Classifications

• • 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
• • 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
  • H01B3/20—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils
• • 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
  • H01B3/20—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils
  • H01B3/22—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils hydrocarbons

Definitions

• a DIELECTRIC GELLING COMPOSITION A METHOD OF MANUFACTURING SUCH A DIELECTRIC GELLING COMPOSITION AND AN ELECTRIC DC- CABLE COMPRISING AN INSULATION SYSTEM IMPREGNATED WITH SUCH A DIELECTRIC GELLING COMPOSITION
• the present invention relates to a dielectric gelling composition
• a dielectric gelling composition comprising an electrical insulation oil with additions of a gelator comprising a polymer compound.
• gelator is in this application meant a compound, a blend or system of compounds or blends which when added to an oil interacts to transform the oil from a liquid state to a gelled state, comprising a gelled state, wherein the oil in the gelled state comprises a three dimensional structure that imparts a high viscosity and elasticity to the gelled oil.
• the invention relates to such an oil based gelling composition that exhibits a thermo-reversible transition between the free flowing liquid state and the gelled state, a thermo-reversible liquid-gel transition.
• the present invention relates in another aspect to an insulated electric device, such as a DC-cable, with an insulation system comprising such a dielectric gelling composition with a thermo-reversible liquid-gel transition.
• the dielectric fluids are typically used in combination with a porous, fibrous and or laminated solid part, wWch is impregnated with the dielectric fluid.
• the active part of an impregnated insulation is the solid part.
• the oil protects the insulation against moisture pickup and fills all pores, voids or other interstices, whereby any dielectrically weak air in the insulation is replaced by the oil. Impregnation is typically a time consuming .and delicate process carried out after the solid part of the insulation have been applied and needs to be carefully monitored and controlled.
• the impregnation of a DC-cable intended for a long distance transmission of electric power typically exhibit a process cycle time extending over days or weeks or even months.
• this time consuming impregnation process is made according to a carefully developed and strictly controlled process cycle with specified ramping of both temperature and pressure conditions in the impregnation vessel used during heating, holding and cooling to ensure a complete and even impregnation of the fiber-based insulation.
• a fluid exhibiting a low- viscosity is desired.
• the fluid shall also preferably be viscous at operation conditions for the electrical device to avoid migration of the fluid in the porous insulation.
• Darcy's law (1) is often used to describe the flow of a fluid through a porous or capillary medium.
• v is the so called Darcy velocity of the fluid, defined as the volume flow divided by the sample area
• k is the permeability of the porous medium
• P is the pressure difference across the sample
• ⁇ is the dynamical viscosity of the fluid
• L is the thickness of the sample.
• the flow velocity of a fluid within a porous medium is essentially reciprocally proportional to the viscosity.
• a fluid exhibiting a low-viscosity or a .highly temperature dependent viscosity at operating temperature will have a tendency to migrate under the influence of temperature fluctuations naturally occurring in an electric device during operation and also due to any temperature gradient building up across a conductor insulation in operation and might result in unfilled voids being farmed in the insulation. Temperature fluctuations and temperature gradients are present in a .high-voltage DC cable thus any problem associated with migration of the dielectric fluid must be carefully considered. Unfilled voids or other unfilled interstices or pores in an insulation operating under an electrical high-voltage direct current field constitute deficiencies where space charges tend to accumulate. Accumulated space charge might under unfavourable conditions initiate dielectric breakdown through discharges which will degrade the insulation and ultimately might lead to its breakdown.
• the ideal dielectric fluid should exhibit a low- viscosity under impregnation and be highly viscous under operation conditions.
• the retention shall also be essentially unaffected of any temperature gradient building up over an insulation. This typically leads to a high impregnation temperature being used to ensure that the insulation will be essentially fully impregnated.
• a high impregnation temperature is disadvantageous as it risks affecting the insulation material, the surface properties of the conductor and promoting chemical reactions within and between any material present in the device being impregnated. Also energy consumption during production and overall production costs are negatively affected by a high impregnation temperature. .Another aspect to consider is the thermal expansion and shrinkage of the insulation which implies that the cooling must be controlled and slow, adding further time and complexity to an already time consuming and complex process.
• Other types of oil impregnated cables employ a low viscosity oil.
• these cables then comprise tanks or reservoirs along the cable or associated with the cable to ensure that the cable insulation remains fully impregnated upon thermal cycling experienced during operation.
• these cables filled with a low viscosity oil, there is a risk for oil spillage from a damaged cable. Therefore, .an oil exhibiting a highly temperature dependent viscosity with a high viscosity at operating temperature is preferred.
• a polymer e.g. polyisobuthene
• an oil as disclosed in US-A-3 668 128 comprising additions of from 1 up to 50 percent by weight of an alkene polymer with a molecular weight in the range 100-900 derived from an alkene with 3, 4 or 5 carbon atoms, e.g. polybutene can be chosen for its low viscosity at low temperatures.
• This oil exhibits a low viscosity at low temperatures, good oxidation resistance and also good resistance to gassing, i.e. the evolution of hydrogen gas which might occur, especially when an oil of low aromatic content, as the oil suggested in US-A-3 668 128, is exposed to electrical fields.
• the oil according to the disclosure in US-A-3 668 128, although offering a major advance on the traditional electrical insulating oil for impregnation of fibrous or laminated insulations, still suffers the risk of oil migration caused by temperature fluctuations and/or temperature gradient building up under operation as the low viscosity oil is typically not retained during operation at elevated temperatures.
• the earlier not yet published International Patent Application PCT/SE97/01095 discloses a DC-cable impregnated with a gelling dielectric fluid, such as an oil.
• the dielectric fluid comprises a gelling polymer additive that imparts to the fluid a thermo-reversible transition between a gelled state at low temperatures and an essentially Newtonian easy flowing state at high temperatures. This substantial transition in viscosity occurs over a limited temperature r.ange.
• the fluid and the gelling polymer additive are matched to impart a thermo-reversible gelling behavior with a liquid-gel transition range to the fluid to suit the desired properties both during impregnation and operation.
• the fluid is, at high temperatures, in a liquid state and cxliibits the viscosity of an easy flowing Newtonian fluid. At low temperatures the fluid is in a gelled state, with a viscosity of a highly viscous, elastic gel.
• the transition temperature is determined by the selection of fluid and additive and the content of additive.
• Such a cable exhibits a substantial potential for reduction of the time period needed for impregnation but it still requires a strictly controlled temperature cycle during impregnation.
• the gelling polymer additive and the dielectric fluid are matched or optimized to, in the best way, meet the typically conflicting demands during impregnation and use of the cable.
• This publication discloses a gel-forming compound with slow forming and thermally reversible gelling properties intended to be used as an encapsulant to ensure a good sealing and blocking of any interstices in a cable comprising an all solid insulation, such as an extruded polymer based insulation.
• the slow-forming thermally reversible gelling compound comprises an admixture of a polymer to a naphtenic or paraffinic oil, and also embodiments using fiirther admixtures of a co-monomer and/or a block copolymer to an oil are considered suitable as encapsulant due to their hydrofobic nature and the fact that they can be pumped into the interstices at a temperature below the maximum service temperature of the encapsulant itself.
• the gelling composition shall exhibit properties whereby the impregnation can be enhanced and the impregnation time shortened. It shall exhibit a high viscosity at the temperature range within which the device is designed to operate, thereby reducing the risks for migration and formation of voids upon thermal cycling and/or under thermal gradients. The volume changes upon thermal cycling shall be reduced. In particular importantly, the shrinkage upon cooling after impregnation and any problems associated with such shrinkage shall be reduced. Further the gelling composition shall exhibit such thermal, mechanical and electric properties and stability in these properties such that it opens for an increase in load, i.e. an increase in both operation voltages and current densities used in the device.
• a typical DC-transmission cable includes a conductor and an insulation system comprising a plurality of layers, such as an inner semi-conductive shield, an insulation body and an outer semi-conductive shield.
• the cable is typically complemented with casing, reinforcement etc, to withstand water penetration and any mechanical wear or forces during, production installation and use.
• Almost all the DC cable systems supplied so far have been for submarine crossings or the land cable associated with them.
• the mass-impregnated solid paper insulated type cable is chosen because there are no restrictions on length due to pressurizing requirements. It has to date been supplied for operating voltages of 450 kN. These voltages are likely to be increased in the near future.
• transient voltages is a factor that has to be taken into account when determining the insulation thickness of DC cables. It has been found that the most onerous condition occurs when a transient voltage of opposite polarity to the operating voltage is imposed on the system when the cable is carrying full load. If the cable is connected to an overhead line system, such a condition usually occurs as a result of lightning transients.
• a commercially available insulated electric DC-cable such as a transmission or distribution cable designed for operation at a high voltage, i.e.
• a voltage above 100 kN is typically manufacture by a process comprising the winding or spinning of a porous, fibrous and/or laminated solid insulation based on cellulose or paper fiber .and the impregnation of this cable.
• the impregnation process, the times and controlled processing involved have already been described in the foregoing.
• an insulated DC-cable with an electrical insulation system that ensures stable dielectric properties also when operating at high operation temperatures close to the impregnation temperature and/or under conditions where the insulation during operation is subjected to a high voltage direct current field in combination with thermal fluctuations .and/or a build up of a substantial thermal gradient within the insulation.
• the dielectric fluid employed shall exhibit a high viscosity index such that it during impregnation has a sufficiently low viscosity, i.e. a viscosity deemed suitable and technically and economically favourable for impregnation, and that it after impregnation has a high viscosity and elasticity, i.e.
• the DC- cable shall thus comprise a dielectric fluid with a sufficiently low viscosity prior to and during impregnation to ensure stable flow properties and flow behaviour within these ranges, and which ejdiibits a substantial change in viscosity upon impregnation, i.e. a change in the order of hundreds of Pas or more.
• a DC-cable impregnated with a fluid exhibiting such high viscosity index will provide an opportunity for a substantial reduction in the lengthy time consuming batch-treatment for impregnation of the insulation system.
• the reliability, low maintenance requirements and long working life of conventional DC-cables, comprising an impregnated paper-based insulation shall be maintained or improved. That is, the DC-cable shall have stable and consistent dielectric properties and a high and consistent electric strength and, as an extra advantage, open for an increase in the electrical strength and thus allow an increase in operation voltages, improved handleability and robustness of the cable.
• the present invention it is an object to provide a dielectric gelling composition, which exhibits a thermo-reversible liquid-gel transition at a high temperature with the desirous features discussed in the foregoing. This is, for a dielectric gel according to the preamble of claim 1, accomplished by the features of the characterizing part of claim 1. Further developments of the dielectric gel according to the present invention are characterized by the features of the additional claims 2 to 16.
• an insulated electric device comprising such a dielectric gelling composition as impregnant in its impregnated insulation system.
• This is for an electric device according to the preamble of claim 22 accomplished by the features of claim 22 .
• Further developments of the electric device according to the present invention are characterized by the features of the additional claims 22 to 26.
• it is an object to provide a method for manufacturing such an insulated electric device. This is for the method according to the preamble of claim 30 accomplished by the features of the characterizing part of claim 30. Further developments of the method are characterized by the features of the additional claims 31 to 35.
• the primary object is accomplished with a dielectric gelling composition, exhibiting a thermo-reversible liquid-gel transition at a transition temperature, T t , wherein the gel comprises an oil and a gelator comprising a block copolymer comprising an olefin based block and at least one further block comprising aromatic rings in its backbone structure, wherein each one of the two blocks has a molecular weight of more than 3000 g/mole, and the block with aromatic rings in its backbone structure exhibits a rigid backbone structure and a temperature dependent solubility in the oil.
• the polymer compound can either be a di-block copolymer or a tri-block copolymer with the olefinic block (A) as midblock surrounded on both sides with end blocks consisting of the block (B) comprising aromatic rings in its backbone structure.
• the block with aromatic rings in its backbone structure has a molecular weight of from 5000 to 300 000 g/mole and the olefin based block has a preferred molecular weight of from 3000 to 500 000 g/mole.
• the gelling composition when in the gelled state typically comprises a gelled network with physical cross-links, where the cross-links comprise regions formed by the block with aromatic rings at temperatures below the liquid-gel transition temperature T t .
• These cross-links provide both the mechanical and the dielectric strength to the gelling composition and thus contribute both to the improved mechanical and electrical properties of the insulation system and also to the increased stability of these properties.
• the gelled network with its physical cross-links is typically formed at temperatures below the transition temperature, which for a gelling composition according to the present invention is below 120 °C, typically the liquid-gel transition temperature T t is within the r-ange of from 20°C to 120 °C and preferably is within the range of from 30°C to l00 °C.
• a suitable polymer for block (B) with aromatic rings in its backbone structure is; - a polyimide or a polyimide based polymer, i.e. a polymer comprising polyimide groups in its backbone structure;
• a polyurethane or a polyurethane based polymer i.e. a polymer comprising polyurethane groups in its backbone structure
• a polyphenylene or a polyphenylene based polymer i.e. a polymer comprising polyphenylene groups in its backbone structure
• aromatic polyamide or a polymer based on aromatic polyamide, i.e. a polymer comprising aromatic polyamide groups in its backbone structure
• a bisphenol-A-epoxy or a polymer based on a bisphenol-A-epoxy, i.e. a polymer comprising aromatic bisphenol-A-epoxy groups in its backbone structure, or
• phenol- foimaldehyde or a polymer based on a phenol-formaldehyde, i.e. a polymer comprising aromatic phenol-formaldehyde groups in its backbone structure.
• the polymer for the block (B) is thermally stable and electrically insulating such that it contributes to an increased thermal stability and electric strength of the dielectric gelling composition. Further it shall have a limited solubility in the oil at temperatures below the tra. nsition temperature T t but be substantially dissolved at temperatures above the transition temperature T t . It shall be noted that T t typically is a narrow range of temperatures.
• the B block polymer has a limited solubility in the oil at ambient temperatures and in some cases up to 50 °C or 60 °C but is substantially dissolved at temperatures above 80 °C. Thus the gelling composition will come to exhibit a transition temperature or a narrow transition range of temperatures in the temperature range of from 30 °C to 100 °C.
• the olefin based A block typically comprises an ethylene/butylene block but can also comprise other suitable defines such as butadiene.
• the copolymer comprised in the gelling composition according to the present invention has typically been synthesized by a condensation reaction of a hydroxyl or amine terminated ethylene/butylene or butadiene with polymers containing chemical moieties towards hydroxyl or amine groups.
• moieties reactive towards hydroxyl groups are carboxylic acids, acid chlorides, anhydrides and isocyanates.
• suitable polymers to be included in the di or tri block polymer with an ethylene/butylene block in order to obtain a more thermally stable block copolymer than the prior art styrenic block copolymer comprise polyimid, polyphenylene oxide, polyurethane, aromatic polyamide, bisphenol-A-epoxy, phenol-formaldehyde and the like.
• either a di-block copolymer or a tri-block copolymer with the olefinic block (A) as midblock surrounded on both sides with end blocks consisting of the block (B) comprising aromatic rings in its backbone structure can be formed.
• the dielectric gelling composition and the oil interact to develop a three dimensional, physically cross-linked network at temperatures below the transition temperature T t .
• the transition temperature T t is a narrow range of temperatures above 20 °C and below 120 °C, preferably of from 30 °C to 100 °C.
• the gelled network with physical cross-links comprises regions formed by the block with aromatic rings at temperatures below the liquid-gel transition temperature T t .
• the network increases the viscosity index of the oil such that the gelled network in the oil according to the present invention at temperatures below the transition temperature T t exhibits the properties of .an highly viscous elastic or viscoelastic gel.
• Another advantage of the gelling composition used according to the present invention is that the gelling kinetics can be modified by altering the blocks or the content of the block copolymer added to the oil, which opens for a delayed significantly slower gelling if so desired, this delay can in some cases exceed 24 h.
• An insulated electric device such as a DC-cable having at least one conductor and an impregnated insulation system, wherein the insulation system comprises a solid electrically insulating dielectric part with a porous, fibrous and or laminated structure impregnated with a dielectric gelling composition comprising an oil and a gelator, comprising a block copolymer with an olefin based block and ejdiibiting a thermo-reversible liquid-gel transition at a transition temperature, T t , wherein the gelling composition at temperatures below T t is in a highly viscous elastic gelled state and, at temperatures above T t , is in a liquid easy flowing essentially Newtonian state, comprises according to the present invention a block copolymer with an olefin based block and at least one further block comprising aromatic rings in its backbone structure, wherein each one of the two blocks has a molecular weight of more than 3000 g/mole, and the block with aromatic rings in its backbone structure exhibit
• the block with aromatic rings in its backbone structure has a molecular weight of from 5000 to 300 000 g/mole while the olefin based block has a molecular weight of from 3000 to 500 000 g/mole.
• the gelling composition when in the gelled state comprises, as already described in detail in the foregoing, a gelled network with physical cross-links comprising regions formed by the block with aromatic rings at temperatures below the liquid- gel transition temperature T t .
• the transition temperature is typically below 120 °C and suitably within a range of from 30°C to 100 °C.
• the dielectric gelling composition is selected such that it comprises groups or further additives that interact with the surface of the porous and/or laminated structure.
• An interaction between the dielectric gelling composition and the surface of the porous and/or laminated structure can provide conditions that increase the oil penetration into voids and capillary interstices within the porous and/or laminated structure upon filling or that increase the oil retention within the porous and/or laminated structure upon operation at a high temperature, fluctuating temperatures and/or under a substantial temperature gradient.
• the interaction with the solid parts of the insulation can thus depending on its nature result in an improved wetting which shortens the impregnation time period due to an increase in the oil penetration into voids and capillary interstices within the porous and/or laminated structure upon filling.
• the interaction can also under other circumstances increase the oil retention within the porous and/or laminated structure upon operation at a high temperature, fluctuating temperatures and/or under a substantial temperature gradient.
• the insulation system comprises a surfactant to further enhance the wetting during impregnation.
• a surfactant to further enhance the wetting during impregnation.
• the surfactant can be added either to the gelling composition, i.e. the impregnant or the solid porous, fibrous and/or laminated part to be insulated as deemed suitable from case to case.
• the gelling composition comprises fine dielectric p.articles with a particle size in the nanometer range trapped in or bonded to the network.
• a DC-cable according to the present invention typically comprises from the center and outwards;
• a conductor of any desired shape and constitution such as a stranded multi-wire conductor, a solid conductor or a sectional conductor;
• the two semi-conducting shields are typically wound and impregnated insulation according to the present invention, with a dielectric electrically insulating solid part exhibiting a porous and/or laminated structure as described in the foregoing impregnated with an oil based gelling composition.
• the cable can when deemed appropriate be complemented with reinforcing and a sealing compound or a water swelling powder for filling any interstices in and around the conductor, other metal/polymer interfaces may be sealed in order to prevent water from spreading along such interfaces.
• a gasabsorbing additive is included in the insulating system.
• a suitable gasabsorbing additive is a low molecular polyiosbutene with a molecular weight less than 1000 g/mole.
• a DC-cable according to the present invention is, through the improved electrical and mechanical strength of the gelled network formed at temperatures below the transition temperature and the long term stability of these improved properties also at elevated temperatures approaching the transition temperature, ensured long term stable and consistent dielectric properties and a high and consistent electric strength as good as or better than for any conventional DC-cable comprising such impregnated porous and/or laminated body. This is especially important due to the long life such installations typically are designed for, and the limited access for maintenance to such installations.
• the special composed block copolymers used as gelling additives and oils provide gelling impregnants, which ensure the long term stable properties of the insulation system also when used at elevated temperatures, at excessive thermal fluctuations and/or under thermal gradients.
• the temperature sensitivity during production can be substantially reduced by a suitable design of the block copolymer used and matching of oil and any other components added to the gelator system, which opens for a delayed gelling, thereby reducing sensitivity of the post-filling step.
• Figure 1 shows a cross-section of a typical DC-cable for transmission of electric power comprising a wound and impregnated insulation according to the present invention
• the DC-cable according to the embodiment of the present invention shown in figure 1 comprises from the center .and outwards; - a stranded multi-wire conductor 10; - a first semi-conducting shield 11 disposed around and outside the conductor 10 and inside a conductor insulation 12;
• the cable is further complemented with a reinforcement in the form of metallic, preferably steel, wires outside the outer extruded shield 13, a sealing compound or a water swelling powder is introduced in any interstices in and around the conductor 10.
• the dielectric gelling composition of the present invention is applicable for any arbitrary DC-cable with an insulation system comprising a solid porous or laminated part impregnated with a dielectric fluid or mass.
• the application of the present invention is independent of conductor configuration. It can also be used with DC-cables having an insulation system of this type comprising any arbitrary functional layer(s) and ioespective of how these layers are configured. Its application to DC-cables of this type is also independent of the configuration of the system for transmission of electric power in which the cable is included.
• the DC-cable according to the present invention can be a single multi-wire conductor DC-cable as shown in Figure 1, or a DC-cable with two or more conductors.
• a DC-cable comprising two or more conductors can be of any known type with the conductors placed side-by-side in a flat cable arrangement, or in a two conductor a . rrangement with one first central conductor surrounded by a concentrically arranged second outer conductor.
• the outer conductor is typically aoanged in the form of an electrically conductive sheath, screen or shield, typically a metallic screen not restricting the flexibility of the cable.
• a DC-cable according to the present invention is suitable for use in both bipolar and monopolar DC-systems or installations for transmission of electric power.
• a bipolar system typically comprises two or more associated single conductor cables or at least one multiconductor cable, while a monopolar installation has at least one cable and a suitable current return path arrangement.
• EXAMPLE 1 An ethylene/butylene polymer terminated at both ends with hydroxyl groups was dissolved in p-xylene and heated to 150 °C under stirring and nitrogen atmosphere. A poly-(2,6-dimetyl- phenylene oxide) terminated at one end with a cyclic acid anhydride was added to the solution under stirring. The mixture was kept at 150 °C for 60 minutes. The mixture was subsequently cooled to room temperature. The polymer was precipitated in methanol, washed with cyclohexane and dried. 4 % by weight of the resulting polymer was added to a naphtenic mineral oil and the blend was heated to 120 °C and kept at this temperature for 60 minutes. Substantially all polymer was dissolved. The blend was cooled and the blend or oil composition exhibited a liquid-gel transition in the temperature range 50 °C to 100 °C.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Insulating Materials (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Manufacturing Of Electric Cables (AREA)

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• 1997
  • 1997-12-22 SE SE9704826A patent/SE511214C2/sv not_active IP Right Cessation
• 1998
  • 1998-12-15 JP JP2000525888A patent/JP2001527129A/ja active Pending
  • 1998-12-15 CN CN98813761A patent/CN1285076A/zh active Pending
  • 1998-12-15 KR KR1020007006862A patent/KR20010033393A/ko not_active Application Discontinuation
  • 1998-12-15 WO PCT/SE1998/002311 patent/WO1999033066A1/en not_active Application Discontinuation
  • 1998-12-15 EP EP98964595A patent/EP1042759A1/en not_active Withdrawn
  • 1998-12-15 AU AU19887/99A patent/AU737200B2/en not_active Ceased
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• 2000
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