US3465192A

US3465192A - Triggerable arc discharge devices and trigger assemblies therefor

Info

Publication number: US3465192A
Application number: US580998A
Authority: US
Inventors: James M Lafferty
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-09-21
Filing date: 1966-09-21
Publication date: 1969-09-02
Anticipated expiration: 1986-09-02
Also published as: JPS485545B1; SE324187B; GB1190957A; DE1640255A1

Description

Sept. 2, 1969 J. M. LAFFERTY 3,465,192

TRIGGERABLE ARC DISCHARGE DEVICES AND TRIGGER ASSEMBLIES THEREFOR Filed Sept. 21, 1966 4 3 Sheets-Sheet l- F-fg/ I r0 LINE 4 23 TOLIIVE I Q 5 PULSE SOURCE is Attorney.

Sept. 2, 1969 J. M. LAFFERTY 3,465,192

' TRIGGEHABLE ARC DISCHARGE DEVICES AND TRIGGER ASSEMBLIES THEREFOR Filed Sept. 21, 1966 3 Sheets-Sheet 2 PUL .95

SOURCE 7'0 L/IVE T0 LINE KI V// //k [r7 vci rr'v 1707 t dd (I :2 a L by I a Z I is Attorney P 1959 .1. M. LAFFERTY 3,465,192

TRIGGERABLE ARC DISCHARGE DEVICES AND TRIGGER ASSEMBLIES THEREFOR Filed Sept. 21, 1966 5 Sheets-Sheet 3 PULSE SOURCE [r7 venzrcbr-v I M. Ld FFe rt United States Patent US. Cl. 3l3174 12 Claims ABSTRACT OF THE DISCLOSURE Improved trigger assemblies for vacuum are devices such as vacuum switches and triggerable vacuum gap devices, having a primary arc gap and a trigger assembly in which the trigger assembly includes a cavity containing a trigger gap and a trigger anode, and means adjacent the trigger gap for evolving ionizable species when the trigger gap is pulsed. The trigger assembly is separated from the primary gap by a nozzle which permits egress of the ionized species from the cavity into the primary arc gap, but inhibits ingress of particles and vapor from the are gap to the trigger gap. In one specific device, a large central post-like trigger anode further constricts the nozzle.

This application is a continuation-in-part of my copending application Ser. No. 516,914, filed Dec. 28, 1965, now abandoned, and assigned to the present assignee.

This invention relates to improved vacuum gap devices and particularly those which are triggerable upon receipt of a predetermined signal to cause breakdown thereof and electrical conduction therethrough by a high current are. More particularly, the invention relates to such devices having improved trigger electrode configurations designed for long-life and heavy duty operation.

Vacuum switches and vacuum gaps, particularly those triggerable to cause breakdown thereof by receipt of an electric signal, have recently been the subject of intense improvement and development. Until recently, a very serious limiting factor as to the current carrying capacity of such devices and their adaptability for high current, high voltage operation, particularly with a heavy-duty cycle, has been the instability or unreliability of breakdown insofar as voltage and time are concerned. Thus, for example, the voltage at which a given gap would breakdown to cause the establishment of an electric arc was very often a function of the history of previous breakdowns of the gap. Similarly the length of time required for such breakdown also appeared to be a function of the history of the gap, of the prior breakdowns and the intervening periods of time. In accord with my issued US. Patent No. 3,087,092, entitled Gas Generating Switching Tube, issued Apr. 23, 1963, I have made possible the establishment of a high current are between the electrodes of a vacuum gap by providing a trigger means for injecting into the primary gap a gaseous plasma sufiicient to cause the breakdown thereof, which injection may be accomplished with great speed and accuracy to eliminate the instabilities in time and breakdown voltage of the devices of the prior art.

While the vacuum gaps of my aforementioned invention are exceedingly useful and their development has literally opened entirely new fields to the vacuum gap, under certain circumstances it is desirable to provide additional improvements to render the devices more suitable for heavy duty operation. Thus, for example, when the voltage and/or current with which the devices are operating becomes quite large, it becomes difiicult to protect the trigger assembly which is associated with at least the cathode electrode from the deleterious effects of being closely associated with the high current are.

Accordingly it is an object of the present invention to provide triggerable vacuum gap devices suitable for operation with high currents or voltages and suitable for longlife and heavy duty.

Another object of the present invention is to provide triggerable vacuum gap devices having structures wherein the triggering means is protected from the influences of the high current are established therein.

Another object of the present invention is to provide improved vacuum gap devices in which the trigger assembly thereof is protected from short circuiting thereof.

In accord with one feature of the present invention I provide a vacuum gap device including a pair of primary electrodes defining therebetween a vacuum gap. These electrodes are located within an evacuated envelope, which envelope is composed partially of metal and at least in part of a high voltage insulating substance so as to provide electrical isolation between the primary electrodes to prevent short-circuiting of the gap defined thereby. 'In one embodiment of the invention, both electrodes may be fixed electrodes defining a fixed gap. In another embodiment, one electrode may be attached to a suitable vacuum type bellows which permits the relative motion between the two primary electrodes so as to allow the gap to be manually operable and/or reclosable.

In accord with this invention a trigger electrode is located concentrally within at least one of said primary electrodes. If the device is particularly adapted to be utilized with unidirectional voltages, as for example, in crowbarring a bank of capacitors, the trigger electrode need only be associated with one electrode, namely the cathode electrode and is concentrically recessed within an aperture in the center thereof. On the other hand if the device is to be associated with an alternating voltage, as for example a high voltage transmission line or a voltage across a transformer associated with such a line, a trigger electrode and associated assembly are concentrically located within an aperture in each of the cathode and anode electrodes so that irrespective of which electrode is cathode at the time that are interruption or closure is affected, that electrode which is instantnaneously the cathode has a trigger electrode associated therewith.

In further accord with the present invention the trigger electrode assembly includes a central cylindrical trigger electrode member with an insulating member surrounding and concentric therewith, both of which are recessed within the main or primary electrode, the inner surface of which is shaped so as to provide limited access between the primary gap, which sustains the main breakdown voltage, and the region in which a pulse causes the feneration of arc initiating means within the trigger electrode assembly. Thus, upon recepit of an electrical pulse the trigger gap within the trigger electrode assembly is broken down and a pulse of electron-ion plasma is propelled through a restricted orifice into the main gap causing the breakdown thereof. On the other hand it is difi'icult, if not impossible, for the electric arc to penetrate through the restricted orifice into the trigger electrode assembly where the trigger gap is located to cause damage thereto. In further accord with one feature of the invention the trigger gap of the trigger assembly is located on a vertical surface within the assembly to further prevent shortcircuiting thereof.

The novel features believed characteristic of the pres ent invention are set forth in the appended claims. The invention itself together with further objects and advantages thereof may be more readily understood by reference to the attached drawings in which:

FIGURE 1 is a vertical cross-sectional view of a triggerable vacuum gap device constructed in accord with the present invention;

FIGURE 2 is a vertical cross-sectional view of the trigger electrode assembly of the device of FIGURE 1;

FIGURE 3 is a vertical cross-sectional view of an alternative embodiment of the present invention;

FIGURE 4 is a vertical cross-sectional view of the trigger electrode assembly of the device of FIGURE 3;

FIGURE 5 is a vertical cross-sectional view of a trigger assembly in accord with another embodiment of the invention; and

FIGURE 6 is a vertical view, with parts broken away, of a vacuum switch in accord with the invention.

In FIGURE 1, a triggerable vacuum gap device constructed in accord with the present invention includes a gas impervious insulating envelope 1 which is composed of a lower flanged disc envelope assembly 2, a cylindrical sidewall member 3 and an upper end plate 4. A discshaped electrode support member 5 is supported between end wall assembly 2 and cylindrical sidewall member 3. A pair of arc-

electrodes

6 and 7 are supported in spaced apart relationship with envelope 1 to define a primary gap 8. Anode arc-electrode 7 is supported by anode support members 21. A shield member 22 is also fastened to and supported by anode support 21. Shield 22 is for screening a portion of the interior surface of envelope 1 from vaporized metal to retain the insulating characteristic thereof.

The details of cathode arc-electrode and the trigger assembly contained therein are more clearly illustrated in FIGURE 2 which bears like numeral identification. Cathode arc-electrode 6 is a solid block of electrode material with a central aperture therein having a first smaller diameter bore 9 and a second larger diameter bore 10 of approximately one half the depth of penetration as bore 9. Bore 9 penetrates to within a relatively close proximity to the inwardly depending surface 11 of cathode arc-electrode 6. The distance between the inward termination of bore 9 and surface 11 is penetrated by a frusto-conical aperture 12 which constitutes, in effect, a nozzle as will be more fully described hereinafter. Nozzle 12 has a smaller diameter at the inwardly depending surface 11 of electrode 6 and a larger diameter at the intersection with counterbore 9. A hollow cylindrical metal sleeve 13 having an annular flanged portion 14 abuts against the collar formed at the intersection of

counterbores

9 and 10 with the exterior edge of flange member 14 resting against the inner diameter of counterbore 10 and the transverse surface of collar 14 resting against the body of cathode 6. This causes cylinder 13 to be concentrically located within the central orifice within electrode 6. A second cylinder member 15 containing an annular ceramic insert 16 through which passes a trigger electrode 17 is inserted into counterbore 10 and abuts the outwardly depending surface of flange portion 14 of cylinder member 13. Trigger electrode 17 extends to substantially the end of cylinder member 13 where it terminates, and is substantially of the same diameter as the smaller diameter end of nozzle 12. The inwardly depending surface 18 of ceramic insert 16 is coated with a suitable active-gas-storing material as for example titanium metal, and an annular groove 19 is scored therein so as to provide an annular trigger gap at groove 19 one side of which is connected through cylinder 13 and cylinder 15, to the exterior of the device and the other side of which is connected through trigger electrode 17 to the exterior of the device, both electrical connections being made to pulse source 20.

Envelope members 2 and 3 may be fabricated from any gas-impervious, nonconducting material which may be hermetically sealed to a metal electrode. Generally, any gas-impervious ceramic may be utilized, such as Coors V-200 or American Lava-T-164. Alternatively, an aluminum oxide or fosterite ceramic body may be used. It is to be understood, however, that although these specific materials have been enumerated, any gas-impervious ceramic or glass which may be hermetically sealed to metal members may also be utilized.

Electrodes

6 and 7 are fabricated from copper that is substantially free from all gaseous impurities or impurities which, upon decomposition, may produce gasses. This copper should contain less than one part in 10' atomic parts of all gasses and gas-forming constituents and should be operative under arcing conditions to keep the pressure within the device always at a pressure of less than 10* mm. of Hg. Such material may readily be formed by a special zone-refining process as for example that set forth in the U.S. Patent 3,234,351 to M. H. Hebb, issued Feb. 8, 1966.

Electrode support members

5 and 20, although of nominally gas free metal, need not meet the stringent criterion set forth with respect to

electrodes

6 and 7 since they are not brought into contact with an electric arc and therefore are not a potential source of vacuum spoiling gasses.

Trigger electrode 17 may conveniently be constructed of a refractory metal such as a tungsten or rhenium. Cylinder 13 may be conveniently constructed of a refractory metal suitable for withstanding the temperature of the footpoint of an arc as for example with molybdenum or tungsten but the interior thereof is surface coated with a layer 13 of a susbtance which may serve as a reservoir for active gasses such as hydrogen and conveniently may be coated with titanium metal or titanium hydride. Alternately layer 13 may be of a hydride forming metal as is set forth in my copending application Ser. No. 565,204, filed July 14, 1966, now Patent No. 3,331,988, and assigned to the present assignee. Additionally layer 13 may be formed of a high vapor pressure (as compared with tungsten and rhenium) having boiling points in excess of 1500 C. but not in excess of 5000" C. and work functions preferably in excess of 4 ev. as for example copper beryllium, tin aluminum, iron, nickel, cobalt and lead, as are disclosed and claimed in my copending application Ser. No. 516,942, filed Dec. 28, 1965, and now abandoned, the disclosures of which are incorporated herein by reference thereto. In this instance the metalic coating itself supplies the conduction carriers to cause breakdown of the primary gap.

In fabricating the device of FIGURE 1, the arc-electrode bodies are prepared and suitably shaped from highly purified copper or other suitable high purity materials as is set forth hereinbefore. Electrode support 21 is fastened to electrode 7, as for example, by brazing, and shield member 22 is fastened to electrode support member 21 in a similar fashion. Electrode 6 is fastened to electrode support member 5 by a suitable brazing step. Molybdenum cylinder 13 is prepared and shaped and the interior thereof coated with a suitable active gas storing material, as for example a thin layer of titanium, or a suitable low vapor metal such as copper or beryllium. Trigger electrode 17 is inserted within disc 16 and a layer of titanium or of copper or other low vapor pressure metal, is deposited upon the inwardly depending surface 18 thereof. Alternatively the trigger electrode may be uncoated. Groove 19 is cut in the inwardly depending surface of disc 16 through the deposited titanium or copper etc. layer and the disc and electrode are inserted with, and sealed to, molybdenum cylinder 15. The assembly so formed is inserted into electrode 6 and appropriately sealed thereto by appropriate brazing between molybdenum cylinder 10 and copper electrode 6.

The cathode arc-electrode 6 and its associated parts are then fitted to cylinder member 3. End plate 2 is placed thereover, anode electrode 7 and its associated parts are fastened by a suitable brazing step to end cap 4 and the two end caps are appropriately sealed by ceramic-tometal seals to envelope 1. This process may be accomplished in a suitable pressure of an active gas for example in one atmosphere pressure of hydrogen in a hydrogen furnace, so that the active gas storing material within the device collects the trapped gas as it cools, thus lowering the pressure to a hard vacuum of mm. Hg or less. Alternatively an appropriate tubulation 23 may be connected to a vacuum pump and the device may be evacuated, filled and sealed subsequent to the formation of the ceramic-to-metal seals. It a low vapor pressure metal is used, no active gas is necessary and the processing may be conducted entirely in vacuo.

In operation, a source of high voltage, in this instance unidirectional voltage in the hundreds of kilovolts. range as illustrated, is connected between electrode support member 21 and electrode support member 5 and held oil by the high dielectric strength of the vacuum within gap 8. Alternatively the identical trigger to that illustrated in FIGURE 1 and associated with cathode electrode 2 may be built into, and associated with, anode electrode 7 and the device may be connected to an alternating voltage source or line. In either event, if the device is to be used as a circuit interrupter or to discharge a capacitor bank or the like, the primary electrodes are connected in series with a high current line which may for example carry or be adapted to carry currents in the hundreds of kilovolts range. A suitable source of pulse voltage sufiicient to cause a trigger are as for example from 50 to 1000 volts, is applied to cylinder 10 and trigger electrode 17. When this source causes a pulse to be applied to these members the voltage appears across the gap formed by groove 19 on the surface 18 of ceramic disc 16 and vacuum breakdown occurs. The heat of the discharge causes hydrogen or other stored active gas to be released from the titanium hydride or other active gas storing substance with which the disc is coated and the space between the trigger electrodes 17 and cylindrical member 13 becomes filled with evolved gas which is readily ionized. If a low vapor pressure metal is utilized the metal ions are boiled off and ionized to produce an ion-electron plasma. An electric arc is then established between these two members. Since the current path is up electrode 17, through the arc to cylinder 13, down cylinder 13 to cylinder 15, and back to the pulse source, a current loop is formed which produces magnetic forces which interact with the are causing it to be rapidly propelled to nozzle 12. When the arc reaches nozzle 12 a cloud of electronion plasma is injected through nozzle 12 into gap 8. Since a high voltage and a high electric field exist across gap 8 the appearance of a burst of electron-ion plasma causes the immediate breakdown of gap 8 and a high current discharge is initiated between

electrodes

6 and 7. Since the gap-adjacent end of nozzle 12 is of substantially the same diameter as the trigger electrodes 17 the interior of the trigger electrode assembly, and more specifically, the trigger gap is substantially shielded from the arc so that the arc may not be destructively terminated in this vicinity, nor will metallic vapors evolved from

electrodes

6 and 7 cool and condense upon gap 19 to short-circuit the same. Thus, the operation of the device is permitted at substantially identical conditions of breakdown voltage and time of breakdown for many operations and during heavy duty at high voltage and high current ratings.

When the purpose for the establishment of a high current discharge between

electrodes

6 and 7 has passed, as for example, when a fault in an electric transmission line has been cleared or after the stored electric charge in a capacitor bank has been discharged, the discharge between

electrodes

6 and 7 is extinguished. In alternating current operation this will occur each time the voltage wave passes through a current zero and, unless the arc is retriggered, it will be extinguished in less than one half cycle. If the voltage is a unidirectional voltage, as for example, through a capacitor bank, the voltage must be disconnected or dissipated before the arc is extinguished, or the charge upon the capacitor bank must be exhausted. Upon the extinction of the are between

electrodes

6 and 7, the conduction carriers, which are electrons and metallic ions evaporated from

electrodes

6 and 7, are immediately cooled and migrate to either the electrodes or to the interior walls of shield 22 where they are removed from the atmosphere thus returning the device to a high vacuum. Since the diameter of trigger electrode 17 is substantially the same as that of the smaller orifice in nozzle 12 substantially no metallic vapors will penetrate into and condense upon the trigger gap. Because the high vacuum is immediately restored upon the extinction of the electric discharge the device is almost instantaneously, within a matter of a few microseconds or less, ready for another firing. Likewise, since the next breakdown of the gap is established by virtue of a second pulsing of the trigger, the previous arcing history of the gap does not determine the breakdown characteristics of the primary In FIGURE 1 of the drawing a single pulse source has been indicated as being connected between the electrodes of the trigger gap. If an alternating current adapted device is utilized, it will readily be apparent to those well versed in the art that a scond pulse source could be likewise connected to the other electrodes or, alternatively, the same pulse source could apply the pulse to both anode and cathode electrodes and, assuming that the pulse source is grounded and the voltage upon each of the line conductors has a predetermined relationship to ground potential, the trigger pulse will occur only between the electrodes that is most negative with respect to ground and the associated electrode assembly.

In FIGURE 3 of the drawing another embodiment of the invention having unique advantages which are obtained with relative simplicity is illustrated. In FIG- URE 2 the elements of the device are identical with that of the device of FIGURE 1 with the exception of the configuration of the trigger electrode and the adjacent portions of the primary electrode, which will herein be referred to as cathode. With these exceptions, like numerals are used to identify like parts to those in FIG- URE 1 of the drawing. An enlarged view of the trigger assembly of FIGURE 3 is illustrated in FIGURE 4 and similarly numbered. In FIGURES 3 and 4, electrode 6 has an axial aperture therein into which fits a trigger assembly 25. Trigger assembly 25 is composed of a molybdenum cylinder having a regular right circular cylindrical exterior surface and an interior surface which is right circular cylindrical at the outwardly depending edge end thereof but which changes into a curvilinear surface which constitutes an axis symmetric convergent divergent nozzle. This shape is characterized by a cylinder of revolution which starts to converge or decrease in diameter from a large value to a small value which is the minimum dimension and is indicated at 26 on FIGURES 3 and 4 from which the interior diameter regularly and curvilinearly increases to the value of the exterior diameter. A trigger electrode assembly is inserted into the regular portion of the interior bore of trigger electrode assembly 25 and constitutes an annular ceramic washer 27 having a metallized inwardly depending surface 28 with an annular groove 29 cut therein. This disc fits into the central aperture within cylinder 25 and rests upon a shoulder 30 which is the intersection between the regular and irregular portions of the interior surface of cylinder 25. A trigger electrode 31 having an interior, larger diameter 32 is bonded to the inwardly depending surface of ceramic annular disc 27 and forms an hermetic seal therewith. The main protiou of electrode 31 extends through a central aperture in disc 27 and terminates in a trigger electrode lead 33.

In the operation of devices of the general class to which this invention relates there is an ever present danger that, particularly at high voltage operation, an arc will be initiated between the trigger gap and the anode immediately upon the creation of an electron-ion plasma in the vicinity of the trigger gap. The structure of the trigger electrode assembly of the device of FIGURE 3 completely obviates this possibility. The breakdown of gap 29 upon the application of a pulsed voltage thereto causes the evolution of a plasma into the throat 34 of the nozzle and, because of the severe constriction of the space between the trigger electrode 32 and the interior of the interior surface 26 of the cylindrical member the arc cannot extend down into the vicinity of the trigger gap without requiring the expenditure of a greater amount of energy than is required to establish an arc termination in the open throat of nozzle 34. Thus the farthest point within the throat 34 of the nozzle to which an arc foot-pc-intmay be located is in the vicinity of the constricted portion at 26.

The operation of the device of FIGURE 3 is essentially the same as that of the device of FIGURE 1. The triggering pulse is applied between cathode electrode connection 5 and trigger lead 33. Upon initiation of the trigger pulse, which may be from 50 to 1000 volts for example, breakdown occurs accross annular gap 29 and an electron-ion plasma is caused to be injected into the throat 34, an electric arc is established between

electrodes

6 and 7. If under high voltage conditions the arc should establish quickly the nearest it can get to the trigger gap is at 26 or higher in the throat of the nozzle. Similarly, during operation, the trigger gap is protected from short-circuiting or loss of resistance by the condensation of metallic particles thereon because the annular gap is constantly in the shadow of the smallest diameter portion of the throat of the nozzle by virtue of the shape of the nozzle throat.

Thus, in accord with the present invention which has been specifically discussed with respect to two particular embodiments, the main gap discharge establishes a cathode spot on the negative primary electrode with less energy than would be required for the discharge to pass down the restricted portion of the trigger assembly particularly in the embodiment of FIGURE 2 wherein only a narrow annular slot is the entrance thereto.

While the embodiments of the invention and the general principles thereof described hereinbefore are particularly effective in preventing establishment of the main arc with a footpoint upon the trigger gap so as to cause damaging thereof, under certain circumstances other difficulties require additional features. Thus, for example, when interrupting currents of the order of 100,000 amperes at kilovolt potentials, wherein there may be a substantial amount of melting of one or more of the main electrodes or the ejection of large particles therefrom and when the gap device is mounted vertically with the gap in the lower portion thereof, the constriction between the central trigger electrode and the throat or nozzle portion of the main electrode, illustrated in detail in FIGURES 2 and 4, that constitutes the protection of the trigger gap may be shorted by accumulated particles. Similarly the possibility exists, under these circumstances, that liquid arc electrode material may fall to the bottom of the trigger gap area and may spread over the surface of the ceramic insulator and short-circuit the trigger gap.

In FIGURE 5 of the drawing, an embodiment of the invention comprising a trigger electrode assembly, specifically constructed to avoid the aforementioned difficulties, is illustrated. In FIGURE 5 trigger electrode assembly 39 comprises a hollow cylindrical member 40 resting upon and electrically and mechanically fastened to an apertured disk 41, which in turn rests upon and is similarly fastened by welding, brazing or other suitable means to hollow arc-electrode support member 42. The exterior active surface of electrode assembly 39 includes the upper surface 43 of cylindrical member 40 and the upper surface 44 of an annular apertured concave inwardly tapered nozzle member 45 which is tightly fitted within the inside diameter of cylindrical member 40 and securely electrically and mechanically fastened thereto, so as to cause the upper surface to be flush with the upper surface 43 of cylindrical member 39. An annular insulator such as a ceramic washer or ring 46 is disposed immediately beneath the lower surface of annular nozzle member 45 and is tightly fitted within a counterbore in the underside thereof forming a collar 47. Annular ceramic member 46 in turn rests upon, fits over, and surrounds an annular shoulder 48 in a trigger electrode cup 49, which is cupshaped with a central aperture in the lower portion thereof. Cup 49 constitutes the walls of the trigger electrode cavity 50 and is, electrically, the trigger anode.

Trigger electrode cup member 49 is securely seated upon an apertured insulating disk 51, which in turn is supported by a helical refractory metal spring 52, which rests upon and holds the entire assembly tightly together in spring tension, but not in hermetic seal upon disk member 41 of trigger electrode assembly 39. A trigger anode lead 53 passes upwardly through the hollow core in electrode support member 42 and the aperture in electrode disk member 41, through the aperture in ceramic disk member 51 and is suitably inserted into the aperture in trigger electrode cup and anode member 49 and suitably fastened thereto in mechanical and electrical connection by welding, brazing or other appropriate means.

Members

40, 45, 46 and 49 are all concentrically disposed about a longitudinal axis running through nozzle 45, cavity 50 and trigger anode lead 53.

As with the arc-supporting members described hereinbefore, disk members 41 and cylinder member 40 are conveniently constructed of a highly purified gas-free refractor metal, as for example, molybdenum, as is spring member 52. Annular member 45 may be coated with copper, beryllium, or other high vapor pressure metal, if desired. Ceramic insulating

members

46 and 51 may conveniently be constructed of the same material as the other insulating

members

16 and 27 in the embodiments of FIGURES l to 4, respectively, as for example, a suitable fosterite ceramic, high density alumina, or the like. The inner cylindrical surface of ceramic washer 46, concentric with the longitudinal axis of the nozzle and cavity, is coated with a film of active gas storage metal such as titanium or a high vapor pressure metal such as copper or beryllium and an annular groove is scored therein to form a trigger gap 54 with a pair of electrically conductive metallic ionizable material supplying films 55 and 56 immediately adjacent thereto.

The electrode assembly of FIGURE 5 which includes the trigger electrode configuration specifically adapted to avoid the aforementioned difficulties functions essentially as follows. The electrode assembly may be mounted upon disk 5 in the embodiment of the device of FIGURE 5 in lieu of the cathode electrode structure therein. Alternatively, the electrode assembly may be assembled in the embodiment of FIGURE 6 as will be discussed more fully hereinafter. Irrespective of its location, the main body of the electrode may be connected generally to the negative pole of the applied voltage and a slightly positive (as compared with line voltage) trigger signal voltage is applied to trigger anode lead 53. The upper gap adjacent ionizable material source film 55 may be connected through

members

45, 40, 41 and 42 to one pole of the electrical line to which the gap device is connected. The other gap adjacent metalized ionizable material source film 56 is connected through electrode cup member 49 and trigger anode lead 53 to a source of positive pulsed voltage so that, upon the application of a pulse, the trigger gap breaks down. This breakdown causes the release of either ionized active gas, as for example, hydrogen, or ionized high vapor pressure metal, as for example, copper or beryllium, which fills the cavity 50 of the trigger electrode assembly and is propagated out into the interelectrode space through the aperture in annular electrode nozzle member 45.

The effect of the propagation of the cloud of ionized particles, constituting an electron-ion plasma, into the interelectrode spacing between the arc cathode 6 and the arc anode 7 (as for example in FIGURE 1 or 3), is the same as in the embodiment of the devices illustrated in 9 FIGURES 1 and 3 hereinbefore, and initiates breakdown of the primary gap.

As with the embodiments of FIGURES 1 and 3, as is shown in greater detail in FIGURES 2 and 4, the trigger gap 54 is recessed away from the interaction space between the primary arc-electrodes. Hence there is no path for line of sight transmission between the interelectrode space and the trigger gap 54, so that metallic particles may be projected or diffused directly to the gap 54 to cause shorting or high resistance degradation thereof. Additionally, since the gap is upon a vertical wall, concentric with the longitudinal axis of the nozzle and the cavity, and substantially removed from the possible resting point of any molten arc-electrode material or the final resting place of any particles of electrode material, the gap may not be shorted or further degraded by molten arc-electrode material or large solid particles thereof. This feature may be further enhanced by making the depth of cup 49 deeper for higher current devices; Accordingly the trigger electrode assembly of the illustration of FIGURE possesses the advantages of the embodiments of FIGURES 2 and 4 and the additional advantage of being protected from falling solid particles or liquid arc-electrode metal which could short-circuit the gap under exceedingly heavy arcing currents. In another alternative structure, the trigger electrode of FIGURE 5 may be electrically and mechanically isolatedfrom the primary arc-electrodes but so disposed adjacent the interelectrode gap as to effectively cause the breakdown thereof when pulsed by a trigger pulse substantially in the same manner as if the trigger electrode assembly were a part of one primary arc-electrode.

FIGURE 6 of the drawing illustrates, in vertical sectical sectional view with parts broken away, an embodiment of the invention alternative to those of FIGURES 1 and 3, wherein a pair of arc-electrodes are disposed in opposed relationship, each of which contains a trigger assembly locataed therein, particularly adapting the device for use with alternating currents. Each of the trigger electrode assemblies is substantially that illustrated in FIGURE 4 of the drawing and the trigger anodes thereof are connected to a grounded pulse source adapted to provide a positive voltage pulse, while each of the primary arc-electrodes is connected, either in series or parallel circuit relationship, depending upon the application to which the device is to be used, to a voltage or current line to be protected, switched, or otherwise controlled. In accord with this embodiment of the invention, one of the arc-

electrodes

6 and 7 is always more negative and the positive pulse is applied to both trigger anodes. The trigger breakdown then occurs at the trigger assembly associated with the primary arc-electrode which is most negative with respect thereto.

An additional feature of the device of FIGURE 6 is the utilization of a sylphon bellows 60 which is connected between arc-electrode support member 61 and insulating bushing 62 to allow arc-electrode 6 to be moved with a reciprocating motion into and out of engagement with arc-electrode 7 for circuit making and breaking operations. Although the trigger electrode configuration illustrated in FIGURE 4 of the drawing has been represented in FIGURE 6 it is to be understood that the trigger electrode configuration of FIGURE 2 or of FIGURE 5 could similarly be utilized in the device of FIGURE 1, either with the double trigger electrode assembly or with the feature of a moveable primary electrode for circuit-making and breaking operations.

While the invention has been disclosed herein with respect to particular embodiments thereof, many modifications and changes will occur to those of routine skill in the art. Accordingly, by the appended claims I intend to cover all such modifications and changes as fall within the true spirit and scope of this invention.

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

1. A triggerable vacuum gap device comprising:

(a) an evacuable envelope at least a part of which is formed of electrically insulating material so as to provide at least two electrically isolated portions thereof and evacuated to a hard vacuum of 10* mm. Hg or less;

(b) a pair of primary arc-electrodes disposed in electrically insulated relationship within said envelope and juxtaposed with respect to one another so as to define a primary gap,

(c) means adjacent said primary arc gap defining a central cavity with a restricted diameter nozzle adjacent the said primary arc gap;

(d) means located within said central cavity for injecting a pulse of plasma into said primary gap upon receipt of an electrical signal and including:

(d at least one metal-to-ceramic interface comprising a trigger gap,

(d means adjacent said trigger gap for storing ionizable material during non-operating conditions under a vacuum of 10- mm. Hg or less and for releasing ionizable particles upon electrical breakdown of said trigger gap,

(d and a trigger anode mounted in electrical contact with one side of said trigger gap, and located within said central cavity; said trigger anode projecting upwardly into the restricted diameter of said nozzle to further restrict communication between said primary gap and said central cavity to prevent meltable particles from said primary gap from entering said cavity and reaching said trigger gap;

(e) said nozzle having an inside diameter and being positioned with respect to said trigger gap and said trigger anode as to effectively shield said trigger gap from the effects of a high current are between said primary arc-electrodes; and

(f) means for supplying an electric voltage pulse of predetermined magnitude to said trigger gap to cause a trigger discharge thereacross and the subsequent breakdown of the primary gap.

2. The device of claim 1 wherein the ionizable material is hydrogen and the ionizable material storing means is a film of titanium.

3. The device of claim 1 wherein the ionizable material storage means is a film of a high vapor pressure metal.

4. The device of claim 1 wherein both of said primary arc-electrodes are fixed to define a fixed gap.

5. The device of claim 1 wherein at least one of said electrodes is movable to define a variable gap.

6. The device of claim 1 wherein the nozzle is in the form af a truncated cone and the trigger electrode associated therewith has a diameter of approximately the same dimension as the smaller diameter of said truncated cone.

7. The device of claim 1 wherein the nozzle is an axisymmetric convergent-divergent nozzle having a minimum diameter portion which shields the triggger gap from straight line communication with the primary gap and said trigger anode projects into the minimum dimension portion thereof to further increase said shielding.

8. A triggerable vacuum gap device comprising:

(a) an evacuable envelope at least a part of which is formed of electrically insulating material so as to provide at least two electrically isolated portions thereof and evacuated to a hard vacuum of 10 mm. Hg or less;

(b) a pair of primary arc-electrodes disposed in electrically insulated relationship within said envelope and juxtaposed with respect to one another so as to define a primary gap;

(c) means adjacent said primary arc gap defining a central cavity with a restricted diameter nozzle adj acent said primary arc gap;

(d at least one metal-to-ceramic interface comprising a trigger gap, said trigger gap being an annular groove in the inner wall of an annular metalized insulating member located behind the inwardly projecting portion of said restricted diameter nozzle, said inner wall being coaxial with the longitudinal axis of said nozzle;

(d a cup-shaped trigger anode within said cavity and located sufiiciently remote from said gap on the opposite side thereof from said nozzle to facilitate the accumulation therein of ejected solid and molten parts of said primary electrodes incident thereinto without degrading the electrical characteristics of said gap,

(d means adjacent said trigger gap for storing ionizable material during non-operating conditions under a vacuum of 10- mm. Hg or less and for releasing ionizable particles upon electrical breakdown of said trigger gap;

(c) said nozzle having an inside diameter and being positioned with respect to said trigger gap as to eifectively shield said trigger gap from the eifects of a high current arc between said primary arc-electrodes; and

9. In a vacuum gap device including an evacuable envelope, at least a portion of which is electrically insulated from the remainder thereof, and a pair of primary arc-electrodes disposed in insulating relationship therein to define a primary breakdown gap, the improvement of a trigger assembly comprising:

(a) an apertured outer body having a hollow central cavity therein;

(b) a restricted diameter nozzle at said aperture, said nozzle including an annular inwardly depending portion having an inner diameter substantially smaller than the diameter of said hollow cavity;

(c) a trigger gap located within said cavity and juxtaposed therein so as to be shielded from line-of-sight communication with said primary breakdown gap;

((1) means adjacent said trigger gap for storing readily ionizable material adapted to sustain a vacuum of mm. Hg but to emit vaporized and ionized material upon breakdown of said trigger gap;

(e) a trigger anode being electrically connected to one side of said trigger gap and having a rod like cylindrical shape and a diameter substantially the same as the inside diameter of the smallest portion of said nozzle and being closely juxtaposed thereto to permit the escape of electron-ion plasma from said cavity but prevent the entrance of material from said primary gap into said cavity, and

(f) means for applying a trigger voltage pulse to said trigger gap to cause the generation of an electron-ion plasma and the subsequent injection of said plasma outwardly through said nozzle to cause said primary gap to be rendered conducting while said nozzle is eflective to shield said trigger gap from contamination by the efiects of said conducting primary gap.

10. The improvement of claim 9 wherein said nozzle is an asymmetric convergent-divergent nozzle and a rod shaped cylindrical trigger anode having a diameter only slightly less than the minimum diameter of said nozzle interior projects to within the minimum diameter portion of said nozzle to permit the injection of electron-ion plasma into said gap but prevent the entrance of products of arcing between said primary gap to reach said trigger gap.

11. In a vacuum gap device including an evacuable envelope, at least a portion of which is electrically insulated from the remainder thereof, and a pair of primary arc-electrodes disposed in insulating relationship therein to define a primary breakdown gap, the improvement of a trigger assembly comprising:

(a) an apertured outer body having a hollow central cavity therein;

(d) means adjacent said trigger ga for storing readily ionizable material adapted to sustain a vacuum of 10- mm. Hg but to emit vaporized and ionized material upon breakdown of said trigger gap,

(c) said nozzle being formed by an inwardly depending annular member between said primary breakdown gap and said cavity, said cavity being lined with a metallic member comprising a trigger anode and said breakdown gap being located along the lateral walls of said cavity between said nozzle and said trigger anode and electrically connected therebetween, and

(f) means for applying a trigger voltage pulse to said trigger gap to cause the generation of an electron-ion plasma and the subsequent injection of said plasma outwardly through said nozzle to cause said primary gap to be rendered conducting while said nozzle is efiective to shield said trigger gap from contamination by the effects of said conducting primary gap.

12. The improvement of claim 11 wherein the trigger anode is a refractory metal cup and the trigger gap is a scored groove in a cylindrical surface of an annular insulating member, said cylindrical surface being coaxial with the longitudinal axis of said cavity and nozzle and coated with a metallic film.

References Cited UNITED STATES PATENTS 3,087,092 4/1963 Laiferty 313-197 X 3,188,514 6/1965 Cobine 3l3l97 X 3,303,376 2/1967 Lafferty 3l3-l98 X JAMES W. LAWRENCE, Primary Examiner PALMER C. DEMEO, Assistant Examiner US. Cl. X.R.