Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/12—Overvoltage protection resistors; Arresters
  • H01C7/126—Means for protecting against excessive pressure or for disconnecting in case of failure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/12—Overvoltage protection resistors; Arresters

Definitions

• the present invention relates to a surge arrester comprising a stack of a plurality of cylindrical arrester elements which are preferably made of metal oxide varistor material and which are arranged one after the other in the axial direction of the arrester elements between two end elec ⁇ trodes and surrounded by an elongated outer casing.
• the outer casing of currently used surge arresters is usually made of porcelain.
• a porcelain casing has good electrical insulating properties and also has sufficient mechanical strength to take up, inter alia, the axially directed compressive force on the arrester elements, which is generated by springs and which is required to obtain good electrical contact between the elements.
• some form of overpressure relief arrangement is required to avoid an explosion-like failure, if, for example in the event of a fault on an arrester element, a short-circuit arc is formed inside the arrester with an ensuing pressure increase.
• the object of the present invention is to obtain a surge arrester which is provided with polymer casing and which does not suffer from the above-mentioned drawbacks.
• This is achieved according to the invention by using, for mechanical reinforcement of the polymer casing, a fibre-reinforced plastic tube which is made by profile drawing, so-called pultrusion, whereby all reinforcement fibres extend in the axial direction of the tube.
• a pultruded fibre-reinforced tube has a very high tensile strength.
• the required bending strength is obtained by choosing a suitable wall thickness and amount and type of reinforcement fibres.
• a relatively low strength in the radial direction is obtained. This permits a favourable failure process since the tube easily cracks up also at low short-circuit currents .
• pultruded tubes are very cost- effective.
• the surge arrester shown in the figure is primarily intended for use in distribution networks with operating voltages of up to about 40 kV. However, the same design principle may be ⁇ used to advantage also in surge arresters for operating voltages of the order of magnitude of 100 kV and higher.
• the arrester shown comprises a stack of arrester elements 1 in the form of circular-cylindrical ZnO blocks, possibly with heat-absorbing spacers of metal, and an end electrode 2 in the form of a metal pellet at each end of the stack.
• the end electrodes 2 and the spacers, if any, may suitably be made of aluminium.
• the entire stack of ZnO blocks 1, end elec- trodes 2 and spacers, if any, is arranged in an elongated tube 4 of glassfibre-reinforced plastic, which in turn is surrounded by an insulating casing 3 made of polymeric material .
• the stack is axially fixed to the tube 4 by means of metal cases 5, which surround the end portions of the tube 4 and are fixed to the tube by pressing the cylindrical mantle part of the respective case into annular slots 6 in the tube.
• the figure shows, on opposite sides of the centre line of the surge arrester, the metal case 5 before and after the pressing of the mantle part into the annular slots.
• the metal cases 5 are formed with a collar 7, which surrounds the respective end portion of the polymer insulator 3 and is fixed to the insulator by a surrounding indentation 8. Between the metal collar 7 and the insulator 3 there is a seal 9, for example in the form of an O-ring.
• the pressing of the metal cases 5 onto the plastic tube 4, in certain types of plastic material, may be performed with ⁇ out the tube being provided in advance with the surrounding slots 6. In this case, the slots in the plastic material are formed directly in connection with the pressing of the metal cases.
• a spring device in the form of a disc spring assembly 10 is arranged near the end electrodes.
• the end electrodes 2 are provided with threaded fixing holes 11 for connection members.
• the tube 4 is a glassfibre-reinforced tube of plastic material, for example polyester, polyvinyl ester, epoxy or a thermoplastic resin.
• the tube is made by profile drawing, so-called pultrusion. This is a method of production for fibre composites in which the raw materials included are continuously and automatically directly converted into a finished product. In tubes manufactured according to this method, all reinforcement fibres are arranged axially. This gives the tube very special properties, of which a high tensile strength in combination with a low strength in the radial direction are particularly important properties for the present invention. Tubes of this type are available on the market.
• the outer insulating casing 3 may be an elastomer, for example an ethylene-propylene-terpolymer (EPDM rubber) which is fitted over the tube 4. It may also consist of shrinking plastic, for example a crosslinked ethylene-propylene polymer or crosslinked HD-polyethylene which is applied to the tube 4 by shrinking.
• the insulating casing 3 may also be formed directly on the tube 4 by casting or injection moulding.
• the gap between the stack and the tube may be filled with an electrically insulating compound, for example epoxy or silicone compound.
• the tube 4 may consist of a shrinkable plastic material and be applied on the ZnO stack by shrinkage.
• ZnO blocks are usually manufactured in a number of different transverse dimensions (diameters) to make it possible to build surge arresters for different current ranges in an economical way.
• a surge arrester according to the present invention it may be an advantage from the manufacturing point of view if the pultruded tube 4 can be manufactured with one and the same outside diameter for all sizes of ZnO blocks. Tubes which are intended for the smaller blocks are thereby provided internally with a number of longitudinal bars for centering the blocks, the spaces between the bars then being filled with silicone compound or the like.
• the tube 4 will burst in the longi ⁇ tudinal direction in a controlled manner at a relatively low internal overpressure. The risk of explosion causing perso ⁇ nal danger is thereby eliminated.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Thermistors And Varistors (AREA)
• Insulators (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=20383906

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (9)

Family Cites Families (2)

• 1991
  • 1991-10-04 SE SE9102881A patent/SE469247B/sv not_active IP Right Cessation
• 1992
  • 1992-09-25 DE DE69206812T patent/DE69206812T2/de not_active Expired - Fee Related
  • 1992-09-25 AU AU27501/92A patent/AU2750192A/en not_active Abandoned
  • 1992-09-25 EP EP93906332A patent/EP0606409B1/de not_active Expired - Lifetime
  • 1992-09-25 WO PCT/SE1992/000667 patent/WO1993007630A1/en not_active Ceased

Non-Patent Citations (1)

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