US3769538A

US3769538A - Vacuum arc devices with ferrous electrodes

Info

Publication number: US3769538A
Application number: US00236278A
Authority: US
Inventors: L Harris
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-03-20
Filing date: 1972-03-20
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: CA977407A; FR2176902A1; JPS496435A; DE2308913A1; GB1401867A; FR2176902B1

Abstract

Vacuum arc devices having a pair of primary arc-electrode assemblies in the form of a rod array structure utilize hardened ferrous materials exhibiting high hardness, ductility and high recovery strength for the attainment of higher voltage handling capacity and higher current interrupting characteristics than devices utilizing conventional nonferrous cuprous alloy electrode materials.

Description

[ Oct. 30, 1973 6/1965 Hoeh 313/311 X 4/1926 Brach...... 3l3/3ll X ABSTRACT 19 Claims, 5 Drawing Figures United States Patent [1 1 Harris VACUUM ARC DEVICES WITH FERROUS 3,189,777 1,532,330

ELECTRODES [75] Inventor: Lawson P. Harris, Scotia, N.Y.

[73] Assignee: General Electric Company,

Primary Examiner-John Corbin Attorney-John F. Ahern et al.

[22] Filed:

Vacuum are devices having a pair of primary arc- [21] Appl. No.: 236,278

[52] US. 313/233, 200/144 B, 313/267,

electrode assemblies in the form of a rod array struc- 313,311 ture utilize hardened ferrous materials exhibiting high hardness, ductility and high recovery strength for the 7 Q6 12 s 4 2 3 3 3/ 3 1 3 1. m m mh c r a e S m l d Ld mm 1] 8 55 attainment of higher voltage handling capacity and higher current interrupting characteristics than devices utilizing conventional nonferrous cuprous alloy electrode materials.

[56] References Cited UNITED STATES PATENTS PATENTEU EU 30 L973 SHEET 1 BF 3 PATENIEUHU 3 0 I975 13,769,538 SHEET 20F 3 PATENTEU 001 3 0 I973 SHEET 3 BF 3 BACKGROUND OF THE INVENTION The present invention relates to improved vacuum are devices. More particularly, the invention relates to such improved devices as vacuum gaps, triggerable vacuum gaps, vacuum switches and the like, wherein a rod array structure of interleaved individual arc electrode members presents a large arcing surface for the attainment of high current and low current density power arcing characteristics. In the development of vacuum arc devices such as vacuum gaps and vacuum switches, a number of problems have been encountered and solved. One of the most recent problems solved is that of the formation of anode spots due to the bunching of arc current conduction paths between the cathode and anode assemblies in structures wherein a plurality of interleaved electrode members is utilized in order to attain a large area of arcing surface in order to maintain a low arc current density. In many prior art devices, the configuration of such electrodes caused inter-electrode arcing currents and the magnetic fields caused by conduction of current in electrode members to interact so that the resultant TX B forces caused the formation of bunching of current paths and the formation of destructive anode spots. Recently, as is set forth in application Ser. No. l07, 51 I, filed Jan. 18, 1971, now U.S. Pat. No. 3,679,474, Joseph A. Rich assigned to the present assignee and incorporated herein by reference thereto, thisproblem has largely been overcome by the provision of electrode assemblies each comprising opposed rod arrays of individual arcing electrode members which are disposed in a circular pattern normal to an arc-electrode plate to which they are electrically and mechanically affixed, and juxtaposed with respect to an oppositely poled arc-electrode assembly of like configuration so that the individual rods of opposite arc-electrode assemblies interleave between one another to cause a plurality of arcing paths electrically in parallel. This arrangement has resulted in a substan; tial cancellation of all but residual azimuthal J X B forces, with the resultant substantial elimination of bunching of arcing paths at the anode electrode and the formation of destructive anode spots.

While devices of the Rich invention are a great advance upon the art and make possible the attainment of heretofore unobtainable current-interrupting and current-carrying capacities without the formation of anode spots, the utilization of conventional arcelectrode materials as, for example, zone-refined OFHC copper, does not over-come the disadvantage existing in previous vacuum arc devices wherein such materials do not exhibit a high enough recovery strength nor dielectric hold-ofi' strength to accommodate higher voltages and further possess certain limitations in physical strength which limit the currentinterrupting capacities.

Accordingly, it is an object of the present invention to provide vacuum are devices wherein the advantage of previous structures which avoid anode spot formation is utilized and wherein higher dielectric and dielectric-recovery strength is obtainable.

Still another object of the present invention is to pro vide such vacuum arc devices as possess improved mechanical strength which facilitates the attainment of higher current interruption than devices of the prior art.

Yet another object of the present invention is to provide improved vacuum are devices suitable for holding off higher voltages, interrupting higher currents, operating with better electrical characteristics than devices of the prior art and which are fabricated from inexpensive materials which do not require expensive fabrication processes.

BRIEF DESCRIPTION OF THE INVENTION Briefly stated, in accord with one embodiment of the present invention, vacumm are devices in accord with the invention include a pair of primary arc electrode assemblies each of which comprises a base plate and a plurality of rod-like arcing members normal thereto formed in a substantially circular pattern and adapted, so that when a pair of oppositely-poled assemblies are interleaved with one another, a plurality of electrically parallel arcing paths are formed. In further accord with the present invention, such arc electrode assemblies are fabricated of a gas-free hardened ferrous material which exhibits a high hardness and ductility and a higher dielectric strength than materials previously utilized in such applications.

The novel features characteristic of the present invention are set forth in the appended claims. The invention itself together with further objects and advantages thereof may best be understood by reference to the following detailed description taken in connection with the appended drawing in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic vertical cross-sectional view constructed in accord with the present invention.

FIG. 2 is a plan view taken along the lines 22 of the device of FIG. 1.

FIG. 3 is a graphical representation of the voltage recovery characterics of arc electrodes in vacuum fabricated of materials utilized in the construction of devices in accord with the present invention as compared with the similar characteristics of arc-electrodes fabricated of materials normally used in vacuum arc devices.

FIG. 4 is a schematic vertical cross-sectional view of a triggerable vacuum gap device constructed in accord with the present invention, and

FIG. 5 is a schematic vertical cross-sectional view of a vacuum switch constructed in accord with the present invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, a vacuum gap device constructed in accord with the present invention is represented generally at 10. Device 10 includes an upper arc-electrode assembly 11 and a lower arc-electrode assembly 12 which are joined by an insulating cylindrical sidewall member 13 hermetically sealed to upper and lower electrode assemblies 11 and 12 to form an hermetically-sealed evacuable envelope 14. Upper arc-electrode assembly 11 includes a base plate or disk member 15 and a plurality of downwardly-depending electrode members 16 electrically and mechanically attached thereto. Lower electrode assembly 12 includes a base plate or disk member 17 and a plurality of upwardly-depending electrode members 18 electrically and mechanically attached thereto and disposed in perpendicular relationship therewith, as are the electrode members 16 with respect to baseplate member 15. i

Each of

electrode members

16 and 18 are solid, smooth-surfaced rod-like members, as illustrated. Although a cylindrical geometry is believed ideal, it is within contemplation of the invention that rounded wedge-shaped or radial vanes with no sharp edges may also be used for attainment of increased arcing area.

The interleaving of arc-electrode assemblies of 11 and 12 into one another results in the creation of a plurality of parallel interelectrode gaps illustrated at 21 in FIG. 2 of the drawing wherein the arc-electrodes of one polarity are indicated with a single peripheral line and the electrode members of the opposite polarity are indicated with a double peripheral line.

Envelope 14 is completed and seals are made by the provision of conventional ceramic-to-metal seals by collar-

shaped seal members

22 and 23 which seal upper electrode and lower electrode assemblies to insulating sidewall member 13, respectively. These seals are protected from the deleterious effects of being exposed to an electron-ion plasma caused during intense arcing conditions within envelope 14 by the provision of

end shields

24 and 25 connected to stepped peripheral portions of endwall members and 17, respectively. The insulating integrity of insulating sidewall member 13 which may for example be a glasssuch as General Electric REX or Corning Pyroceram or a higher density alumina or any of the many vacuum tight glasses well known to the art, is further protected by a doubly truncated cylindrical central shield member 26 which is supported laterally about the region in which

arc electrode members

16 and 18 overlap and which overlaps the inwardly-depending ends of

end shields

24 and 25. Shield 26 is supported by shield support member 27 which is secured in ceramic-to-metal bond within the central portion of insulating sidewall member 13. A pair of

terminal members

28 and 29 comprise means for connecting the device 10 of FIG. 1 in circuit with an electric circuit or circuit element to be protected. Such relationship may be in series circuit relationship with an inductive load member for example or in parallel circuit relationship with a capacitive load member for example.

Terminal members

28 and 29 are in good nonresistive electrical contact with arc electrode assemblies l1 and 12, respectively, and are adapted to conduct hundreds of kiloamperes.

In the pertinent history of the development of vacuum are devices, development has been directed along the line of providing materials of intermediate vapor pressure to provide arc conduction specie for such devices and which, additionally, may readily be vacuum processed to remove therefrom all sorbed gases or gasforming constituents which, upon the formation of a high current arc can cause the evolution of gaseous contaminants which would permanently affect the maintenance of a steady state equilibrium vacuum of the order of 10 torr. A further consideration has been the seeking of arcing materials which exhibit good chopping" characteristics, namely, the ability to hold a current as a cycle of a current alternation upon which an arc has been struck approaches zero without having the current chop and abruptly fall from a relatively high value to zero, with the creation of high transient voltages which can be highly detrimental to inductive loads for example. FOr these reasons, among others, the art has concentrated upon the use of copper and cuprous alloys in vacuum arc devices. Furthermore, there has been an unwritten folklore that the use of any ferromagnetic materials in arcing electrodes in vacuum are devices would result in unpredictable and deleterious electromagnetic effects and is, therefore, to be avoided. For this reason, innovators working with arcing materials have generally avoided ferrous materials.

In accord with my invention, however, I find that ferrous materials provide unique advantages in the state of the art to which it has developed for the attainment of very high current interruption and the maintenance of high dielectric strength. I further find that, so long as ferrous materials are not utilized for steady-state conduction of high currents that their use in the sustenance of kiloampere arcs and arcing currents for the order of one cycle of power frequency alternating current does not provide any problem, even considering the much higher resistivity of ferrous materials than cuprous materials. This is true at this time because present vacuum arc device technology has overcome early (e.g. 19501960) problems relating to maintenance of sufficient arcing specie to sustain an arc, avoiding unacceptable chopping currents, and avoiding the formation of destructive arc footpoint spots, particularly anode spots. The present problems facing innovators in the vacuum arc device relate largely to extending the magnitude of voltage whichmay be safely impressed between arcing members and increasing the currents which may be interrupted and terminated thereby.

Since the chopping characteristic of iron and of ferrous materials in general is compatible with vacuum are use, and so long as ferrous materials are not used for steady-state conduction, there is no electrical disadvantage to their proper use in vacuum arc devices. I find, however, there are decided advantages. Thus, for example, the degassification of ferrous matierals is relatively simple. Initial degassification of the bulk material may be provided by vacuum melting, particularly of the consumable electrode type vacuum melting wherein each portion of a ferrous bar from which the finally utilized ferrous electrode is formed is at one point the arcing point of a vacuum arc and each portion of the arc electrode source material is melting under vacuum conditions to cause the removal of all gas and gasforming constituents before formation of the electrode. Once the electrodes have been formed from such material, the problem of surface degassification is much simpler than that with cuprous materials which have relatively low softening and melting points. Ferrous materials may be degassified of adsorbed gases merely by assembling them in the vacuum arc device and during normal bakeout subjecting them to the temperature and time of bakeout necessary to degassify the other materials in the device. No special precautions need to be taken.

when one considers the structure as is set forth in FIG. 1 of the drawing and considers the electromagnetic forces which may be applied to each individual rod electrode upon the passage of a current of the order of hundreds of kiloamperes through the device, it is apparent that great stress is placed upon each individual rod. I find that utilizing ferrous materiala, particularly hardenable steels which have high ductility, rather than cuprous materials precludes deformation of the rods for currents which materials, attainable within the limitations of other parameters of such devices so that possible deformation of individual rods vanishes as a problem, thus creating another advantage for the use of ferrous materials. Finally, and perhaps of greatest importance, ferrous metals as used in accord with the invention are usually very hard and reasonably ductible. I have found that such hardness and ductility is associated with high dielectric recovery characteristics and high electrical breakdown strength, thereby greatly facilitating a substantial increase in voltage rating of devices in accord with the invention as compared with prior art devices utilizing conventional electrode materials. This advantage is in addition to the mechanical advantage gained by the use of hard, ductile electrodes. While numerous ferrous materials are useful in the production of vacuum arc devices in accord with the present invention, I find that certain hardenable steels having martensitic grain structure and certain precipitated inclusions are particularly useful. Many of these steels may be machined while relatively soft in condition and then heat-treated to cause an increase in hardness and yield strength and are ideally suited for devices in accord with the present invention. One general grouping of such steels is well known and generally identified as age hardening or precipitation hardening steels. In general, these steels are martensitic steels obtained by quenching rapidly an austenitic steel to obtain dispersion of impurities and small grain size. Hardening is effectuated by the presence of impurities, which also contribute to the necessary ductility. The hardening may result from a heat treatment generally performed at a relatively low temperature (as compared with the temperature of the original quenching), as for example between 900-1000 F. Some such steels are iron-nickel maraging steels (generally containing also minor quantities of molybdenum and cobalt, and sometimes titanium) with from 15 to 30 weight percent nickel. Some such steels are described in an article entitled 18% Nickel Maraging Steel by Decker, Eash and Goldman, published in the Transactions of the ASM, pp. 58-76, 1962. Certain specific maraging steels which have been found suitable for use in the invention are available from Vanadium Alloy Steel Co., Latrobe, Pennsylvania, and are described in a brochure copyrighted by that firm in 1966 entitled VASCOMAX 200-250-300-350 which brochure lists many specific compositions of suitable steels.

Maraging steels are often manufactured by vacuummelting practices and are relatively free of dissolved gases as commercial steels go. Developmental tests have verified that the gas contents of these steels is acceptable for use in arc electrodes in vacuum are devices. As purchased commercially, maraging steels may typically have a hardness of approximately 30 Rockwell C and exhibit a yield strength of approximately 100,000 psi, approximately six times that of copper. In this condition the steels are, nevertheless, readily machinable, much more so than copper. After machining, forming and other preparation for assembly into the devices of the invention, the maraging steels may be hardened by a high-temperature aging treatment, the temperature and time of which may be varied compatibly to achieve the useful result. Thus, for example, a typical 30 Rockwell C 100,000 psi maraging steel, after treatment at 520 C for approximately three hours, exhibits a hardness of 54 Rockwell C and a yield strength in excess of 250,000 psi with remarkably high ductility in excess of percent of 2 inch standard section. Such characteristics are uniquely adapted for the formation of electrode assemblies in vacuum arc devices since the bakeout and curing time of such devices may be made sufficient to cause appropriate hardening of a marging steel.'i"hus, for example, I have constructed vacuum devices in accord with the present invention utilizing a particular maraging steel known as Vascomax 300 CVM to form arc-electrode members exhibiting the foregoing mechanical characteristics. A similar Vascomax 300 CVM maraging steel having a 30 Rockwell C hardness was machined to provide

base plates

15, 17 and

rods

16, 18 of vacuum arc electrode assemblies in accord with the present invention, assembled, and the device was baked out for 24 hours at 550C. After such treatment, the steel was found to exhibit a hardness of approximately 41 Rockwell C and a corresponding yield strength of 150,000 psi, at least ten times stronger than conventional vacuum processed OFHC copper, generally utilized in such devices and a ductility in excess of 10 percent. As is mentioned hereinbefore, for short term arcing characteristics, the steels of the invention are comparable to copper insofar as arcing current-carrying capacity is concerned. Developmental tests of Vascomax 300 steel utilized as described herein have shown an ability to carry without deleterious effect a current density of approximately 225 amperes/cm over the surface thereof for a half cycle of arcing, which exceeds the same value as may be carried by copper electrodes.

Other hardened or hardenable steels from which ferrous arc-electrodes for use in devices in accord with the invention are made, include precipitation hardened stainless steel such as those set forth on pages 81 and 83 of the 1972 Materials Selector published by Materials Engineering Journal, Stamford, Connecticut. Such precipitation-hardened stainless steels, no one of which is unique in desirable properties as used herein, usually contain low carbon, high nickel and chromium and minor precipitates of other elements. They are generally hard, having tensile strengths in excess of 150,000 and usually in excess of 200,000 psi, are easily outgassed and have ductility of the order of 10 percent elongation of standard 2 inch section. Many other precipitation hardened stainless, austenitic and martensitic steels may be found therein.

One specific precipitation hardened stainless steel possessing characteristics ideally adapted for use in devices in accord with the invention is identified as Carpenter Custom 455 and is available from Carpenter Technology Corporation, Reading, Pennsylvania. This steel contains approximately 12 percent chromium, 8.5 percent nickel, 1.2 titanium, 2.25 percent copper, less than 1 percent each of carbon, manganese and columbium, balance iron. Its tensile strength is in excess of 225,000 psi, readily outgassed and has high ductility as represented by a 5-10 percent elongation in a standard 2 inch test section.

Still another class of uniquely adapted hardened fer rous materials or alloys well adapted for use in devices in accord with the invention are the so-called TRIP steels (Transformation Induced Plasticity). Such steels are normally austenitic, but their composition places them near the phase line so that warm working causes a transformation to martensite under stress at service temperatures. A description of TRIP steels may be found in an article appearing in preprint No. -UCRL 18609 (Lawrence Radiation Laboratory), University of California, November 1968, by W. W. Gerberich and entitled Metastable Austenitic Steels With Ultrahigh Strength and Toughness." See also TRANS. ASM 60, 252 (l967), The Enhancement of Ductility in High Strength Steels by Zackey et al.

In general, another class of ferrous alloy materials which may be utilized in accord with the present invention is that of carbon alloy steels. These steels differ from maraging steels, and other hardenable steels which are often softened by quench from a high temperature in excess of 1500F and hardened by later exposure to intermediate temperatures of the order of 900F l200F that correspond reasonably well to bakeout temperatures of vacuum are devices in accord with the present invention. Carbon alloy steels, on the other hand, as is epitomized, for example, by Vascojet 1000 CFM, a carbon alloy steel'available from Vanadium Alloy Steel Co., Latrobe, Pennsylvania, and comprising approximately 0.40 percent carbon, 5.0 percent chromium, 3 percent molybdenum, 0.5 percent vanadium, the remainder iron, are hardened by a quench from a high temperature (l800-l900F for Vascojet) and later tempered to slightly decrease the hardness and increase theductility by exposure to intermediate temperatures such as those utilized in the bakeout of vacuum arc devices in accord with the present invention. 7

The importance of ductility in arc-electrodes of vacuum are devices in accord with the invention cannot be stressed too heavily. The enormous shocks caused by the electromagnetic forces of kiloampere arcs can deform strong arc electrode structures. If the structures are merely made hard, they may be brittle, and, when stressed, may crack or break. The advantages 'of the invention are only achieved when the hard ferrous material utilized is sufficiently ductile, as is defined herein,

to withstand the shocks and absorb the same without deforming or shattering.

It is apparent to those skilled in the art that with the opening of the possibilities of hard, ductile ferrous alloys such as maraging precipitation hardened steels, TRIP steels, and carbon steels which are capable of having their crystal structure grain size and other metallurgical characteristics altered by temperatures of annealing which may correspond with acceptable temperatures for the bakeout of vacuum are devices in accord with the present invention, that this invention may be practiced with numerous such steels, many of which may provide the increased strength, hardness and ductility which are desirable and consistent with the attainment of more stable vacuum arc structures for the attainment of higher current-carrying capabilities and greater dielectric strength. Accordingly, it is well within the contemplation of those skilled in the metallurgical arts to apply the teachings of the present invention to the use of an infinity of ferrous alloys for the provision of improved vacuum arc devices.

As used herein, and in the appended claims, the terms hardness, hard and the like are intended to connote a tensile strength in excess of 100,000 psi and preferably in excess of 150,000 psi. As used herein, the terms high ductility," ductile and the like are meant to connote a ductility as evidenced by a percentage elongation of a standard 2 inch long sample of standard cross section of at least percent and preferably 10 percent. All percentages of compositions are expressed in weight percent.

As is stated hereinbefore, yet another unexpected advantage of devices in accord with the present invention is the discovery of a unique dielectric recovery strength characteristic of ferrous arc electrodes of ductile, hardenable steels, when used in accord with the present invention. FIG. 3 of the drawing illustrates a typical plot of recovery strength in volts plotted as a function of time after arcing of gas-free arc-electrodes of a specific configuration utilized in vacuum are devices of the present invention fabricated from different electrode materials and tested under identical test conditions. As may be seen, the voltage recovery strength of arc electrodes fabricated from cuprous and ferrous materials increases rapidly at a rate of approximately 15 kilovolts per microsecond on a more or less straight line characteristic and saturates at a value which is dependent upon the material of the electrode and its physical characteristics, principally hardness. As may readily be seen from the graph of FIG. 3, the curve representing cuprous electrodes saturates at 30 kilovolts while the curve representative of electrodes of Vascomax 300 maraging steel as an example of hard ferrous electrodes does not saturate until kilovolts, nearly three times higher than that for the copper electrodes, thus making it possible for devices constructed in accord with the present invention and utilizing such hard ferrous alloy electrodes to operate at greatly increased voltages without the danger of spurious breakdown or, in the alternative, to locate the arc electrodes much closer together for a given holdoff voltage. This characteristic seems to be associated with hardness of the electrode and therefore is to be found in other hard ferrous metal electrodes as well.

In general, in addition to the steels set forth herein, many other steels containing nickel, chromium and other similar transition metals, are uniquely adapted to possess the highly desirable temperature and age hardening characteristics which optimize the use of ferrous arc electrode assemblies in accord with the present invention.

Devices constructed in accord with the invention have been operated repeatedly to hold off 100,000 volts in open circuit position. In closed circuit position, they have routinely successfully carried 33,000 amperes peak current. This current has been interrupted successfully by causing arc to be struck which exhibits a 50 V are drop and which has been extinguished at a first current zero with no noticeable deleterious effects to the arc-electrodes and the applied voltage held off without restrike.

FIG. 4 of the drawings illustrates a triggerable vacuum gap device 30 in accord with the present invention which is a modification of the device of FIG. 1. In FIG. 4, like numerals have been utilized to identify like parts thereto. Triggerable vacuum arc device 30 includes envelope 14 and its constituent parts, as illustrated in FIG. 1. Additionally, a trigger electrode assembly 31 is electrically connected at one terminal thereof to lower endplate l7 and includes a metallic plated and scored insulator 32, a trigger anode 33, and a trigger anode connector 34. Trigger assembly 31 may conveniently be any of the trigger assemblies set forth in Lafferty US. Pat. Nos. 3,394,281, 3,465,192 and 3,465,205, or the functional equivalents thereof. In operation, the trigger is operative, with the electrode assembly 12 momentarily negatively biased, to receive a positive pulse to trigger anode lead 34, causing the establishment of a trigger arc between trigger anode 33 and the surface of arc electrode plate 17 to cause the injection of an electron ion plasma into the volume of envelope l4 and the breakdown of the respective interelectrode gaps 21 to cause the main voltage applied between

terminals

28 and 29 to establish parallel arcs, the aggregate of which may be in the hundreds of kiloamps range between the individual

arc electrode rods

16 and 18 of arc electrode assemblies 11 and 12. In operation, normally triggerable vacuum arc device 30 may be connected across a circuit constituent as, for example, a capacitor to be protected. Upon the occurrence of an overload, a signal applied to trigger anode 33 to cause the instantaneous breakdown thereof, short-circuiting the line therethrough while the fault which caused the transient is remedied or while the transient, as for example, lightning-induced transient, passes. Upon the occurrence of the next value of current zero, conduction species, which are the metallic particles ejected from the arc electrode assemblies, condense on the shield and the electrodes. This occurs very rapidly in view of the rapid dielectric strength recovery characteristic of the ferrous arc electrode materials in accord with the present invention, as described hereinbefore. The arc is then not restruck upon the next half-cycle of the alternating voltage and the device remains in the nonconducting, equilibrium state until the next trigger operation occurs.

FIG. of the drawings illustrates a vacuum switch constructed in accord with the present invention. Basically, the switch 40 of FIG. 5, wherein like numerals are used to identify like parts to those of the device of FIG. 1, comprises an array of a pair of arc electrode assemblies 11, 12, constructed of hard, ductile ferrous materials, as described hereinbefore, but also containing a pair of butt-type electrical contacts 41, 42 which constitute means for providing an electron-ion plasma within the arcing chamber of envelope 40. Normally, this device may be utilized in a closed circuit condition and the starter electrodes 41 and 42, which are respectively mounted upon fixed supportrod 43 and movable support rod 44, which is connected through bellows means 45 to an actuating arm (not shown), carry the steady-state current.

As is mentioned hereinbefore, the ferrous materials of the present invention are not adapted to carry a steady-state high circuit in vacuum arc devices in accord with the present invention. In such an arrangement, therefore, the

central portions

46 and 47 of

support rods

43 and 44, respectively, are normally fabricated from copper, silver, alloy or equivalent conductor which exhibits a low resistivity so as not to cause excessive heating and other deleterious effects. Such cuprous and equivalent low resistivity materials are ideally not suited for exposure to the operation of the device under arcing conditions, however. Should this occur, the vapor pressure of the copper or cuprous alloy could cause the emission of copper or other vapor which may deposit upon the surface of the ferrous arc electrode and shield members of the device so as to degrade the dielectric strength and the recovery characteristics of the device. Accordingly, in such device a pair of cladding members 48 and 49, which may for example be cylindrical'in nature, are press-fitted, or otherwise caused to enclose totally any surface of

support members

43 and 44 that is within envelope 14, so that the only materials exposed to the operation of the highcurrent arc during operation are ferrous materials.

In operation, the device 40 of FIG. 5 is in a normally conductive condition with current flowing through the

support members

43 and 44 and across contacts 41 and 42 which are ferrous, as is described hereinbefore, but of minimal thickness so as not to cause undue heating. Upon the occurrence of a fault or other reason for interrupting the flow of current within the circuit, a mechanical system (not shown) may be actuated to cause the movable support member 44 to be urged outwardly, as indicated by arrow 50, to cause the establishment of an interelectrode gap between now separated starter electrodes 41 and 42. When the distance between starter electrodes 41 and 42 exceeds the dimension of interelectrode gaps 21 between respective

rodlike members

16, 18, of arc electrode assemblies 11 and 12, particularly in view of the normal characteristic of the butt-type electrode to impel an arc outwardly, the arc is transferred to the parallel rod array and is distributed over the parallel paths 21 of FIG. 2 between oppositely poled parallel rods of arc electrode assemblies 11 and 12. This condition exists until the occurrence of a current zero, as is described hereinbefore, at which time the arc is extinguished.

Under certain circumstances, the delay caused by the mechanical manipulation of starter electrodes 41 and 42 and the support rods therefor may not be fast enough for the operation of the device. Thus, with the device in the normally open position, a triggerable vacuum switch may function by the addition of the trigger electrode structure as illustrated in the triggerable vacuum gap device 30 of FIG. 4 which may be actuated instantaneously upon the occurrence of a fault or overvoltage to change the device to the closed circuit condition and cause the fault current to be distributed across the rod array of assemblies 11, 12 even before the approaching starter electrodes 41 and 42 have an oportunity to close and carry the fault current.

As is readily apparent from the foregoing, the invention disclosed herein is applicable to a variety of devices, all of which are characterized as vacuum arc devices, but which may be switches, reclosers, gaps, triggered vacuum gaps, or the like. Accordingly, it is within the true spirit and scope of the invention that such applications of the principles of this invention to similar devices as fall within the purview of one skilled in the art shall be considered a practice of the invention.

While the invention has been disclosed hereinbefore with respect to certain specific embodiments and specific and illustrative examples of the invention, many modifications and changes will readily occur to those skilled in the art. Accordingly, I intend by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A vacuum arc device adapted tp carry high currents at high voltages and comprising:

a. an hermetically-sealed envelope evacuated to a pressure of 10 torr, or less;

b. a first primary arc electrode assembly disposed within said envelope and including a first plurality of spaced, substantially parallel, rod-like electrode members having smooth arcing surfaces extending substantially'normal to a first common base member;

c. a second primary arc electrode assembly within said envelope and including a second plurality of spaced, substantially parallel, rod-like electrode members having smooth arcing surfaces extending substantially normal to a second common base 'member and interleaved in alternating sequence between the spaced electrode members of said first arc electrode assembly;

d. said first and second spaced electrode members being positioned so as to form a ring-like array of electrode members within said envelope, said members alternating in polarity about said ring;

e. said electrode assemblies comprising ferrous material having a hardness as evidenced by a tensile strength of at least 100,000 psi and a ductility as evidenced by at least a percent elongation of a standard two inch long sample of standard ductility test cross section and having a substantial freedom of sorbed gases and gas-forming impurities therein so as to withstand arcing current densities of approximately 200 amperes/cm for a half-cycle of power-alternating voltage without the emission of any substantial quantityof gaseous material inconsistent with continued maintenance of said low pressure after having been arced thereby;

f. shield means surrounding said are electrode members to confine arcing specie to the interior thereof; and

g. means connecting said arc electrode assemblies in circuit with an electric load.

2. The device of claim 1 wherein said first electrode assembly includes an upper base member and a plurality of downwardly-depending smooth surface, rod-like electrode members and said second electrode assembly includes a base member and aplurality of upwardlydepending smooth surface, rod-like electrode members.

3. The device of claim 2 wherein each of said ferrous electrode assemblies is a vacuum-melted steel.

4. The device of.claim 3 wherein said ferrous electrode assemblies are fabricated from hardened steel having a Rockwell C hardness in excess of 30, a yield strength in excess of approximately 150,000 psi, and a ductility corresponding to an elongation of at least approximately percent of a 2 inch long standard cross section test sample.

5. The device of claim 4 wherein said ferrous material is a transformation induced plasticity steel.

6. The device of claim 4 wherein said ferrous metal is a maraging steel.

7. The device of claim 4 wherein said ferrous material is a carbon alloy steel having from 0.2 to 0.6 weight percent carbon therein.

8. The device of claim 4 wherein said ferrous assemblies are fabricated of a temperature annealing steel which increases in ductility during vacuum bakeout cycles used to fabricate vacuum arc devices of the order of 500 600 C.

9. The device of claim 2 wherein the device further includes means for establishing an electric arc between said arc electrode assemblies by establishing an electron-ion plasma therebetween.

10. The device of claim 9 wherein said device is a triggerable vacuum gap device and the means for supplying an electron-ion plasma therein is a trigger electrode assembly.

1 l. The device of claim 9 wherein the device is a vacuum switch and the means for supplying an electronion plasma therein is a starter electrode assembly adapted to establish a starter arc discharge therein.

12. The device of claim 9 wherein said starter electrode assembly constitutes a pair of arc electrodes located at the approximate longitudinal axis of said array.

13. The device of claim 12 wherein said starter electrodes are comprised of the same materials as said primary arc electrode assemblies.

14. The device of claim 12 wherein said starter electrodes are supplemented by a trigger electrode assembly to facilitate a recloser mode of operation.

15. The device of claim 12 wherein said starter electrodes are supported upon a pair of arc support members, the exterior surfaces of which consist essentially of ferrous material.

16. The device of claim 1 wherein said ferrous assemblies are fabricated of age-hardened steel which increases in hardness and yield strength during vacuum bakeout cycles used to fabricate vacuum are devices.

17. The device of claim 16 wherein saidbakeout temperatures are of the order of 900l 200F and are utilized for periods of from 5 24 hours.

18. The device of claim 16 wherein said hardness after vacuum bakeout is approximately at least 40 Rockwell C and is accompanied by a yield strength of at least approximately 150,000 psi.

19. The device of claim 1 wherein said ferrous metal is precipitation hardened.

Claims

1. A vacuum arc device adapted tp carry high currents at high voltages and comprising: a. an hermetically-sealed envelope evacuated to a preSsure of 10 5 torr, or less; b. a first primary arc electrode assembly disposed within said envelope and including a first plurality of spaced, substantially parallel, rod-like electrode members having smooth arcing surfaces extending substantially normal to a first common base member; c. a second primary arc electrode assembly within said envelope and including a second plurality of spaced, substantially parallel, rod-like electrode members having smooth arcing surfaces extending substantially normal to a second common base member and interleaved in alternating sequence between the spaced electrode members of said first arc electrode assembly; d. said first and second spaced electrode members being positioned so as to form a ring-like array of electrode members within said envelope, said members alternating in polarity about said ring; e. said electrode assemblies comprising ferrous material having a hardness as evidenced by a tensile strength of at least 100,000 psi and a ductility as evidenced by at least a 5 percent elongation of a standard two inch long sample of standard ductility test cross section and having a substantial freedom of sorbed gases and gas-forming impurities therein so as to withstand arcing current densities of approximately 200 amperes/cm2 for a half-cycle of power-alternating voltage without the emission of any substantial quantity of gaseous material inconsistent with continued maintenance of said low pressure after having been arced thereby; f. shield means surrounding said arc electrode members to confine arcing specie to the interior thereof; and g. means connecting said arc electrode assemblies in circuit with an electric load.

2. The device of claim 1 wherein said first electrode assembly includes an upper base member and a plurality of downwardly-depending smooth surface, rod-like electrode members and said second electrode assembly includes a base member and a plurality of upwardly-depending smooth surface, rod-like electrode members.

4. The device of claim 3 wherein said ferrous electrode assemblies are fabricated from hardened steel having a Rockwell C hardness in excess of 30, a yield strength in excess of approximately 150,000 psi, and a ductility corresponding to an elongation of at least approximately 10 percent of a 2 inch long standard cross section test sample.

6. The device of claim 4 wherein said ferrous metal is a maraging steel.

8. The device of claim 4 wherein said ferrous assemblies are fabricated of a temperature annealing steel which increases in ductility during vacuum bakeout cycles used to fabricate vacuum arc devices of the order of 500* - 600* C.

11. The device of claim 9 wherein the device is a vacuum switch and the means for supplying an electron-ion plasma therein is a starter electrode assembly adapted to establish a starter arc discharge therein.

16. The device of claim 1 wherein said ferrous assemblies are fabricated of age-hardened steel which increases in hardness and yield strength during vacuum bakeout cycles used to fabricate vacuum arc devices.

17. The device of claim 16 wherein said bakeout temperatures are of the order of 900*-1200*F and are utilized for periods of from 5 - 24 hours.

19. The device of claim 1 wherein said ferrous metal is precipitation hardened.