EP0107762A1 - Ausfallsicherer Überspannungsschutz - Google Patents

Ausfallsicherer Überspannungsschutz Download PDF

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Publication number
EP0107762A1
EP0107762A1 EP83108747A EP83108747A EP0107762A1 EP 0107762 A1 EP0107762 A1 EP 0107762A1 EP 83108747 A EP83108747 A EP 83108747A EP 83108747 A EP83108747 A EP 83108747A EP 0107762 A1 EP0107762 A1 EP 0107762A1
Authority
EP
European Patent Office
Prior art keywords
electrodes
pair
washers
spigot
breakdown voltage
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.)
Withdrawn
Application number
EP83108747A
Other languages
English (en)
French (fr)
Inventor
James Edward Anderson
Michael John Coleman
Frederick Caldwell Livermore
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.)
Nortel Networks Ltd
Original Assignee
Northern Telecom 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 Northern Telecom Ltd filed Critical Northern Telecom Ltd
Publication of EP0107762A1 publication Critical patent/EP0107762A1/de
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T4/00—Overvoltage arresters using spark gaps
    • H01T4/10—Overvoltage arresters using spark gaps having a single gap or a plurality of gaps in parallel
    • H01T4/12—Overvoltage arresters using spark gaps having a single gap or a plurality of gaps in parallel hermetically sealed
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T1/00—Details of spark gaps
    • H01T1/14—Means structurally associated with spark gap for protecting it against overload or for disconnecting it in case of failure

Definitions

  • the invention relates to overvoltage protection devices particularly for use in protecting communications equipment, for example telephone equipment, against hazardous voltages due to lightning or induced power surges in interconnecting cables.
  • a primary protector for example a gas tube or carbon block device, which will operate repeatedly to shunt surge energy away from the equipment.
  • a gas tube may leak and admit air to replace the gas.
  • the breakdown voltage of the gap increases, perhaps to a level too high for the equipment to tolerate.
  • the secondary protection will have a breakdown voltage slightly higher than that of the primary device so it will only operate if the primary protector fails to operate. It is preferable for the secondary protector to operate in air. For telephony and similar equipment, its breakdown voltage will usually need to be about, or less than 1,000 volts. A normal spark gap designed to operate at this voltage in air would have a gap of 0.005 inches or less, which would be difficult to set and maintain. It would also be susceptible to contamination.
  • a voltage sensitive switch which does not employ a spark gap and which will operate at less than 1,000 volts has been disclosed in U.S. patent specification number 3,412,220 issued November 19th, 1968. That switch comprises a piece of aluminum foil having a double layer of oxide formed on one surface. The first oxide layer is porous and the second layer is dense. A conductive film provided over the second layer and electrodes are adhered to the film and foil, respectively, by epoxy resin. The entire switch is then encapsulated in resin.
  • Such a switch is not entirely satisfactory for use as a secondary protector because its operating voltage is too low and the provision of two layers and use of epoxy resins complicates manufacture with consequent increased costs, a serious disadvantage for a device which is to be mass produced.
  • An object of the present invention is to overcome these problems in providing a secondary overvoltage protection device which is cheap and simple to construct yet reliable in operation.
  • an overvoltage protection device for protecting telephone or other communications equipment against lightning or power surges, comprises a pair of electrodes having respective surface portions disposed in abutting relationship. At least one of the electrodes has an oxide layer formed on its surface portion. The oxide layer serves to insulate the electrodes from one another and has a dielectric strength equivalent to a required breakdown voltage for the device. When this breakdown voltage is exceeded, the oxide layer breaks down and permits conduction therethrough between the pair of electrodes.
  • the electrodes of the present device are in contact with each other.
  • a significant advantage of this feature is that ingress of dirt or other contaminants is prevented and the dielectric thickness is determined solely by the oxide thickness, which can be accurately controlled during manufacture.
  • both electrodes Preferably both electrodes have surface oxide layers which between them define the required breakdown voltage. It has been found in practice that, for a required breakdown voltage, two thin films will give a more easily determinable dielectric strength than a single equivalent thick film.
  • a particularly compact and cheap embodiment of the invention comprises a pair of washers, each having an annular surface coated with oxide.
  • the washers may readily be combined with a conventional protector, such as a gas-filled tube device, conveniently by fitting them upon an insulated spigot extending from one electrode of the gas-filled tube.
  • Figure 1 shows an overvoltage protection device comprising two switching means connected in parallel.
  • the primary switching means is a gas-filled tube device of generally known construction and is formed by a pair of coaxial cylindrical metal electrodes 10 and 12 sealed in a ceramic tube 14, which is filled with inert gas at sub-atmospheric pressure.
  • the innermost end faces 16 and 18 of the electrodes 10 and 12, respectively, are spaced apart by a small distance, approximately 0.020 inches, to form a spark gap.
  • the outer end of electrode 10 has a reduced-diameter axial extension forming a spigot 20.
  • the secondary or back-up switching means comprises a pair of metal electrodes in the form of aluminum washers 22 and 24 respectively.
  • Each of the washers 22 and 24 has an annular surface 26 coated with an insulating layer of aluminum oxide.
  • Each layer 26 is formed by anodizing the chemically cleaned surface area of the washer using conventional techniques, for example hard anodizing by immersion in a bath of sulphuric acid electrolyte at low temperature, for a prescribed period of time.
  • Each layer extends across the entire annular surface and at least part of the way across the inner and outer edge surfaces. The enclosed corners are rounded to prevent electric stress concentration.
  • the washers 22 and 24 are arranged with their coated surfaces in contact with each other, but are not bonded, and are supported by the spigot 20.
  • the washers 22 and 24 are a friction fit on the sleeve 28.
  • the innermost washer 22 abuts a flanged end part 30 of the electrode 10, which projects radially across the end of the ceramic tube 14.
  • the outermost washer 24 is retained by an inwardly-turned annular flange 32 of a metal cylindrical collar 34 which surrounds the end part of the ceramic tube 14 around the electrode 10.
  • the combination of gas-filled tube and oxide-coated washers is housed in a metal casing 36 which is closed at one end.
  • the closed end is formed externally as a hexagon and houses a compression spring 38.
  • the spring 38 acts between the interior end at the casing 36 and a fusible disc 40, made for example of bismuth/tin, disposed between the free end of the spring 38 and the opposed outer end face 42 of electrode 12 projecting from the gas-filled tube.
  • a retainer member 44 in the form of a circular base 46 with a plurality of axially-extending spring arms 48 spaced around its periphery, is located with its base 46 between the spring 38 and the disc 40.
  • the spring contact arms 48 extend in the space between the outside of the gas-filled tube and the interior of the casing 36. The arrangement is such that the casing 36 presses the arms into contact with the metal collar 34. Inturned ends 50 of the arms extend beyond the end of the collar and serve to retain the sub-assembly of gas-filled tube and washers
  • the secondary device will only operate a limited number of times, possibly only once if the current is high enough, before "failing" short-circuit. This is quite intentional since its operation only takes place when the gas tube has failed. Once the secondary device has failed, the fact that it has done so can readily be detected and the faulty protection device, including gas tube, can be replaced.
  • the breakdown voltage range of the secondary protection device is arranged to be slightly higher than that of the gas-tube device, but significantly less than the breakdown voltage of the spark gap between surfaces 16 and 18, should the tube 14 become filled with air instead of gas.
  • a typical operating voltage range for the secondary protection device is about 700 to 1,000 volts. This was obtained using two oxide coated layers, each about 0.0005 inches thick. Other breakdown voltages can be predicted by interpolating from the following table of breakdown voltages against thickness for single oxide layers:-
  • Figure 2 is a graph plotting number of samples against breakdown voltage to illustrate this effect.
  • curve A represents single oxide layer devices and curve B represents two separate layer devices, one layer on each electrode.

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  • Emergency Protection Circuit Devices (AREA)
  • Thermistors And Varistors (AREA)
EP83108747A 1982-10-06 1983-09-06 Ausfallsicherer Überspannungsschutz Withdrawn EP0107762A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA412937 1982-10-06
CA412937 1982-10-06

Publications (1)

Publication Number Publication Date
EP0107762A1 true EP0107762A1 (de) 1984-05-09

Family

ID=4123730

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83108747A Withdrawn EP0107762A1 (de) 1982-10-06 1983-09-06 Ausfallsicherer Überspannungsschutz

Country Status (2)

Country Link
EP (1) EP0107762A1 (de)
JP (1) JPS5999928A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2237149A (en) * 1989-10-17 1991-04-24 Semitron Cricklade Ltd Air gap arrangement
DE4331215B4 (de) * 1992-09-28 2005-02-10 Epcos Ag Baugruppe zur Ableitung elektrischer Überspannungen

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2443442A (en) * 1947-02-25 1948-06-15 Gen Electric Lamp cutout
US3386007A (en) * 1965-07-22 1968-05-28 Sprague Electric Co Multi-shot voltage sensitive switch for protecting components or circuits subject tovariable voltage conditions
US3412220A (en) * 1963-11-26 1968-11-19 Sprague Electric Co Voltage sensitive switch and method of making
US3898533A (en) * 1974-03-11 1975-08-05 Bell Telephone Labor Inc Fail-safe surge protective device
EP0017337A1 (de) * 1979-03-22 1980-10-15 Reliance Electric Company Leitungsschutz für eine Nachrichtenverbindung
DE2951467A1 (de) * 1979-12-20 1981-07-02 Siemens AG, 1000 Berlin und 8000 München Ueberspannungsableiter mit parallelgeschalteter luftfunkenstrecke

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2443442A (en) * 1947-02-25 1948-06-15 Gen Electric Lamp cutout
US3412220A (en) * 1963-11-26 1968-11-19 Sprague Electric Co Voltage sensitive switch and method of making
US3386007A (en) * 1965-07-22 1968-05-28 Sprague Electric Co Multi-shot voltage sensitive switch for protecting components or circuits subject tovariable voltage conditions
US3898533A (en) * 1974-03-11 1975-08-05 Bell Telephone Labor Inc Fail-safe surge protective device
EP0017337A1 (de) * 1979-03-22 1980-10-15 Reliance Electric Company Leitungsschutz für eine Nachrichtenverbindung
DE2951467A1 (de) * 1979-12-20 1981-07-02 Siemens AG, 1000 Berlin und 8000 München Ueberspannungsableiter mit parallelgeschalteter luftfunkenstrecke

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2237149A (en) * 1989-10-17 1991-04-24 Semitron Cricklade Ltd Air gap arrangement
DE4331215B4 (de) * 1992-09-28 2005-02-10 Epcos Ag Baugruppe zur Ableitung elektrischer Überspannungen

Also Published As

Publication number Publication date
JPS5999928A (ja) 1984-06-08

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Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Designated state(s): AT DE FR GB SE

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19841110

RIN1 Information on inventor provided before grant (corrected)

Inventor name: LIVERMORE, FREDERICK CALDWELL

Inventor name: COLEMAN, MICHAEL JOHN

Inventor name: ANDERSON, JAMES EDWARD