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WO1996008020A1 - Dispositif electrique - Google Patents

Dispositif electrique Download PDF

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Publication number
WO1996008020A1
WO1996008020A1 PCT/SE1995/000978 SE9500978W WO9608020A1 WO 1996008020 A1 WO1996008020 A1 WO 1996008020A1 SE 9500978 W SE9500978 W SE 9500978W WO 9608020 A1 WO9608020 A1 WO 9608020A1
Authority
WO
WIPO (PCT)
Prior art keywords
cellulose
insulation
electric device
mass
insulating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/SE1995/000978
Other languages
English (en)
Inventor
Stefan Backa
Lars Tornberg
Thomas Worzyk
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ABB AB
Original Assignee
Asea Brown Boveri AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Asea Brown Boveri AB filed Critical Asea Brown Boveri AB
Publication of WO1996008020A1 publication Critical patent/WO1996008020A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • H01B3/48—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials
    • H01B3/485—Other fibrous materials fabric

Definitions

  • the present invention relates to an electric device which at least comprises one or more current- or voltage-carrying bodies, conductors, and an electrical insulation, arranged between or around these conductors, in the form of a cellulose-based fibre-containing insulation.
  • Electric devices such as high-voltage cables, transformers, generators etc. , comprise current- and voltage-carrying bodies, conductors, and an electrical insulation arranged between and/or around these conductors.
  • high voltages above 100 kv, there are substantially used cellulose-based or polymeric insulating material for this insulation.
  • Polymeric materials such as polyethylene, PE, ethylene- propylene rubber, EPD , are used to advantage in, for example, cables. They are characterized by great flexibility and a possibility of being applied on the conductors included in the cable by means of extrusion, which permits a high rate of production. Further, polymeric materials, and in particular PE, have a very high mass resistivity, whereby leakage currents through the insulation become extremely small; how ⁇ ever, the mass resistivity is greatly dependent on temperature and also dependent on inclusions or other inhomogeneities in the material.
  • polymeric materials are not used commercially as insulation in devices included in transmission networks for high-voltage direct current since in these appli ⁇ cations the field distribution is controlled by the resisti ⁇ vity of the insulating material and the resistivity in the insulation may vary. This can lead to very unevenly distri ⁇ ubbed fields when using polymeric insulations for high-voltage devices.
  • Conventional cellulose-based electrical insulations consist of wound, spun, layers of paper tape or of preformed bodies manu ⁇ factured by dewatenng and/or pressing of a fibre mass, for example pressboard. Both wound and preformed insulations are impregnated with an electrically insulating fluid, usually an organic fluid such as oil, prior to, in connection with, or after the application.
  • cellulose fibres mean pulp fibres which contain cellulose and, to a varying extent, lignin and hemi- cellulose.
  • this insulation after having been applied to the conductor, must be dried and impregnated with an electrically insulating fluid in time-consuming operations to attain the high dielectric strength which is required of insulations included in insulated high-voltage devices.
  • an electric device with an electrical insulation in the form of at least one insulating body comprising at least cellulose fibres and impregnated with an electrically insulating liquid By liquid is meant a fluid which, under the conditions prevailing during the forming, is a liquid and which is essentially non- polymerized. After the forming, the liquid may change into solid state. This liquid fills essentially all pores and voids present in the fibrous insulation.
  • the fibrous insulation is applied around the conductor by means of a fast and reliable process and exhibits the high dielectric strength which is required of insulations included in insulated high-voltage devices without having undergone, during the manufacturing process, the time-consuming impregnation operations as for known cellulose-based insulations.
  • the electrical insulation which at least comprises cellulose fibres impregnated with an elec ⁇ trically insulating fluid, may be applied and formed around the conductors, for example during mounting or repair, as, for example, during cable jointing and other types of installa ⁇ tions and repair work in the field.
  • This insulating mass comprises dielectric-strength cellulose fibres dispersed in an electrically insulating fluid which, under the condi ⁇ tions prevailing during application and forming, is liquid.
  • the fibrous insulation consists at least of an electrically insulating fluid, prefe ⁇ rably a hydrocarbon-based liquid, such as a viscous mineral oil.
  • a hydrocarbon-based liquid such as a viscous mineral oil.
  • liquid is meant a fluid which, under the conditions prevailing during the forming, is a liquid and which is essen- tially non-polymerized. After the forming, the liquid may change into solid state. This liquid essentially fills all the pores and voids present in the fibrous insulation and consti ⁇ tutes during the forming/extrusion an incompressible medium in which the cellulose fibres are dispersed.
  • the cellulose in the cellulose fibres is at least partially transformed into cellu ⁇ lose derivate.
  • cellulose derivate in this applica ⁇ tion cellulose for which hydrogen included in hydroxyl groups has been at least partially replaced by other groups, for example aromatic groups or alkyl groups such as benzyl groups.
  • cellulose in the form of parti ⁇ cles or fibres is pretreated in a basic solution, whereby the cellulose swells and is activated. Thereafter, compounds such as organic halogenides, epoxy compounds or acid chloride are added and are allowed to react with the cellulose.
  • the cellu- lose which after the reaction at least partially comprises cellulose derivate, is washed and dried before being supplied to and dispersed in the above-mentioned insulating liquid.
  • cellulose in the form of fibres or particles is mixed with an organic acid in the presence of an acid catalyst such as trifluoro acetic acid.
  • the acid process may be performed in an organic solvent.
  • the cellulose, which now at least partially contains cellulose derivate is washed and dried before being supplied to and dispersed in the insulating liquid.
  • Cellulose fibres containing cellulose derivate and suitable for this use may also be obtained by means of other processes such as grafting.
  • the electric device according to the invention preferably comprises a fibrous insulation which is formed from an insulating mass which comprises at least modified cellulose fibres with dielectric strength and dispersed in an electri- cally insulating liquid, preferably a viscous mineral oil.
  • cellulose fibres which have been modified by a pretreatment according to the above and thus, at least partially, comprise cellulose derivate. In this way it is ensured that the insu ⁇ lating mass exhibits the desirable mechanical and dielectric properties during application as well as during use.
  • the insulating mass or its constituents have suitably been dried and degassed to remove moisture and gases before it is applied around the conductors in an electric device according to the invention.
  • the percentage of fibres and the fibre composition has been optimized to improve the dielectric properties while at the same time the good mechanical strength is maintained or improved.
  • a good dispersion of fibres in insulating liquid is required and also that the insulating liquid wets the fibres and fills all the voids between the individual fibres. This is achieved, for example, by modifying the cellulose according to the above described pretreatment, before being supplied to and dispersed in the insulating liquid.
  • additives may have been supplied to the fibres or the insulating liquid.
  • Such additives influence chemical and physical conditions in the boundary layer between fibres and insulating medium, the viscosity of the insulating medium/insulating mass, and/or bring about a chemical or physical bond of the cellulose fibres into a network.
  • the presence of inhomogeneities in the insulation gives rise to disturbances in the electric field strength distribution in case of electric loading and must, therefore, be avoided to eliminate a degradation of the insulation associated there ⁇ with, for example as a result of internal corona.
  • a fibre insulation with cellulose-based fibres impregnated by an electrically insulating liquid according to the invention is extrudable during the application but exhibits sufficient mechanical stability and good electrical properties under the normal conditions of use of the electric device.
  • this combination of mouldabi- lity during the application and mechanical strength/resistance to deformation under the conditions of use of the device is achieved in that the cellulose-based fibrous insulating mass impregnated with insulating liquid exhibits a temperature- dependent viscosity.
  • the insulating mass has thereby been extruded at an elevated temperature where the insulating mass was mouldable and then it has solidified during cooling in order to constitute an insulation which is resistant to defor ⁇ mation and has sufficient mechanical strength when being used at the normally prevailing temperatures.
  • the temperature dependence of the viscosity of the insulating mass has been guided by the choice of insulating liquid and/or by additives which influence the viscosity of the cellulose-based insula ⁇ ting mass.
  • a shear- thinning insulating mass has been used. By the addition of shear forces during and in connection with the applica ⁇ tion/forming of the mass around the conductors included in the invented device, the mass has been made less viscous. Thereafter, resistance to deformation has been imparted to the mass to form an insulation with the required mechanical strength.
  • An increase of the mechanical strength and the resistance to deformation of an insulation in a device according to the invention after the application/forming is obtained in another embodiment by forming the insulation by means of a forming process where insulating liquid has been removed from the insulation/insulating mass during or in connection with the application and forming of the insulation around a conductor included in the device.
  • insulating liquid is removed, the percentage of fibres is increased and the impregnated cellulose-based insulation thus obtained has been given a higher percentage of fibre in relation to the insulating mass and a cross linking of the fibres.
  • This cross linking has preferably arisen by increasing the contact between the fibres and bonding the fibres to each other by physical and/or chemical bonds.
  • the insulation in a device according to this embodiment of the invention exhibits an essentially non- reversible resistance to deformation.
  • Insulating liquid may be removed with a number of techniques such as by being pressed out of the insulation/the insulating mass or by partially volatilizing it and driving it off by an increase in tempera- ture during or in connection with the application/forming.
  • the device comprises an impregnated cellulose-based insulation where an insulating mass with a temperature-dependent viscosity is formed by means of a forming process where insulating liquid is removed from the insulating mass in or in connection with the application and forming of the insulation in order to reinforce and render the resistance to mechanical deformation of the insulation non-reversible.
  • the device comprises an impregnated cellulose-based insulation where the bonding or cross linking of the fibres has been further reinforced by supplying additives such as cellulose acetate to the insula- ting mass or by modifying the surface of the fibres.
  • additives such as cellulose acetate to the insula- ting mass or by modifying the surface of the fibres.
  • the hydroxide groups on the surface of the cellulose fibres have been completely or partially replaced by non-polar groups to increase the wettability.
  • insulating liquid a mineral oil has preferably been described, but this may be replaced by other liquids which exhibit the necessary dielectric properties, stability to degradation under the conditions of use, and by means of which the necessary floatability may be achieved in the insulating mass during application and forming while at the same time this mass may form, together with the cellulose fibres and any additives, an insulation which is resistant to deformation and which has the necessary electrical and mechanical properties under normal conditions of use. It is advantageous if the insulation obtained exhibits a sufficient mechanical flexibi ⁇ lity to be able elastically to follow movements and expan ⁇ sion/contraction of electric conductors and other live bodies or layers which are included in the device and with which it makes contact during use, for example as a result of tempera ⁇ ture fluctuations.
  • the additives used are not allowed to have a negative influence on the dielectric properties of the impregnated cellulose-based insulation, nor on its stability relative to degradation as a result of electrical, thermal or other loading. Where necessary, substances such as antioxidants, voltage stabilizers, etc., have been added to the insulating mass, which substances stabilize the mass against oxidation or other influence from external factors such as electric or magnetic fields as well as heat or other radiation. The additives must not result in the insulating liquid being polymerized.
  • a wood meal of, for example, birch and with a grain size less than 500 ⁇ m was introduced into a container with nitrogen atmosphere and mixed at room temperature with a caustic soda solution which has a content of 44 per cent by weight caustic soda.
  • the mixture was stirred continuously by means of a mechanical stirrer. After an hour the temperature was raised to 100°C and benzyl chloride was added in two equally large portion at 45 minutes' interval. In total, the same quantity of benzyl chloride was added as caustic soda. After a total reaction time of 4 hours under continuous stirring, the reaction was interrupted by an addition of glacial acetic acid.
  • cellulose was washed with methane alcohol, boiled for 2 hours in water and dialysed against water for 48 hours before it was dried under vacuum at 70°C for 48 hours.
  • Benzylated cellulose can then be prepared into an extrudable insulating mass.
  • insulating masses with cellulose fibres comprising cellulose derivates and dispersed into an electrically insulating liquid will be described.
  • a high-voltage cable comprises at lest one or more electric conductors and an electrical insula ⁇ tion around and/or between the conductor or conductors.
  • This insulation comprises, at least in part, an impregnated cellulose-based insulation comprising cellulose fibres with dielectric strength dispersed in an electrically insulating liquid and any additional substances.
  • this insula ⁇ tion has been applied and formed around and/or between the conductors in the form of a mouldable mass.
  • This insulating mass has preferably been prepared according to the below and has, during or in connection with its application/forming around a conductor, been transformed into an insulation resistant to deformation.
  • a cable insu ⁇ lation usually also includes one or more semiconductive layers, the task of which is to equalize the electrical vol ⁇ tage gradient in certain of the boundaries of the insulation.
  • these semiconductive layers are arranged in the form of a cellulose-based fibrous material to which, during the preparation according to the above, a semi ⁇ conductive or conductive substance, such as soot, has been added.
  • an insulating mass which is mouldable under the conditions prevailing during the extrusion, has been prepared.
  • the insulating mass or its constituents has/have been dried and degassed.
  • This mouldable insulating mass comprises at least
  • cellulose fibres with dielectric strength preferably in the form of cellulose fibres modified according to the above- described pretreatment but also other cellulose fibres which exhibit suitable dielectric and mechanical properties may be included, as well as mixtures of two or more types of cellu ⁇ lose fibres,
  • an electrically insulating fluid which under the conditions prevailing during the application is liquid, such as a viscous mineral oil, and - any additional substances, which have been added to the insulating fluid and/or applied to the fibres to ensure that the cellulose fibres are dispersed in the insulating fluid and that no flocks of cellulose fibres remain or are formed and/or that the surface of the cellulose fibres is wetted by the insulating fluid and that no gas-filled voids remain between the fibres.
  • liquid such as a viscous mineral oil
  • additives are also desired which modify the surfaces of the cellulose fibres chemically or physically, for example to increase the degree of bonding of the fibres and hence the mechanical strength of the insulation and/or influence the viscosity of the insulating medium, for example to make it less viscous during the application, and which do not have any negative influence on the dielectric properties of the impregnated cellulose-based insulation, nor on its stability in relation to degradation as a result of electrical, thermal or other loading.
  • a conductive/semiconductive preferably particular substance, such as soot, is also added and dispersed.
  • a cable for transmission of high-voltage direct current accor- ding to the invention comprises conductors in the form of one or more metal wires around which is applied a triple layer consisting of:
  • the insulating layer consists of an impregnated cellulose-based insulating mass which has at least partially been prepared according to the above and applied and formed by extrusion.
  • a cable termination according to the prior art is built up around a cable end where the conductor has been stripped and the cable end provided with an insulating body, for example consisting of wound paper.
  • the shape of the insulating body has been calculated for optimizing the electric field which arises near the cable termination.
  • the insulating body is arranged enclosed in a casing of, for example, porcelain and is impregnated with an insulating oil.
  • a cable termination according to the invention is built up around an exposed cable insulation, around which an insulation comprising at least cellulose fibres with dielectric strength dispersed in an electric mineral oil is formed.
  • the insulation has a composition which essentially corresponds to the insula ⁇ ting layer in the previously described high-voltage cable and has been applied in the form of a mouldable insulating mass.
  • This insulating mass has been mixed and prepared in accordance with the description given above for the example of a high- voltage cable, and after drying and degassing it has been applied directly around the exposed cable insulation.
  • the mouldable insulating mass has been pressed into a press mould arranged around the cable end and been formed into an optimum shape from the electrical point of view.
  • the insulating mass has preferably been mixed, dried and degassed in the factory before being shipped to the site of installation.
  • an external insulation such as a ceramic insulator body has been applied and filled with an appropriate oil, which fills up the entire volume between the insulating body according to the invention and the external insulation.
  • the external insulator has constituted the press mould during the forming of the insulating body and is then allowed to remain, and in that case normally no extra addition of oil is necessary in addition to the oil which is present in the fibre-based insulating mass.
  • a cable joint according to the invention is achieved in a fast, simple and reliable manner by applying, after the con ⁇ ductor welding, a press mould over the joint whereupon a mouldable impregnated cellulose-based insulating mass is pressed into the press mould to form an insulation with an optimum shape from an electrical point of view and with the required dielectric and mechanical properties, whereupon the sheath and the reinforcement are taken care of.
  • the cellulose- based fibre mass has a composition and has been prepared according to the previous example relating to a high-voltage cable. The risk of contamination and the occurrence of other defects, caused by external factors, when building up a cable joint according to the invention is greatly reduced relative to a conventional cable joint.
  • the time for building up the cable joint is essentially reduced without lowering the requirements for the performance of the joint.
  • additional advan ⁇ tages from the point of view of handling and quality have been achieved by preparing, drying and degassing the insulating mass prior to the shipping to the installation site.
  • the primary winding consists of a strong conductor which has the shape of a hair pin with an extended loop in which the transformer core is placed. In this way, the conductor forms half a turn around the transformer core. Around this conductor, an insulating winding of paper is applied. The winding of the paper is time- consuming due to the shape of the conductor.
  • An impregnated cellulose-based insulation for a current transformer according to the invention is applied by applying a press mould with a shape suitable for the purpose around the conductor, whereupon the space between the press mould and the conductor is filled, under overpressure, with a mouldable insulating mass consis ⁇ ting of at least cellulose fibre and an electrically insula ⁇ ting liquid.
  • the insulating mass then forms an optimum insula ⁇ ting body from an electrical point of view.
  • the insulating mass Prior to the forming, the insulating mass has been prepared under controll ⁇ ed conditions and the constituents included have been dried and degassed, preferably in a room suitable for this purpose.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Organic Insulating Materials (AREA)

Abstract

Dispositif électrique comprenant au minimum un ou plusieurs corps électro-conducteurs. Ces conducteurs comportent, au moins sur une partie, une isolation électrique constituée de fibres de cellulose d'une certaine résistance diélectrique, impregnées d'un fluide isolant électrique. L'isolation est réalisée à partir d'une masse isolante renfermant les fibres à base de cellulose dispersées dans un fluide isolant électrique, ces fibres étant aptes au moulage dans les conditions prévues pour leur application et leur formage.
PCT/SE1995/000978 1994-09-05 1995-08-31 Dispositif electrique Ceased WO1996008020A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9402933A SE505246C2 (sv) 1994-09-05 1994-09-05 Elektrisk anordning innefattande en elektrisk isolering som formats utifrån en isolermassa innehållande cellulosafibrer
SE9402933-7 1994-09-05

Publications (1)

Publication Number Publication Date
WO1996008020A1 true WO1996008020A1 (fr) 1996-03-14

Family

ID=20395111

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1995/000978 Ceased WO1996008020A1 (fr) 1994-09-05 1995-08-31 Dispositif electrique

Country Status (2)

Country Link
SE (1) SE505246C2 (fr)
WO (1) WO1996008020A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7964798B2 (en) 2004-11-11 2011-06-21 Koninklijke Philips Electronics N.V. Electrical high field/high voltage unit and method of manufacturing same
US8696939B2 (en) * 2003-06-18 2014-04-15 Koninklijke Philips N.V. High voltage insulating materials

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1282049A (en) * 1969-08-06 1972-07-19 Dow Chemical Co Conductor insulation
EP0304785A2 (fr) * 1987-08-25 1989-03-01 Bayer Ag Masses à mouler de polyphénylène sulfure avec des propriétés électriques

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1282049A (en) * 1969-08-06 1972-07-19 Dow Chemical Co Conductor insulation
EP0304785A2 (fr) * 1987-08-25 1989-03-01 Bayer Ag Masses à mouler de polyphénylène sulfure avec des propriétés électriques

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DIALOG INFORMATION SERVICE, File 351, World Patent Index 81-95, Dialog Accession No. 009169431, WPI Accession No. 92-296865/36, HITACHI CABLE LTD, "High Expansion Ratio Foamed Polyethylene Small Dia. Wire Mfr. - by Foam Extruding Polyethylene Contg. Short Fluoro-Plastic Fibres on a Conductor or Conductor Shield Layer, Giving Wireless *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8696939B2 (en) * 2003-06-18 2014-04-15 Koninklijke Philips N.V. High voltage insulating materials
US7964798B2 (en) 2004-11-11 2011-06-21 Koninklijke Philips Electronics N.V. Electrical high field/high voltage unit and method of manufacturing same

Also Published As

Publication number Publication date
SE9402933L (sv) 1996-03-06
SE9402933D0 (sv) 1994-09-05
SE505246C2 (sv) 1997-07-21

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