephthalate) soft blocks in the ratio of 70:30 as the secondary tracking control layer.
  • a 6-7 ⁇ m silica arc control layer on top of a 7 ⁇ m aluminium interlayer was coated with 125 um of polyaryletheretherketone as an insulating layer.
  • polyaryletheretherketone as the inner insulating layer with 100 ⁇ m of a blend of polytetramethylene terephthalate and a poly(ether-ester)block copolymer comprising approximately 57% by weight poly(tetramethylene terephthalate) hard blocks and approximately 43% by weight poly(tetramethylene glycol polyether terephthalate) soft blocks in the ratio of 70:30 as the outer insulating layer.

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Claims (19)

  1. Elektrischer Draht, welcher einen länglichen elektrischen Leiter (11), eine anorganische Lichtbogenlösch-Schicht (12), die den Leiter umgibt, eine isolierende Schicht (13), welche die Lichtbogenlösch-Schicht umgibt und ein aromatisches Polymer enthält, sowie eine sekundäre Kriechstrom-Steuerungsschicht (14), die die isolierende Schicht umgibt, umfaßt, wobei die sekundäre Kriechstrom-Steuerungsschicht eine vergleichende Kriechstromfestigkeit von mindestens 300 V hat.
  2. Draht nach Anspruch 1, wobei die Lichtbogenlösch-Schicht (12) eine Dicke im Bereich von 0,1 bis 10 Mikrometer hat.
  3. Draht nach Anspruch 2, wobei das Material der anorganischen Lichtbogenlösch-Schicht (12) durch ein Vakuum-Beschichtungsverfahren abgeschieden worden ist.
  4. Draht nach Anspruch 2 oder Anspruch 3, wobei das anorganische Material ein Oxid, Nitrid oder Oxynitrid von Aluminium, Silizium oder Titan umfaßt.
  5. Draht nach einem der Ansprüche 1 bis 4, wobei das aromatische Polymer ein Polyaryletherketon, ein Polyarylethersulphon, einen Polyarylether, ein Polyarylat und/oder ein Polyetherimid umfaßt.
  6. Draht nach Anspruch 5, wobei das aromatische Polymer umfaßt:
    i) Einheiten der allgemeinen Formel:



            -Ar-Q-



    wobei die Einheiten gleich oder verschieden sind,
    worin Ar ein unsubstituiertes oder substituiertes aromatisches zweiwertiges Radikal darstellt und Q -O-, -S-, -SO₂-, -CO-, -NH-CO- oder -COO- darstellt; oder Ar ein polyvalentes Radikal darstellt und Q
    Figure imgb0029
     darstellt, wobei das Q-Radikal vorzugsweise direkt an ein aromatisches Kohlenstoffatom gebunden ist;
    ii) einen kristallinen Polyarylenether, der Repetiereinheiten der folgenden Formel enthält:



            -O-E-O-E'-



    worin E der Rest eines Zweiwertigen Phenols ist und E' der Rest einer aromatischen Verbindung ist, die eine elektronenanziehende Gruppe in mindestens einer der zu den Valenzbindungen ortho- und para-ständigen Positionen aufweist, die E- und E'-Radikale durch aromatische Kohlenstoffatome an die -O- Radikale gebunden sind; oder
    iii) Polyetherimid oder Polysulphonimid, welches Repetiereinheiten der folgenden Formel enthält:
    Figure imgb0030
     worin Q -O- oder -SO₂ ist, Z ein dreiwertiges aromatisches Radikal ist, R ein zweiwertiges aromatisches Radikal und R' ein zweiwertiges organisches Radikal ist.
  7. Draht nach Anspruch 6, wobei das aromatische Polymer ein Polymer enthält, das Repetiereinheiten der folgenden Formeln aufweist:
    Figure imgb0031
     worin x, m und n jeweils 0 oder 1 ist, wobei n gleich 0 ist, wenn x gleich 1 ist; p eine ganze Zahl von 1 bis 4 ist, wobei m gleich 1 und x gleich 0 ist, wenn p größer als 1 ist,
    Figure imgb0032
    Figure imgb0033
     in welcher die Einheiten vollständig von Terephthalsäure oder Isophthalsäure oder beiden abgeleitet sind;
    Figure imgb0034
  8. Draht nach einem der Ansprüche 1 bis 7, wobei das aromatische Polymer mit einem oder mehreren aliphatischen Polymeren vermischt ist.
  9. Draht nach einem der Ansprüche 1 bis 8, wobei die isolierende Schicht als eine Vielzahl von Schichten ausgebildet ist, bei denen zumindest die äußerste Schicht das aromatische Polymer enthält und zumindest die innere Schicht ein Polymer enthält, die ein Polymer mit einem kohlenstoffhaltigen Verkohlungsrückstand von nicht mehr als 10 Gew.-% umfaßt.
  10. Draht nach Anspruch 9, wobei die innere Schicht der isolierenden Schicht ein aliphatisches Polymer enthält.
  11. Draht nach einem der Ansprüche 8 bis 10, wobei das oder jedes aliphatische Polymer der isolierenden Schicht ein Polyolefin; ein Copolymer eines Olefins mit einem Olefin, ein Alkylacetat, ein Alkylacrylat, einen Vinylester; ein Polyamid; ein Polyether; einen Polyester, ein Ionomer oder ein Acrylpolymer umfaßt.
  12. Draht nach einem der Ansprüche 1 bis 11, wobei die sekundäre Kriechstrom-Steuerungsschicht (14) eine vergleichende Kriechstromfestigkeit von mindestens 400, vorzugsweise 500 aufweist.
  13. Draht nach einem der Ansprüche 1 bis 12, wobei die sekundäre Kriechstrom-Steuerungsschicht (14) einen Verkohlungsrückstand von nicht mehr als 5% hat.
  14. Draht nach einem der Ansprüche 1 bis 13, wobei die sekundäre Kriechstrom-Steuerungsschicht (14) ein aliphatisches Polymer beinhaltet.
  15. Draht nach Anspruch 14, wobei das aliphatische Polymer der sekundäre Kriechstrom-Steuerungsschicht (14) ein Polyolefin, ein Copolymer eines Olefins mit einem Olefin, ein Alkylacetat, ein Alkylacrylat oder ein Vinylester, ein Polyamid, ein Polyester, ein Ionomer oder ein Acrylkautschuk ist.
  16. Draht nach Anspruch 15, bei dem das aliphatische Polymer der sekundäre Kriechstrom-Steuerungsschicht (14) Polyethylen, ein kristallines Polyamid, ein amorphes aromatisches/aliphatisches Polyamid, ein Ionomer auf der Basis eines Metallsalzes von methacryliertem Polyethylen, Polybutylenterephthalat, ein Styrol/Dien-di- oder tri-Blockcopolymer oder eine hydrierte Form desselben oder ein Blockpolymer mit langkettigen Estereinheiten der folgenden allgemeinen Formel:
    Figure imgb0035
     und kurzkettigen Estereinheiten der folgenden Formel enthält:
    Figure imgb0036
     in welcher G ein zweiwertiges Radikal, nach der Entfernung der endständigen Hydroxylgruppen aus einem (Polyalkylenoxid)glykol, vorzugsweise einem Poly-(C₂ bis C₄-Alkylenoxid) mit einem Molekulargewicht von etwa 600 bis 6000 übrigbleibt;
    R ein zweiwertiges Radikal ist, das nach der Entfernung von Carboxylgruppen aus mindestens einer Dicarbonsäure mit einem Molekulargewicht von weniger als 300 übrigbleibt; und D ein zweiwertiges Radikal ist, das nach Entfernung von Hydroxylgruppen aus mindestens einem Diol, das ein Molekulargewicht von weniger als 250 hat, übrigbleibt.
  17. Draht nach Anspruch 14, bei dem das aliphatische Polymer der sekundäre Kriechstrom-Steuerungsschicht (14) ein fluoriertes Polymer ist.
  18. Draht nach Anspruch 17, bei dem das aliphatische Polymer der sekundäre Kriechstrom-Steuerungsschicht (14) ein Homopolymer oder Copolymer von Vinylidenfluorid-Polymer, ein Hexafluorpropylen, Polytetrafluorethylen oder ein mit C₁-C₅-Perfluoralkoxy substituiertes Perfluorethylen ist.
  19. Draht nach einem der Ansprüche 1 bis 17 wobei die sekundäre Kriechstrom-Steuerungsschicht (14) vernetzt ist.
EP88905962A 1987-07-10 1988-07-08 Elektrischer draht Expired - Lifetime EP0360836B1 (de)

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GB878716305A GB8716305D0 (en) 1987-07-10 1987-07-10 Electrical wire
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EP0360836A1 (de) 1990-04-04
WO1989000757A1 (en) 1989-01-26
CA1319402C (en) 1993-06-22
DE3885749T2 (de) 1994-03-10
GB8716305D0 (en) 1987-08-19
JPH02504086A (ja) 1990-11-22

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