EP0242688B1 - Surge arrester - Google Patents

Surge arrester Download PDF

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Publication number
EP0242688B1
EP0242688B1 EP87105067A EP87105067A EP0242688B1 EP 0242688 B1 EP0242688 B1 EP 0242688B1 EP 87105067 A EP87105067 A EP 87105067A EP 87105067 A EP87105067 A EP 87105067A EP 0242688 B1 EP0242688 B1 EP 0242688B1
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EP
European Patent Office
Prior art keywords
electrode
electrodes
gap
cylindrical
pot
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EP87105067A
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German (de)
French (fr)
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EP0242688A1 (en
Inventor
Jürgen Dipl.-Ing. Boy
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Siemens AG
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Siemens AG
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    • 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
    • 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
    • H01T1/24—Selection of materials for electrodes
    • 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
    • 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

Definitions

  • the present invention relates to a surge conductor according to the preamble of patent claim 1.
  • the invention is in the field of electrical components and is applicable to the structural design of a surge arrester which has a cup-shaped first electrode and a cylindrical second electrode protruding into this first electrode, at least one of the two electrodes being in the region of the discharge gap an activator mass is coated.
  • the invention has for its object to design the arrester so that it has a high glow voltage and a low spread of both the glow voltage and the ignition voltage.
  • the activator coating consists of a melted silver layer or of a melted layer of at least two metal components, of which the first component is aluminum in a proportion of approximately 10 to 40% by weight and the second component consists of a metal that forms a eutectic with the aluminum with a melting point below the soldering temperature of the brazed connection between the electrodes and the ceramic housing; it is further provided that at least one ignition line is connected to the cylindrical electrode, which ends with the leaving of a residual insulation gap in the rear space of the pot-shaped electrode.
  • an activator mass is used which is load-stable but tends to atomize.
  • this atomization is controlled by the fact that a sufficiently large receiving space is available for the metal vapor and that a high degree of metal vapor condensation is made possible at non-critical points, in particular on the cylindrical electrode.
  • the critical isolator sections, in the area of which the one or more ignition lines end, are therefore hardly vaporized.
  • the materials silver, copper, silicon, tin and chromium are particularly suitable as the second component of an activation compound with aluminum as the first component.
  • a silver layer can also be used. It can be applied in powder form or by means of known coating processes (for example galvanically).
  • the metals added to the aluminum as a second component in an aluminum-based activator compound prevent roughening of the electrode surface; Such a roughening in the form of beads would occur when the electrodes were soldered in or when the arrester was operated if aluminum was used as the activator mass without these additives. Such roughening would change the characteristic values and could lead to a short circuit.
  • the aluminum portion of the activator mass advantageously acts simultaneously as a getter.
  • each electrode is provided in one piece with a soldering flange, then a great depth of the low-vaporization rear space of the pot-shaped electrode can be easily achieved with a given length of the arrester and thus also ensures a reliable effectiveness of the ignition line.
  • a particularly powerful and space-saving embodiment is characterized by the features that the electrodes consist essentially of copper, that at least the second electrode is soldered onto the ceramic housing with an eutectic AgCu solder, and that an Ag-containing metal layer is applied to both electrodes in the region of the discharge gap is applied as an activator layer that the condensation gap has at least approximately the same width as the discharge gap, that the low-vaporization rear space is approximately 1.5 times as wide as the discharge gap, that the length of the condensation gap and the gap-shaped low-vaporization rear space is at least five times the corresponding gap width is that the circumferential edges of the end face of the cylinder wall to any part of the cylindrical contact is at least about 1.5 times the width of the discharge gap.
  • the dimensioning mentioned does not result in any discharges outside the discharge gap and a very space-saving surge arrester.
  • the shortest path from the ignition line along the ceramic housing to the first electrode is at least as long as the smallest mutual distance between the two electrodes in the region of the discharge gap.
  • a simple to implement embodiment with little variation in the electrical characteristics contains the features that the inside diameter of the insulating material housing is larger by approx. 1 mm than the outside diameter of the pot-shaped electrode and that the inside diameter of the ceramic housing and the outside diameter of the pot-shaped electrode do not differ from their respective nominal values deviate more than ⁇ 0.1 mm.
  • a surge arrester according to the invention is advantageously filled with a gas mixture of argon and hydrogen, the hydrogen content being between 5% and 20%.
  • the first electrode 1 a cylindrical ceramic housing 3 and a second electrode 2 are hard-soldered to one another on the soldering surfaces 4 in a vacuum-tight manner.
  • the first electrode 1 F 1 is pot-shaped and has a blind bore 12, which is composed of the cylindrical inner wall 19 and the bottom 13.
  • the second electrode 2 is cylindrical and has an end face 14 and a lateral surface 18.
  • the gap 5 lies between the end face 14 and the bottom 13.
  • the two electrodes 1 and 2 are preferably made of copper; but they can e.g. also consist of an alloy of the metals Fe, Ni, Co.
  • the end face 11 of the cylinder wall 15 is rounded or chamfered.
  • the distance from the end face 11 to any parts of the second electrode 2 is at least about 1.5 times the width of the smaller of the gaps 5 or 6.
  • the low-vaporization rear space 7 lies between the cylinder wall 15 and the ceramic housing 3. Its length is approximately five times its width. At least one ignition line 10 is connected to the electrode 2 in an electrically conductive manner and extends into the low-vapor deposition space 7. Its end point is at least approximately the same distance from the first electrode 1 along the inner wall 16 of the ceramic housing 3 as the two electrodes 1 and 2 from one another in the columns 5 or 6.
  • the one or more ignition lines 10 are preferably designed as graphite lines.
  • An activator layer 8, 9, 21, 22 is applied to the boundary surfaces of columns 5 and 6. As a result, the discharge is held in the area of this activator layer, and the surge arrester can be reduced both in diameter and in axial extent, without discharges occurring at undesired points, which could reduce the lifespan of the surge arrester.
  • the surge arrester can tolerate a very high surge current load.
  • FIG. 2 A particularly simple to produce embodiment is shown in Fig. 2, in which the end face 24 and the bottom 23 are each approximately conical and the angle of the cone shell to its axis of rotation corresponds to the angle of the cutting edge of a twist drill to its axis of rotation.
  • the activator layers 29 and 30 are provided on the end face 24 and the bottom 23.
  • the gap 5 is narrower than the gap 6, the dimensions of the surge arrester in the axial direction can be kept relatively small.
  • Fig. 3 shows an embodiment with a particularly long life.
  • activator layers 8 and 9 are applied in the area of the gap 5, while there are no activator layers in the area of the gap 6.
  • the gap 6 essentially acts as an additional condensation gap; the metal vapors that are produced do not for the most part reach the insulating material housing.
  • the gap 6 is narrower than the gap 5.
  • the second contact 2 in the vicinity of the end faces 11 has a region 28 with a reduced diameter, so that the distance between the end face 11 and the second contact 2 also meets the insulation requirements in this embodiment.
  • the end faces 14 and the bottom 13 in this case have the shape of truncated cones which are delimited on the side with a smaller cross section by circular surfaces 25 and 26, respectively.
  • the circular surfaces 25 and 26 have different diameters, so that their edges 27 and 31 are offset from one another in the radial direction.
  • the circular area 25 is smaller than the circular area 26. This prevents a current concentration along the edge 27.
  • the gap 6 is narrower than the gap 5, so that the diameter of the surge arrester can be kept relatively small and the metal evaporating in the gap 5 is quickly deposited in the relatively narrow gap 6.
  • the area 17 on the ceramic insulator vapor-coated with metal is thereby kept particularly small. This embodiment thus ensures a particularly long service life of the surge arrester.

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

Abstract

An overvoltage arrester for handling high surge currents including a pair of electrodes one of which includes a blind bore into which the second electrode projects, thereby providing at least one discharge gap between the two electrodes. The arrester of the present invention has a long useful life and a high surge current carrying capability.

Description

Die vorliegende Erfindung betrifft einen Überspannungsleiter nach dem Oberbegriff des Patentanspruchs 1.The present invention relates to a surge conductor according to the preamble of patent claim 1.

Die Erfindung liegt auf dem Gebiet der elektrischen Bauelemente und ist bei der konstsruktiven Ausgestaltung eines Überspannungsableiters anzuwenden, der eine topfartig ausgebildete erste Elektrode und eine in diese erste Elektrode hineinragende, zylindrisch ausgebildete zweite Elektrode aufweist, wobei wenigstens eine der beiden Elektroden im Bereich des Entladungsspaltes mit einer Aktivatormasse beschichtet ist.The invention is in the field of electrical components and is applicable to the structural design of a surge arrester which has a cup-shaped first electrode and a cylindrical second electrode protruding into this first electrode, at least one of the two electrodes being in the region of the discharge gap an activator mass is coated.

Bei einem bekannten Oberspannungsableiter dieser Art können die beiden Elektroden mittels spezieller Halterungen mit den beiden Stirnflächen eines zylindrischen Keramikgehäuses vakuumdicht hartverlötet sein. Der Entladungsspalt wird dabei von einem ebenen Spalt zwischen dem Boden der topfartigen Elektrode und der Stirnfläche der zylindrischen Elektrode sowie einem ringförmigen Spalt zwischen der Innenwand der topfartigen Elektrode und der Mantelfläche der zylindrischen Elektrode gebildet. Er kann auch nur von einem dieser beiden Spalte gebildet werden. Zur Herabsetzung der Ausstrittsarbeit nach dem Zünden des Ableiters sind die Stimfläche der zylindrischen Elektrode und der Boden der topfförmigen Elektrode mit einer geeigneten Masse beschichtet. (DE-A 1 944 564, Fig. 2).

  • - Als Aktivierungsmasse ist im übrigen eine Paste bekannt, die als pulverförmige metallische Komponente ein Alkalimetall, eine Barium-Aluminium-Legierung und zusätzlich metallisches Wolfram und/oder Molybdän enthält. Diese Masse wird durch einen Tempervorgang auf den Elektroden eines Ableiters fixiert. Derartig ausgebildete Ableiter können zusätzlich mit Zündstrichen auf der Innenseite des Isolators versehen sein (EP-A 0 138 082).
  • - Zündstriche gehen bei Ableitem mit sich axial gegenüberstehenden Elektroden in aller Regel alternierend von der einen und der anderen Elektrode aus und enden etwa auf der Höhe des Zündspaltes (US-A 4 491 893).
In a known surge arrester of this type, the two electrodes can be brazed in a vacuum-tight manner to the two end faces of a cylindrical ceramic housing by means of special holders. The discharge gap is formed by a flat gap between the bottom of the pot-like electrode and the end face of the cylindrical electrode and an annular gap between the inner wall of the pot-like electrode and the outer surface of the cylindrical electrode. It can also consist of only one of these two columns. To reduce the work function after igniting the arrester, the end face of the cylindrical electrode and the bottom of the cup-shaped electrode are coated with a suitable compound. (DE-A 1 944 564, Fig. 2).
  • - As an activation compound, a paste is known which contains an alkali metal, a barium-aluminum alloy and additionally metallic tungsten and / or molybdenum as the powdery metallic component. This mass is fixed on the electrodes of an arrester by a tempering process. Arresters designed in this way can additionally be provided with ignition lines on the inside of the insulator (EP-A 0 138 082).
  • - Detection lines in the case of leads with axially opposing electrodes generally alternate from one and the other electrode and end approximately at the height of the ignition gap (US Pat. No. 4,491,893).

Ausgehend von einem Überspannungsableiter mit den Merkmalen des Oberbegriffes des Patentanspruches 1 liegt der Erfindung die Aufgabe zugrunde, den Ableiter so auszugestalten, daß er eine hohe Glimmbrennspannung und eine geringe Streuung sowohl der Glimmbrennspannung als auch der Zündspannung aufweist.Starting from a surge arrester with the features of the preamble of claim 1, the invention has for its object to design the arrester so that it has a high glow voltage and a low spread of both the glow voltage and the ignition voltage.

Zur Lösung dieser Aufgabe ist gemäß der Erfindung vorgesehen, daß die Aktivatorbeschichtung aus einer aufgeschmolzenen Silberschicht oder aus einer aufgeschmolzenen Schicht aus wenigstens zwei metallenen Komponenten besteht, von die erste Komponente Aluminium mit einem Anteil von etwa 10 bis 40 Gew.-% und die zweite Komponente aus einem Metall besteht, das mit dem Aluminium ein Eutektikum mit einem Schmelzpunkt unterhalb der Löttemperatur der Hartlötverbindung zwischen den Elektroden und dem Keramikgehäuse bildet; weiterhin ist vorgesehen, daß nur mit der zylindrischen Elektrode wenigstens ein Zündstrich verbunden ist, der unter Freilassung einer Restisolationsstrecke im Hinterraum der topfartig ausgebildeten Elektrode endet.To achieve this object, it is provided according to the invention that the activator coating consists of a melted silver layer or of a melted layer of at least two metal components, of which the first component is aluminum in a proportion of approximately 10 to 40% by weight and the second component consists of a metal that forms a eutectic with the aluminum with a melting point below the soldering temperature of the brazed connection between the electrodes and the ceramic housing; it is further provided that at least one ignition line is connected to the cylindrical electrode, which ends with the leaving of a residual insulation gap in the rear space of the pot-shaped electrode.

Bei einem derart ausgebildeten Überspannungsableiter wird eine Aktivatormasse verwendet, die belastungsstabil ist, aber zur Zerstäubung neigt. Diese Zerstäubung wird jedoch dadurch beherrscht, daß ein ausreichend großer Aufnahmeraum für den Metalldampf zur Verfügung steht und an unkritischen Stellen, insbesondere an der zylindrischen Elektrode, ein hohes Maß an Metalldampfkondensation ermöglicht ist. Die kritischen Isolatorstrecken, in deren Bereich auch der bzw. die einseitig angeordneten Zündstriche enden, werden daher kaum bedampft.In the case of a surge arrester designed in this way, an activator mass is used which is load-stable but tends to atomize. However, this atomization is controlled by the fact that a sufficiently large receiving space is available for the metal vapor and that a high degree of metal vapor condensation is made possible at non-critical points, in particular on the cylindrical electrode. The critical isolator sections, in the area of which the one or more ignition lines end, are therefore hardly vaporized.

Als zweite Komponente einer Aktivierungsmasse mit Aluminium als erster Komponente eignen sich insbesondere die Stoffe Silber, Kupfer, Silizium, Zinn und Chrom. Alternativ kann auch eine Silberschicht verwendet werden. Sie kann in Pulverform oder mittels bekannter Beschichtungsverfahren (beispielsweise galvanisch) aufgebracht sein.The materials silver, copper, silicon, tin and chromium are particularly suitable as the second component of an activation compound with aluminum as the first component. Alternatively, a silver layer can also be used. It can be applied in powder form or by means of known coating processes (for example galvanically).

Die bei einer Aktivatormasse auf Aluminiumbasis dem Aluminium als zweite Komponente zugesetzten Metalle verhindern eine Aufrauung der Elektrodenoberfläche; eine solche Aufrauung in Form von Kügelchen würde beim Einlöten der Elektroden oder beim Betrieb des Ableiters entstehen, wenn man Aluminium ohne diese Zusätze als Aktivatormasse einsetzt. Eine solche Aufrauung würde die Kennwerte verändern und könnte zum Kurzschluß führen. - Der Aluminiumanteil der Aktivatormasse wirkt vorteilhaft gleichzeitig als Getter.The metals added to the aluminum as a second component in an aluminum-based activator compound prevent roughening of the electrode surface; Such a roughening in the form of beads would occur when the electrodes were soldered in or when the arrester was operated if aluminum was used as the activator mass without these additives. Such roughening would change the characteristic values and could lead to a short circuit. - The aluminum portion of the activator mass advantageously acts simultaneously as a getter.

Wenn man im übrigen jede Elektrode einstückig mit einem Lötflansch versieht, dann ist auf einfache Weise bei vorgegebener Länge des Ableiters eine große Tiefe des bedampfungsarmen Hinterraumes der topfförmigen Elektrode erreichbar und damit auch eine sichere Wirksamkeit des Zündstriches gewährleistet.If, moreover, each electrode is provided in one piece with a soldering flange, then a great depth of the low-vaporization rear space of the pot-shaped electrode can be easily achieved with a given length of the arrester and thus also ensures a reliable effectiveness of the ignition line.

Eine besonders leistungsstarke und dabei raumsparende Ausführungsform ist durch die Merkmale gekennzeichnet, daß die Elektroden im wesentlich aus Kupfer bestehen, daß zumindest die zweite Elektrode mit einem eutektischen AgCu-Lot auf das Keramikgehäuse aufgelötet ist, daß im Bereich des Entladungsspaltes auf beide Elektroden eine Aghaltige Metallschicht als Aktivatorschicht aufgebracht ist, dass der Kondensationsspalt eine zumindest etwa gleiche Breite wie der Entladungsspalt aufweist, daß der bedampfungsarme Hinterraum etwa 1,5 mal so breit ist wie der Entladungsspalt, daß die Länge des Kondensationsspaltes und des spaltförmigen bedampfungsarmen Hinterraumes mindestens das Fünffache der entsprechenden Spaltbreite beträgt, daß die umlaufenden Kanten der Stirnfläche der Zylinderwand zu beleibigen Teilen des zylindrischen Kontaktes mindestens etwa das 1,5-fache der Breite des Entladungsspaltes beträgt. Die genannte Bemessung ergibt im Zusammenhang mit der genannten Aktivatormasse und dem genanntem Lot keine Entladungen außerhalb des Entladungsspaltes und einen sehr platzsparenden Überspannungsableiter. Dabei sind Zündstriche aus Graphit für eine gleichmäßige Zündspannung vorteilhaft.A particularly powerful and space-saving embodiment is characterized by the features that the electrodes consist essentially of copper, that at least the second electrode is soldered onto the ceramic housing with an eutectic AgCu solder, and that an Ag-containing metal layer is applied to both electrodes in the region of the discharge gap is applied as an activator layer that the condensation gap has at least approximately the same width as the discharge gap, that the low-vaporization rear space is approximately 1.5 times as wide as the discharge gap, that the length of the condensation gap and the gap-shaped low-vaporization rear space is at least five times the corresponding gap width is that the circumferential edges of the end face of the cylinder wall to any part of the cylindrical contact is at least about 1.5 times the width of the discharge gap. In connection with the activator mass and the solder mentioned, the dimensioning mentioned does not result in any discharges outside the discharge gap and a very space-saving surge arrester. There are dashes made of graphite advantageous for a uniform ignition voltage.

Für die Einhaltung der dynamischen Zündspannung reicht es aus, wenn der kürzeste Weg von dem Zündstrich entlang dem Keramikgehäuse zur ersten Elektrode (die Restisolationsstrecke) zumindest ebenso groß ist wie der kleinste gegenseitige Abstand der beiden Elektroden im Bereich des Entladungsspaltes.To maintain the dynamic ignition voltage, it is sufficient if the shortest path from the ignition line along the ceramic housing to the first electrode (the residual insulation section) is at least as long as the smallest mutual distance between the two electrodes in the region of the discharge gap.

Ein einfach realisierbare Ausführungsform mit geringer Exemplarstreuung der elektrischen Kennwerte enthält die Merkmale, daß der Innendurchmesser des Isolierstoffgehäuses um ca. 1 mm größer ist als der Außendurchmesser der topfförmigen Elektrode und daß der Innendurchmesser des Keramikgehäuses und der Außendurchmesser der topfförmigen Elektrode von ihrem jeweiligen Nennwert um nicht mehr als ± 0,1 mm abweichen.A simple to implement embodiment with little variation in the electrical characteristics contains the features that the inside diameter of the insulating material housing is larger by approx. 1 mm than the outside diameter of the pot-shaped electrode and that the inside diameter of the ceramic housing and the outside diameter of the pot-shaped electrode do not differ from their respective nominal values deviate more than ± 0.1 mm.

Ein erfindungsgemäßer Überspannungsableiter ist vorteilhaft mit einem Gasgemisch aus Argon und Wasserstoff gefüllt, wobei der Wasserstoffanteil zwischen 5% und 20% liegt.A surge arrester according to the invention is advantageously filled with a gas mixture of argon and hydrogen, the hydrogen content being between 5% and 20%.

Drei Ausführungsbeispiele des neuen Überspannungsableiters sind in den Figuren 1 bis 3 im Schnitt dargestellt. Dabei zeigt

  • Figur 1 einen Ableiter mit ebenem Boden und ebener Stirnfläche der beiden Elektroden,
  • Figur 2 einen Ableiter mit kegelförmiger Ausgestaltung von Boden und Stirnfläche der beiden Elektroden und
  • Figur 3 einen Ableiter mit kegelstumpfförmiger Ausgestaltung von Boden und Stirnfläche der beiden Elektroden.
Three exemplary embodiments of the new surge arrester are shown in section in FIGS. 1 to 3. It shows
  • FIG. 1 shows an arrester with a flat bottom and a flat end face of the two electrodes,
  • Figure 2 shows an arrester with a conical design of the bottom and end face of the two electrodes and
  • Figure 3 shows an arrester with a frustoconical configuration of the bottom and end face of the two electrodes.

Gemäß erste Elektrode 1, ein zylinderförmiges Keramikgehäuse 3 und eine zweite Elektrode 2 miteinander an den Lötflächen 4 vakummdicht hartverlötet. Die erste Elektrode 1 F1 ist topfförmig ausgebildet und weist eine Sackbohrung 12 auf, die sich aus der zylindrischen Innenwand 19 und dem Boden 13 zusammensetzt. Die zweite Elektrode 2 ist zylindrisch ausgebildet und weist eine Stirnfläche 14 und eine Mantelfläche 18 auf.According to the first electrode 1, a cylindrical ceramic housing 3 and a second electrode 2 are hard-soldered to one another on the soldering surfaces 4 in a vacuum-tight manner. The first electrode 1 F 1 is pot-shaped and has a blind bore 12, which is composed of the cylindrical inner wall 19 and the bottom 13. The second electrode 2 is cylindrical and has an end face 14 and a lateral surface 18.

Zwischen der Stirnfläche 14 und dem Boden 13 liegt der Spalt 5. An diesem Spalt 5 schließt sich zwischen der Innenwand 19 der ersten Elektroden 1 und der Mantelfläche 18 der zweiten Elektrode 2 ein Spalt 6 an, der zumindest dieselbe Breite aufweist wie der Spalt 5. Die beiden Elektroden 1 und 2 sind vorzugsweise aus Kupfer; sie können aber z.B. auch aus einer Legierung der Metalle Fe, Ni, Co, bestehen.The gap 5 lies between the end face 14 and the bottom 13. A gap 6, which has at least the same width as the gap 5, adjoins this gap 5 between the inner wall 19 of the first electrodes 1 and the lateral surface 18 of the second electrode 2. The two electrodes 1 and 2 are preferably made of copper; but they can e.g. also consist of an alloy of the metals Fe, Ni, Co.

Die Stirnfläche 11 der Zylinderwand 15 ist abgerundet oder angefast. Der Abstand von der Stirnfläche 11 zu beliebigen Teilen der zweiten Elektrode 2 beträgt zumindest etwa das 1,5-fache der Breite des kleineren der Spalte 5 oder 6.The end face 11 of the cylinder wall 15 is rounded or chamfered. The distance from the end face 11 to any parts of the second electrode 2 is at least about 1.5 times the width of the smaller of the gaps 5 or 6.

Zwischen der Zylinderwand 15 und dem Keramikgehäuse 3 liegt der bedampfungsarme Hinterraum 7. Seine Länge beträgt etwa das Fünffache seiner Breite. Mindestens ein Zündstrich 10 ist mit der Elektrode 2 elektrisch leitend verbunden und reicht in den bedampfungsarmen Hinterraum 7 hinein. Sein Endpunkt besitzt zur ersten Elektrode 1 entlang der Innenwand 16 des Keramikgehäuses 3 zumindest etwa denselben Abstand, wie die beiden Elektroden 1 und 2 voneinander in den Spalten 5 oder 6. Der oder die Zündstriche 10 sind vorzugsweise als Graphitstriche ausgebildet.The low-vaporization rear space 7 lies between the cylinder wall 15 and the ceramic housing 3. Its length is approximately five times its width. At least one ignition line 10 is connected to the electrode 2 in an electrically conductive manner and extends into the low-vapor deposition space 7. Its end point is at least approximately the same distance from the first electrode 1 along the inner wall 16 of the ceramic housing 3 as the two electrodes 1 and 2 from one another in the columns 5 or 6. The one or more ignition lines 10 are preferably designed as graphite lines.

Auf die Begrenzungsflächen der Spalte 5 und 6 ist eine Aktivatorschicht 8, 9, 21, 22 aufgebracht ist. Dadurch wird die Entladung im Bereich dieser Aktivatorschicht gehalten, der Überspannungsableiter kann sowohl im Durchmesser als auch in der axialen Ausdehnung verkleinert werden, ohne daß Entladungen an unverwünschten Stellen auftreten, welche die Lebensdauer des Überspannungsableiters herabsetzen könnten.An activator layer 8, 9, 21, 22 is applied to the boundary surfaces of columns 5 and 6. As a result, the discharge is held in the area of this activator layer, and the surge arrester can be reduced both in diameter and in axial extent, without discharges occurring at undesired points, which could reduce the lifespan of the surge arrester.

Da die Spalte 5 und 6 vollständig als Entladungsspalte ausgenutzt sind, kann der Überspannungsableiter eine sehr hohe Stoßstrombelastung vertragen.Since columns 5 and 6 are fully used as discharge columns, the surge arrester can tolerate a very high surge current load.

Eine besonders einfach herzustellende Ausführungsform ist in Fig. 2 dargestellt, bei der die Stirnfläche 24 und der Boden 23 jeweils annähernd kegelförmig ausgebildet sind und der Winkel des Kegelmantels zu seiner Rotationsachse dem Winkel der Schneide eines Spiralbohrers zu dessen Rotationsachse entspricht. In diesem Beispiel sind nur die Aktivatorschichten 29 und 30 auf der Stirnfläche 24 und dem Boden 23 vorgesehen. Der Spalt 5 ist schmaler als der Spalt 6, die Abmessungen des Überspannungsableiters in axialer Richtung kann relativ klein gehalten werden.A particularly simple to produce embodiment is shown in Fig. 2, in which the end face 24 and the bottom 23 are each approximately conical and the angle of the cone shell to its axis of rotation corresponds to the angle of the cutting edge of a twist drill to its axis of rotation. In this example, only the activator layers 29 and 30 are provided on the end face 24 and the bottom 23. The gap 5 is narrower than the gap 6, the dimensions of the surge arrester in the axial direction can be kept relatively small.

Fig. 3 zeigt eine Ausführungsform mit einer besonders langen Lebensdauer. Auch hier sind Aktivatorschichten 8 und 9 im Bereich des Spaltes 5 angebracht, während im Bereich des Spaltes 6 keine Aktivatorschichten vorhanden sind. Dadurch wirkt der Spalt 6 im wesentlichen als zusätzlicher Kondensationsspalt, die entstehenden Metalldämpfe gelangen zum größten Teil nicht an das Isolierstoffgehäuse. Der Spalt 6 ist schmaler als der Spalt 5. Um garantiert Fehlzündungen im Bereich der Stirnflächen 11 zu vermeiden, weist der zweite Kontakt 2 in der Nachbarschaft der Stirnflächen 11 einen Bereich 28 mit verringertem Durchmesser auf, so daß der Abstand zwischen der Stirnfläche 11 und dem zweiten Kontakt 2 auch bei dieser Ausführungsform den Isolationsanforderungen genügt.Fig. 3 shows an embodiment with a particularly long life. Here, too, activator layers 8 and 9 are applied in the area of the gap 5, while there are no activator layers in the area of the gap 6. As a result, the gap 6 essentially acts as an additional condensation gap; the metal vapors that are produced do not for the most part reach the insulating material housing. The gap 6 is narrower than the gap 5. In order to reliably avoid misfires in the region of the end faces 11, the second contact 2 in the vicinity of the end faces 11 has a region 28 with a reduced diameter, so that the distance between the end face 11 and the second contact 2 also meets the insulation requirements in this embodiment.

Die Stirnflächen 14 und der Boden 13 weisen in diesem Fall die Form von Kegelstümpfen auf, die auf der Seite mit kleinerem Querschnitt durch Kreisflächen 25 bzw. 26 begrenzt sind. Die Kreisflächen 25 und 26 weisen unterschiedliche Durchmesser auf, so daß ihre Kanten 27 und 31 in radialer Richtung gegeneinander versetzt liegen. Die Kreisfläche 25 ist dabei kleiner als die Kreisfläche 26. Dadurch wird eine Stromkonzentration entlang der Kante 27 vermieden. In dieser Ausführungsform ist der Spalt 6 schmaler als der Spalt 5, so daß der Durchmesser des Überspannungsableiters relativ klein gehalten werden kann und im relativ engen Spalt 6 das im Spalt 5 abdampfende Metall sich schnell niederschlägt. Der mit Metall bedampfte Bereich 17 auf dem Keramikisolator wird dadurch besonders klein gehalten. Diese Ausführungsform gewährleistet also eine besonders lange Lebensdauer des Überspannungsableiters.The end faces 14 and the bottom 13 in this case have the shape of truncated cones which are delimited on the side with a smaller cross section by circular surfaces 25 and 26, respectively. The circular surfaces 25 and 26 have different diameters, so that their edges 27 and 31 are offset from one another in the radial direction. The circular area 25 is smaller than the circular area 26. This prevents a current concentration along the edge 27. In this embodiment, the gap 6 is narrower than the gap 5, so that the diameter of the surge arrester can be kept relatively small and the metal evaporating in the gap 5 is quickly deposited in the relatively narrow gap 6. The area 17 on the ceramic insulator vapor-coated with metal is thereby kept particularly small. This embodiment thus ensures a particularly long service life of the surge arrester.

Claims (4)

1. Surge arrester comprising a cylindrical ceramic casing and two electrodes which are hard-soldered in vacuum-tight manner to the two end faces of the ceramic casing, wherein one electrode is pot- shaped and is disposed in radial spaced relationship to the ceramic casing and the other electrode consists of a cylindrical body, while the electrode of cylindrical from extends into the potshaped electrode in such manner that the gap between the base of the pot-shaped electrode and the face of the cylindrical electrode or the gap between the inside wall of the pot-shaped electrode and the bounding surface of the cylindrical electrode or both gaps together form the discharge gap, and wherein at least one of the two electrodes is coated with an activator mass in the discharge region, characterised in that the activator coating (8, 9) consists of a fused-on silver layer or of a fused-on layer comprising at least two metallic components, of which the first component is aluminium in a proportion of about 10% to 40% by weight and the second component consists of a metal which forms with the aluminium a eutectic having a melting point below the temperature employed in making the hard-soldered joint between the electrodes (1, 2) and the ceramic casing (3), and in that there is connected only to the cylindrical electrode (2) at least one firing strip (10) which terminates in the rear chamber (7) of the pot-shaped electrode (1) so as to leave free a residual insulation path(16).
2. Surge arrester according to claim 1, characterised in that the second component of the activator coating (8, 9) consists of one of the substances Ag, Cu, Si, Sn and Cr.
3. Surge arrester according to claim 1 or 2, characterised in that the shortest path from the firing strip (10) along the ceramic housing (3) to the pot- shaped electrode (1) is at least equal to the minimum distance between the two electrodes (1, 2) in the region of the discharge gap (5, 6).
4. Surge arrester according to one of claims 1 to 3, characterised in that each electrode (1, 2) is formed in one piece with a soldering flange.
EP87105067A 1986-04-22 1987-04-06 Surge arrester Expired - Lifetime EP0242688B1 (en)

Applications Claiming Priority (2)

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DE3613599 1986-04-22
DE3613599 1986-04-22

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EP0242688B1 true EP0242688B1 (en) 1990-07-18

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JP (1) JPS62256394A (en)
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Also Published As

Publication number Publication date
US4739439A (en) 1988-04-19
DE3763733D1 (en) 1990-08-23
JPS62256394A (en) 1987-11-09
EP0242688A1 (en) 1987-10-28
KR870010658A (en) 1987-11-30
KR950009084B1 (en) 1995-08-14

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