Button overvoltage arrester with cup-shaped electrodes with different side and end wall thicknesses
0 United States Patent 11 1 1111 3,876,894 Peche Apr. 8, 1975 BUTTON OVERVOLTAGE ARRESTER 2,365,517 12/1944 Berkey 313/44 WITH CUP SHAPED ELECTRODES WITH 2,365,518 12/1944 Berkey et al 313/217 X 2,478,119 8/1949 Mitchel 313/217 x DIFFERENT SIDE AND END WALL 3,263,112 7/1966 KOlb et a1. 313/220 x THICKNESSES Inventor: Gerhard Peche, Berlin, Germany Siemens Aktiengesellschaft, Berlin &amp; Munich, Germany Filed: Sept. 29, 1970 Appl. No.: 76,501  
 Assignee:  
 Foreign Application Priority Data Oct. 9, 1969 Germany 1951015 References Cited UNITED STATES PATENTS 4/1939 Kelting 313/217 X Primary Examiner-Palmer C. Demeo Attorney, Agent, or Firm1-lill, Gross, Simpson, Van Santen, Steadman, Chiara &amp; Simpson [57] ABSTRACT A button overvoltage arrester is provided with frustroconical cup-shaped electrodes each of which have an active area electrode wall thickness of at least twice the thickness of the conical side wall to prevent burning of the electrodes and to promote heat dissipation via the respective lead conductors which are connected to the electrode active areas. The cup-shaped electrodes are formed by drawing cups from a flat metal plate, preferably a Ni-Fe-Co alloy.  
 3 Claims, 1 Drawing Figure i&#39;fIEiHEM 85575 $876,894  
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 &#39; BUTTON OVERVOLTAGE ARRESTER WITH CUP-SHAPED ELECTRODES WITH DIFFERENT SIDE AND END WALL THICKNESSES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a symmetrical overvoltage arrester with a gas-tight housing in which the electrodes are arranged opposite each other, which electrodes are designed frustum-shaped and which are inserted and sealed in a gas-tight manner into the ends of a tubular insulating member with their acts turned to each other.  
 2. Description of the Prior Art Symmetrical overvoltage arresters of this kind are generally known. They have the name button arrester, due to their shape. Button arresters, among other things, have the advantages that they allow particularly small dimensions and that the areas where the electrodes and the insulating member meet are not stressed by currents which flow through the electrodes if the electrode bottom has lead wire connections. However, an essential problem with button arresters is the heat capacitance of the electrodes in the range of their active electrode surfaces. To avoid that the insulator electrode connection is heated excessively, which heating might cause the connection to become loose, the electrodes are provided with such thin walls that the heat is dissipated primarily via the feed lines. However, there is the danger with thin-wall electrodes that holes will burn in the range of the active electrode surface if strong-current changing stresses or impactcurrent stresses occur, due to the large heat loss, and that the button arrester thus becomes loose and fails to operate. This danger exists even more if the electrodes are waffled in the range of their active surfaces, for the application of an activating material, since the waffling has portions with partly reduced wall thicknesses.  
 SUMMARY OF THE INVENTION It is the primary object of this invention to prevent the aforementioned danger. To realize this objective, it is proposed, according to this invention, with an overvoltage arrester of the above-mentioned kind, that the electrodes be frustum-shaped electrodes having a wall thickness, in the range of the active electrode surfaces, which is several times higher than the wall thickness of the conical side walls in the range of the transition to the insulating member. The wall thickness which, in the range of the active electrode surface, is several times higher, must thereby differ sensibly, i.e., at least the factor 2, from the wall thickness of the side walls.  
  An essential advantage of this invention is that the efficiency of a button arrester is essentially increased since, onone hand, heat conductivity from the active electrode surfaces via the thin wall thickness of the side walls is strongly hindered while, on the other hand, the active electrode surfaces accomodate essentially higher heat loads due to the wall thickness which is several times higher in the active surface areas without danger of destruction, to transfer the heat loads to the current that of the conical side walls might be 0.3 mm at an average.  
  A preferred method for the production of an overvoltage arrester according to this invention consists in producing the frustum shaped electrodes in a drawing process in which the conical side walls are pulled out of a small metal plate, the wall thickness of which plate corresponds to the wall thickness in the range of the active electrode surface, and which, during the pulling process, is reduced in its wall thickness to the desired measure in the range of the conical side walls.  
 BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will be best understood from the following description taken in conjunction with the single FIG. drawing of an embodiment of the invention illustrated in crosssection.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows a button arrester with frustumshaped electrodes 3 and 3 which are inserted and sealed gas-tightly into a tubular insulating member 1, with their arcs turned to each other. Preferably ceramic serves as material for the insulating member 1, while the electrodes 2 and 3 consist of a Ni-Fe-Co alloy. Massive, metallic contact pieces 8 and 9 can be soldered hard against the electrodes 2 and 3, to form the feed lines of the button arrester. The contact pieces 8 and 9 thereby can be measured in their axial diameter in a way that they, corresponding to the wall thickness of the electrodes, eliminate sufficient amounts of heat in active range.  
  The frustum-shaped electrodes 2 and 3 have active surfaces 4 and 5, respectively, i.e., surfaces which are stressed during arrestings, in the range of which the wall thickness is about 1 mm. Conical side walls 6 or 7 which are reduced in their&#39;wall thickness to an average of about 0.3 mm extend from these surface ranges 4 or 5 to the outside to the transition or connection areas of the electrodes 2 and 3 and the insulating member 1.  
  The electrodes of the button arrester which, according to the invention, are essentially reinforced in their active surface ranges, guarantee that the space of the button arrester which is available for the active electrode ranges represents an essentially increased metallic heat capacity which accomodates heat produced during discharges in the button arrester, and, since the thin walls hinder strongly a heat conductivity, dissipates this heat almost exclusively via the contact members 8, 9.  
  The invention is not limited to the sample embodiments shown. For instance the conical side walls can also be produced in another way, besides shallow drawing.  
  Many changes and modifications of the invention may be made by one skilled in the art without departing from the spirit and scope of the invention. It is therefore to be understood that it is intended that the patent warranted hereon include all sure changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.  
 I claim:  
  1. A symmetrical overvoltage arrester comprising a gas-tight housing including a tubular insulating member, a pair of identical one-piece cup-shaped electrodes sealed to respective ends of said tubular insulating member, each of said electrodes including a side wall and an end wall integral therewith, each of said end walls disposed spaced from and including a surface facing the like surface of the other within said tubular insulating member, and a pair of electrical leads connected to respective other surfaces of respective end walls and extending outside of said tubular insulating member, said end walls each having a thickness of at least a multiple greater than the thickness of the respective side walls to hinder heat transfer to said tubular insulating member so that heat is dissipated through said leads.  
  2. An overvoltage arrester according to claim 1, wherein the thickness of each of said end walls is at least three times the thickness of the respective side walls.  
  3. An overvoltage arrester according to claim 2, wherein the thickness of each said side wall is about 0.3 mm and the thickness of each said end wall is in the range between i and 2 mm.