US3887778A - Vacuum arc device with improved arc-resistant electrodes - Google Patents

Abstract

Improved vacuum arc devices include an hermetically sealed envelope evacuated to a hard vacuum and including a pair of gasfree arc-electrode assemblies each of which has a surfaceadjacent portion thereof adapted to sustain the footpoint of a vacuum arc. The arc sustaining portion of at least one arcelectrode includes titanium as a base constituent and another constituent having a relatively high vapor pressure as compared with titanium, but having a vapor pressure of less than 10 3 torr at a pressure of 500*C. In a preferred embodiment, the minor constituent comprises beryllium.

Description

United States Patent Farrall June 3, 1975 [54] VACUUM ARC DEVICE WITH IMPROVED 3,627,963 l2/ 1971 Lindsay 200/166 C ARC'RESISTANT ELECTRODES FOREIGN PATENTS OR APPLICATIONS Inventor: George Farrall, Schenectady, 693,827 9/1964 Canada 200/144 B [73] Assignee: General Electric Company, Primary Examiner-Robert Macon Schenectady NY. Attorney, Agent, or FzrmLeo I. MaLossi; Joseph T.

Cohen; Jerome C. Squillaro [22] Filed: Sept. 13, 1973 [2]] Appl. No.: 396,817 [57] ABSTRACT Related Application- Data Improved vacuum arc devices include an hermetically [63] Continuationdm an of Ser No 305 649 Nov 10 sealed envelope evacuated to a hard vacuum and in- 1972 which is g continuation)? eluding a pair of gas-free arc-electrode assemblies Feb. 1971 abandoned each of which has a surface-adjacent portion thereof adapted to sustain the footpoint of a vacuum arc. The [52] US. Cl 200/144 B are Sustaining Portion of at least one arc'electmde 51 Int. Cl. HOlh 33/66 dudes titanium as a base nstituem and another [58] Field of Search 200/144 B 166 c Stiwent having a relatively high vapor Pressure as 7 compared with titanium, but having a vapor pressure [56] References Cited of less than 10 torr at a pressure of 500C. In a preferred embodiment, the minor constituent comprises UNITED STATES PATENTS beryllium. 3,328,545 6/1967 Holliday 200/144 B 3,497,755 2/1970 Horn 200/144 B 3 laims, 1 Drawing Figure LQ Z 2 f I l6 VACUUM ARC DEVICE WITH IMPROVED ARC-RESISTANT ELECTRODES This invention relates to improved vacuum are devices, more particularly to such devices which are adapted to sustain higher current arcs and higher voltage by the use of improved arc-electrode materials. This application is a continuation-in-part of my copending application Ser. No. 305,649 filed Nov. 10, 1972 which is a continuation of then co-pending application Ser. No. 117,924, filed Feb. 24, 1971, now abandoned.

In the art of vacuum are devices, there has been a rapid development from the first breakthrough wherein practicable and useful vacuum arc devices for high current switching and arc interrupting became available approximately a decade ago. In the rapidly developing vacuum art since that time, a large variety of vacuum switches, triggerable vacuum gap devices, triggerable vacuum switches and other such devices, each usually adapted to a specific purpose, has been made feasible.

In general, a main objective in the development of improved vacuum arc devices has been the development of devices which maintain the high dielectric characteristics of a vacuum in switches and the like devices over a long lifetime, such as to render the devices completely reliable for many years of operation and/or many thousand switching or interrupting events.

Another objective in the development of such devices has been to provide within the same given volume, vacuum arc devices which, operating with a useful lifetime, are capable of switching, interrupting or otherwise handling increasingly higher currents at higher values of voltage without causing destructive erosion or other such detrimental effects to the device itself, and particularly to the arc-electrodes thereof. In the development of vacuum are devices, the material comprising the arc-electrode surface at which the vacuum arc is anchored greatly influences the efficacy and the lifetime of the device.

Accordingly, it is an object of the invention to provide vacuum are devices with improved electrical and mechanical characteristics.

Another object of the invention is to provide vacuum arc devices with improved arc-electrodes able to withstand high current, high voltage operation.

Still another object of the present invention is to provide improved vacuum arc devices having improved arc-electrodes capable of exhibiting good mechanical and electrical characteristics for the interruption of high current and high voltages without the necessity of utilizing very expensive or dangerous arc-electrode materials or processing thereof.

Briefly stated, the objects of the present invention are achieved in one embodiment thereof by providing a vacuum arc device including an evacuated envelope containing therein at least a pair of arc-electrodes each of which has an arcing surface-adjacent region adapted to sustain the footpoint of a vacuum arc, at least one of which arc sustaining regions comprises an alloy of titanium and beryllium which is substantially free of all sources of gases which may be released during arcing thereof.

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 with reference to the appended drawing in which the sole FIGURE is a schematic vertical cross-sectional view of a vacuum arc device constructed in accord with the invention.

In the FIGURE of the drawing, a vacuum arc device, more specifically in this instance a vacuum switch or interrupter, includes an evacuable envelope represented generally at 10 and including a cylindrical side wall member 11, which is constructed of a suitable insulating material, having at the ends thereof a pair of metallic conducting end wall members 12 and 13 respectively, which are hermetically sealed to side wall member 11 utilizing suitable insulator-to-metal seals 14, as is well-known in the art. Within envelope 10, a pair of arc- electrodes 15 and 16 are juxtaposed in close relationship to one' another and are supported upon arc-electrode support members 17 and 18, respectively. Arc-electrode support member 17 is electrically and mechanically rigidly affixed to end wall member 12 to provide a fixed electrode. Support member 18 is reciprocably affixed by means of a bellows assembly 19, which is hermetically sealed by seal 20 to an aperture 21 within end wall member 13. The movable nature of support member 18 makes the outer portion thereof an actuating rod so as to allow movement of arcelectrodes 15 and 16 from a circuit-making, abutting position to a circuit-breaking, non-abutting position wherein an interrupter gap 22 is defined therebetween.

In order to maintain the insulating integrity of insulating cylindrical sidewall member 11, a metallic shield 23 having a rounded ferruled end 24 is suspended from end wall member 12 and encloses the arcing region including arc-electrodes l5 and 16 and arcing gap 22. Any arc-ejected species which are evaporated or sputtered from the arc-electrodes during arcing, or when the electrodes are in open-circuit position, diffuse to the inner walls of shield member 23 rather than depositing upon the interior walls of side wall member 11 and short-circuiting the insulator between the two primary electrodes. A pair of terminal members 25 and 26 are respectively affixed in electrical contact with opposite primary arc-electrodes l5 and 16. As illustrated, terminal 25 is affixed to end wall member 12 and terminal 26 is affixed to support member 18 exterior of bellows member 19. In effect, these members are electrically connected to thearc-electrodes.

The volume within interrupter envelope I0 is suitably evacuated through an exhaust tubulation, (not shown) during the final assembly thereof. For proper operation of the interrupter as a vacuum switch for alternating current, the space within envelope 10 must be maintained at a low pressure of the order of 10 torr in order that the high dielectric strength of vacuum be obtained. This is necessary in order that the breakdown gap not be broken down when a high voltage is applied thereto under normal operations due to ionizable specie within the envelope. It is further necessary in order that, upon the extinction of an alternating current arc, when the current goes through a Zero value of current, no ionizable gaseous materials be present to cause restriking of the arc upon the re-application of the steady-state voltage.

In a preferred embodiment of the invention, arcelectrodes 15 and 16, or at least the portions thereof which serve as the footpoint for a vacuum arc and which are susceptible of being locally and temporarily melted by the cathode spot of the vacuum arc, so as to cause the possible release of contaminants into envelope 11, are composed principally of titanium. Other materials may be added to the titanium in order to improve the characteristics thereof as an arc-electrode. In a preferred embodiment, beryllium is utilized in this respect.

Early vacuum switches utilized copper as the arcelectrode material thereof. This was because copper possessed a relatively high vapor pressure and was suitable to provide conduction carriers for the vacuum arc. As is well-known to those skilled in the art, during the operation of a vacuum arc device, conduction between the arc-electrodes is by virtue of an are which comprises ionized specie derived from the electrodes thereof. Thus, in a copper-electrode vacuum arc device during arcing, the arc is comprised of electrons and copper ions. It is axiomatic in the construction of vacuum arc devices that there be no source of gases which may be evolved during arcing and thus cause degradation of the vacuum and make impossible a rapid recovcry of the device upon arc extinction. For this reason, all parts of the arc device, which are effected by the heat of the are, particularly the arc-electrodes, must be substantially free of sorbed gases so that no gas is evolved during arcing. This is readily easy for structural material such as shields, are support members and the like which may readily be made from high melting point metal such as stainless steel, for example, which may be outgassed at high temperatures. For arcelectrodes, it is more difficult since the materials must have a substantially high vapor pressure to function, e.g., by supplying species for the arc, and this generally precludes outgassing at high temperature. For this reason, in early switches copper served as what was then thought to be an ideal material, because copper could readily be purified by zone refining, vacuum melting, or fractional crystallization processes, which made it possible to remove gases under high vacuum.

As vacuum switches became more refined, the chopping characteristic of devices utilizing copper arc-electrodes became a problem. As is well-known in the art, chopping is a phenomena which causes premature extinction of the vacuum arc prior to the occurrence of the current zero and results in the generation of destructive transients which can be damaging to equipment.

Because of the chopping characteristics of copper, higher vapor pressure materials are often utilized. Some such higher vapor pressure materials are disclosed and claimed in U.S. Pat. No. 2,975,256 to Lee et al., for example. Although the metals and alloys set forth in the Lee et al. patent provide greatly improved vacuum arc device electrodes, these materials, as well as others utilized in this fashion, all require purification as, for example, by vacuum melting or zone refining prior to fabrication to remove all ionizable sorbed gases and gas-forming constituents therefrom.

In a later development, as is described and claimed in U.S. Pat. No. 3,140,373, vacuum are devices utilizing beryllium arc-electrodes have been utilized to overcome the aforementioned difficulties, inter alia, because with beryllium arc-electrodes purification is not a problem due to the high affinity of beryllium for oxygen and also the highly refractory nature of beryllium oxides. It is well known, however, that beryllium can be toxic and its use as a major constituent in a vacuum arc device electrode may cause a manufacturing hazard.

In accord with the present invention, I form vacuum arc devices utilizing arcing electrodes which are principally titanium. Titanium is advantageous in this use in that titanium is a highly active metal which need not be zone refined or vacuum melted. or the like, in order to provide freedom from the evolution of gases when arcs are struck therefrom. Although titanium is moderately expensive as compared with copper, its increased use in the aerospace industry has reduced its cost to a point at which the quantity utilized in vacuum arc-electrodes does not add a prohibitive cost. Titanium has not heretofore been utilized nor considered as an electrode operative to supply arcing species of its own ions in vacuum arc devices previously, as opposed to the use of titanium as a sponge for evolution of an ionizable gas which is the conducting species of gaseous arc type devices such as is taught by I-Iolliday U.S. Pat. No. 3,328,545, because titanium is quite refractory and does not provide a sufficient quantity of conduction carriers for the operation of a vacuum arc and, hence, has very bad chopping characteristics. Additionally, in vacuo at high temperatures, titanium, due to its highly reactive nature in that environment and its inherently soft nature, forms strong adherent welds that allow for one arcing event only because of inevitable welding together of the electrodes.

Combinations of titanium with material, such as are set forth in the Lee et a1 patent and similar developments to avoid the foregoing problems, have not been commercially feasible because of the solid solubility problems and also because of the highly chemically active nature of titanium.

In accord with the preferred embodiment of my invention, I combine a relatively small quantity of beryllium with a major quantity of titanium to form a vacuum arc-electrode which is suitable in use for vacuum are devices such as gap devices. switches and the like, under high vacuum for the interruption of high current arcs at very high voltages without any of the detrimental effects of many similar devices. Vacuum are devices constructed in accord with the present invention are relatively inexpensive because the arc-electrodes need not be subjected to expensive gas removal operations, but need only be purified to a requisite amount of chemical purity which is readily obtainable by conventional vacuum metallurgy. It is necessary, however, that the titanium alloy electrodes of the invention be fabricated with due care, in vacuo, and that the heated titanium is not exposed to an atmosphere of sorbable gas as, for example, hydrogen.

I preferably utilized approximately l-5% by weight of beryllium, with the remainder titanium, as the materials for arc-electrodes in accord with the present invention. At values below 1% of beryllium, the characteristics of titanium due to its refractory nature and its tendency to chop on alternating current at high values of current prior to the attainment of a current zero predominate and, therefore, less than 1% of beryllium does not appear to be sufficient to provide the necessary conduction carriers to avoid current chopping at high currents. Also, less than 1 weight percent beryllium does not appear to harden titanium sufficiently to avoid unacceptable welding. At values of beryllium in excess of approximately 5%, the handling of the beryllium in the alloy may conceivably become hazardous, whereas a 5% beryllium, remainder titanium, alloy is relatively easy and nonhazardous to handle in manufacturing processes.

While the invention has been described herein with respect to a pair of arc-electrodes utilized in a vacuum arc device, each of which is comprised of titaniumberyllium alloy, it is readily apparent that with direct current arcs or with alternating current circuits that have a particular circuit arrangement whereby a predictable arc-electrode is always the arc cathode, only the arc cathode need be fabricated of the alloy described herein. Accordingly, in such cases, the other material may be a conventional refractory material, such as tungsten, molybdenum or any other welloutgassed material which does not provide too high a resistance for the flow of high currents, as is well known in the art.

Similarly, while the invention is disclosed herein with respect to vacuum switches, it is readily apparent to those skilled in the art that triggerable vacuum gap devices such as those disclosed and claimed in US. Pat. No. 3,087,092 Lafferty, may be fabricated utilizing the arc-electrode alloy disclosed herein. Such a device differs from that illustrated herein principally in that the gap between the arc-electrodes l5 and 16 is fixed and that a suitable trigger device as, for example, that disclosed in the aforementioned Lafferty patent, be incorporated to provide triggering means.

While the invention has been disclosed herein with respect to certain embodiments thereof, many modifications and changes will readily occur to those skilled 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:

l. A vacuum arc device comprising:

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

b. at least a pair of arc-electrodes within said envelope adapted to form an inter-electrode gap;

0. at least a surface portion of each of said arcelectrodes being capable of sustaining a high current vacuum arc,

C at least one of said surface portions comprising an alloy of titanium and approximately 1-5 weight percent of beryllium,

c said alloy having less than 10' atomic parts of sorbed gases and containing no constituents thereof which exhibit a vapor pressure higher than 10 torr at 500C.

d. said device operating to conduct high current between said arc electrodes through an arc consisting essentially of electrons and ionized metallic specie evolved from said electrodes.

2. The vacuum arc device of claim 1 wherein both of said arc-electrodes contain surface portions comprising said alloy.

3. The vacuum arc device of claim 1 wherein one of said arc-electrodes is movable and adapted to move from a circuit-closed position abutting the remaining arc-electrode to a circuit-opened position separated from the remaining arc-electrode.

Claims (3)

1. A VACUUM ARE DEVICE COMPRISING: A. AN HERMETICALLY SEALED ENVELOPE EVACUATED TO A PRESSURE OF 10**5 TORR OR LESS, B. AT LEAST A PAIR OF ARC-ELECTRODES WITHIN SAID ENVELOPE ADAPTED TO FORM AN INTER-ELECTRODE GAP, C. AT LEAST A SURFACE PORTION OF EACH OF SAID ARC-ELECTRODES BEING CAPABLE OF SUSTAINING A HIGH CURRENT VACUUM ARC, C1, AT LEAST ONE OF SAID SURFACE PORTIONS COMPRISING AN ALLOY OF TITANIUM AND APPROXIMATELY 1-5 WEIGHT PERCENT OF BERYLLIUM, C2, SAID ALLOY HAVING LESS THAN 10**6 ATOMIC PARTS OF SORBED GASES AND CONTAINING NO CONSTITUENTS THEREOF WHICH EXHIBIT A VAPOR PRESSURE HIGHER THAN 10**3 TORR AT 500*C. D. SAID DEVICE OPERATING TO CONDUCT HIGH CURRENT BETWEEN SAID ARCH ELECTRODES THROUGH AN ARC CONSISTING ESSENTIALLY OF ELECTRONS AND IONIZED METALLIC SPECIE EVOLVED FROM SAID ELECTODES.

1. A vacuum arc device comprising: a. an hermetically sealed envelope evacuated to a pressure of 10 5 torr or less; b. at least a pair of arc-electrodes within said envelope adapted to form an inter-electrode gap; c. at least a surface portion of each of said arc-electrodes being capable of sustaining a high current vacuum arc, c1. at least one of said surface portions comprising an alloy of titanium and approximately 1-5 weight percent of beryllium, c2. said alloy having less than 10 6 atomic parts of sorbed gases and containing no constituents thereof which exhibit a vapor pressure higher than 10 3 torr at 500*C. d. said device operating to conduct high current between said arc electrodes through an arc consisting essentially of electrons and ionized metallic specie evolved from said electrodes.

2. The vacuum arc device of claim 1 wherein both of said arc-electrodes contain surface portions comprising said alloy.

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