EP0147607B1 - Zinc oxide varistor - Google Patents

Zinc oxide varistor Download PDF

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Publication number
EP0147607B1
EP0147607B1 EP84113877A EP84113877A EP0147607B1 EP 0147607 B1 EP0147607 B1 EP 0147607B1 EP 84113877 A EP84113877 A EP 84113877A EP 84113877 A EP84113877 A EP 84113877A EP 0147607 B1 EP0147607 B1 EP 0147607B1
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EP
European Patent Office
Prior art keywords
oxide
oxygen
zinc oxide
barrier layer
materials
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Expired
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EP84113877A
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German (de)
French (fr)
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EP0147607A1 (en
Inventor
Elias Dr. Jülke
Tony Dr. Kaiser
Maged A. Dr. Osman
Roger S. Dr. Perkins
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BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]
    • Y10T428/31551—Of polyamidoester [polyurethane, polyisocyanate, polycarbamate, etc.]
    • Y10T428/31609—Particulate metal or metal compound-containing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]
    • Y10T428/31652—Of asbestos
    • Y10T428/31663—As siloxane, silicone or silane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31504—Composite [nonstructural laminate]
    • Y10T428/31786—Of polyester [e.g., alkyd, etc.]

Definitions

  • the invention relates to a zinc oxide varistor according to the preamble of claim 1.
  • JP-PS 957 072 the degradation of zinc oxide varistors in SF 6 can be considerably slowed down by adding 10-30% oxygen. Apart from the fact that it cannot be used when the varistors are surrounded by a liquid or solid medium, this method has the disadvantage that it requires a gas-tight partitioning of the space containing the varistors from other system parts and complicates maintenance. There is also a reduction in dielectric strength.
  • the object of the invention is to improve a generic zinc oxide varistor with respect to the oxygen impermeability of the coating covering the peripheral lateral surface.
  • the at least one oxygen barrier layer contained in the coating of a zinc oxide varistor according to the invention prevents oxygen from diffusing out of the peripheral layer of the varistor part because of the substantially oxygen-impermeable inorganic filler which drastically lengthens the diffusion paths or even gives off oxygen counteracts more than the coating of known generic zinc oxide varistors.
  • the coating of a zinc oxide varistor according to the invention is hardly more difficult to produce.
  • the organic matrix material which determines the mechanical, thermodynamic and chemical properties of said oxygen barrier layer can also be significantly determined , optimized with regard to heat resistance, elasticity, thermal expansion coefficients, corrosion resistance, mechanical strength etc. and in particular also to the conditions of use such as the surrounding medium can be adapted to given special requirements essentially without regard to its oxygen permeability.
  • FIGS. 1-4 show zinc oxide varistors, which in their basic structure each contain a cylindrical active part 1 made of a sintered mass, which consists of metal oxides with a predominant proportion of zinc oxide, and on the base and top surface of the active part 1, contact layers 2a, b made of conductive material, for example aluminum, which form opposite contact surfaces 3a, b.
  • the peripheral side surface between the contact surfaces 3a, b is covered with a coating 4 consisting at least partially of an organic polymer.
  • the coating 4 is designed entirely as an oxygen barrier layer 5.
  • 6 filler particles 7 are distributed in an organic matrix material. They are platelet-shaped and consist of one of the following materials: natural mica, artificial mica, vermiculite, iron mica, glass. Epoxy resins, alkyd resins, polyurethanes, silicone resins, unsaturated polyester resins, acrylates are suitable as organic matrix material 6. These substances are also commercially available as paints. They can be mixed with the filler and the side surface of the uncoated active part can be sprayed with this mixture several times. Vortex sintering or electrostatic powder coating are also suitable as methods for applying the oxygen barrier layer. Casting is also possible, but less suitable for series production.
  • the degradation-inhibiting effect of the oxygen barrier layer 5 should be due to the fact that the filler particles 7, which are practically impermeable to oxygen, are oriented essentially parallel to the side surface of the active part 1 and thereby form a dense structure in which diffusion paths through the oxygen barrier layer 5, which run exclusively in the organic matrix material 6, are compared with the thickness of which are very long. Oxygen diffused from the edge layer of the active part 1 is thereby retained in the vicinity thereof, which increases the oxygen partial pressure there and prevents further diffusion of oxygen from the active part 1.
  • a first variant type I
  • the side surface of the active part 1 was sprayed three times with Wacotop @ (registered trademark of Heinrich Wagner & Co., Zurich, Switzerland), an epoxy resin paint containing iron mica.
  • Wacotop @ registered trademark of Heinrich Wagner & Co., Zurich, Switzerland
  • the thickness of the oxygen barrier layer 5 was 0.5 mm.
  • one or more oxygen barrier layers 5 are formed by coating a mica tape with a carrier 8 made of paper, plastic or glass fabric, which is wound around the active part 1 in one or more layers.
  • the coating faces the active part 1, the carrier 8 is on the outside.
  • the coating in turn consists of an organic matrix material 6 with embedded filler particles 7.
  • Mica is preferably suitable as the filler, but the use of other substances in connection with the previously described or the embodiment described below is also possible.
  • the mode of operation of the oxygen barrier layer or layers 5 is of course the same as in the other embodiments.
  • the carrier 8 enables oxygen barrier layers 5 to be applied very easily and quickly by machine winding.
  • a varistor according to the invention according to the second embodiment was produced as follows (type III):
  • the cylindrical active part 1 was covered with a layer of mica glass fabric tape Samicatherm @ (registered trademark of Isola, Pope, Switzerland), glued and cured at 130 ° C. for 16 hours.
  • the thickness of the tape was 0.2 mm.
  • the coating 4 is again entirely designed as an oxygen barrier layer 5.
  • Filler particles 7, which consist of one of the following metal oxides, are distributed in an organic matrix material 6: iridium oxide (IrO 2 ), osmium oxide (OsO 2 ), tellurium oxide (TeO 2 ), copper oxide (Cu 2 0), bismuth oxide (Bi 2 0 3 ), Lead oxide (PbO), antimony oxide (Sb 2 0 3 ), cobalt oxide (Co0), nickel oxide (NiO), manganese oxide (Mn0 2 , Mn 2 0 3 ), cadmium oxide (CdO), molybdenum oxide (Mo03), tin oxide (SnO 2 ), Tungsten oxide (W0 3 ), iron oxide (Fe 3 0 4 ), vanadium oxide (V 2 0 5 ), zinc oxide (ZnO). Powdered active part material is also an option.
  • the substances listed in connection with the first embodiment are suitable as organic
  • the degradation-retarding effect of the coating should be due to the fact that the filler particles 7 release oxygen and keep the ambient oxygen partial pressure in the immediate vicinity of the edge layer of the active part 1 at a level at which the active part material does not or only slightly releases oxygen.
  • the physical effect of the mostly poorly oxygen-permeable filler as a diffusion barrier should also play a role here.
  • a zinc oxide varistor according to the third embodiment was implemented in the following form (type IV):
  • Epoxy molding material Araldit @ (registered trademark of the company Ciba Geigy, Basel, Switzerland) Cy 227 was mixed with the corresponding hardener Cy 227 and zinc oxide (ZnO) of the quality Weissiegel heated to 160 °.
  • the active part 1 was cast around this mixture in a silicone mold. The mixture was then 16 h at 130 ° C. hardened.
  • the thickness of the oxygen barrier layer 5 after curing was 2 mm.

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

Description

Die Erfindung bezieht sich auf einen Zinkoxid-Varistor gemäss dem Oberbegriff des Anspruchs 1.The invention relates to a zinc oxide varistor according to the preamble of claim 1.

Es ist bekannt, dass sich die Eigenschaften von Zinkoxid-Varistoren, wenn sie in sauerstoffloser Umgebung betrieben werden, nach verhältnismässig kurzer Zeit merklich verschlechtern. Insbesondere steigt der Leckstrom und damit die Energieaufnahme, was zur Erwärmung und in der Folge zu weiterer Erhöhung des Leckstroms führt und in letzter Konsequenz zur thermischen Zerstörung des Varistors. Man hat festgestellt, dass die Degradation des Varistormaterials vor allem in einer dünnen seitlichen Randschicht auftritt und vermutet daher, dass sie auf Bildung unterstöchiometrischen Zinkoxids durch Abdiffusion von Sauerstoff aus der Randschicht in die Umgebung des Varistors zurückzufüren ist.It is known that the properties of zinc oxide varistors, when operated in an oxygen-free environment, deteriorate markedly after a relatively short time. In particular, the leakage current and thus the energy consumption increases, which leads to heating and subsequently to a further increase in the leakage current and ultimately to the thermal destruction of the varistor. It has been found that the degradation of the varistor material occurs primarily in a thin lateral edge layer and it is therefore suspected that it is due to the formation of substoichiometric zinc oxide by diffusion of oxygen from the peripheral layer into the environment of the varistor.

Aus der DE-31 23 552 AI ist ein Varistor bekannt, weicher zwecks Verhinderung oder Verlangsamung der Sauerstoffabdiffusion auf der zwischen seinen Kontaktflächen umlaufenden Seitenfläche mit einer Beschichtung aus einem organischen Polymer versehen ist, welches gasundurchlässig sein soll.From DE-31 23 552 AI a varistor is known, which is provided for the purpose of preventing or slowing down oxygen diffusion on the side surface running between its contact surfaces with a coating of an organic polymer which is said to be gas impermeable.

Nun ist bei üblichen Betriebstemperatur von Zinkoxid-Varistoren, nämlich ca. 120-130 °C, die Sauerstoffdurchlässigkeit von organischen Polymeren allgemein ziemlich hoch und es erscheint zweifelhaft, ob eine reine Polymerbeschichtung eine die Degradation des Zinkoxid-Varistors wesentlich verlangsamende Sauerstoffbarriere bilden kann.Now, at the usual operating temperature of zinc oxide varistors, namely approx. 120-130 ° C, the oxygen permeability of organic polymers is generally quite high and it appears doubtful whether a pure polymer coating can form an oxygen barrier that significantly slows down the degradation of the zinc oxide varistor.

Aus der genannten Schrift, wie auch bereits aus der US-PS 3 959 543, ist es auch bekannt, Zinkoxid-Varistoren seitlich mit einem Glasüberzug zu versehen. Wie insbesondere aus der zuletzt genannten Schrift deutlich wird, weisen Gläser, deren thermischer Ausdehnungskoeffizient hinreichend nahe bei demjenigen des Varistormaterials liegt, verhältnismässig hohe Schmelzpunkte auf. Der Varistor muss nach seiner Fertigstellung zum Zweck der Aufbringung des Glasüberzugs noch einmal auf ca. 650 °C erwärmt werden, was sich auf seine elektrischen Eigenschaften ungünstig auswirken kann. Weitere Nachteile liegen in der die Handhabung des Varistors erschwerenden Sprödigkeit des Glasüberzugs sowie unter Umständen in seiner chemischen Korrodierbarkeit durch Flussäure.From the cited document, as also already from US Pat. No. 3,959,543, it is also known to provide zinc oxide varistors with a glass coating on the side. As can be seen particularly clearly from the last-mentioned document, glasses whose thermal expansion coefficient is sufficiently close to that of the varistor material have relatively high melting points. After completion, the varistor has to be heated again to approx. 650 ° C for the purpose of applying the glass coating, which can have an unfavorable effect on its electrical properties. Further disadvantages are the brittleness of the glass coating, which complicates the handling of the varistor, and possibly its chemical corrodibility by hydrofluoric acid.

Gemäss JP-PS 957 072 kann die Degradation von Zinkoxid-Varistoren in SF6 durch Zugabe von 10-30 % Sauerstoff wesentlich verlangsamt werden. Diese Methode hat, abgesehen davon, dass sie nicht anwendbar ist, wenn die Varistoren von einem flüssigen oder festen Medium umgeben sind, den Nachteil, dass sie eine gasdichte Abschottung des die Varistoren enthaltenden Raums gegen andere Anlagenteile erfordert und die Wartung kompliziert. Dazu kommt die Verringerung der dielektrischen Festigkeit.According to JP-PS 957 072, the degradation of zinc oxide varistors in SF 6 can be considerably slowed down by adding 10-30% oxygen. Apart from the fact that it cannot be used when the varistors are surrounded by a liquid or solid medium, this method has the disadvantage that it requires a gas-tight partitioning of the space containing the varistors from other system parts and complicates maintenance. There is also a reduction in dielectric strength.

Aufgabe der Erfindung ist es, einen gattungsgemässen Zinkoxid-Varistor bezüglich der Sauerstoffundurchlässigkeit der die umlaufende seitliche Fläche bedeckenden Beschichtung zu verbessern.The object of the invention is to improve a generic zinc oxide varistor with respect to the oxygen impermeability of the coating covering the peripheral lateral surface.

Diese Aufgabe wird durch die Erfindung, wie sie in den Ansprüchen gekennzeichnet ist, gelöst.This object is achieved by the invention as characterized in the claims.

Die Vorteile der Erfindung sind vor allem darin zu sehen, dass die mindestens eine im Ueberzug eines erfindungsgemässen Zinkoxid-Varistors enthaltene Sauerstoffsperrschicht einer Abdiffusion von Sauerstoff aus der Randschicht des Varistorteils wegen des im wesentlichen sauerstoffundurchlässigen, die Diffusionswege drastisch verlängernden oder selbst Sauerstoff abgebenden anorganischen Füllstoffs wesentlich stärker entgegenwirkt als die Beschichtung bekannter gattungsgemässer Zinkoxid-Varistoren. Dabei ist die Beschichtung eines erfindungsgemässen Zinkoxid-Varistors kaum schwieriger herzustellen.The advantages of the invention are to be seen above all in the fact that the at least one oxygen barrier layer contained in the coating of a zinc oxide varistor according to the invention prevents oxygen from diffusing out of the peripheral layer of the varistor part because of the substantially oxygen-impermeable inorganic filler which drastically lengthens the diffusion paths or even gives off oxygen counteracts more than the coating of known generic zinc oxide varistors. The coating of a zinc oxide varistor according to the invention is hardly more difficult to produce.

Dadurch, dass die Funktion, die Sauerstoffdiffusion durch die Beschichtung zu sperren oder doch stark zu verringern, im wesentlichen von dem in der Sauerstoffsperrschicht feinverteilten anorganischen Füllstoff übernommen wird, kann zudem das organische Matrixmaterial, das die mechanischen, thermodynamischen und chemischen Eigenschaften besagter Sauerstoffsperrschicht wesentlich bestimmt, bezüglich Hitzebeständigkeit, Elastizität, thermischen Ausdehnungskoeffizienten, Korrosionsbeständigkeit, mechanischer Festigkeit etc. optimiert und insbesondere auch an die durch die jeweiligen Einsatzbedingungen wie z.B. das umgebende Medium gegebenen speziellen Anforderungen im wesentlichen ohne Rücksicht auf seine Sauerstoffdurchlässigkeit angepasst werden.Because the function of blocking or at least greatly reducing the oxygen diffusion through the coating is essentially taken over by the inorganic filler which is finely distributed in the oxygen barrier layer, the organic matrix material which determines the mechanical, thermodynamic and chemical properties of said oxygen barrier layer can also be significantly determined , optimized with regard to heat resistance, elasticity, thermal expansion coefficients, corrosion resistance, mechanical strength etc. and in particular also to the conditions of use such as the surrounding medium can be adapted to given special requirements essentially without regard to its oxygen permeability.

Im folgenden wird die Erfindung anhand von nur Ausführungswege darstellenden Zeichnungen näher erläutert.In the following, the invention will be explained in more detail with reference to drawings that show only the possible embodiments.

Es zeigen :

  • Fig. 1 einen axialen Schnitt durch einen gattungsgemässen Zinkoxid-Varistor,
  • Fig. 2 einen Schnitt durch die Randzone eines erfindungsgemässen Zinkoxid-Varistors gemäss einer ersten Ausführungsform,
  • Fig. 3 einen gleichartigen Schnitt bei einem erfindungsgemässen Zinkoxid-Varistor gemäss einer zweiten Ausführungsform,
  • Fig. 4 einen gleichartigen Schnitt bei einem erfindungsgemässen Zinkoxid-Varistor gemäss einer dritten Ausführungsform, und
  • Fig. 5 die relative zeitliche Aenderung der Verlustleistung verschiedener gattungsgemässer Zinkoxid-Varistoren beim Betrieb derselben in SF6- Atmosphäre.
Show it :
  • 1 is an axial section through a generic zinc oxide varistor,
  • 2 shows a section through the edge zone of a zinc oxide varistor according to the invention in accordance with a first embodiment,
  • 3 shows a similar section in a zinc oxide varistor according to the invention in accordance with a second embodiment,
  • 4 shows a similar section in a zinc oxide varistor according to the invention in accordance with a third embodiment, and
  • Fig. 5 shows the relative temporal change in the power loss of various generic zinc oxide varistors when operating them in SF 6 - atmosphere.

In den Figuren 1 - 4 sind Zinkoxid-Varistoren dargestellt, welche in ihrem grundsätzlichen Aufbau jeweils einen zylindrischen Aktivteil 1 aus einer gesinterten Masse, welche aus Metalloxiden mit einem überwiegenden Anteil an Zinkoxid besteht, enthält sowie auf Grund- und Deckfläche des Aktivteils 1 Kontaktschichten 2a, b aus leitendem Material, z.B. Aluminium, welche einander gegenüberliegende Kontaktflächen 3a, b bilden. Die zwischen den Kontaktflächen 3a, b umlaufende Seitenfläche ist mit einer mindestens teilweise aus einem organischen Polymer bestehenden Beschichtung 4 bedeckt.FIGS. 1-4 show zinc oxide varistors, which in their basic structure each contain a cylindrical active part 1 made of a sintered mass, which consists of metal oxides with a predominant proportion of zinc oxide, and on the base and top surface of the active part 1, contact layers 2a, b made of conductive material, for example aluminum, which form opposite contact surfaces 3a, b. The peripheral side surface between the contact surfaces 3a, b is covered with a coating 4 consisting at least partially of an organic polymer.

Gemäss einer ersten, in Fig. 2 veranschaulichten Ausführungsform ist erfindungsgemäss die Beschichtung 4 zur Gänze als Sauerstoffsperrschicht 5 ausgebildet. Dabei sind in einem organischen Matrixmaterial 6 Füllstoffpartikel 7 verteilt. Sie sind plättchenförmig und bestehen aus einem der folgenden Materialien : Naturglimmer, Kunstglimmer, Vermiculit, Eisenglimmer, Glas. Als organisches Matrixmaterial 6 eignen sich Epoxidharze, Alkydharze, Polyurethane, Siliconharze, ungesättigte Polyesterharze, Acrylate. Diese Substanzen sind auch als Lacke im Handel. Sie können mit dem Füllstoff vermischt und die Seitenfläche des unbeschichteten Aktivteils mit dieser Mischung mehrere Male gespritzt werden. Wirbelsintern oder elektrostatisches Pulverbeschichten Kommen als Verfahren zur Aufbringung der Sauerstoffsperrschicht ebenfalls in Frage. Auch Umgiessen ist möglich, aber für die Serienfertigung weniger geeignet.According to a first embodiment, illustrated in FIG. 2, the coating 4 is designed entirely as an oxygen barrier layer 5. 6 filler particles 7 are distributed in an organic matrix material. They are platelet-shaped and consist of one of the following materials: natural mica, artificial mica, vermiculite, iron mica, glass. Epoxy resins, alkyd resins, polyurethanes, silicone resins, unsaturated polyester resins, acrylates are suitable as organic matrix material 6. These substances are also commercially available as paints. They can be mixed with the filler and the side surface of the uncoated active part can be sprayed with this mixture several times. Vortex sintering or electrostatic powder coating are also suitable as methods for applying the oxygen barrier layer. Casting is also possible, but less suitable for series production.

Die degradationshemmende Wirkung der Sauerstoffsperrschicht 5 dürfte darauf beruhen, dass sich die für Sauerstoff praktisch undurchlässigen Füllstoffpartikel 7 im wesentlichen parallel zur Seitenfläche des Aktivteils 1 orientieren und dadurch ein dichtes Gefüge bilden, in weichem ausschliesslich im organischen Matrixmaterial 6 verlaufende Diffusionswege durch die Sauerstoffsperrschicht 5 verglichen mit der Dicke derselben sehr lang sind. Von der Randschicht des Aktivteils 1 abdiffundierter Sauerstoff wird dadurch in der Umgebung derselben zurückgehalten, wodurch sich der Sauerstoffpartialdruck dort erhöht und weitere Abdiffusion von Sauerstoff aus dem Aktivteil 1 verhindert wird.The degradation-inhibiting effect of the oxygen barrier layer 5 should be due to the fact that the filler particles 7, which are practically impermeable to oxygen, are oriented essentially parallel to the side surface of the active part 1 and thereby form a dense structure in which diffusion paths through the oxygen barrier layer 5, which run exclusively in the organic matrix material 6, are compared with the thickness of which are very long. Oxygen diffused from the edge layer of the active part 1 is thereby retained in the vicinity thereof, which increases the oxygen partial pressure there and prevents further diffusion of oxygen from the active part 1.

Erfindungsgemässe Zinkoxid-Varistoren gemäss der ersten Ausführungsform wurden etwa in den folgenden Varianten hergestellt :Zinc oxide varistors according to the invention in accordance with the first embodiment were produced in approximately the following variants:

Bei einer ersten Variante (Typ I) wurde die Seitenfläche des Aktivteils 1 drei Mal mit Wacotop@ (eingetragene Marke der Firma Heinrich Wagner & Co., Zürich, Schweiz), einem Eisenglimmer enthaltenden Epoxidharzlack gespritzt. Die Dicke der Sauerstoffsperrschicht 5 betrug 0,5 mm.In a first variant (type I), the side surface of the active part 1 was sprayed three times with Wacotop @ (registered trademark of Heinrich Wagner & Co., Zurich, Switzerland), an epoxy resin paint containing iron mica. The thickness of the oxygen barrier layer 5 was 0.5 mm.

Bei einer zweiten Variante (Typ II) wurde die Seitenfläche des Aktivteils 1 mit Synodur@ (eingetragene Marke der Firma Dold AG, Wallisellen, Schweiz), einem Glimmer enthaltenden Epoxidharzlack drei Mal gespritzt. Die Dicke der Sauerstoffsperrschicht 5 wiederum 0,5 mm.In a second variant (type II), the side face of the active part 1 was sprayed three times with Synodur @ (registered trademark of Dold AG, Wallisellen, Switzerland), an epoxy resin paint containing mica. The thickness of the oxygen barrier layer 5 in turn 0.5 mm.

Gemäss einer zweiten, in Fig. 3 veranschaulichten Ausführungsform werden erfindungsgemäss eine oder mehrere Sauerstoffsperrschichten 5 durch die Beschichtung eines Glimmerbandes mit einem Träger 8 aus Papier, Kunststoff oder Glasgewebe gebildet, welches in einer oder mehreren Lagen um den Aktivteil 1 gewickelt ist. Die Beschichtung ist dabei dem Aktivteil 1 zugewandt, der Träger 8 liegt aussen. Die Beschichtung besteht wiederum aus einem organischen Matrixmaterial 6 mit eingebetteten Füllstoffpartikeln 7. Als Füllstoff eignet sich vorzugsweise Glimmer, jedoch ist auch die Verwendung anderer im Zusammenhang mit den bereits geschilderten oder der nachfolgend beschriebenen Ausführungsform aufgeführter Substanzen möglich.According to a second embodiment, illustrated in FIG. 3, according to the invention one or more oxygen barrier layers 5 are formed by coating a mica tape with a carrier 8 made of paper, plastic or glass fabric, which is wound around the active part 1 in one or more layers. The coating faces the active part 1, the carrier 8 is on the outside. The coating in turn consists of an organic matrix material 6 with embedded filler particles 7. Mica is preferably suitable as the filler, but the use of other substances in connection with the previously described or the embodiment described below is also possible.

Die Wirkungsweise der Sauerstoffsperrschicht oder -schichten 5 ist natürlich gleich wie bei den übrigen Ausführungsformen. Der Träger 8 ermöglicht jedoch, Sauerstoffsperrschichten 5 sehr einfach und rasch durch maschinelles Wickeln aufzubringen.The mode of operation of the oxygen barrier layer or layers 5 is of course the same as in the other embodiments. However, the carrier 8 enables oxygen barrier layers 5 to be applied very easily and quickly by machine winding.

Ein erfindungsgemässer Varistor gemäss der zweiten Ausführungsform wurde folgendermassen hergestellt (Typ III) :A varistor according to the invention according to the second embodiment was produced as follows (type III):

Das zylindrische Aktivteil 1 wurde mit einer Lage Glimmer-Glasgewebeband Samicatherm@ (eingetragene Marke der Firma Isola, Breitenbach, Schweiz) bedeckt, verklebt und 16 h bei 130 °C ausgehärtet. Die Dicke des Bandes betrug 0,2 mm.The cylindrical active part 1 was covered with a layer of mica glass fabric tape Samicatherm @ (registered trademark of Isola, Breitenbach, Switzerland), glued and cured at 130 ° C. for 16 hours. The thickness of the tape was 0.2 mm.

Gemäss einer dritten, in Fig. 4 veranschaulichten Ausführungsform ist erfindungsgemäss die Beschichtung 4 wiederum zur Gänze als Sauerstoffsperrschicht 5 ausgebildet. Dabei sind in einem organischen Matrixmaterial 6 Füllstoffpartikel 7 verteilt, welche aus einem der folgenden Metalloxide bestehen : Iridiumoxid (IrO2), Osmiumoxid (OsO2), Telluroxid (TeO2), Kupferoxid (Cu20), Wismuthoxid (Bi203), Bleioxid (PbO), Antimonoxid (Sb203), Kobaltoxid (Co0), Nickeloxid (NiO), Manganoxid (Mn02, Mn203), Kadmiumoxid (CdO), Molybdänoxid (Mo03), Zinnoxid (SnO2), Wolframoxid (W03), Eisenoxid (Fe304), Vanadiumoxid (V205), Zinkoxid (ZnO). Auch pulverisiertes Aktivteilmaterial kommt in Frage. Als organische Matrixmaterialien eignen sich die im Zusammenhang mit der ersten Ausführungsform aufgeführten Stoffe.According to a third embodiment, illustrated in FIG. 4, the coating 4 is again entirely designed as an oxygen barrier layer 5. Filler particles 7, which consist of one of the following metal oxides, are distributed in an organic matrix material 6: iridium oxide (IrO 2 ), osmium oxide (OsO 2 ), tellurium oxide (TeO 2 ), copper oxide (Cu 2 0), bismuth oxide (Bi 2 0 3 ), Lead oxide (PbO), antimony oxide (Sb 2 0 3 ), cobalt oxide (Co0), nickel oxide (NiO), manganese oxide (Mn0 2 , Mn 2 0 3 ), cadmium oxide (CdO), molybdenum oxide (Mo03), tin oxide (SnO 2 ), Tungsten oxide (W0 3 ), iron oxide (Fe 3 0 4 ), vanadium oxide (V 2 0 5 ), zinc oxide (ZnO). Powdered active part material is also an option. The substances listed in connection with the first embodiment are suitable as organic matrix materials.

Die degradationsverzögernde Wirkung der Beschichtung dürfte darauf zurückgehen, dass die Füllstoffpartikel 7 Sauerstoff abgeben und den Umgebungssauerstoffpartialdruck in der unmittelbaren Umgebung der Randschicht des Aktivteils 1 auf einem Niveau halten, bei welchem das Aktivteilmaterial nicht oder nur geringfügig Sauerstoff abgibt. Dabei dürfte auch die physikalische Wirkung des meist wenig sauerstoffdurchlässigen Füllstoffs als Diffusionsbarriere eine Rolle spielen.The degradation-retarding effect of the coating should be due to the fact that the filler particles 7 release oxygen and keep the ambient oxygen partial pressure in the immediate vicinity of the edge layer of the active part 1 at a level at which the active part material does not or only slightly releases oxygen. The physical effect of the mostly poorly oxygen-permeable filler as a diffusion barrier should also play a role here.

Ein erfindungsgemässer Zinkoxid-Varistor gemäss der dritten Ausführungsführungsform wurde in folgender Form realisiert (Typ IV) :A zinc oxide varistor according to the third embodiment was implemented in the following form (type IV):

Epoxidformstoff Araldit@ (eingetragene Marke der Firma Ciba Geigy, Basel, Schweiz) Cy 227 wurde mit dem entsprechenden Härter Cy 227 und auf 160° erhitztem Zinkoxid (ZnO) der Qualität Weissiegel vermischt. Das Mischungsverhältnis Lack : Härter : Zinkoxid betrug in Gewichtsprozenten 25 : 25: 50. Mit dieser Mischung wurde das Aktivteil 1 in einer Silikongiessform umgossen. Anschliessend wurde 16 h bei 130 °C ausgehärtet. Die Dicke der Sauerstoffsperrschicht 5 nach dem Aushärten betrug 2 mm.Epoxy molding material Araldit @ (registered trademark of the company Ciba Geigy, Basel, Switzerland) Cy 227 was mixed with the corresponding hardener Cy 227 and zinc oxide (ZnO) of the quality Weissiegel heated to 160 °. The mixing ratio of paint: hardener: zinc oxide was 25: 25: 50 in percent by weight. The active part 1 was cast around this mixture in a silicone mold. The mixture was then 16 h at 130 ° C. hardened. The thickness of the oxygen barrier layer 5 after curing was 2 mm.

Die Herstellung einer ähnlichen Beschichtung durch Spritzen der Seitenfläche des Aktivteils 1 mit einem zinkoxidhaltigen Epoxidharzlack wurde ebenfalls mit befriedigendem Resultat erprobt.The production of a similar coating by spraying the side surface of the active part 1 with a zinc oxide-containing epoxy resin lacquer was also tested with a satisfactory result.

Beim Betrieb von bekannten gattungsgemässen und von wie beschrieben realisierten erfindungsgemässen Zinkoxid-Varistoren während 48 h in SF6-Atmosphäre bei 1 bar, 130 °C und 0,34-facher Restspannung ergaben sich folgende Resultate für die prozentuelle Aenderung der Verlustleistung :

Figure imgb0001
When operating known generic and zinc oxide varistors according to the invention implemented as described for 48 h in an SF 6 atmosphere at 1 bar, 130 ° C. and 0.34 times the residual voltage, the following results were obtained for the percentage change in the power loss:
Figure imgb0001

Die zeitliche Entwicklung der Verlustleistung im Vergleich zur Anfangsverlustleistung Pv(t)/Pv(O) beim Betrieb in SF6-Atmosphäre bei 1 bar, 115°C und bei 0,34-facher Restspannung wurde gemessen und ist in Fig. 5 dargestellt für unbeschichtete Aktivteile (punktierte Kurve), bekannte gattungsgemässe Zinkoxid-Varistoren mit Polyimidbeschichtung (durchgezogene Kurve), wie oben beschrieben realisierte erfindungsgemässe Zinkoxid-Varistoren vom Typ I (kurzgestrichelte Kurve), vom Typ II (langgestrichelte Kurve) und vom Typ IV (strichpunktierte Kurve). Wie aus der Darstellung ersichtlich, kann die Degradation von gattuhgsgemässen Zinkoxid-Varistoren durch die erfindungsgemässen Massnahmen wesentlich verlangsamt werden. Die besten Resultate wurden dabei mit erfindungsgemässen Zinkoxid-Varistoren vom Typ II erzielt.The development over time of the power loss compared to the initial power loss Pv (t) / Pv (O) when operating in an SF 6 atmosphere at 1 bar, 115 ° C. and at 0.34 times the residual voltage was measured and is shown in FIG. 5 for uncoated active parts (dotted curve), known generic zinc oxide varistors with polyimide coating (solid curve), zinc oxide varistors of type I (short dashed curve), type II (long dashed curve) and type IV (dashed curve) realized as described above . As can be seen from the illustration, the degradation of generic zinc oxide varistors can be considerably slowed down by the measures according to the invention. The best results were achieved with type II zinc oxide varistors according to the invention.

Claims (8)

1. Zinc oxide varistor having an active part (1), which has two mutually opposite contact faces (3a, 3b) and a side face going all round between the latter, and having a coating (4) which covers the side face and consists at least partially of an organic polymer, characterized in that the coating (4) contains at least one oxygen barrier layer (5) consisting of a suspension of filler particles (7) of an inorganic filler in an organic matrix material (6) which consists at least predominantly of one or more organic polymers, the inorganic filler consisting in each case essentially of one or more constituents which each belong to at least one of the following groups of materials :
- inorganic non-metallic materials, the oxygen diffusion coefficient of which is smaller than that of the organic matrix material,
- inorganic materials which release oxygen when the oxygen partial pressure in the surroundings falls below a defined positive limit.
2. Zinc oxide varistor according to Claim 1, in which at least one oxygen barrier layer (5) contains one or more constituents from the group comprising inorganic non-metallic materials, the oxygen diffusion coefficient of which is smaller than that of the organic matrix material, characterized in that these constituents are predominantly in the form of platelets or flakes and are preferably selected from the following materials or groups of materials : natural mica, artificial mica, vermiculite, iron .mica and glass.
3. Zinc oxide varistor according to Claim 1 or 2, in which at least one oxygen barrier layer (5) contains one or more constituents from the group comprising inorganic materials which release oxygen when the oxygen partial pressure in the surroundings falls below a defined limit, characterized in that, in the case of at least one of these constituents, the limit of the oxygen partial pressure in the surroundings, below which oxygen is released, is not lower than in the case of the material of the active part (1).
4. Zinc oxide varistor according to Claim 3, characterized in that the constituent, of which there is at least one, of at least one oxygen barrier layer (5), in the case of which the limit of the oxygen partial pressure in the surroundings, below which oxygen is released, is not lower than in the case of the material of the active part (1), is selected from the following materials : iridium oxide (Ir02), osmium oxide (OsO2), tellurium oxide (Te02), copper oxide (Cu20), bismuth oxide (Bi203), lead oxide (PbO), antimony oxide (Sb203), cobalt oxide (CoO), nickel oxide (NiO), manganese oxide (Mn02, Mn203), cadmium oxide (CdO), molybdenum oxide (Mo03), tin oxide (Sn02), tungsten oxide (W03), iron oxide (Fe304), vanadium oxide (V205), zinc oxide (ZnO), and the material of the active part in powdered form.
5. Zinc oxide varistor according to one of Claims 1 to 4, characterized in that the organic matrix material (6) consists at least predominantly of a polymer selected from one of the following groups of materials ; epoxide resins, alkyd resins, polyurethanes, silicone resins, unsaturated polyester resins and acrylates.
6. Zinc oxide varistor according to Claims 4 and 5, having an oxygen barrier layer (5), characterized in that the organic matrix material is an epoxide resin and the inorganic filler is zinc oxide (ZnO).
7. Zinc oxide varistor according to one of Claims 1 to 5, characterized in that the oxygen barrier layer (5), of which there is at least one, is formed by coating a tape with a carrier (8) of paper, plastic or glass fabric, of which at least one ply has been applied to the side face of the active part (1).
8. Zinc oxide varistor according to Claim 7, characterized in that the tape is a mica/glass fabric tape.
EP84113877A 1983-12-22 1984-11-16 Zinc oxide varistor Expired EP0147607B1 (en)

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