Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
  • H01H33/60—Switches wherein the means for extinguishing or preventing the arc do not include separate means for obtaining or increasing flow of arc-extinguishing fluid
  • H01H33/66—Vacuum switches
  • H01H33/662—Housings or protective screens
  • H01H33/66207—Specific housing details, e.g. sealing, soldering or brazing
• • 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
  • H01B3/002—Inhomogeneous material in general
  • H01B3/004—Inhomogeneous material in general with conductive additives or conductive layers
• • 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
  • H01B3/002—Inhomogeneous material in general
  • H01B3/006—Other inhomogeneous material
• • 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
  • H01B3/008—Other insulating material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
  • H01H33/60—Switches wherein the means for extinguishing or preventing the arc do not include separate means for obtaining or increasing flow of arc-extinguishing fluid
  • H01H33/66—Vacuum switches
  • H01H33/662—Housings or protective screens
  • H01H33/66207—Specific housing details, e.g. sealing, soldering or brazing
  • H01H2033/6623—Details relating to the encasing or the outside layers of the vacuum switch housings

Definitions

• the present invention relates to an electrically insulating material for overmolding on medium or high voltage apparatuses.
• the invention also relates to medium and high voltage electrical devices using such a material.
• the invention relates more particularly to circuit breakers using such a material.
• Medium and high voltage electrical devices have conductive elements between which a high voltage can prevail. This is the case, in a circuit breaker, of the conductive elements connected respectively to the contacts of the circuit breaker and placed partly outside the breaking chamber, when the contacts are separated from one another to make a breaking. For safety reasons, it is imperative that the conductive elements remain isolated from one another and that an electric arc cannot be established between them in the air outside the breaking chamber.
• the second technique consists in increasing the distance between the conductive elements which is effective from the point of view of insulation, called bypass distance. It is the distance corresponding to a path which connects the conductive elements following the external contour of the device.
• Such an increase is achieved by placing around the apparatus an insulator of appropriate geometry, generally comprising a series of protrusions or fins which lengthen the said path. It has been common for a long time to make such insulators out of glass or ceramic. However, these materials are fragile and do not lend themselves to the manufacture of elements by overmolding on an apparatus.
• polymers such as epoxy resins or elastomers, which lend themselves well to the technique of overmolding, but the field of industrial application of these polymers is limited to relatively low voltages, not exceeding 36 kV .
• the implementation of these polymers requires very special care, which makes the process delicate and expensive.
• polymers in the solid state have voids in which the electrical permittivity ⁇ is much lower than that of the polymer itself. It follows that the electric field due to the voltage between the conductive elements is preferably distributed at the limit of these voids. This causes partial discharges inside these voids which have the effect of damaging the polymer and affecting its insulating power.
• the invention aims to provide a means of solid electrical insulation for medium or high voltage electrical devices, allowing a compact and economical production of said devices and avoiding the use of gas for insulation.
• the invention relates to an insulating material suitable for forming an overmolding on a medium or high voltage device, characterized in that it comprises a mineral charge having an increasing electrical permittivity ⁇ with the applied electric field, in a proportion of between 5 and 50% by volume, and a matrix in which said material is dispersed.
• This material to have an electrical permittivity which increases with the applied field has the effect of ensuring a regular distribution of the electric field in the material, the distribution of the latter being a function of the permittivity, and of avoiding l establishment of high fields in certain areas.
• said filler is chosen from the group consisting of (i) doped zinc oxide ZnO, the dopant being chosen from bismuth oxide Bi 2 O 3 , cobalt oxide Co 3 O 4 or CoO, antimony oxide Sb 2 O 3 , manganese oxide MnO 2 or Mn 3 0 4 and the oxides of the transition metals, and (ii) a forbidden broadband semiconductor.
• the matrix is suitably formed from a polymer composition chosen from the family of elastomers, thermosets and thermoplastics.
• the mineral filler is suitably formed from a particulate material having a particle size between 100 nm and 500 ⁇ m.
• the proportion of mineral filler is suitably between 15 and 30% by volume.
• the mineral filler preferably consists of doped zinc oxide powder having a particle size of 50 to 200 ⁇ m and is present in a proportion of approximately 18% by volume.
• the invention relates to a medium or high voltage electrical device, comprising at least one pair of spaced apart conductive elements, between which prevails said voltage in an operating state of the device, characterized in that 'It comprises an overmolding formed of an electrically insulating material as defined above and arranged to keep the two conductive elements insulated from each other.
• the invention relates to a medium or high voltage circuit breaker, comprising a breaking chamber, contacts placed inside the breaking chamber, a mechanism for creating a relative displacement between the contacts, comprising conductive elements respectively connected to the contacts and arranged at least partially outside the interrupting chamber, characterized in that it comprises an overmolding formed on the interrupting chamber, made of an insulating material as defined above above.
• the invention relates to a medium-voltage circuit breaker, comprising a vacuum interrupter, contacts placed inside the vacuum interrupter, a mechanism for moving at least one of the contacts, comprising conductive elements respectively connected to the contacts and arranged at least partially outside the vacuum interrupter, characterized in that it comprises an overmolding formed on the vacuum interrupter, made of an insulating material such as defined above.
• FIG. 1 is a graph showing the variation of the electrical permittivity as a function of the field for a possible constituent of the insulating material according to the invention
• Figure 2A shows a model used to study by simulation the distribution of the electric field in an insulating material according to the invention, and Figure 2B represents the result of the simulation;
• FIG. 3 schematically shows a circuit breaker of the vacuum bulb type according to an exemplary embodiment of the invention.
• the insulating material for medium and high voltage according to the invention comprises an inorganic filler dispersed in a matrix.
• the mineral charge has the property of having an electrical permittivity ⁇ which increases substantially as a function of the applied electric field. This property is illustrated in FIG. 1, which shows the variation of the relative permittivity ⁇ as a function of the electric field in N / mm (on a logarithmic scale), for an example of insulating material according to the invention.
• the material in question comprises 30% by volume of a mineral filler formed from doped zinc oxide ZnO, obtained by grinding a ceramic used for commercial varistors.
• the charge has a particle size of 250 ⁇ m. It is dispersed in a matrix formed of LSR type silicone. As shown in FIG.
• the relative permittivity ⁇ of this material remains at a constant value, of around 7, up to a field of around 270 N / mm.
• the relative permittivity ⁇ increases rapidly. It reaches 15 for a field of 300 N / mm, 32 for a field of 340 V / mm and 37 for a field of 360 V / mm.
• FIG. 2A represents a model used to study by simulation the effect on the distribution of the field lines of an insulating material according to the invention.
• This model comprises a layer formed by an electrode 1 and a part 2 made of insulating material according to the invention, placed between two layers 3 and 4 of insulating polymer.
• the electrode 1 has a section in the shape of a right triangle and at its base 5 connected to a voltage source 6.
• the part 2 has a complementary trapezoidal section.
• the end 6 of the electrode 1 is located in the median plane of the layers 3 and 4.
• the layer 3 of polymer is connected to the earth at a point 7 located in the said median plane.
• the insulating material according to the invention consists, as indicated above, of a mineral charge having an increasing electrical permittivity ⁇ with the electric field applied, in a proportion of between 5 and 50% by volume, and a matrix in which said material is dispersed.
• said filler consists of particles of doped zinc oxide ZnO, the dopant being chosen from bismuth oxide Bi 2 O 3 , cobalt oxide Co O or CoO, oxide d antimony Sb 2 O, manganese oxide MnO 2 or Mn 3 0 and the oxides of the transition metals.
• Such a constituent is known for its use in the form of ceramic in the varistors of surge arresters.
• the charge of doped ZnO in the form of particles it is possible to start from a commercial varistor in the form of ceramic, having the desired permittivity characteristics, and to grind this ceramic using a suitable grinder.
• the shape of the particles of the filler is suitably spherical or ellipsoidal, but it is also possible to use particles of elongated shape, such as pieces of fibers, or particles of random shape.
• the particle size of the charge is suitably between 100 nm and 500 ⁇ .
• the particle size is to be chosen in particular according to the operating voltage.
• a particle size suitable for medium tensions, from 10 to 50 kN, is between 50 ⁇ m and 200 ⁇ m. For higher tensions, a finer grain size is suitable.
• Another constituent that can be envisaged for the mineral filler is a semiconductor with a wide forbidden band such as silicon carbide SiC, in particles as described above with reference to doped ZnO.
• the matrix is suitably formed from a polymer composition suitable for making overmoldings for medium or high voltage electrical devices.
• a polymer composition suitable for making overmoldings for medium or high voltage electrical devices.
• a composition can be chosen from the family of elastomers and thermosetting resins.
• EPDM ethylene-propylene-diene
• suitable resin mention will be made of silicones and epoxy resins.
• Thermoplastic polymers such as polyethylene or polymethyl methacrylate can also be used.
• the choice of the polymer composition will be made by a person skilled in the art depending on the elements specific to each case, in particular: operating voltage, geometry of the device on which the overmolding is to be formed and the external shape of the overmolding, ambient conditions (temperature, humidity).
• the proportion of mineral filler is suitably between 15 and 30% by volume.
• an overmolding material comprising approximately 18% by volume of a doped ZnO powder, with a particle size of 50 to 200 ⁇ m, dispersed in a thermosetting resin or an elastomer, is an exemplary embodiment suitable for carrying out an overmolding. on a medium voltage device such as a medium voltage circuit breaker.
• FIG. 3 schematically represents a medium-voltage circuit breaker, the breaking device of which is a vacuum interrupter generally designated by the reference 10.
• the vacuum interrupter comprises a casing 11 of generally cylindrical shape inside of which are arranged a fixed contact 12 and a movable contact 13, the latter being movable to move away from the fixed contact, as shown in FIG. 3 A, to make the cut.
• Conductive elements 14 and 15 respectively connected to the fixed contact 12 and to the movable contact 13 pass through openings in the walls end respectively 16 and 17 of the housing 10, the conductive element 15 being movable in translation to move the contact 13 and connected to an actuating member, not shown.
• a bellows 18 is arranged around the movable conductive element 15 to ensure the vacuum resistance of the interior space of the housing 10.
• the housing 10 is coated in an overmolding which, in the exemplary embodiment of FIG. 3, is made up in a homogeneous manner of an insulating material as defined above, namely a doped ZnO powder dispersed in a matrix such as silicone or thermosetting resin.
• the circuit breaker as described has the advantage over known devices of not containing SF 6 insulating gas. It is also very compact.

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• Thermistors And Varistors (AREA)
• Organic Insulating Materials (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Inorganic Insulating Materials (AREA)
• Communication Cables (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Insulating Bodies (AREA)
• Soft Magnetic Materials (AREA)

Applications Claiming Priority (3)

Publications (3)

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• 2001
  • 2001-02-28 FR FR0102739A patent/FR2821479B1/fr not_active Expired - Fee Related
• 2002
  • 2002-01-28 AT AT02701328T patent/ATE478424T1/de not_active IP Right Cessation
  • 2002-01-28 EP EP02701328.3A patent/EP1366499B2/de not_active Expired - Lifetime
  • 2002-01-28 WO PCT/FR2002/000331 patent/WO2002069352A1/fr not_active Application Discontinuation
  • 2002-01-28 DE DE60237351T patent/DE60237351D1/de not_active Expired - Lifetime

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