US3775642A

US3775642A - Gas discharge excess voltage arrester

Info

Publication number: US3775642A
Application number: US00203277A
Authority: US
Inventors: G Lange
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1971-01-25
Filing date: 1971-11-30
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: GB1330623A

Abstract

A compact highly efficient multipath gas discharge type excess voltage arrester comprises first and second axially aligned electrodes projecting in opposite directions through a metallic end cap means to a point within a tubular third electrode. The metallic end caps are each constructed of a pair of axially aligned oppositely disposed first and second dished members which each have a facing groove receiving an insulating ring member in sealing relation. The walls of the frusto conical dished members serve to protect the insulating ring from metallic electrode vapors. The metallic end cap means close opposite ends of a tubular third electrode means to form the gas discharge tube. Contact members of the first, second and third electrodes extend beyond the ends and circumference respectively, to provide additional protection for the end caps and insure structural integrity of the arrester.

Description

United States Patent 1191 l2/l966 Gray 317/61 Lange 5] Nov. 27, 1973 GAS DISCHARGE EXCESS VOLTAGE ARRESTER Primary Examiner-J. D. Miller [75] Inventor: Gerhard Lange, Berlin, Germany jifgfgfigigz fif g Fendelman [73] Assignee: Siemens Aktiengesellschaft, Berlin &-

' Munich, G y 1 57 ABSTRACT [22] Filed: Nov. 30, 1971 A compact highly efficient multipath gas discharge t e excess volta e arrester com rises first and second [2]] App! 203377 azt ially aligned el ctrodes projeciing in opposite direcv tions through a metallic end cap means to a point [30] Foreign Application P io it D t wthin a tubular third electrode. The metallic end caps Jan.- 25, 1971 Germany o 71 02 611.4 are each. constructed a Pair axially aligned sitely disposed first and second dished members which 52 us. (:1. 317/615, 317/62 each have facing receiving an insulating ring 511 rm. c1. H02h 3/22 memberin Sealing relation The walls of the frusto [58] Field of Search, 3 17/61 61.5 66, mica! dished members Serve to prom:t h insulating 7 337/28, 31 32 315/36; 313/220, ring from metallic electrode vapors. The metallic end 282,312, DIG. 5 cap means close opposite ends of a tubular third electrode means to form the gas discharge tube. Contact 5 References Cited 1 members of the first, second and third electrodes ex- UNITED STATES PATENTS tend beyond the ends and circumference respectively, to provide additional protection for the end caps and 53:2: 't 3 3 insure structural integrity of the arrester. 3,292,030 6 Claims, 1 Drawing Figure This invention gen erally'relates toja gas discharge type excess voltage arrester having a pair of electrodes The first dished member of the metallic end cap'has an opening just large enough to allow the cylindrical electrode to 'pass'therethrough'anda contact member provides a's'eal on the outside of the opening. In this which are arranged opposite eachother so that their innerends'are spaced from each other in a gas tight dischargechamb'erofa multipath discharge tube. A' cylinydricall y shaped third electrode separates alpair of metallic ends caps which close the ends of the third electrode in gas tight relation. The first and second electrodes are cylindrical rods which are arranged coaxially and extend through the metallic end caps into the discharge chamber.

Multipath excess voltage arresters are well known in the art as shown, for example, by the German Letters Pat No. 930,400 and 1.089.482. They have the advantage in that a first discharge on one path pre-ionizes the gas in the discharge chamber of the excess voltage arrester so that the" ignition of the seconddischarge path .is accelerated. There are a number of essential requirements for these multipath arresters. Thus, there must be sufficient insulation of the electrodes from each other even after the arrester has been loaded or stressed. In addition, they must provide for the formation of a permanent short circuit when the electrodes are overloaded and there must be a high reliability of the vacuurn density of the discharge tube and a low reaction ir'n'pact voltage. In addition to the foregoing requirements it is important that thearrester be as compaet'in construction as possible. While these require- SUMMARY OF THE INVENTION arrester wherein first" and second metallic end caps closing opposite ends of a tubular cylindrical electrode form the discharge tube with the metallic end caps each ments have been known to those skilled in theart there has neverthelessb een along standing. need for an excess voltage arrester which meets all ofthe above noted requirements.

being constructed of first and second dished members which dished members have a first end and a second end with the secondendhavingflaterally projecting grooved rim thereabout so that the first ends face towards each other and the secondends face away from each other with the tubular insulating ring having oppositeend edges received in the-grooves of the rims.

' The insulating ring is of a length whereby the firstends of the dished member are spaced I from each other. Each of the first and secondmetallic end capshas a respective first and second electrode extendingthrough openings in thefirst end of eachof the dished memberswhereby the inner ends of the first and second elec- I ing ring fromthe discharge-chambers of the discharge tube. The metallic end caps may take'theform of a frustum of a cone and be of a metallic'material which has a thickness less then that of the adjacent electrodes.

way the first dished member is in electrical contact with its respective electrode. At the same time the second 1 dished member of the metallic end cap is spaced from the first dished member and is in electrical contact with exceeds the largest lateral dimension of the voltage arrester. The contact members of the first and second electrodes projectbeyond the ends of the metallic cap members. In this way the voltage arrester forms a very compact construction. The discharge tube contains a gas which gas may be preionized by substance receivedin the tube. v j

The voltage arrester according to the invention meets the requirements set forth above and overcomes the deficiencies of the prior art by means of its combination of features. Thus, the shading ofthe portions of'th'e innersurface of the insulator rings will assure that the electrode material does not evaporate due to the arc discharge which occurs in the chamber. Aslo, it prevents conductive bridges from forming on insulator rings and thus maintains the integrity of the insulation between the electrodes. The frustum shape of the surface also gives a certain elasticity to theidished members which connect the electrodes with the insulator rings'to thereby increase the safety with respect to the fracture of the discharge tube. Since the wall thickness I of the frustum shaped surface is designedlto be less then that of the adjacent electrodes a heat conductivity towards the insulator rings is lowered so that they are protected from over heating which over heatin'g'rnight burst the insulator rings. The insulating rings are advantageously made of a ceremic material and sealed in the grooves with a glass sealant. This seal connection is protected from harmful thermic influences due to the provision of massive contact members for the electrodes which contacts have a dimension that surpasses the dimension of the other portions of the excess voltage arrester. This design assures that the currents which flow through the arrester travel only via the mentioned massive contact members and are not further guided through the metal partsof the discharge tube that are connected to the insulator rings.

The excess voltage arrester according to the invention has the further advantageous property of being able to short circuit when overloaded which short circuit is caused by the melting off of the top of the rodlike electrodes during an overload to thereby produce a conductive bridge which extends towards the hollow cylindrical electrode. Because'of the coaxial arrangement of the hollow cylindrically shaped central or third electrode about the ends of the first and second rod-' like electrodes a very dynamic arrester is produced which has a lower reaction impact voltage. In orderto lower the reaction impact voltage still further the dis charge chamber of the discharge tube may be'provided with at least a piece of a material which preionizes the gas in the tube.

BRIEF DESCRIPTION OF THE DRAWING M Other objects, featuresand advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof,,taken in conjunction with the accompanying drawing, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosureand in which:

The FIGURE is a longitudinal cross section view of a gas discharge multipath excess voltage arrester according to the invention.

Referring to the drawing it may-be seen that the two 'path excess voltage arrester according to the invention generally indicated at includes a first electrode 1 extending through an end cap means generally indicated at l l and a secondelectrode 2 extending through a second end cap means generally indicated at 12. A third generally tubular electrode 3 has its first end 30 closed by the first end cap means 11 and its second end 3b closed by the second end cap means 12 to form a gas tight multipath discharge tube. v

The first and second electrodes 1 and 2 respectively take the form of cylindrically shaped rods which are coaxially arranged with their

first ends

1a and 2a respectively, spaced from each other and located in a 7 central portion of the discharge tube surrounded by the third electrode 3.

end 4a has an opening 4d therein of a size to just receive the first electrode 1 therethrough so that only the thin end wall at end 4a is in contact with an adjacent portion of electrode 1. A massive contact 8 extends beyond the hole and forms a seal about the electrode 1. A second dished member 6 has a first end 6a and a second end 611 which second end is configured similar to the second end 4b to have a groove 60 therein. The first end 6a has an opening 6d therein of a diameter larger then the diameter of the electrode 1 and generally equal to the inner diameter of the tubular third electrode 3. This configuration provides a mimimum contact area between member 6 and electrode 3 since only i the end edge at end 3a of electrode 3 is in 'contact with a rim side wall at end 60 of member 6.

As may be seen in the drawing the dished members 4 and 6 are generally coaxially aligned with their first ends 4a, 6a closest to each other, their grooves 4c, 60, facing each other and their second ends 41;, 6b, spaced the grooves distance from each other. A tubular insulating ring 21 is positioned with its opposite end edges received in the

grooves

40 and 6c. The tubular insulating ring 21 is of a ceremic material and has its ends sealed in the grooves 40, 60 by means of a glass sealingmaterial to provide a gas tight seal between the edges of the insulating rings 21 and the grooves 40, 60. Where theinsulating ring 21 may be of a metallized ceremic it is contemplated by the invention herein that it could be soldered into the grooves to form a gas tight housing. With thisconstruction the first end cap means 11 is in electrical contact with the first electrode 1 and in electrical contact with the third electrode 3 by means of the second dished member 6 contacting the first end of the third electrode 3a about its first end 6a. The insulating ring 21 is of a length so that the first ends 4a, 6a

of the dished members 4 and 6 respectively are spaced from each other. I

The connection of the insulating ring 21 with thefirst and third electrodes to form a gas tight excess voltage given off by the electrodes during operation of the excess voltage arrester. In addition, the seams or joints of the discharge tube or arrester 10 which are the most critical to the vacuum tightness of the arrester, namely the metallic-insulating ring connections, are portected because the metallic parts 4 and 6 have thinner walls then the adjacent electrodes. Accordingly, the vacuum tight connection between the metal and insulating material of the insulating ring 21 is not thermically stressed. To prevent the metallic portions 4 and 6 which are connected to the insulating ring 21 from being heated by passing currents, a massive contact member 8 is provided on the outer end lb of the electrode l. The contact member 8 extends in anaxial direction beyond the end of the end cap means 11 so that the currents which flow through the arrester are not guided via the metal parts of the discharge tube which are connected with the insulating rings, but are guided only through the massive contact members 8. For a similarreason the contact 18 of the. third electrode 3 also extends radially outwardly beyond the diameter of the discharge tube 10. The extension of the

contact members

8, 18 and 28 also has the advantage that the end cap means are protected when the voltage arrester is handled or mounted.

The end cap means 12 may be constructed indentical to the construction heretofore described with regard to the end cap 11 and the corresponding parts and elements have been indicated with a prefix 2 before the references numerals of the end cap 11.

The electrodes 1 and 2 and particularly their

inner ends

1a and 2a are of a material such that when the arrester is overloaded the tips la and 2a will melt off and contact the third electrode 3 to create a continuous short circuit. Another advantage of the construction according to the invention is that the coaxial arrangement of the electrodes causes a lower reaction-impact voltage then washeretofore possible with the prior art. Moreover, the reaction-impact voltage may be further improved by the preionizing of the gas which fills the interior of the discharge tube 10. For this purpose it is possible according to the invention herein to add to the insulating rings 21 and 22 a spot of material made of a radioactive substance or to add a radioactive gas-like substance such as tritium or crypton to the gas filling. From the foregoing description of the invention it may be seen that thedeficiencies of the prior art had been overcome by the very efficient and'compact construction of my excess voltage arrester 10. It is again emphasized that the frusto conical shape of the dished

members

4, 6, 24, 26, provides a certain elasticity to' the metallic parts which connect the electrodes with the insulator rings whereby the possibility of fracture of has.

thedischargetube is greatly reduced. It will be undertended to belimited only by th'eappended claims. Al-

though minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as might reasonably and properly come within the scope of my contribution to the'art. I

I claim as my invention: 1. In a gas discharge excess voltage arrester, first and second axially aligned electrodes, each having an inner and outer end interconnected by a side surface, said electrodes extending toward one another so that said electrodes are spaced from each other only at-their adjacent inner ends; a third electrode having two end surfaces interconnected by a side surface, said third electrode side surface being substantially uniformly spaced radially from said first and second electrode side surfacesand surroundingand extending along said first and second electrode side surfaces for a greater portion of the length thereof; dished endcap means for each end 'of said third electrode, each end cap means having a frusto-conical' wall portion extending from an end of said third electrode inwardly therealong and diverging therefrom, each end cap means having a first rim extending radially inwardly of an outer end portion of said frusto-conical wall and having an inner rim side wall in direct contact with an end surface of said third electrode, and each end cap means having a second rim extending radially outwardly of an inner end portion of said frusto-conical wall and an axially extending flange at the end of said second rim and with said frusto-conical wall and said second rim forming a sealing groove; 7

dished end cap means for said outer ends of said first and second electrodes, each end cap means being spaced inwardly of said outer ends of said first and second electrodes, each end cap means having a frusto-conical wall portion extending towardv an outer end of an associated electrode and diverging therefrom, each end cap means having a first rim outer end portion of saidfrusto-conical wall and an axially extending flange at the end of said second rim and with said frusto-conical wall and said second rim forming a sealing groove;

inslulator rings in said sealing grooves spacing said first, second and third electrodes in a spaced-apart relation with respect to each other; i

means sealing said v insulator" rings to said sealing grooves to form a gas-discharge container having at least two discharge paths, wherein the inner surface of said insulator rings are screened off from said discharge paths by at least one of said frustoconical walls connected between said electrodes and said insulator rings and wherein the wall thicknesses of said frusto-conical walls is less than the wall thickness of said electrodes so as to minimize energy transfer between said electrodes andsaid walls; and

massive contact members on-each of said electrodes extending outwardly of said electrodes and end cap means in both axial and radial directions.

2. The excess voltage arrester of claim 1,

wherein the metallic end caps at each end of the arrester are opposed to one another, and Y wherein the insulating member is of such a length as to space said end cap means from each ohter and to hold the adjacent ends of said first and second electrodes in spaced relation with respect to each other.

3. The excess voltage arrester of claim 2,

wherein said insulating rings is of a ceramic material and sealing means are provided to seal said ring in said grooves at its ends to form a gas tight connection.

4. The excess voltage arrester of claim 3,

wherein the first and second electrodes have cylindrical heads at their outer ends of larger diameters than the diameters of said electrodes and abutted by said dished end cap means to proivide massive contacts and space the adjacent ends of said first and second electrodes from each other.

5. The excess voltage arrester of claim 4, wherein said gas discharge container contains a gas preionized by a substance in said tube.

6. The excess voltage arrester of claim 5, wherein said third electrode has an integrally formed radial flange portion extending outwardly of said side surfaces thereof between said end cap means at the outer ends of said third electrode to form a massive contact membet on said third electrode.

Claims

1. In a gas discharge excess voltage arrester, first and second axially aligned electrodes, each having an inner and outer end interconnected by a side surface, said electrodes extending toward one another so that said electrodes are spaced from each other only at their adjacent inner ends; a third electrode having two end surfaces interconnected by a side surface, said third electrode side surface being substantially uniformly spaced radially from said first and second electrode side surfaces and surrounding and extending along said first and second electrode side surfaces for a greater portion of the length thereof; dished end cap means for each end of said third electrode, each end cap means having a frusto-conical wall portion extending from an end of said third electrode inwardly therealong and diverging therefrom, each end cap means having a first rim extending radially inwardly of an outer end portion of said frusto-conical wall and having an inner rim side wall in direct contact with an end surface of said third electrode, and each end cap means having a second rim extending radially outwardly of an inner end portion of said frusto-conical wall and an axially extending flange at the end of said second rim and with said frusto-conical wall and said second rim forming a sealing groove; dished end cap means for said outer ends of said first and second electrodes, each end cap means being spaced inwardly of said outer ends of said first and second electrodes, each end cap means having a frusto-conical wall portion extending toward an outer end of an associated electrode and diverging therefrom, each end cap means having a first rim extending radially inwardly of inner end portions of said frusto-conical wall and having rim end walls in direct contact with the adjacent side surfaces of the associated electrode, and each end cap means having a second rim extending radially outwardly of an outer end portion of said frusto-conical wall and an axially extending flange at the end of said second rim and with said frusto-conical wall and said second rim forming a sealing groove; inslulator rings in said sealing grooves spacing said first, second and third electrodes in a spaced-apart relation with respect to each other; means sealing said insulator rings to said sealing grooves to form a gas-discharge container having at least two discharge paths, wherein the inner surface of said insulator rings are screened off from said discharge paths by at least one of said frusto-conical walls connected between said electrodes and said insulator rings and wherein the wall thicknesses of said frusto-conical walls is less than the wall thickness of said electrodes so as to minimize energy transfer between said electrodes and said walls; and massive contact members on each of said electrodes extending outwardly of said electrodes and end cap means in both axial and radial directions.

2. The excess voltage arrester of claim 1, wherein the metallic end caps at each end of the arrester are opposed to one another, and wherein the insulating member is of such a length as to space said end cap means from each ohter and to hold the adjacent ends of said first and second electrodes in spaced relation with respect to each other.

3. The excess voltage arrester of claim 2, wherein said insulating rings is of a ceramic material and sealing means are provided to seal said ring in said grooves at its ends to form a gas tight connection.

4. The excess voltage arrester of claim 3, wherein the first and second electrodes have cylindrical heads at their outer ends of larger diameters than the diameters of said electrodes and abutted by said dished end cap means to proivide massive contacts and space the adjacent ends of said first and second electrodes from each other.

6. The excess voltage arrester of claim 5, wherein said third electrode has an integrally formed radial flange portion extending outwardly of said side surfaces thereof between said end cap means at the outer ends of said third electrode to form a massive contact member on said third electrode.