EP0058336A2 - ZnO-Varistor mit vermindertem Randleckstrom - Google Patents

ZnO-Varistor mit vermindertem Randleckstrom Download PDF

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Publication number
EP0058336A2
EP0058336A2 EP82100710A EP82100710A EP0058336A2 EP 0058336 A2 EP0058336 A2 EP 0058336A2 EP 82100710 A EP82100710 A EP 82100710A EP 82100710 A EP82100710 A EP 82100710A EP 0058336 A2 EP0058336 A2 EP 0058336A2
Authority
EP
European Patent Office
Prior art keywords
disc
varistor
perimeter
zinc oxide
providing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP82100710A
Other languages
English (en)
French (fr)
Other versions
EP0058336B1 (de
EP0058336A3 (en
Inventor
Herbert Reynold Philipp
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
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 General Electric Co filed Critical General Electric Co
Publication of EP0058336A2 publication Critical patent/EP0058336A2/de
Publication of EP0058336A3 publication Critical patent/EP0058336A3/en
Application granted granted Critical
Publication of EP0058336B1 publication Critical patent/EP0058336B1/de
Expired legal-status Critical Current

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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
    • H01C7/105—Varistor cores
    • H01C7/108—Metal oxide
    • H01C7/112—ZnO type
    • 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
    • H01C7/102—Varistor boundary, e.g. surface layers

Definitions

  • U.S. Patent 3,913,056 discloses a method for preventing currents from channeling through preferred current paths within zinc oxide varistors.
  • Zinc oxide varistors as currently manufactured, comprise a sintered disc of zinc oxide material having a pair of electrodes on opposing surfaces of the disc.
  • the perimeter of the disc is covered with an insulating layer of glass or ceramic material to prevent the transport of current across the outside surface of the disc perimeter.
  • the electrodes When the electrodes are applied to the flat faces of the disc, a portion of the disc material in the vicinity of the disc rim is not covered with the electrode material because the physical transition from the flat disc surface to the peripheral rim may not be well defined.
  • current transports directly through the zinc oxide material covered by the electrode material. However, in actuality some current also transports through the zinc oxide material in the vicinity of the rim not covered by electrode material.
  • fring current This current is referred to as "fringing current" and can be a source of failure when the varistor is operated during conditions of overload.
  • fring current The transport of fringing current in the rim portion of the disc not covered by electrode material causes a concentration of current at the edges of the disc electrodes. The current concentration at the electrode edges causes an excess electrical stress in this area which leads to premature disc failure during overload conditions.
  • the purpose of this invention is to provide a zinc oxide varistor having substantially reduced fringing current effects and consequently a greater overload capability.
  • Zinc oxide varistors are provided with a reduced cross section in the vicinity of the rim.
  • One or more circumferential grooves formed around the disc perimeter substantially reduces the effects of fringing current during varistor operation.
  • FIGURE 1 A zinc oxide varistor 10 having the composition disclosed within U.S. Patent 3,928,245 is shown in FIGURE 1.
  • Varistor 10 comprises a sintered zinc oxide disc 11 having a pair of top and bottom metallic electrodes 12A, 12B on opposing surfaces. Electrodes 12A, 12B extend across disc 11 leaving a top portion D 1 between edge 13 of top electrode 12A and edge 14 of disc 11. A portion D 2 on the bottom of disc 11, between edge 15 of bottom electrode 12B and edge 14 of disc 11, is also not covered by electrode material. The height of disc 11 is defined by D 3 .
  • Dotted path 16 extending between top electrode 12A and bottom electrode 12B through disc 11 defines "fringe" area S 1 through which fringe current B I transports in the direction indicated by arrows. The direction of ordinary current transport between electrodes 12A,12B is depicted by arrow A. As described earlier, the transport of current through fringe area S 1 causes damage to the disc material near the edges 13 and 15 of top and bottom electrodes 12A and 12B respectively.
  • Dotted paths A and B 1 of-FIGURE 1 represent filaments of current flowing from top electrode 12A to bottom electrode 12B due to a difference of potential between the two electrodes.
  • dotted paths-A and B 1 of FIGURE 1 represent paths of constant current density, the field along each path is constant and inversely proportional to the path length.
  • FIGURE 2 shows a zinc oxide varistor 10 having a top electrode 12A and a bottom electrode 12B with areas D1 and D 2 between electrode edges 13 and 15 and disc periphery 14. Perimeter 14 in this embodiment is concave such that the minimum disc diameter approximates that for the electrodes 12A, 12B. Fringing current path B 2 , as shown, is greater than fringing current path B 1 of FIGURE 1. Consequently, the fringing current density is greatly reduced for the embodiment depicted in FIGURE 2.
  • a disadvantage with the embodiment of FIGURE 2 is that the disc corners 17 are sharp and become. subject to damage by chipping.
  • FIGURE 3 A further embodiment having reduced fringing current is shown in FIGURE 3 to consist of a zinc oxide disc 11 similar to that of FIGURE 1, with at least one circumferential groove 18 formed by abrading, machining or mold-forming techniques.
  • two grooves 18 are shown, one proximate the top and the other proximate the bottom of disc 11 and extending within disc 11 to a distance approximately in line with electrode edges 13 and 15.
  • the fringing current path B 3 is seen to be greater than b 1 of FIGURE 1, such that the fringing current density is proportionately reduced.
  • the arrangement of grooves 18 can be modified depending upon the desired results.
  • One or more grooves 18 can be employed, and the shape and depth of the grooves can be designed to accommodate various manufacturing techniques.
  • a specific example containing two grooves 18, such as shown in FIGURE 3, and ranging from 0.06 to 0.10 inches in radius extending entirely around the perimeter of disc 11 was manufactured having the following dimensions. Height D 3 measured 1.375 inches and separation distances D1 and D 2 for top and bottom electrodes 12A and 12B measured approximately 0.086 inches. The maximum electric strength measured higher for this example than any previous varistors having the configuration shown in FIGURE 1.
  • Varistor 10 also contained an insulating coating of glass or ceramic material 9 around the perimeter of the disc and covering the zinc oxide material within grooves 18.
  • a plurality of grooves 18 extending along the disc perimeter can increase the voltage "creep" to the extent that no glass or ceramic coating 9 need be employed.
  • the addition of a glass or ceramic coating 9 over discs. having a plurality of grooves 18 further increases the breakdown voltage capability of varistor 10.

Landscapes

  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
EP19820100710 1981-02-13 1982-02-02 ZnO-Varistor mit vermindertem Randleckstrom Expired EP0058336B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US23436981A 1981-02-13 1981-02-13
US234369 1988-08-19

Publications (3)

Publication Number Publication Date
EP0058336A2 true EP0058336A2 (de) 1982-08-25
EP0058336A3 EP0058336A3 (en) 1983-05-11
EP0058336B1 EP0058336B1 (de) 1987-08-19

Family

ID=22881087

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19820100710 Expired EP0058336B1 (de) 1981-02-13 1982-02-02 ZnO-Varistor mit vermindertem Randleckstrom

Country Status (4)

Country Link
EP (1) EP0058336B1 (de)
JP (1) JPS57152106A (de)
DE (2) DE3277042D1 (de)
MX (1) MX157914A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4451815A (en) * 1982-09-27 1984-05-29 General Electric Company Zinc oxide varistor having reduced edge current density
DE3405834A1 (de) * 1984-02-17 1985-08-22 Siemens AG, 1000 Berlin und 8000 München Varistor aus einer scheibe aus durch dotierung halbleitendem zinkoxid-material und verfahren zur herstellung dieses varistors
EP0171642A1 (de) * 1984-07-31 1986-02-19 Siemens Aktiengesellschaft Varistor in Chip-Bauweise zur Verwendung in gedruckten Schaltungen und Verfahren zu seiner Herstellung
GB2321135A (en) * 1997-01-11 1998-07-15 Furse W J & Co Ltd Thermal trip arrangement

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH257857A (de) * 1946-06-20 1948-10-31 Sprecher & Schuh Ag Spannungsabhängiger Widerstand.
DE1414326A1 (de) * 1955-08-25 1968-12-12 Siemens Ag Halbleiteranordnung zur Gleichrichtung und/oder Verstaerkung
GB1204702A (en) * 1966-09-06 1970-09-09 Energy Conversion Devices Inc Improvements in or relating to electrical circuits using symmetrical electric current control devices
DE2738367A1 (de) * 1977-08-25 1979-03-01 Siemens Ag Metalloxidvarisator

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH257857A (de) * 1946-06-20 1948-10-31 Sprecher & Schuh Ag Spannungsabhängiger Widerstand.
DE1414326A1 (de) * 1955-08-25 1968-12-12 Siemens Ag Halbleiteranordnung zur Gleichrichtung und/oder Verstaerkung
GB1204702A (en) * 1966-09-06 1970-09-09 Energy Conversion Devices Inc Improvements in or relating to electrical circuits using symmetrical electric current control devices
DE2738367A1 (de) * 1977-08-25 1979-03-01 Siemens Ag Metalloxidvarisator

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4451815A (en) * 1982-09-27 1984-05-29 General Electric Company Zinc oxide varistor having reduced edge current density
DE3405834A1 (de) * 1984-02-17 1985-08-22 Siemens AG, 1000 Berlin und 8000 München Varistor aus einer scheibe aus durch dotierung halbleitendem zinkoxid-material und verfahren zur herstellung dieses varistors
EP0171642A1 (de) * 1984-07-31 1986-02-19 Siemens Aktiengesellschaft Varistor in Chip-Bauweise zur Verwendung in gedruckten Schaltungen und Verfahren zu seiner Herstellung
GB2321135A (en) * 1997-01-11 1998-07-15 Furse W J & Co Ltd Thermal trip arrangement
GB2321135B (en) * 1997-01-11 2001-06-27 Furse W J & Co Ltd Improvements in or relating to thermal trip arrangements

Also Published As

Publication number Publication date
DE3277042D1 (en) 1987-09-24
DE58336T1 (de) 1983-01-05
JPS57152106A (en) 1982-09-20
EP0058336B1 (de) 1987-08-19
EP0058336A3 (en) 1983-05-11
MX157914A (es) 1988-12-20

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