WO2006118536A1 - Electric insulation material, an electric device and a method for producing an electric insulation material - Google Patents

Electric insulation material, an electric device and a method for producing an electric insulation material Download PDF

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Publication number
WO2006118536A1
WO2006118536A1 PCT/SE2006/000540 SE2006000540W WO2006118536A1 WO 2006118536 A1 WO2006118536 A1 WO 2006118536A1 SE 2006000540 W SE2006000540 W SE 2006000540W WO 2006118536 A1 WO2006118536 A1 WO 2006118536A1
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WO
WIPO (PCT)
Prior art keywords
insulation material
filler particles
electric insulation
impregnation medium
fibrous matrix
Prior art date
Application number
PCT/SE2006/000540
Other languages
French (fr)
Inventor
Anders Björklund
Hans-Åke ERIKSSON
Henrik Hillborg
Olof Hjortstam
Peter Isberg
Erik Johansson
Eva MÅRTENSSON
Jens Rocks
Bengt Rothman
Peter SJÖBERG
Robert STÅHL
Vincent Tilliette
Tobias WIKSTRÖM
Carina ÖNNEBY
Original Assignee
Abb Research Ltd.
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 Abb Research Ltd. filed Critical Abb Research Ltd.
Priority to EP06733394A priority Critical patent/EP1878027A4/en
Priority to CN200680015200.8A priority patent/CN101189686B/en
Publication of WO2006118536A1 publication Critical patent/WO2006118536A1/en

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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
    • H01B3/48—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

Definitions

  • Electric insulation material an electric device and a method for producing an electric insulation material
  • the present invention concerns electric insulation material - formed by a porous fibrous matrix that is impregnated with an impregnation medium.
  • the invention also relates to an electrical bushing, an electrical machine winding and an electric device comprising such material and a method for producing said mate- rial.
  • Epoxy resin is widely used for electric insulation purposes in the electrical power industry in devices such as surge arrestors, high voltage breakers and transformers.
  • the thermal conductiv- ity of epoxy resin is however relatively low, which increases the risk of encountering thermal problems and overheating in certain applications in which electric insulation material comprising epoxy resin is used.
  • Resin impregnated paper (RIP-) electrical bushings are often used in electrical systems that transform and switch AC or DC voltages ranging from a few hundred volts to several thousand volts. The electrical bushings used in such applications are quite large since a substantial thickness of electric insulation material is required.
  • the object of the present invention is to provide an improved electric insulation material.
  • the electric insulation material according to the invention is formed by a porous fibrous matrix that is impregnated, i.e. partly or completely filled, with an impregnation medium that contains filler particles having a higher thermal conductivity than the impregnation medium and having at least one dimension, i.e. width, length and/or height, smaller than 1 ⁇ m, preferably having at least one dimension smaller than 100 nm, i.e. "nano-particles".
  • the fibrous matrix is at least partly penetrated by such filler particles of the impregnation medium.
  • the thermal conductivity of the impregnated fibrous ma- trix and the electric insulation material formed thereof will be improved as compared to a conventional insulation material formed by a fibrous matrix impregnated with an impregnation medium containing no particles of the above-indicated type.
  • porous fibrous matrix refers to a fibrous matrix that has such permeability that the impregnation medium is capable of penetrating into the cavities between the fibres of the matrix.
  • the filler particles may be of any regular or irregular shape and have several or all dimensions smaller than the dimensions given above.
  • the filler particles may for example be in the form of spheres, tubes or fibres etc.
  • the size of at least some of the filler particles should however be small enough to allow the par- tides to penetrate into the porous fibrous matrix during the impregnation phase.
  • the size of at least some of the filler particles should therefore be smaller than the size of the pores or cavities in the porous fibrous matrix.
  • a way to take advantage of the enhanced thermal conductivity of the inventive electric insulation material is to increase the cur- rent rating of the electric device whose conventional electric insulation has been replaced with an electric insulation of the inventive electric insulation material.
  • Nano-particles are used rather than micro-particles since nano-particles are able to - penetrate into the fibrous matrix more easily and they remain dispersed in the impregnation medium without creating sediment and without causing wear on the fibrous matrix. Nano-particles may also be used to obtain field-grading properties suitable for high field stress control. This could prevent long-term deterioration of the electric insulation material and allow for higher design fields and thus a decrease in the insulation thickness.
  • the impregnation medium contains up to 25 vol% filler particles, preferably up to 15 vol% filler particles and most preferably up to 5 vol% filler particles. Due to the incorporation of extremely small filler particles into the impregnation medium, thermal, physical and electrical properties of the electric insulation material may improve substantially with the addition of only a small amount of filler particles, thus enabling the inventive electric insulation material to maintain low weight and volume. Small filler particle concentrations in the impregnation medium will furthermore not significantly increase the viscosity of the impregnation medium.
  • the viscosity of the liquid is often increased since the highly polar nature of the filler particles makes them incompatible with non-polar impregnation media. Moreover, the viscosity increases with de- creasing particle size due to an increased surface area between particles and impregnation medium. This is a drawback since a more viscous liquid will not impregnate a porous matrix as well as a less viscous liquid during vacuum impregnation for example.
  • the filler particles are surface-modified according to an embodiment of the invention so as to decrease the viscosity of the impregnation medium containing filler particles.
  • Surface modification is achieved by a conventional reaction of a compound that is capable of reacting and/or interacting with the surface groups of the filler particles giving rise to covalent, ionic, hydrogen or van der Waals bonding between the filler particles and surface-modifying component and consequently good compatibility between the filler particles and the impregnation medium.
  • the surface of the filler particles is modified either before or after they have been incorporated into the impregnation medium or in a process comprising steps that are carried out before and after filler particles are incorporated into the impregnation medium or while they are being incorporated into the impregnation medium.
  • the surface of the filler particles is surface modified by attaching silane (i.e. any compound having the general formula Si n H 2n + 2 ).
  • silane i.e. any compound having the general formula Si n H 2n + 2
  • a silane comprising a functional group to polar groups, such as free hydroxyl groups, on the surface of the filler particles.
  • the functional group is for example a chloro, methoxy, ethoxy, amino or mercapto group or any other functional group that makes the filler particles more soluble in the impregnation medium.
  • Silanes will hydrolyze in the presence of moisture and condense to the surface of the filler particles.
  • the func- tional groups will react further and form strong covalent bonds between the surface of the filler particles and the fibrous matrix, resulting in strong adhesion there between.
  • a similar result may be obtained by using titanes or silazanes instead of silanes.
  • the electric insulation material is arranged to have different filler-particle- contents in different parts of the material, such as 0 vol% in one part of the material and 10 vol% in another part.
  • the thermal and mechanical properties of different parts of the material may thereby be tailor-made to suit a particular application.
  • a diffusion barrier to stop water and/or gas passing from one side of the diffusion barrier to the other may be created.
  • Such a diffusion barrier may be used to prevent the diffusion of oxygen through the electric insulation material, resulting in a material with increased flame resistance.
  • the filler particles are homogeneously dispersed throughout the electric insulation material.
  • the filler particle nature and content will affect the electrical, thermal and mechanical properties of the electric insulation material
  • said material can be tailor-made to suit a particular application by varying the amount and type of filler particles.
  • the thermal expansion of the electric insulation material could be arranged to match the thermal expansion of metal contacts adjacent to or embedded in the material.
  • the resistivity, dielectric constant or field grading of the material could also be tailored to have the required value for a particular application so as to reduce or eliminate electrical, mechanical and/or thermal stresses.
  • the present invention also concerns an electrical bushing and an electrical machine winding, such as a motor or generator stator winding, that comprises electric insulation material according to any of the embodiments described herein, and an electric device, such as a dry type transformer, instrument transformer, motor, generator, capacitor, electric cable etc., ac- cording to claim 15.
  • an electrical machine winding such as a motor or generator stator winding
  • an electric device such as a dry type transformer, instrument transformer, motor, generator, capacitor, electric cable etc., ac- cording to claim 15.
  • the present invention furthermore relates to a method for producing an electric insulation material which comprises the step of impregnating a porous fibrous matrix with an impregnation medium containing filler particles having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 ⁇ m, preferably having at least one dimension smaller than 100 nm, so as to allow such filler particles to penetrate into the fibrous matrix.
  • the impregnated - fibrous matrix may then be cured, i.e. hardened, set or dried at room temperature or by heating, by using radiation such as UV- radiation or by any other means well known to a skilled person.
  • the fibrous matrix may be processed into any desired shape either before or after impregnation and curing.
  • the method comprises the step of impregnating the porous fibrous matrix with impregnation medium under vacuum and/or pressure so as to provide a void free structure not subject to layer separation and to render the fibrous matrix impervious to harmful conductive particle intrusion by water for example.
  • Fig 1 is a TEM (Transmission Electron Microscopy) micrograph of filler particles in an impregnating medium usable for forming electric insulation material according to the invention
  • Fig 2a shows electric insulation material according to an embodiment of the invention in a schematic cross-sectional view
  • Fig 2b shows electric insulation material not conforming to the present invention in a schematic cross-sectional view
  • Fig 3a is a schematic perspective view of an electrical bushing formed by electric insulation material according to an embodiment of the invention.
  • Fig 3b is a graph showing the radial thermal conductivity of the electric insulation of Fig 3a as a function of filler particle concentration for different particle sizes
  • Fig 3c is a graph showing the axial thermal conductivity of the electric insulation of Fig 3a as a function of filler particle concentration for different particle sizes
  • Fig 4 is a flow chart showing the steps of a method according to an embodiment of the invention.
  • Fig 1 is a TEM micrograph showing 50 nm AI 2 O 3 nano-particles 1 dispersed in an impregnation medium in the form of epoxy resin 2.
  • Such an impregnation medium 2 containing filler parti- cles 1 may be prepared simply by combining and mixing the - particles 1 and impregnation medium 2, preferably at room temperature or by conventional melt-mixing.
  • the AI 2 O 3 nano-particles 1 are surface-modified using (3-Glycidoxypropyl) trimethox- ysilane and de-agglomerated prior to incorporating them into the epoxy resin 2. It has been found that the radial thermal conductivity of a RIP-bushing can be increased by 150% by replacing its conventional electric insulation material with inventive insulation material having an impregnation medium filler content of 25% by volume of 300 nm AI 2 O 3 .
  • Fig 2a shows electric insulation material 3 formed by several layers of a porous cellulose matrix 4 impregnated with an impregnation medium 2 containing filler particles having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 ⁇ m, preferably having at least one dimension smaller than 100 nm.
  • the fibrous matrix layers 4 are completely penetrated by said filler particles of the impregnation medium 2, i.e. filler particles and impregnation medium occupies essentially all the cavi- ties between the fibres of the fibrous matrix.
  • the impregnation medium 2 has been allowed to cure so as to form several cellulose layers 4 with cured impregnation medium 2 and filler particles dispersed therein and with intermediate layers 2' of cured impregnation medium 2 having filler particles dispersed therein.
  • Fig 2b shows electric insulation material corresponding to the electric insulation material of Fig 2a but with larger filler particles contained in the impregnation medium 2.
  • the filler particles have a larger size than the cavities between the fibres of the fibrous matrix 4.
  • the filler par- tides are prevented from penetrating into the cellulose matrix layers and will be concentrated to the layers 2' of cured impregnation medium between these matrix layers.
  • the electric insulation material will have a good thermal conductivity in the axial direction A2 but a substantially lower thermal conductivity in the radial direction A1.
  • the fibrous matrix 4 included in the electric insulation material according to the present invention preferably comprises cellulose fibres and/or glass fibres and/or polymeric fibres.
  • the polymeric fibres may be of polyethylene, polypropylene, nylon, polyester, polyacrylonitrile, polyurethane or an aramid such as Nomex ® (a synthetic aromatic polyamide polymer) or Kevlar ® .
  • the fibrous matrix 4 is suitably in the form of paper, pressboard, laminate, tape, weave or sheets.
  • the fibrous matrix is in the form of glass fibre tape, glass fibre weave or cellulose paper.
  • the impregnation medium 2 is to be electrically non-conductive and is suitably a thermosetting resin, such as an epoxy resin or a polyester, a thermoplastic resin, a thermoplastic elastomer or a silicone gel.
  • the impregnation medium 2 is with advantage an epoxy resin in the form of epoxy diacrylate (EPDA).
  • EPDA epoxy diacrylate
  • the impregnation medium 2 is to have a sufficiently low viscosity to allow the impregnation medium to flow into the cavities between the fibres of the fibrous matrix.
  • the above-indicated filler particles 1 that are dispersed in the impregnation medium are of material having a higher thermal conductivity than the impregnation medium so as to achieve the desired improvement of the thermal conductivity of the electric insulation material formed by the impregnated fibrous matrix.
  • the filler particles are of electrically non-conductive material or of material having a certain electrical conductivity adapted to a specific insulation application for the produced electric insulation material.
  • the filler particles are preferably of non-metallic material and may with advantage be of one or more materials selected from the following groups: oxides, nitrides and carbides.
  • the filler particles are preferably of inorganic oxi- dic compounds or ceramics, such as AI 2 O 3 , AIN, BeO, B 4 C, BN, CuO, SiC, SiO 2 , Si 3 N 4 , TiB 2 , TiO 2 , MgO or ZO.
  • the filler particles may be oriented in an ordered or specific way in at least part of the electric insulation material depending on whether isotropic or anisotropic properties are desired.
  • Fig 3a schematically illustrates an electrical bushing 5 comprising a cylindrical member 6 of electric insulation material according to the present invention.
  • the cylindrical member 6 surrounds an electrical conductor 7 and is formed by a porous fibrous matrix 4 in the form of cellulose paper wrapped around the conductor 7.
  • the fibrous matrix has been impregnated with an impregnation medium in the form of liquid epoxy resin containing nano-sized filler particles of AI 2 O 3 dispersed in the impregnation medium, whereupon the impregnation medium has been cured.
  • the radial thermal conductivity ⁇ r and the axial thermal conductivity ⁇ a of the cylindrical member 6 are indicated by arrows in Fig 3a.
  • Fig 3b illustrates how the radial thermal conductivity ⁇ r of the cylindrical member 6 of Fig 3a increases with increased filler concentration of AI 2 O 3 nano-particles in the impregnation medium used for forming the cylindrical member 6.
  • Fig 3c illustrates how the axial thermal conductivity ⁇ a of the cylindrical member 6 of Fig 3a increases with increased filler concentration of AI 2 O 3 nano-particles in the impregnation medium used for forming the cylindrical member 6.
  • Fig 4 is a flow chart showing the steps of a method according to an embodiment of the invention.
  • the method comprises the step of attaching a silane, optionally a functionalised silane, such as a chloro-silane, to OH-groups on the surface of filler particles of the above-indicated type.
  • the surface-modified filler particles are then incorporated into an impregnation medium, such as for instance transformer oil or an 'epoxy resin.
  • an impregnation medium such as for instance transformer oil or an 'epoxy resin.
  • a porous fibrous ma- trix is then impregnated with the filler particle-containing impregnation medium, optionally under vacuum and/or pressure.
  • the viscosity of epoxy resin is essentially unaffected up to a filler content of approximately 15 vol% sur- face-modified AI 2 O 3 nano-particles.
  • the viscosity of epoxy resin is essentially unaffected up to a filler content of approximately 5 vol% when non-surface-modified AI 2 O 3 nano-particles are used.
  • Electric insulation material according to the present invention may for instance be used for insulating the windings of a dry type transformer.
  • the windings of the transformer may be encased by electric insulation material formed by casting epoxy resin provided with filler particles of the above-indicated type under vacuum in a mould or applying epoxy resin mouldless to a fibrous matrix in the form of a glass fibre weave that surrounds the windings.
  • the inventive electric insulation material may also be used in electrical bushings of condenser type for AC applications or in electrical bushings for DC converter transformer applications. These types of bushings may be provided with inventive electric insulation material in the form of oil impregnated paper or paper impregnated with epoxy resin.
  • the inventive electric insulation material may also be used to form electrical insulation in instrument transformers, such as current and voltage transformers.
  • electrically conducting or semi-conducting filler particles such as carbon nano-particles
  • electrically conducting or semi-conducting filler particles could be incorporated in at least one part of the electric insulation material for example to provide an electrode or conductor inside, or on the surface of the electric insulation material or alternatively to alter the thermal, physical or electrical properties of said at least one part of the material to suit a particular application.

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

Abstract

The invention relates to an electric insulation material (3) - formed by a porous fibrous matrix that is impregnated with an impregnation medium (2) containing filler particles (1 ) having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 µm, preferably having at least one dimension smaller than 100 nm, the fibrous matrix (4) being at least partly penetrated by such filler particles (1 ) of the impregnation medium (2).

Description

Electric insulation material, an electric device and a method for producing an electric insulation material
TECHNICAL FIELD OF THE INVENTION AND PRIOR ART
The present invention concerns electric insulation material - formed by a porous fibrous matrix that is impregnated with an impregnation medium. The invention also relates to an electrical bushing, an electrical machine winding and an electric device comprising such material and a method for producing said mate- rial.
Epoxy resin is widely used for electric insulation purposes in the electrical power industry in devices such as surge arrestors, high voltage breakers and transformers. The thermal conductiv- ity of epoxy resin is however relatively low, which increases the risk of encountering thermal problems and overheating in certain applications in which electric insulation material comprising epoxy resin is used. Resin impregnated paper (RIP-) electrical bushings are often used in electrical systems that transform and switch AC or DC voltages ranging from a few hundred volts to several thousand volts. The electrical bushings used in such applications are quite large since a substantial thickness of electric insulation material is required.
High electrical stresses may also occur around the tips of metal foils inside the electrical bushings and high service temperatures may give rise to thermal expansion problems in and around the electrical bushing. Such harsh conditions in combination with difficult wetting properties and mismatch of thermal expansion coefficients between epoxy resin and other materials can also lead to delamination of the electric insulation material, which in turn can result in destructive partial discharges.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an improved electric insulation material.
This object is fulfilled by electric insulation material having the features of claim 1. The electric insulation material according to the invention is formed by a porous fibrous matrix that is impregnated, i.e. partly or completely filled, with an impregnation medium that contains filler particles having a higher thermal conductivity than the impregnation medium and having at least one dimension, i.e. width, length and/or height, smaller than 1 μm, preferably having at least one dimension smaller than 100 nm, i.e. "nano-particles". The fibrous matrix is at least partly penetrated by such filler particles of the impregnation medium. Hereby, the thermal conductivity of the impregnated fibrous ma- trix and the electric insulation material formed thereof will be improved as compared to a conventional insulation material formed by a fibrous matrix impregnated with an impregnation medium containing no particles of the above-indicated type.
In this description and the subsequent claims, the term "porous fibrous matrix" refers to a fibrous matrix that has such permeability that the impregnation medium is capable of penetrating into the cavities between the fibres of the matrix.
The filler particles may be of any regular or irregular shape and have several or all dimensions smaller than the dimensions given above. The filler particles may for example be in the form of spheres, tubes or fibres etc. The size of at least some of the filler particles should however be small enough to allow the par- tides to penetrate into the porous fibrous matrix during the impregnation phase. The size of at least some of the filler particles should therefore be smaller than the size of the pores or cavities in the porous fibrous matrix.
It has been found that the incorporation of suitable filler parti- cles increases the thermal conductivity of the electric insulation material whilst maintaining its electrical insulation properties.
A way to take advantage of the enhanced thermal conductivity of the inventive electric insulation material is to increase the cur- rent rating of the electric device whose conventional electric insulation has been replaced with an electric insulation of the inventive electric insulation material.
Several advantages are attained if nano-particles are used rather than micro-particles since nano-particles are able to - penetrate into the fibrous matrix more easily and they remain dispersed in the impregnation medium without creating sediment and without causing wear on the fibrous matrix. Nano-particles may also be used to obtain field-grading properties suitable for high field stress control. This could prevent long-term deterioration of the electric insulation material and allow for higher design fields and thus a decrease in the insulation thickness.
According to an embodiment of the invention the impregnation medium contains up to 25 vol% filler particles, preferably up to 15 vol% filler particles and most preferably up to 5 vol% filler particles. Due to the incorporation of extremely small filler particles into the impregnation medium, thermal, physical and electrical properties of the electric insulation material may improve substantially with the addition of only a small amount of filler particles, thus enabling the inventive electric insulation material to maintain low weight and volume. Small filler particle concentrations in the impregnation medium will furthermore not significantly increase the viscosity of the impregnation medium. When filler particles are incorporated into a liquid, the viscosity of the liquid is often increased since the highly polar nature of the filler particles makes them incompatible with non-polar impregnation media. Moreover, the viscosity increases with de- creasing particle size due to an increased surface area between particles and impregnation medium. This is a drawback since a more viscous liquid will not impregnate a porous matrix as well as a less viscous liquid during vacuum impregnation for example. In order to alleviate this drawback, the filler particles are surface-modified according to an embodiment of the invention so as to decrease the viscosity of the impregnation medium containing filler particles. Surface modification is achieved by a conventional reaction of a compound that is capable of reacting and/or interacting with the surface groups of the filler particles giving rise to covalent, ionic, hydrogen or van der Waals bonding between the filler particles and surface-modifying component and consequently good compatibility between the filler particles and the impregnation medium.
The surface of the filler particles is modified either before or after they have been incorporated into the impregnation medium or in a process comprising steps that are carried out before and after filler particles are incorporated into the impregnation medium or while they are being incorporated into the impregnation medium.
According to another embodiment of the invention, the surface of the filler particles is surface modified by attaching silane (i.e. any compound having the general formula SinH2n+2). such as a silane comprising a functional group, to polar groups, such as free hydroxyl groups, on the surface of the filler particles. The functional group is for example a chloro, methoxy, ethoxy, amino or mercapto group or any other functional group that makes the filler particles more soluble in the impregnation medium. Silanes will hydrolyze in the presence of moisture and condense to the surface of the filler particles. During thermal curing, the func- tional groups will react further and form strong covalent bonds between the surface of the filler particles and the fibrous matrix, resulting in strong adhesion there between. A similar result may be obtained by using titanes or silazanes instead of silanes.
Surface modification not only results in an impregnation medium containing filler particles having a lower viscosity as compared to non-surface-modified particles but also provides stronger adhesion between the filler particles and the fibrous matrix as compared to non-surface-modified particles
According to another embodiment of the invention, the electric insulation material is arranged to have different filler-particle- contents in different parts of the material, such as 0 vol% in one part of the material and 10 vol% in another part. The thermal and mechanical properties of different parts of the material may thereby be tailor-made to suit a particular application. For example by incorporating suitable filler particles in a section of an electric insulation material, a diffusion barrier to stop water and/or gas passing from one side of the diffusion barrier to the other may be created. Such a diffusion barrier may be used to prevent the diffusion of oxygen through the electric insulation material, resulting in a material with increased flame resistance. Alternatively, the filler particles are homogeneously dispersed throughout the electric insulation material.
Since the filler particle nature and content will affect the electrical, thermal and mechanical properties of the electric insulation material, said material can be tailor-made to suit a particular application by varying the amount and type of filler particles. For example the thermal expansion of the electric insulation material could be arranged to match the thermal expansion of metal contacts adjacent to or embedded in the material. The resistivity, dielectric constant or field grading of the material could also be tailored to have the required value for a particular application so as to reduce or eliminate electrical, mechanical and/or thermal stresses.
The present invention also concerns an electrical bushing and an electrical machine winding, such as a motor or generator stator winding, that comprises electric insulation material according to any of the embodiments described herein, and an electric device, such as a dry type transformer, instrument transformer, motor, generator, capacitor, electric cable etc., ac- cording to claim 15.
The present invention furthermore relates to a method for producing an electric insulation material which comprises the step of impregnating a porous fibrous matrix with an impregnation medium containing filler particles having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 μm, preferably having at least one dimension smaller than 100 nm, so as to allow such filler particles to penetrate into the fibrous matrix. The impregnated - fibrous matrix may then be cured, i.e. hardened, set or dried at room temperature or by heating, by using radiation such as UV- radiation or by any other means well known to a skilled person. The fibrous matrix may be processed into any desired shape either before or after impregnation and curing.
According to an embodiment of the invention, the method comprises the step of impregnating the porous fibrous matrix with impregnation medium under vacuum and/or pressure so as to provide a void free structure not subject to layer separation and to render the fibrous matrix impervious to harmful conductive particle intrusion by water for example.
The electric insulation material, an electrical bushing, an electric device or an electrical machine winding according to any of the embodiments of the invention is intended particularly, but not exclusively, for use in high voltage applications. Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
With reference to the appended drawings, a specific description of preferred embodiments of the invention cited as examples follows below. In the drawings:
Fig 1 is a TEM (Transmission Electron Microscopy) micrograph of filler particles in an impregnating medium usable for forming electric insulation material according to the invention,
Fig 2a shows electric insulation material according to an embodiment of the invention in a schematic cross-sectional view,
Fig 2b shows electric insulation material not conforming to the present invention in a schematic cross-sectional view,
Fig 3a is a schematic perspective view of an electrical bushing formed by electric insulation material according to an embodiment of the invention,
Fig 3b is a graph showing the radial thermal conductivity of the electric insulation of Fig 3a as a function of filler particle concentration for different particle sizes,
Fig 3c is a graph showing the axial thermal conductivity of the electric insulation of Fig 3a as a function of filler particle concentration for different particle sizes, and Fig 4 is a flow chart showing the steps of a method according to an embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVEN- TION
Fig 1 is a TEM micrograph showing 50 nm AI2O3 nano-particles 1 dispersed in an impregnation medium in the form of epoxy resin 2. Such an impregnation medium 2 containing filler parti- cles 1 may be prepared simply by combining and mixing the - particles 1 and impregnation medium 2, preferably at room temperature or by conventional melt-mixing. The AI2O3 nano-particles 1 are surface-modified using (3-Glycidoxypropyl) trimethox- ysilane and de-agglomerated prior to incorporating them into the epoxy resin 2. It has been found that the radial thermal conductivity of a RIP-bushing can be increased by 150% by replacing its conventional electric insulation material with inventive insulation material having an impregnation medium filler content of 25% by volume of 300 nm AI2O3.
Fig 2a shows electric insulation material 3 formed by several layers of a porous cellulose matrix 4 impregnated with an impregnation medium 2 containing filler particles having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 μm, preferably having at least one dimension smaller than 100 nm. In the illustrated example, the fibrous matrix layers 4 are completely penetrated by said filler particles of the impregnation medium 2, i.e. filler particles and impregnation medium occupies essentially all the cavi- ties between the fibres of the fibrous matrix. By adapting the particle size to the porosity of the fibrous matrix 4, i.e. by choosing filler particles having a size that is smaller than the cavities between the fibres of the fibrous matrix, it will be possible to achieve a complete and homogeneous distribution of filler particles within the fibrous matrix and thereby almost the same thermal conductivity in the radial direction (indicated by arrow A1 ) as in the axial direction (indicated by arrow A2) of the insulation material 3. In the example illustrated in Fig 2a, the impregnation medium 2 has been allowed to cure so as to form several cellulose layers 4 with cured impregnation medium 2 and filler particles dispersed therein and with intermediate layers 2' of cured impregnation medium 2 having filler particles dispersed therein.
For the purpose of comparison, Fig 2b shows electric insulation material corresponding to the electric insulation material of Fig 2a but with larger filler particles contained in the impregnation medium 2. In this case, which do not conform to the present invention, the filler particles have a larger size than the cavities between the fibres of the fibrous matrix 4. Hereby, the filler par- tides are prevented from penetrating into the cellulose matrix layers and will be concentrated to the layers 2' of cured impregnation medium between these matrix layers. Hereby, the electric insulation material will have a good thermal conductivity in the axial direction A2 but a substantially lower thermal conductivity in the radial direction A1.
The fibrous matrix 4 included in the electric insulation material according to the present invention preferably comprises cellulose fibres and/or glass fibres and/or polymeric fibres. The polymeric fibres may be of polyethylene, polypropylene, nylon, polyester, polyacrylonitrile, polyurethane or an aramid such as Nomex® (a synthetic aromatic polyamide polymer) or Kevlar®. The fibrous matrix 4 is suitably in the form of paper, pressboard, laminate, tape, weave or sheets. Preferably, the fibrous matrix is in the form of glass fibre tape, glass fibre weave or cellulose paper.
The impregnation medium 2 is to be electrically non-conductive and is suitably a thermosetting resin, such as an epoxy resin or a polyester, a thermoplastic resin, a thermoplastic elastomer or a silicone gel. The impregnation medium 2 is with advantage an epoxy resin in the form of epoxy diacrylate (EPDA). During the impregnation of the fibrous matrix 4, the impregnation medium 2 is to have a sufficiently low viscosity to allow the impregnation medium to flow into the cavities between the fibres of the fibrous matrix.
The above-indicated filler particles 1 that are dispersed in the impregnation medium are of material having a higher thermal conductivity than the impregnation medium so as to achieve the desired improvement of the thermal conductivity of the electric insulation material formed by the impregnated fibrous matrix. Furthermore, the filler particles are of electrically non-conductive material or of material having a certain electrical conductivity adapted to a specific insulation application for the produced electric insulation material. The filler particles are preferably of non-metallic material and may with advantage be of one or more materials selected from the following groups: oxides, nitrides and carbides. The filler particles are preferably of inorganic oxi- dic compounds or ceramics, such as AI2O3, AIN, BeO, B4C, BN, CuO, SiC, SiO2, Si3N4, TiB2, TiO2, MgO or ZO. The filler particles may be oriented in an ordered or specific way in at least part of the electric insulation material depending on whether isotropic or anisotropic properties are desired.
Fig 3a schematically illustrates an electrical bushing 5 comprising a cylindrical member 6 of electric insulation material according to the present invention. The cylindrical member 6 surrounds an electrical conductor 7 and is formed by a porous fibrous matrix 4 in the form of cellulose paper wrapped around the conductor 7. After the wrapping of the fibrous matrix 4 around the conductor 7, the fibrous matrix has been impregnated with an impregnation medium in the form of liquid epoxy resin containing nano-sized filler particles of AI2O3 dispersed in the impregnation medium, whereupon the impregnation medium has been cured. The radial thermal conductivity λr and the axial thermal conductivity λa of the cylindrical member 6 are indicated by arrows in Fig 3a.
Fig 3b illustrates how the radial thermal conductivity λr of the cylindrical member 6 of Fig 3a increases with increased filler concentration of AI2O3 nano-particles in the impregnation medium used for forming the cylindrical member 6. Fig 3c illustrates how the axial thermal conductivity λa of the cylindrical member 6 of Fig 3a increases with increased filler concentration of AI2O3 nano-particles in the impregnation medium used for forming the cylindrical member 6.
Fig 4 is a flow chart showing the steps of a method according to an embodiment of the invention. The method comprises the step of attaching a silane, optionally a functionalised silane, such as a chloro-silane, to OH-groups on the surface of filler particles of the above-indicated type. The surface-modified filler particles are then incorporated into an impregnation medium, such as for instance transformer oil or an 'epoxy resin. A porous fibrous ma- trix is then impregnated with the filler particle-containing impregnation medium, optionally under vacuum and/or pressure.
It has been found that the viscosity of epoxy resin is essentially unaffected up to a filler content of approximately 15 vol% sur- face-modified AI2O3 nano-particles. The viscosity of epoxy resin is essentially unaffected up to a filler content of approximately 5 vol% when non-surface-modified AI2O3 nano-particles are used.
Electric insulation material according to the present invention may for instance be used for insulating the windings of a dry type transformer. In this case, the windings of the transformer may be encased by electric insulation material formed by casting epoxy resin provided with filler particles of the above-indicated type under vacuum in a mould or applying epoxy resin mouldless to a fibrous matrix in the form of a glass fibre weave that surrounds the windings. The inventive electric insulation material may also be used in electrical bushings of condenser type for AC applications or in electrical bushings for DC converter transformer applications. These types of bushings may be provided with inventive electric insulation material in the form of oil impregnated paper or paper impregnated with epoxy resin.
The inventive electric insulation material may also be used to form electrical insulation in instrument transformers, such as current and voltage transformers.
The invention is of course not in any way restricted to the embodiments thereof described above. On the contrary, many pos- sibilities to modifications thereof should be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention as defined in the appended claims.
For example, it should be noted that electrically conducting or semi-conducting filler particles, such as carbon nano-particles, could be incorporated in at least one part of the electric insulation material for example to provide an electrode or conductor inside, or on the surface of the electric insulation material or alternatively to alter the thermal, physical or electrical properties of said at least one part of the material to suit a particular application.

Claims

1. Electric insulation material formed by a porous fibrous matrix (4) that is impregnated with an impregnation medium (2), characterized in that said impregnation medium (2) contains filler particles (1 ) having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 μm, preferably having at least one dimension smaller than 100 nm, the fibrous matrix (4) being at least partly penetrated by such filler particles (1 ) of the impregnation medium (2).
2. Electric insulation material according to claim 1 , characterized in that the impregnation medium (2) comprises up to 5 vol% filler particles (1 ), preferably up to 15 vol% filler particles (1 ) and most preferably up to 25 vol% filler particles (1 ).
3. Electric insulation material according to claim 1 or 2, characterized in that the filler particles (1 ) are substantially uni- formly dispersed in the electric insulation material (3).
4. Electric insulation material according to claim 1 or 2, characterized in that it is arranged to have a different filler-particle- content in different parts of the material (3).
5. Electric. insulation material according to any of the preceding claims, characterized in that the filler particles (1 ) are surface-modified so as to so as to decrease the viscosity of the impregnation medium (2) containing filler particles (1 ).
6. Electric insulation material according to any of the preceding claims, characterized in that said impregnation medium (2) is a thermosetting resin, such as an epoxy resin or a polyester, a thermoplastic resin, a thermoplastic elastomer or a sili- cone gel.
7. Electric insulation material according to any of the preceding claims, characterized in that the fibrous matrix comprises cellulose fibres and/or glass fibres and/or polymeric fibres.
8. Electric insulation material according to any of the preceding claims, characterized in that the fibrous matrix (4) is in the form of paper, pressboard, laminate, tape, weave or sheets.
9. Electric insulation material according to any of the preceding claims, characterized in that the filler particles (1 ) are non- metallic.
10. Electric insulation material according to any of the preceding claims, characterized in that the filler particles (1 ) are of one or more materials selected from the following groups: oxides, nitrides and carbides.
11. Electric insulation material according to claim 10, characterized in that the filler particles (1 ) are of inorganic oxidic com- pounds or ceramics.
12. Electric insulation material according to claim 1 1 , characterized in that the filler particles (1 ) are of AI2O3, AIN, BeO, B4C, BN, CuO, SiC, SiO2, Si3N4, TiB2, TiO2, MgO or ZO.
13. Electrical bushing, characterized in that it comprises electric insulation material (3) according to any of the preceding claims.
14. Electrical machine winding, characterized in that it comprises electric insulation material (3) according to any of claims 1 -12.
15. Electric device, such as a dry type transformer or instrument transformer, characterized in that it comprises electric insulation material (3) according to any of claims 1-12, an electri- cal bushing according to claim 13 or an electrical machine winding according to claim 14.
16. Method for producing an electric insulation material (3) which comprises the step of impregnating a porous fibrous matrix
(4) with an impregnation medium (2) containing filler particles (1 ) having higher thermal conductivity than the impregnation medium and having at least one dimension smaller than 1 μm, preferably having at least one dimension smaller than 100 nm, so as to allow such filler particles (1 ) to penetrate into the fibrous matrix (4).
17. Method according to claim 16, characterized in that it comprises the step of modifying the surface of the filler particles (1 ) so as to decrease the viscosity of the impregnation medium (2) containing filler particles (1 ) before the filler particles (1 ) are incorporated into the impregnation medium (2) or after the filler particles (1 ) have been incorporated into the impregnation medium (2). '
18. Method according to claim 17, characterized in that the surface of the filler particles (1 ) is surface modified by attaching a silane to hydroxyl groups on the surface of the filler particles (1 ).
19. Method according to claim 18, characterized in that the si- lane comprises a functional group such as a chloro, methoxy, ethoxy, amino or mercapto group.
20. Method according to any of claims 16-19, characterized in that it comprises the step of impregnating the fibrous matrix (4) with said impregnation medium (2) under vacuum and/or pressure.
PCT/SE2006/000540 2005-05-04 2006-05-04 Electric insulation material, an electric device and a method for producing an electric insulation material WO2006118536A1 (en)

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EP06733394A EP1878027A4 (en) 2005-05-04 2006-05-04 Electric insulation material, an electric device and a method for producing an electric insulation material
CN200680015200.8A CN101189686B (en) 2005-05-04 2006-05-04 Electric insulation material, an electric device and a method for producing an electric insulation material

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US60/677,342 2005-05-04

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DE102009053253A1 (en) * 2009-11-09 2011-05-12 Siemens Aktiengesellschaft Impregnating resin for composite insulators
WO2012013439A1 (en) * 2010-07-29 2012-02-02 Siemens Aktiengesellschaft Insulation for rotating electrical machines
DE102011079489A1 (en) * 2011-07-20 2013-01-24 Siemens Aktiengesellschaft Method for producing a strip for an electrical insulation system
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WO2013107802A1 (en) * 2012-01-20 2013-07-25 Abb Technology Ltd Cellulose based electrically insulating material
WO2012152580A3 (en) * 2011-05-06 2013-09-12 Siemens Aktiengesellschaft Production method for an electrical insulation system of a conductor in a winding head of an electrical machine
US20160374236A1 (en) * 2014-02-28 2016-12-22 Siemens Aktiengesellschaft Conductive Corona Shielding Paper, In Particular For Outer Corona Shielding
US9928935B2 (en) 2013-05-31 2018-03-27 General Electric Company Electrical insulation system
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WO2008129032A1 (en) * 2007-04-20 2008-10-30 Abb Research Ltd An impregnation medium
CN101816049A (en) * 2007-10-03 2010-08-25 Abb研究有限公司 Electrical insulation system with improved electrical breakdown strength
DE102009039457A1 (en) * 2009-08-31 2011-03-03 Siemens Aktiengesellschaft Conductor mechanism for use in e.g. electrical machine, has set of rectangular conductors braced by impregnating resin that comprises nano-particles, where impregnating resin is cyclo-aliphatic epoxy resin or silicone resin
DE102009039455A1 (en) * 2009-08-31 2011-03-03 Siemens Aktiengesellschaft Conductor mechanism for use in electrical machine, has conductors arranged adjacent to each other with insulating tape, and corona shielding devices provided at upper side and comprised of nano-particles
DE102009039455A8 (en) * 2009-08-31 2011-06-01 Siemens Aktiengesellschaft Ladder and electrical machine
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DE102010032555A1 (en) * 2010-07-29 2012-02-02 Siemens Aktiengesellschaft Insulation for rotating electrical machines
WO2012152580A3 (en) * 2011-05-06 2013-09-12 Siemens Aktiengesellschaft Production method for an electrical insulation system of a conductor in a winding head of an electrical machine
CN103765731A (en) * 2011-05-06 2014-04-30 西门子公司 Method for producing an electrical insulation system for an electric machine
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DE102011079489A1 (en) * 2011-07-20 2013-01-24 Siemens Aktiengesellschaft Method for producing a strip for an electrical insulation system
US9589699B2 (en) 2011-09-22 2017-03-07 Siemens Aktiengesellschaft Insulation systems having improved partial discharge resistance, and method for producing same
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WO2013107802A1 (en) * 2012-01-20 2013-07-25 Abb Technology Ltd Cellulose based electrically insulating material
US10937562B2 (en) 2012-01-20 2021-03-02 Abb Power Grids Switzerland Ag Cellulose based electrically insulating material
US9928935B2 (en) 2013-05-31 2018-03-27 General Electric Company Electrical insulation system
US20160374236A1 (en) * 2014-02-28 2016-12-22 Siemens Aktiengesellschaft Conductive Corona Shielding Paper, In Particular For Outer Corona Shielding
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WO2021063477A1 (en) * 2019-09-30 2021-04-08 Siemens Energy Global GmbH & Co. KG High voltage transformer and method to isolate parts of the voltage transformer

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CN101189686B (en) 2013-01-02

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