WO1997041573A1 - Varistor block - Google Patents

Varistor block Download PDF

Info

Publication number
WO1997041573A1
WO1997041573A1 PCT/SE1997/000668 SE9700668W WO9741573A1 WO 1997041573 A1 WO1997041573 A1 WO 1997041573A1 SE 9700668 W SE9700668 W SE 9700668W WO 9741573 A1 WO9741573 A1 WO 9741573A1
Authority
WO
WIPO (PCT)
Prior art keywords
varistor block
varistor
block
bursting
bandage
Prior art date
Application number
PCT/SE1997/000668
Other languages
French (fr)
Inventor
Björn Lindberg
Per GRÖNBERG
Peter Nygren
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
Priority claimed from SE9601591A external-priority patent/SE507177C2/en
Priority claimed from SE9601593A external-priority patent/SE507382C2/en
Application filed by Asea Brown Boveri Ab filed Critical Asea Brown Boveri Ab
Priority to JP9538795A priority Critical patent/JP2000509210A/en
Priority to EP97921042A priority patent/EP1012856A1/en
Priority to BR9708819A priority patent/BR9708819A/en
Publication of WO1997041573A1 publication Critical patent/WO1997041573A1/en

Links

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
    • H01C7/126—Means for protecting against excessive pressure or for disconnecting in case of failure

Definitions

  • Surge arresters are used for protecting s itchgear and its apparatus against high overvoltages caused by lightning strokes or connections and disconnections in the switchgear.
  • the present invention relates to the varistor blocks which are included in and constitute the active part of a surge arres- ter.
  • the surge arrester normally comprises a stack of a plura ⁇ lity of cylindrical varistor blocks, preferably made of metal oxide, which are arranged one after the other in the axial direction of the varistor blocks between two end electrodes and surrounded by an elongated electrically insulating outer casing of rubber or other polymeric material.
  • Surge arresters of the above-mentioned kind are previously known from a plurality of patent documents, inter alia EP-A- 0 230 103.
  • One drawback with this and several of these known designs is that, if, for example in the event of a fault on a varistor block, an arc is formed inside the surge arrester with an ensuing increase in pressure, parts of the surge arrester may spread explosion-like in a way which is harmful to the environment.
  • Various attempts have been made to solve this problem.
  • the varistor blocks are axially surrounded by compression loops of insulating material to achieve the necessary contact pressure between the various varistor blocks in the stack.
  • the varistor stack and the loops are then radially surrounded, on the centremost part of each varistor block, by bursting-preventing annular bandages with a substan ⁇ tially square cross section made of insulating material with a thick layer of insulating polymer material between bandages and varistor blocks. This means that there are openings in the axial direction between the bandages for pressure relief in the event of a short circuit in the surge arrester.
  • the present invention aims to provide a varistor block and a surge arrester of the above-mentioned kind with improved short-circuit performance in relation to prior art designs by being able to withstand an electrical/thermal breakdown of the stack of varistors without mechanically falling apart.
  • the varistor blocks and a surge arrester comprising these varistor blocks shall have a simple construction and be capable of being manufactured in a cost-effective manner. This is achieved according to the invention by a design with the characteristic features described in the characterizing part of claim 1.
  • the invention comprises two principal designs.
  • the first principal design of the invention is that the varis ⁇ tor block around the circular-cylindrical envelope surface is surrounded by an electrically insulating ring of composite material with a ceramic matrix, for example of silicon carbide or boron carbide.
  • the ring is fixed to the varistor block in connection with the manufacture thereof and is intended to constitute an integral part of and have the same axial length as the varistor block.
  • the ring in order to further improve the short-circuit properties of the varistor block provided with the insulating ring, the ring may be wound with an organic fibrous material.
  • the fibrous material may be so-called ara- mide fibres, for example kevlar or twaron.
  • the second principal design of the invention is that the varistor block around the circular-cylindrical envelope sur ⁇ face is surrounded by a bursting-preventing bandage of an organic fibre.
  • the fibrous material may be so-called aramide fibre, for example kevlar or twaron.
  • the bursting-preventing bandage is formed as a straight circular tube. The axial length of the bandage is somewhat shorter than the axial length of the varistor block.
  • the bandage is axially placed such that the openings between the bandages for a plurality of axial varistor blocks, arranged one after the other, will be positioned right in front of the joints between adjoining varistor blocks. This results in a faster pressure relief at those points where the risk of arcing is greatest, and hence reduced stress on the rings.
  • the scope of the invention allows for the bandage to be applied around the varistor block in a plurality of different ways.
  • the tubular bandage is wound direct onto the varistor block.
  • the bandage is wound, during the manufacture, around a cylindrical frame such that it becomes tubular.
  • the tube consists of tangentially wound fibre.
  • the inner diameter of the bandage is preferably made with a diame- ter which is a few millimetres larger than the outer diameter of the varistor block.
  • the bandage is wound onto a plastic ring shaped as the reel of a sewing-thread, that is, with collars provided with bobbins.
  • the inner diameter of the plastic ring is made with a diameter which is a few millimetres larger than the outer diameter of the varistor block.
  • Figure 1 shows in a side view, half as a section, a preferred embodiment of a varistor block designed according to the in- vention, according to the first principal design of the inven ⁇ tion.
  • Figure 2 shows in a side view, half as a section, an alterna- tive embodiment of a varistor block designed according to the invention, according to the first principal design of the in ⁇ vention.
  • Figure 3 shows in a side view, half as a section, a preferred embodiment of a varistor block designed according to the in ⁇ vention, according to the second principal design of the in ⁇ vention.
  • Figure 4 shows in a side view, half as a section, an alterna- tive embodiment of a varistor block designed according to the invention, according to the second principal design of the in ⁇ vention.
  • Figure 5 shows in a side view, half as a section, an addition- al alternative embodiment of a varistor block designed accor ⁇ ding to the invention, according to the second principal design of the invention.
  • Figures 1 and 2 show embodiments according to the first prin ⁇ cipal design of the invention.
  • Figure 1 shows a circular-cylindrical varistor block 1 with an integrated electrically insulating ring 2 of composite mate ⁇ rial with a ceramic matrix according to the above and with the same axial length as the varistor block.
  • Figure 2 shows the same varistor block 1 with the integrated ring 2 as in Figure 1.
  • the ring is provided with an external annular layer 3 of organic fibre according to the above, wound around the ring.
  • the varistor stack is surrounded by an elongated electrically insulating casing of rubber or other polymeric material.
  • the casing comprises an inner and an outer layer of different polymeric materials.
  • the inner layer which surrounds the varistor blocks and the insulating ring, com ⁇ prises a castable polymer material, for example a so-called RTV or L ⁇ R polymeric material.
  • the outer layer which inter alia forms the shields of the surge arrester, consists of a die-cast polymer material, for example of a so-called HTV or EPDM polymer material.
  • FIGS 3, 4 and 5 show embodiments of the second principal design 3 of the invention.
  • Figure 3 shows a circular-cylindrical varistor block 1 with a tubular bursting-preventing bandage 4 of organic material, wound directly onto the envelope surface.
  • Figure 4 shows the same varistor block.
  • the straight tubular bursting-preventing ban ⁇ dage 5 has been wound separately with an inner diameter a few millimetres larger than the outer diameter of the varistor block. This leads to the creation of an annular concentric space 6 between the varistor block and the bandage.
  • the bandage is fixed concentrically to the varistor block in different ways according to the description below.
  • FIG. 5 also shows the same varistor block 1.
  • the tubular bursting-preventing bandage 6 has been wound onto a plastic ring in the form of a bobbin 6 provided with collars.
  • the inner diameter of the plastic ring has a diameter a few millimetres larger than the outer diameter of the varistor block.
  • an annular concentric space 9 is formed between the varistor block and the bobbin.
  • the bobbin with the bandage is fixed concentrically to the varis ⁇ tor blocks in different ways according to the description below.
  • a surge arrester comprises a plurality of varistor blocks stacked on top of each other and clamped between an upper and a lower end electrode.
  • the axial compression of the varistor stack may suitably be accomplished with the aid of insulating com ⁇ pression loops which are clamped to the lower end electrode.
  • the compression loops are designed such that, during the com ⁇ pression, for one thing the varistor blocks will have the same axial line, and for another the bandages according to Figures 4 and 5 will be fixed concentrically to the varistor blocks with a radial distance determined by the difference in outer diameter for the varistor block and the bandage and the inner diameter of the bobbin, respectively.
  • the bandage shall be axially placed around the varistor block such that the openings between the bandages for a plurality of axial varistor blocks, placed one after the other, will be positioned right in front of the joints between adjoining varistor blocks.
  • a number of spacers 10 with a cross section as that of an HE-A beam or the like, are placed between the bandages and between confronting collars, respectively.
  • the varistor stack is surrounded by an elongated electrically insulating casing of rubber or other polymeric material.
  • the casing comprises an inner and an outer layer of different polymeric materials.
  • the inner layer which surrounds the varistor blocks and the bandages, consists of a castable polymer material, for example of so-called RTV or LSR polymer material.
  • the outer layer which inter alia forms the shields of the surge arrester, consists of a die-cast polymer material, for example of a so-called HTV or EPDM polymer material.

Landscapes

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

Abstract

A varistor block (1) which, around the circular-cylindrical envelope surface, is surrounded by an integrated with a ring (2) of composite material with a ceramic matrix and/or a bursting-preventing bandage (4, 5, 7).

Description

Varistor block
TECHNICAL FIELD
Surge arresters are used for protecting s itchgear and its apparatus against high overvoltages caused by lightning strokes or connections and disconnections in the switchgear. The present invention relates to the varistor blocks which are included in and constitute the active part of a surge arres- ter. The surge arrester normally comprises a stack of a plura¬ lity of cylindrical varistor blocks, preferably made of metal oxide, which are arranged one after the other in the axial direction of the varistor blocks between two end electrodes and surrounded by an elongated electrically insulating outer casing of rubber or other polymeric material.
BACKGROUND ART
Surge arresters of the above-mentioned kind are previously known from a plurality of patent documents, inter alia EP-A- 0 230 103. One drawback with this and several of these known designs is that, if, for example in the event of a fault on a varistor block, an arc is formed inside the surge arrester with an ensuing increase in pressure, parts of the surge arrester may spread explosion-like in a way which is harmful to the environment. Various attempts have been made to solve this problem.
In EP-A-0 335 480, a cross-wound cage with openings for pressure relief has been arranged around the stack of varistor blocks. Such a solution makes the manufacture both complicated and expensive.
In EP-A-0 683 496, the varistor blocks are axially surrounded by compression loops of insulating material to achieve the necessary contact pressure between the various varistor blocks in the stack. The varistor stack and the loops are then radially surrounded, on the centremost part of each varistor block, by bursting-preventing annular bandages with a substan¬ tially square cross section made of insulating material with a thick layer of insulating polymer material between bandages and varistor blocks. This means that there are openings in the axial direction between the bandages for pressure relief in the event of a short circuit in the surge arrester.
SUMMARY OF THE INVENTION
The present invention aims to provide a varistor block and a surge arrester of the above-mentioned kind with improved short-circuit performance in relation to prior art designs by being able to withstand an electrical/thermal breakdown of the stack of varistors without mechanically falling apart. The varistor blocks and a surge arrester comprising these varistor blocks shall have a simple construction and be capable of being manufactured in a cost-effective manner. This is achieved according to the invention by a design with the characteristic features described in the characterizing part of claim 1.
To achieve the above-mentioned object, the invention comprises two principal designs.
The first principal design of the invention is that the varis¬ tor block around the circular-cylindrical envelope surface is surrounded by an electrically insulating ring of composite material with a ceramic matrix, for example of silicon carbide or boron carbide. The ring is fixed to the varistor block in connection with the manufacture thereof and is intended to constitute an integral part of and have the same axial length as the varistor block.
In an alternative embodiment, in order to further improve the short-circuit properties of the varistor block provided with the insulating ring, the ring may be wound with an organic fibrous material. The fibrous material may be so-called ara- mide fibres, for example kevlar or twaron. The second principal design of the invention is that the varistor block around the circular-cylindrical envelope sur¬ face is surrounded by a bursting-preventing bandage of an organic fibre. The fibrous material may be so-called aramide fibre, for example kevlar or twaron. The bursting-preventing bandage is formed as a straight circular tube. The axial length of the bandage is somewhat shorter than the axial length of the varistor block. The bandage is axially placed such that the openings between the bandages for a plurality of axial varistor blocks, arranged one after the other, will be positioned right in front of the joints between adjoining varistor blocks. This results in a faster pressure relief at those points where the risk of arcing is greatest, and hence reduced stress on the rings. The scope of the invention allows for the bandage to be applied around the varistor block in a plurality of different ways.
In a preferred embodiment, the tubular bandage is wound direct onto the varistor block.
In an alternative embodiment, the bandage is wound, during the manufacture, around a cylindrical frame such that it becomes tubular. The tube consists of tangentially wound fibre. The inner diameter of the bandage is preferably made with a diame- ter which is a few millimetres larger than the outer diameter of the varistor block.
In still another embodiment, the bandage is wound onto a plastic ring shaped as the reel of a sewing-thread, that is, with collars provided with bobbins. Also in this embodiment, the inner diameter of the plastic ring is made with a diameter which is a few millimetres larger than the outer diameter of the varistor block.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows in a side view, half as a section, a preferred embodiment of a varistor block designed according to the in- vention, according to the first principal design of the inven¬ tion.
Figure 2 shows in a side view, half as a section, an alterna- tive embodiment of a varistor block designed according to the invention, according to the first principal design of the in¬ vention.
Figure 3 shows in a side view, half as a section, a preferred embodiment of a varistor block designed according to the in¬ vention, according to the second principal design of the in¬ vention.
Figure 4 shows in a side view, half as a section, an alterna- tive embodiment of a varistor block designed according to the invention, according to the second principal design of the in¬ vention.
Figure 5 shows in a side view, half as a section, an addition- al alternative embodiment of a varistor block designed accor¬ ding to the invention, according to the second principal design of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figures 1 and 2 show embodiments according to the first prin¬ cipal design of the invention.
Figure 1 shows a circular-cylindrical varistor block 1 with an integrated electrically insulating ring 2 of composite mate¬ rial with a ceramic matrix according to the above and with the same axial length as the varistor block.
Figure 2 shows the same varistor block 1 with the integrated ring 2 as in Figure 1. In this embodiment of the invention, the ring is provided with an external annular layer 3 of organic fibre according to the above, wound around the ring. As mentioned in the introductory part of the description, the varistor stack is surrounded by an elongated electrically insulating casing of rubber or other polymeric material. Preferably, the casing comprises an inner and an outer layer of different polymeric materials. The inner layer, which surrounds the varistor blocks and the insulating ring, com¬ prises a castable polymer material, for example a so-called RTV or LΞR polymeric material. The outer layer, which inter alia forms the shields of the surge arrester, consists of a die-cast polymer material, for example of a so-called HTV or EPDM polymer material.
Figures 3, 4 and 5 show embodiments of the second principal design 3 of the invention.
Figure 3 shows a circular-cylindrical varistor block 1 with a tubular bursting-preventing bandage 4 of organic material, wound directly onto the envelope surface.
Figure 4 shows the same varistor block. In this embodiment of the invention, the straight tubular bursting-preventing ban¬ dage 5 has been wound separately with an inner diameter a few millimetres larger than the outer diameter of the varistor block. This leads to the creation of an annular concentric space 6 between the varistor block and the bandage. The bandage is fixed concentrically to the varistor block in different ways according to the description below.
Figure 5 also shows the same varistor block 1. In this embo- diment, the tubular bursting-preventing bandage 6 has been wound onto a plastic ring in the form of a bobbin 6 provided with collars. The inner diameter of the plastic ring has a diameter a few millimetres larger than the outer diameter of the varistor block. In this way, an annular concentric space 9 is formed between the varistor block and the bobbin. The bobbin with the bandage is fixed concentrically to the varis¬ tor blocks in different ways according to the description below. As mentioned under the Technical Field, a surge arrester comprises a plurality of varistor blocks stacked on top of each other and clamped between an upper and a lower end electrode. The axial compression of the varistor stack may suitably be accomplished with the aid of insulating com¬ pression loops which are clamped to the lower end electrode. The compression loops are designed such that, during the com¬ pression, for one thing the varistor blocks will have the same axial line, and for another the bandages according to Figures 4 and 5 will be fixed concentrically to the varistor blocks with a radial distance determined by the difference in outer diameter for the varistor block and the bandage and the inner diameter of the bobbin, respectively. As mentioned above, the bandage shall be axially placed around the varistor block such that the openings between the bandages for a plurality of axial varistor blocks, placed one after the other, will be positioned right in front of the joints between adjoining varistor blocks. To ensure this with an embodiment of the bandages according to Figures 4 and 5, a number of spacers 10, with a cross section as that of an HE-A beam or the like, are placed between the bandages and between confronting collars, respectively.
As mentioned in the introductory part of the description, the varistor stack is surrounded by an elongated electrically insulating casing of rubber or other polymeric material. Preferably, the casing comprises an inner and an outer layer of different polymeric materials. The inner layer, which surrounds the varistor blocks and the bandages, consists of a castable polymer material, for example of so-called RTV or LSR polymer material. The outer layer, which inter alia forms the shields of the surge arrester, consists of a die-cast polymer material, for example of a so-called HTV or EPDM polymer material.
The intention with the concentric space 6 and 7, respectively, according to Figures 4 and 5, which is formed between the varistor block and the bandage and between the varistor block and the bobbin, respectively, is to allow it to be filled with the castable polymer material of the inner layer.

Claims

1. A varistor block (1), characterized in that the circu¬ lar-cylindrical envelope surface of the varistor block is surrounded by an electrically insulating ring (2) of composite material with a ceramic matrix and/or a bursting-preventing bandage (4, 5, 7) of organic fibre.
2. A varistor block (1) according to claim 1, characterized in that the electrically insulating ring is made with a matrix material of silicon carbide.
3. A varistor block (1) according to claim 1, characterized in that the electrically insulating ring is made with a matrix material of boron carbide.
4. A varistor block (1) according to claim 1, characterized in that the electrically insulating ring constitutes an inte¬ gral part of the varistor block.
5. A varistor block (1) according to claim 1, characterized in that the electrically insulating ring has the same axial length as the varistor block.
6. A varistor block (1) according to claim 1, characterized in that the electrically insulating ring is surrounded by an annular layer (3) of organic fibre.
7. A varistor block (1) according to claims 1 and 6, characterized in that the wound annular layer (3) of organic fibre consists of aramide fibre.
8. A varistor block (1) according to claims 1 and 6, characterized in that the wound annular layer (3) of organic fibre consists of kevlar.
9. A varistor block (1) according to claims 1 and 6, characterized in that the wound annular layer (3) of organic fibre consists of twaron.
10. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (4) is made of aramide fibre.
11. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (4) is made of kevlar.
12. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (4) is made of twaron.
13. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (4) is formed as a straight circular tube.
14. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (4) is wound direct onto the envelope surface of the varistor block.
15. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (5) is separately wound with an inner diameter larger than the outer diameter of the varistor block.
15. A varistor block (1) according to claim 1, characterized in that the bursting-preventing bandage (5) is wound onto a bobbin with an inner diameter larger than the outer diameter of the varistor block.
PCT/SE1997/000668 1996-04-26 1997-04-21 Varistor block WO1997041573A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP9538795A JP2000509210A (en) 1996-04-26 1997-04-21 Varistor block
EP97921042A EP1012856A1 (en) 1996-04-26 1997-04-21 Varistor block
BR9708819A BR9708819A (en) 1996-04-26 1997-04-21 Varistor block

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
SE9601591A SE507177C2 (en) 1996-04-26 1996-04-26 Surge arresters that do not disintegrate when subject to electrical/thermal breakdown
SE9601593-8 1996-04-26
SE9601591-2 1996-04-26
SE9601593A SE507382C2 (en) 1996-04-26 1996-04-26 Surge arresters that do not disintegrate when subject to electrical/thermal breakdown

Publications (1)

Publication Number Publication Date
WO1997041573A1 true WO1997041573A1 (en) 1997-11-06

Family

ID=26662591

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1997/000668 WO1997041573A1 (en) 1996-04-26 1997-04-21 Varistor block

Country Status (5)

Country Link
EP (1) EP1012856A1 (en)
JP (1) JP2000509210A (en)
CN (1) CN1216631A (en)
BR (1) BR9708819A (en)
WO (1) WO1997041573A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001031661A1 (en) * 1999-10-25 2001-05-03 Alstom Improved lightning arrestor based on electrical varistors
US8912871B2 (en) 2009-12-18 2014-12-16 Schneider Electric Industries Sas Electromagnetic actuator with magnetic latching and switching device comprising one such actuator

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008294291A (en) * 2007-05-25 2008-12-04 Toshiba Corp Current/voltage nonlinear resistor and method of manufacturing the same, and arrester
FR2965656B1 (en) 2010-09-30 2012-10-05 Schneider Electric Ind Sas ELECTROMAGNETIC ACTUATOR WITH MAGNETIC ATTACHMENT AND CUTTING DEVICE COMPRISING SUCH ACTUATOR
CN103580014B (en) * 2012-07-26 2017-07-14 中兴通讯股份有限公司 A kind of lightning protection device

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0382447A1 (en) * 1989-02-07 1990-08-16 Bowthorpe Industries Limited Electrical surge arrester/diverter
US5307046A (en) * 1991-05-22 1994-04-26 Hubbell Incorporated Passivating coating for metal oxide varistors

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0382447A1 (en) * 1989-02-07 1990-08-16 Bowthorpe Industries Limited Electrical surge arrester/diverter
US5307046A (en) * 1991-05-22 1994-04-26 Hubbell Incorporated Passivating coating for metal oxide varistors

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001031661A1 (en) * 1999-10-25 2001-05-03 Alstom Improved lightning arrestor based on electrical varistors
FR2800903A1 (en) * 1999-10-25 2001-05-11 Soule Materiel Electr PERFECTED SURGE PROTECTOR BASED ON ELECTRIC VARISTORS
US7272885B2 (en) 1999-10-25 2007-09-25 Alstom Method of manufacturing surge arrestor
US8912871B2 (en) 2009-12-18 2014-12-16 Schneider Electric Industries Sas Electromagnetic actuator with magnetic latching and switching device comprising one such actuator

Also Published As

Publication number Publication date
EP1012856A1 (en) 2000-06-28
JP2000509210A (en) 2000-07-18
BR9708819A (en) 1999-08-03
CN1216631A (en) 1999-05-12

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